A STREAMLINED SYNTHETlC OCTOPLOID SYSTEM THAT
EMPHASIZES FRAGARIA VESCA AS A BRIDGE SPEClES
A Thesis
Presented to
The Faculty of Graduate Studies
of
The University of Guelph
by
ROBERT HAROLD BORS
In partial fuifilment of requirements
for the degree of
Doctor of Philosophy
Robert Bors O June, 2000 National Library Bibliothèque nationale l*m of Canada du Canada Acquisitions and Acquisitions et Bibliographie Services services bibliographiques 395 Wellington Street 395, nie Wellington OttawaON KIAON4 Ottawa ON K1 A ON4 Canada Canada
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The author retains ownership of the L'auteur conserve la propriété du copyright in this thesis. Neither the droit d'auteur qui protège cette thèse. thesis nor substantial extracts fiom it Ni la thèse ni des extraits substantiels may be printed or otherwise de celle-ci ne doivent être imprimés reproduced without the author's ou autrement reproduits sans son permission. autorisation. ABSTRACT
A STREAMLINEO SYNTHETIC OCTOPLOID SYSTEM T HAT EMPHASIZES
FRAGAR~AVESCA AS A BRIDGE SPECIES
Robert Harold Bors Advisor: 3. A. Sullivan
University of Guelph. 2000
The synthetic octoploid (SO) system is a method of combining diploid, tetraploid and hexaploid Fragaha species into hybrid octoploids for introgression into octoploid strawberry cultivars of F.x ananassa. I n th is stud y, (diplo id x diploid) and (diploid x hexaploid) crosses were used to create tetraploids followed by (tetraploid x tetraploid) crosses to create SOS from a wide germplasm base.
Techniques refined for the SO system included Row cytometry protocols for identification of ploidy levels, in vitro germination and in vitro delivery of colchicine using the dropper method. Of the 36 species combinations investigated, 20 resulted in viable F, plants, 13 bloomed and produced seeds, and seven did not bloom. When nine species were intercrossed at the diploid level, the best crossability occurred with F.pentaphylla and F.vesca; each fomed fertile Ç, hybrids with five other species.
No sig nificant differences in interspecific crossability were found among F-vesca subspecies bractacea, americana, vesca and var. sempeflorens when pollinated with Enilgerensis, F.nubico/a, Epentaphylla, and Eviridis. These hybrids were treated with colchicine to create tetraploids. Tetraploids were also created from Fmoschata (6x) hybridized with F.viridis or F mbicola.
The crossing strategy at the tetraploid level ernphasized F. vesca as a bridge species for F.nilgerrensis. Enubicola, F.pentaphy/la, and F.viridis. A collection of
1O4 tetraploids inct uding (F. vesca x diploid) hybrids, F. vexa (4x), F.onentalis,
(F.nubicola x Fmoschata), (Fmoschata x F.vindis), [F.orientalis x, (Fmoschata x diploid species)] and (F.viridis x F.nubicola) were intercrossed and doubled with colchicine to create SOS.
When the (F.vesca x diploid species) colchi-tetraploids were intercrossed, only 37% fruit set with an average of three seedslflower. When these colchiploids were pollinated with tetraploids derived from F.orientaîis or (Emoschata x diploid species), 52% fruit set and 10 seeds/flower were obtained. A total of 192 SOSwere created from 25 combinations of species. Of the 98 Sots planted in 1997, 28 produced fruit in 1998. The seven species successfully incorporated into SOSwere
F.vesca, F.nilgerrensis, F.nubicola, F.pentaphylla, F-viridis, F. orientalis, and
F.moschata. The results suggests Fragana species are closely related and have great potential for breeding at the diploid and tetraploid levels and for introgression into 8x material. ACKNOWLEDGEMENTS
I wish to express my sincere appreciation to my wife, Loretta, and my children, Kirk, Aurora, and Nicholas who made many sacrifices to allow me to continue rny studies. Their support and enthusiasm was invaluable.
I gratefully acknowledge my advisor, Dr. J. Alan Sullivan for his guidance, support. and encouragement over the entire period of my Ph.D. program.
I am tremendously indebted to committee member Dr. K. Kasha whose
Cytogenetics course formed the theoretical backbone on which this thesis was inspired.
I thank my advisory cornmittee members Drs. D. Wolyn and T. Michaels for their valuable suggestions and encouragement.
I acknowledge Sue Couling and Ron Dutton for assisting the care and culture of field and greenhouse plants.
The technical expertise of Jan Brazelot, Dr. Peter Pauls. and Shawn Rogers is appreciated in utilizing flow cytometry in this thesis. TABLE OF CONTENTS
ACKNOWLEDGMENTS ...... i
TABLE OF CONTENTS ...... ii
LIST OF TABLES ...... vi
LIST OF FIGURES ...... x
LIST OF APPENDICES ...... xii
CHAPTER 1: LITERATURE REVIEW ...... 1
INTRODUCTION ...... 1 FRAGARIA SPECIES ...... 1 INTERSPECIFIC CROSSABILITY IN FRAGARIA ...... 7 Crossability arnong diploid species ...... 14 lncompatibility mechanisms in diploid Fragah ...... 17 Crossability arnong polyploids ...... 19 Outcrossing mechanisms in polyploids ...... 22 Crossability among dipioids and polyploids ...... 24 Surnmary of interspecific crossability ...... 26 GENOMlC INVESTIGATIONS ...... 26 Karyotyping ...... 27 Investigation of chloroplast DNA ...... 28 Investigations of nuclear DNA ...... 29 Isozyme studies ...... 30 Chromosome pairing in diploid hybrids ...... 32 Chromosome pairing in tetraploid hybrids ...... 32 Chromosome pairing in octoploid cultivars ...... 33 Genomic designations proposed for Fragaria species ...... 34 Genomic investigations and introgression strategy ...... 35 Pivotal Genome Theory ...... 37 ADVANTAGES OF USlNG FRAGARIA VESCA AS A BRIDGE SPEClES ...... 39 Introduction ...... 39 F.vesca is widely adapted and rnay be a progenitor species ... 39 F . vesca is self-compatible ...... 41 Some forms of F. vesca are adapted to cultivation ...... 42 Fragana vesca var . sempeflorens has useful traits that facilitate breeding ...... 42 Fruitquality ...... 43 Lack of inbreeding depression ...... 43 F . vesca is amenable to chromosome doubling ...... 44 F. vexa cytoplasrn ...... 44 F-vesca as a bridge species ...... 45 INTROGRESSION OF FRAGARIA SPECIES USlNG SYNTHETIC OCTOPLOID SYSTEMS ...... 46 Crossing strategies to create SOS ...... 47 lmproving SO production ...... 55 lmproved strategy for SO production ...... 57
CHAPTER 2: GENERAL MATERIALS AND METHODS ...... 59
Introduction ...... 59 ln vitro germination ...... 59 Colchicine treatment for chromosome doubling ...... 60 Acclimatization of seedlings ...... 61 Handling of parent plants for crossing ...... 63 Floral induction ...... 63 Pollination ...... 64 Organization of crosses ...... 66 Seed collection and storage ...... 66 Data collection and analysis ...... 66 Visual screening of plants following colchicine treatment ...... 67 Flow cytometry protocol ...... 68 Flow cytometry standards and the estimation of ploidy level ...... 74
CHAPTER 3: FRAGARIA SPECIES DIFFER IN DNA CONTENT 78
ABSTRACT ...... 78 INTRODUCTlON ...... 79 MATERIALS AND METHODS ...... 80 RESULTS AND DISCUSSION ...... 83 CONCLUSION ...... 89
CHAPTER 4: HYBRlDlZATlON OF FRAGARIA VESCA SUBSPECIES AS FEMALE PARENTS WlTH F.NlLGERRENSIS,
F*NUBICOLA. F.PENTAPHYLLA AND F*VIRIDIS rn m a 91 ABSTRACT ...... 91 INTRODUCTION ...... 92 Advantages of using Evesca as a bridge species ...... 93 Advantages of using F.vesca as a female parent ...... 95 Evidence that F .vesca subspecies have diverged ...... 97 Goals of this study ...... 98 MATERIAL AND METHODS ...... 98 Experimental design and data analysis ...... 102 RESULTS ...... 103 Fruit set (%) and seeds/fiower ...... 104 Seeds with embryos and embryo germination ...... 109 Differences in intraspecific crosses ...... 109 Differences among kvesca accessions ...... 111 DISCUSSION ...... 112 CONCLUSION ...... 'Il7 CHAPTER 5: INTERSPECIFIC CROSSABILITY OF NlNE DlPLOlD FRAGANA SPECIES ...... 119
ABSTRACT ...... 119 INTRODUCTION ...... 120 MATERIALS AND METHODS ...... 122 RESULTS ...... 125 DISCUSSION ...... 137 SUMMARY ...... 147
CHAPTER 6: INTERSPEClFlC HYBRlDlZATlON OF Fragaria moschata (6x) WlTH F.nubicola (2x) AND F.viridis (2x) 149
ABSTRACT ...... 149 INTRODUCTION ...... 150 MATERIALS AND METHODS ...... 155 RESULTS ...... 159 DISCUSSION ...... 162 CONCLUSION ...... 168
CHAPTER7 :THE USE OF F.vesca, TETRAPLOID AND HEXAPLOID FRAGAHA SPECIES TO INCORPORATE DlPLOlD FRAGARIA SPECIES INTO SYNTHETIC OCTOPLOIDS ...... 170 ABSTRACT ...... 170 INTRODUCTION ...... 171 Previous crossing strategies to create SOS ...... 172 Tetraploid breeding in Fragaria ...... 172 Emp hasis on F . vesca. F .orientalis and F.moschata in crossing strategy ...... 176 Objectives and hypothesis ...... 179 MATERIALS AND METHODS ...... 179 Germplasm ...... 179 Crosses ...... 186 Techniques ...... 186 Data analysis ...... 187 RESULTS ...... 188 Differences among fernale parents ...... 190 Differences among male parents ...... 192 Interaction among males and fernales ...... 194 Influence of number of F.vesca genomes ...... 200 Lineage and fertility of SOS ...... 201 DISCUSSION ...... 203 SUMMARY ...... 215 CHAPTER 8 :GENEML DISCUSSION AND SUMMARY ..... 217 REFERENCES ...... 223 APPENDICES ...... 235 List of Tables
1.1 lnterspecific crossability of Fragana species with self-compatible diploid species used as males...... 8
1.2 lnterspecific crossability of Fragaria species with self-incompatible diploid species used as males...... 10
1.3 Interspecific crossability of Fragaria species with tetraploid and hexaploid species used as males...... 11
1.4 Interspecific crossability of Fragana species with octoploid species used as males...... 12
1S. Gametophytic system of unilateral interspecific incompatibility of Fragaria species, based on Evans and Jones, 1967...... 18
1.6. Combinations of Fragaria species that have resulted in synthetic octoploids with different fertility levels...... 51
1.7. Results of studies on hybridization of Fragaria tetraploids...... 53
1.8. Results of attempts to create synthetic octoploids (SOS) from 2x. 4x and 6x Fragana species...... 54
2.1. Nuclei isolation solutions...... , . . . . 71
2.2. Nuclei isolation procedure...... 72
2.3. Settings for the Coulter Epics Elite ESP flow cytometer when running Fragana nuclei with trout red blood cells (TRBC) as an internai standard...... 73
2.4. Calculations used to determine chromosome numbers for Fragana hybrids from flow cytometry channel numbers...... 77
3.1. Gemplasm used for fiow cytometry testing of Fragana species...... 81
3.2 Variation in DNA content of various Fragaria species. accessions, and blood cellstandards...... 86
4.1. Results of previous research using Fragaha vexa as a female in crosses with F. vindis, F. nubicola, and F. nilgerensis...... 94 4.2. Fragana vesca accessions used as fernale parents in crosses with F.nilgenensis, F.nubicola, F.pentaphylla, F. vindis and F. vesca...... 99
4.3. Fragana accessions used as male parents in crosses with F.vesca. ... 101
4.4. Fruit set for crosses among Fragana vesca subspecies when pollinated with Ç. nilgerrensis (1 accession), F. nubicola (2), F.pentaphylla (1) . F. viridis (2) and F-vesca (1)...... 105
4.5. Seedslflower for crosses among Fragaia vesca subspecies when pollinated with F. nilgerrensis (1 accession), Enubicola (2), Epentaphylla (1), F. vindis (2) and F. vesca (1) ...... 107
4.6. Seeds with embryos (%) and embryo germination (Oh) for interspecific crosses among Fragana vesca accessions as fernales and six diploid accessions as males...... 1 10
5.1 . Number of reports for interspecific hybridization of diploid Fragana species, listed by crossability categories...... 121
5.2. Diploid Fragada germplasm used in interspecific crosses...... 124
5.3. Crossability categories for interspecific crosses among several diploid Fragana species...... 126
5.4. Results of in vitro germination of seed from interspecific crosses among diploid Fragada species...... 128
5.5. Results of interspecific crosses among several diploid Fragana species, showing differences among SCZx SC, SC x SI, and SI x SI combinations ofspecies...... 135
6.1. Outcomes of interspecific crosses among Fragaria moschata and diploid species...... 153
6.2. Accessions of Fragana moschata (6x), F.nubicola (2x) and F-vindis (2x)used in crossing program for tetraploid production...... 157
6.3. Fruit set, seedsmower, embryos. healthy plants, and one year old hybrids that bloomed, for crosses among accessions of Fragana moschata and F.nubicola or F. viridis...... 161
7.1 . Published reports of lnterspecific crosses of Fragana species and hybrids at the tetraploid level...... 173 7.2. Studies that created Synthetic Octoploids (SOS)from crosses among tetraploid Fraganà species and hybrids...... 175
7.3. Fragaria accessions that were founders of tetraploid germplasm for this experiment...... 181
7.4. Tetraploid Fragarja germplasm derived from diploid species used for synthetic octoploid production...... 182
7.5. Tetraploid Fragana germplasm derived from hexaploid, tetraploid and diploid species without the use of colchicine...... 184
7.6. Effect of number of Fragana vesca genomes and female parentage on fruit set, seeds/pollination, germination, and synthetic octoploids (SOS) for crosses among tetraploid Fragaria hybrids...... 191
7.7. Effect of nurnber of Fragana vesca genomes and male parentage on fruit set, seeds/pollination. germination, and synthetic octoploids (SOS) for crosses among tetraploid Fragana hybrids...... 193
7.8. Fruit set, seedsl Rower, germination and synthetic octoploids (SOS) resulting from interspecific crosses among tetraploid Fragaria hybrids with different numbers of F.vesca genomes...... 195
7.9. Details of the 14 most productive crosses among tetraploid Fragaria which resulted in 128 synthetic octoploids (SOS)...... 202
7.10. Combinations of synthetic and natural Fragana tetraploids used to produce synthetic octoploids (SOS) ...... 204
A2.1. ANOVA for fruit set (%) of interspecific crosses with Evesca subspecies as female parents and six accession of other diploid species...... 237
A2.2. ANOVA for seedslflower of interspecific crosses with Evesca subspecies as female parents and six accession of other diploid species...... 237
A2.3. ANOVA for Seeds with embryos (%) of interspecific crosses with Evesca subspecies as female parents and six accession of other diploid species...... 238
A2.4. ANOVA for embryo germination (%) of interspecific crosses with F.vesca subspecies as female parents and six accession of other diploid species...... 238 A2.5. ANOVA for fruit set (%) of intraspecific crosses with Evesca subspecies as female parents and the control pollinizer w69...... 239
,426.ANOVA for seedsMower of intraspecific crosses with F.vesca subspecies as female parents and the control pollinizer vw69 ...... 239
A3.l. ANOVA for fruit set (%) of intraspecific crosses comparing (F.moschata x F.nubicola), (F-moschatax F.viridis), (F.nubico/ax F.moschata) and (F.viridis xF.moschata)...... 240
A3.2. ANOVA for seeds per pollinated flower of intraspecific crosses comparing (F.moschata x F.nubicola), (F.moschata x F. viridis). (F.nubicola x Fmoschata) and (F.vindis x F.moschata)...... 240
A3.3. ANOVA for seeds containing embryos (%) of intraspecific crosses comparing (F.moschata x F.nubicola), (F.moschata x F. viridis), (F.nubicola x Fmoschata) and (F.vindis x F.moschata)...... 24 1
A3.4. ANOVA for healthy plants per pollination of intraspecific crosses comparing (F-moschata x F.nubicola), (F.moschata x F. vindis), (F.nubicola x F.moschata) and (F.vindis x Fmoschata)...... 241
A3.5. ANOVA for hybrids that bloomed the following year resulting from intraspecific crosses comparing (F-moschatax F.nubicola), (Emoschata x F.vindis), (F.nubicola x F.moschata) and (F.vindis x F.moschata). ... 242
A3.6. Fruit set, seeds, embryos, healthy plants, and one year old hybrids that bloomed, for crosses among accessions of Fragaha moschata and F.nubicola or F. viridis...... 243
A4. Fruit set, seedsl flower, germination and synthetic octoploids (SOS) resulting from interspecific crosses among tetra ploid Fragana accessions...... 246
A5.1. ANOVA for fruit set (%) of tetraploid crosses for data in Chapter 7. .. 271
A5.2. ANOVA for seeds per pollinated flower of tetraploid crosses for data in Chapter7...... 271
A5.3. ANOVA for germination (Oh) of tetraploid crosses for data in Chapter 7...... 272
A5.4. ANOVA for synthetic octoploid production (%) of tetraploid crosses for data inChapter7...... 272 List of Figures
1.1. Leaf morphology of diploid and polyploid Fragaria species ...... 3
1.2. Mature fruit of several Fragaria species ...... 4
1.3. Geographic distribution of diploid Fragana species. based on Evans (1964). Reed (1966). Staudt (1989). and Hummer (1996) ...... 5
1.4. Geographic distribution of polyploid Fragaria species. based on Evans (1964). Reed (1966). Staudt (1989). and Hummer (1996) ...... 6
1.5. Crossability of diploid Fragaria species ...... 16
1.6. Interspecific crossability of polyploid Fragana ...... 20
1.5. Unbalanced ploidy strategies for creating synthetic octoploids ...... 48
1.6. Balanced ploidy strategy for introgression of lower ploidy species into octoploid cultivars...... 49
1.7. A simplified Balanced Ploidy Strategy for synthetic octoploid production . 56
2.1. In vitro treatment of Fragana vesca seedlings with colchicine solution ... 62
2.2. Pollen storage method based on procedures of MacFarlane-Smith and Jones (1989) ...... 65
2.3. Diploid (left) and tetraploid (right) forms of the "Alexandria" variety of F. vesca ssp. vexa var. sempeflorens at identical ages ...... 69
2.4. Leaf morphology of interspecific hybrids of Fragada species ...... 70
2.5. Example of fiow cytometer output for a 4x-8x rnixiploid Fragaria hybrid with an interna1 standard ...... 75
2.6. Example of flow cytometer output for a hexaploid Fragaria plant...... 76
3.1. Example of a secondary peak in flow cytometer output ...... 82
3.2. Regression of channel numbers from secondary peaks ont0 channel numbers of primary peaks for Fragana nuclei...... 84 X1
4.1. Distribution of Fragaria vesca subspecies (Evans, 1964; Reed, 1966; Staudt, 1989)...... 96
5.1. Hybrid vigour for vegetative growth of F. vexa x F.daltoniana F, hybrids. 7-30
5.2. Diploid hybrids shown one year after planting...... 131
5.3. Variation in fruit size and yield of interspecific diploid hybrids...... 133
5.5. Geneflow potential among diploid Fragaria species, showing results of previous investigators combined with this study...... 140
5.6. Combinations of diploid Fragana species that have not resulted in viable progeny, but might be successful if more accessions were investigated ...... 141
6.1. Strategies used by Sebastiampillia and Jones (1 976) and Evans (1977) to create synthetic octoploids with the hexaploid Fragana moschata. . 151
The three Fragada species used in this study: F.moschata, F.virids and F.nubicola...... 156
Crossing strategy: a simplified balanced ploidy strategy for synthetic octoploid production...... 177
Examples of tetraploid hybrids and fruit set resulting from interspecific hybridization...... 189
Crossing plans using Fragaria species that were successful in creating synthetic octoploids in this study...... 205
Synthetic octoploid fruit produced under open pollination conditions. . 206 . . -.--y. -
LIST OF APPENDICES
1. Abb reviations and add resses of gerrnplasm sources...... 235
2. ANOVAs for Chapter 4 ...... 237
3. ANOVAs and data for Chapter 6...... 240
4. Data from tetraploid crosses in Chapter 7...... 246
5. ANOVAs for Chapter 7...... 271 I CHAPTER 1
LITERATURE REVIEW
INTRODUCTlON
A need to expand the narrow germplasm base of octoploid strawberry cultivars (Sjulin and Dale, 1987; Daubney, 1990; Galletta and Maas, 1990;Hancock et al., 1990, 1996; Shaw, 1991; Sullivan. 1991; Dale et al., 1993; Harrison et al.,
1993; McNichol and Graham, 1992; Sangiacorno and Sullivan, 1994; Davidson,
1995) has prompted this investigation into the genetics and breeding of Fragana species. Previous reviews of strawberry breeding (Darrow, 1966; Scott and
Lawrence, 1975; Hancock et al., 1990. 1996) have indicated limited investigation has occurred on interspecific hybridization in Fragana. Besides providing more details regarding d iploid, tetraploid and hexaploid Fragana species, t his review reflects a desire by the author to develap a greater understanding of relationships within the genus. The areas of evolution and interspecific crossability are interconnected in this review. A greater understanding of evolution in Fmgana could help in development of an introgression strategy for bringing wild Fragana gemplasm into strawberry cultivars. Conversely, studies involving interspecific hybridization may help define evolution of the species.
FRAGARIA SPECIES
The commercial strawberry Fragana x ananassa Duch. was the result of hybridization of two wild octoploid species, F. chiloensis L. and F. virginiana Mill., 2 during the mid 1700's (Darrow,I 966). While technically not a wild species, F. x ananassa is included in this review because of its economic importance and because it has been crossed to more species than either of its progenitor parent species.
Fragaria species have a basic chromosome number of x = 7 and diploids are
Zn = 14. Of the known Fragana species, there are 11 diploid, three tetraploid, one hexaploid and four octoploid species. Figures 1.1 and 1.2 show morphological differences present in leaves and fruit of the species. Botanical descriptions of these species have been published by several researchers (Reed, 1966;
Staudt.1989; Hummer, 1996). It has been suggested that the diploid F. yezoensis, should be classified as a variety of F. nipponica based on chromosome karyotyping
(Iwatsubo and Naruhashi, 1989),but a recent review (Hancock et al., 1996) lists it as a distinct species.
Figures 1.3 and 1.4 shows distribution and ploidy levels Fragana. There are probably many Fragana species to be discovered in Asia (Jones, 1976). Numerous intemediate forrns of Fragana exist in herbariums, originally collected in eastern
Asia, that cannot be classified botanically because they lack distinct differences
(Staudt, 1989). A botanical expedition by the University of Tokyo reported Fragana species to be well differentiated in the eastern Hirnalayas (Hara, 1966) thus providing a western border to the location of undifferentiated Fragana. Eastern
China appears to be the centre of diversity for Fragana as more species were located there than other areas. Figure 1.l. Leaf morphology of diploid and polyploid Fragaria species. Figure 1.2. Mature fruit of several Fragana species. 5
Fig. 1.3. Geographic distribution of diploid Fragada species, based on Evans
(1964). Reed (1 966),Staudt (1 989). and Hummer (1996). Fig.1.4. Geographic distribution of polyploid Fragana species, based on Evans
(1964), Reed (1966), Staudt (1989), and Hurnrner (1996). 7
While disease resistance, pest resistance, cold hardiness, desirable flaveurs, specialized ecological adaptations and other valuable traits can be found in wild
Fragana (Darrow, 1949,1966; Scott, 1951; Reed. 1960; Jones, l966,1976; Evans,
1974; Bauer, 1976; Chabot and Chabot, 1977; Kantor, 1984; Galletta and Maas,
1990; Trajkovski, 1990. 1993; Sullivan, 1991; Ahmadi and Bringhurst, 1992;
Sangiacomo and Sullivan, 1994), this literature review will not focus on these characteristics in detail. This thesis focuses on introgression and evolution of
Fragana. Previous attempts to introgress 2x, 4x and 6x species into cultivated octoploids (Darrow, 1966; Evans, 1977,1982~;Kantor 1984) had very low success rates and present an opportunity for improvement of introgression methodology.
INTERSPECIFIC CROSSABILITY IN FRAGARIA
lnterspecific hybridization studies in Fragana have been summarized in
Tables 1.1-1.4. Fragana gracilis Losinsk., F.mandschu#ca Staudt, Epentaphylla
Losinsk. and Eiturpensis Staudt have not been included in these tables since no data could be found on their interspecific crossability. Of the 255 possible interspecific crosses between Fragaria species 54% have not been reported, 17% have been reported by only one researcher, and 29% have been reported by two or more researchers. Researchers have had variable results with interspecific crosses. For example, crosses between F. vesca L. x F.niigerrensis Schltdl. ex J .Gay
have resulted in no seed set, no seed germination, death after germination, sterile
plants, or viable plants (Table 1.1). Table 1.1 lnterspecific crossability of Fragaria species with self-compatible diploid species used as males.
Species used as males in crosses
F.daltoniana Eiinurnae F.nilgerensis F. vesca
Crossability categories' Female Ploidy OCMYABCDEF ABCDEF ABCDEF ABCDEF Fdaltoniana 2x SC ------1 F.iinumae 2x SC F.nilgeuensis 2x SC 1 F. vesca 2x SC 1 1 1 F.nipponica 2x SI F.nubicola 2x SI 1 F. viridis 2x SI 1 F. orientalis 4x Tri 1 F.moupinensis 4x Di 1 Emoschata 6x Tri 1 F.chiloensis 8x Tri 1 F. virginiana 8x Tri 1 F. x ananassa 8x H+f 1 II 11111 21 111 ': Crossability categories: ': OCM outcrossing rnechanism: A = no set SC = self compatible B = seed, no germination SI = Self incompatible C = death after germination Di = dioecious D = sterile plants Tri = trioecious (males, fernales, or hemaphphrodites) E = plants produced, fertility not reported H+F = hermaphrodites and fernales F = fertile plants ': Numben indicate number of reports by researchers.
note: Tables 1.1-1.4 are based on: Yarnell, 1931a; Mandelsdorf & East, 1927; Federova, 1946; Williams, 1959; Staudt, 1959; Evans, 1964,1974,1977; Fadeeva, 1966; Evans and Jones, 1967; Senanake & Bringhurst, 1967; Staudt, 1967b. 1989; Burnagina & Mesaros, 1969; Sebastiampillia and Jones ,1976; Kantor, 1984; Trajkovski, 1993; Noguchi et al., 1997. 9
In al1 these studies researchers were working with a limited number of accessions which may be a limiting factor to their success. A well-established tenet in plant breeding was that interspecific crosses often require the use of many accessions to obtain interspecific hybrids (Burbank, 1921; Stoskopf et al., 1993).
"When initiating a program of using wild species in plant breeding, the first step is to collect as many accessions as possible of related species . . . "(Hermsen,1992).
Variation between accessions for interspecific hybridization has been mentioned for
Fragana species (Mangelsdorf and East. 1927; Williams, 1959; Evans. 1964). An example of the value of having many accessions was provided by Williams (1959) who reported that of the many accessions of F.vesca used. only one F.vesca accession from eastern Europe could successfully hybridize and form viable offspring with F. nilgenensis. Clearly , this hybridizationwas successful only because several accessions from a variety of locations were used. In addition to increasing the probability of success for interspecific hybridization, many accessions may also be important for creation of fertile hybrids. Sterile progeny has been reported 34 times and fertile progeny 32 times (column's D & F in Tables 1.1-1.4) in interspecific
Fragana hybrids. Contradictory reports exist for fertility of ten combinations of species.
Genetic variation between accessions seems a plausible explanation for difiering results reported by many researchers. The possibility exists that environmental conditions rnay also influence interspecific crossability. Octoploid hermaphrodites could Vary in sex expression becauçe of environmental factors
(Ahmadi and Bringhurst, 1991). If a plant appears to be hermaphrodite but is either Table 1.2 lnterspecific crossability of Fragaria species with self-incompatible diploid species used as males.
Species used as males in crosses
F. nipponica F. nubicola F.vin'dis
Crossa bility categories' Fernale Ploidy OCMy ABCDEF ABCQEF ABCDE F F.daltoniana 2x SC 1 1 F. iin urnae 2x SC F.nilgetrensis 2x SC 1 3 1 2 1111 F. vesca 2x SC 1 3 1 14 4 F.nipponica 2x SI 7 1 F.nubicola 2x SI 1 1 11 F. vitidis 2x SI 1 12 2 1 F.orientalis 4x Tri 1 1 121 F.moupinensis 4x Di 1 1 F-moschata 6x Tri 1 12 11 132 F.chiloensis 8x Tri 11 1 2 3 Evirginiana 8x Tri 111 1 12 F. x ananassa 8x H+F
': Crossability categories: OCM outcrossing mechanism: A = no set SC = self compatible B = seed, no germination SI = Self incompatible C = death after germination Di = dioecious D = sterile plants Tri = trioecious E = plants produced, fertility not reported H+F = hermaphrodites and fernales F = fertile plants ': Numben indicate number of reports by researchers. Table 1.3 lnterspecific crossability of Fragaria species with tetraploid and hexaploid species used as males.
Species used as males in crosses
F.corymbosa F.moupinensis F.orientalis F.moschata (44 (4~) (4~) (sx)
Crossability categoriesz Fernale Ploidy OCMYABCDEF ABCDEF ABCDEF A BCDE F Edaltoniana 2x SC 1 1 1 F. iinumae 2x SC F.nilgenensis 2x SC 1 2 2 F. vesca 2x SC 2 3 2 121 3 F.nipponica 2x SI 1 F.nubicola 2x SI 1 1 1 F. viridis 2x SI 11 1 1 12 11112 1 F. otientalis 4x Tri 11 1 1 1 12 1 F.rnoupinensis 4x Di 11 1 11 F.moschata 6x Tri 1 3 1 F.chiloensis 8x Tri 1 1 11 1 1 11 F-virginiana 8x Tri 11 1 12 2 3 F.x ananassa 8x H+F 111 1 3 1 33 2 ': Crossability categories: ': OCM outcrossing mechanism: A = no set SC = self compatible B = seed, no germination SI = Self incompatible C = death after germination Di = dioecious D = sterile plants Tri = trioecious E = plants produced, fertility not reported H+F = hermaphrodites and females F = fertile plants ': Numben indicate nurnber of reports by researchers. Table 1.4 Interspecific crossability of Fragaria species with octoploid species used as males.
Species used as males in crosses
F.chiloensis F. virginiana F.x ananassa
Crossability categoriesZ Female PloidyOCMYAEjCDEF ABCDEF ABCDE F F.daltoniana 2x SC 1 F.iinumae 2x SC F.niigerrensis 2x SC 1 1 2 11 F.vesca 2x SC 11123 123 11 22 1 F.nipponica 2x SI F.n ubicola 2x SI 1 1 11 F.vin'dis 2x SI 2 2 1 1 F. orientalis 4x Tri 2 1 1 1 F.moupinensis 4x Di 1 1 1 F.moschata 6x Tri 2 1 3 11 F.chiloensis 8x Tri ------M M F.virginiana 8x Tri M ------M F. x ananassa 8x H+Ç M M ------': Crossability categories: Y: OCM outcrossing mechanism: A = no set SC = self compatible 8 = seed, no germination SI = Self incompatible C = death after germination Di = dioecious D = sterile plants Tri = trioecious E = plants produced, fertility not reported H+F = hermaphrodites and females F = fertile plants ': Numbers indicate number of reports by researchers. M = many reports, crossability is well established in literature 13 male or female sterile, this would affect the success of interspecific hybridization.
Since Fragana species grow at high elevations in Asia (Reed, 1966; Staudt, 1989), conditions may not be optimal for complete fertility at other locations with different environmental conditions. Temperature is "unquestionably the most critical factor affecting hybridization" (Layne, 1983), for example 60% seed set occurred for
interspecific hybridization crops of peach and apricot with optimum temperature. As these two crops are also in the Rosaceous family, such information may be relevant to Fragana species. Factors such as humidity, light, wind, soi1 fertility, diseases, topography, and plant vigour can also influence the result of hybridization (Layne,
1983). If hybridization is diffwlt or impossible for certain species, mimicking the
natural ecosystem of the species rnay be beneficial.
Besides using many accessions and optimizing environmental conditions, several techniques have been used to en hance crossa bility. Emasculation 1-3 days
before bud break prevented self-fertilization (Scott and Lawrence, 1975). Pollinating on the first and fourth day after emasculation was used to increase seed set in
interspecific crosses of Fragana (Evans. 1964). Proper handling of pollen was also
important to the success of interspecific hybridization (Galletta, 1983; Layne, 1983).
Pollen viability can be maintained for 4 to 7 years if fresh anthers are placed in
cotton stoppered vials in air tight jars containing desiccant and placed in the dark
at 3-4'~ (MacFarlane-Smithet al.. 1989). Additional detail on pollen management such as checking for pollen viability was provided in Galletta's review (1983).
Low seed nurnbers and poor germination rates have been common for
interspecific crosses for Fragana. When 1256 interspecific pollinations were done 13 involving 2x, 4x and 6x Fragaia species, averages of 1.2 seeds per pollination and a 43% germination rate were achieved (Evans, 1964). When Fragaria species and hybrids were intercrossed in 15 different combinations, averages of 21 seeds per fruit and a 27% germination rate were achieved (Fadeeva, 1966). As Fadeeva does not report the unsuccessful crosses, the actual yield of seedlpollination would be expected to be much lower. With low seed numbers likely from interspecific crosses, maximizing germination rates is important. Of the 16 germination methods tested on F. x ananassa seeds, the best rate (97%) occurred with in vitro germination of cut achenes on MS medium with no hormones (Miller et al., 1992).
Only 27% of whole seeds on soilless mix germinated.
The most stringent definition of interspecific crossability requires that two or more species create fertile offspring. Several rnethods such as use of mutagenic compounds (Kantor. l984), chromosome doubling (Scott, 1951; Evans, 1964,
1967,1974,1977,1982~;Fadeeva, 1966; Staudt, 1967;Sebastiampillia and Jones,
1976; Bauer, 1976, 1993; Trajkovski, 'l990, 1993), and unreduced gametes
(Darrow, 1966; Bringhurst and Gill, IWO; Bauer, 1976; Trajkovsk,; l990, 1993;
Bauer, 1993) have been used by researchers to overcome sterility in progeny.
These techniques will be discussed in more detail in a later section.
Crossability between di ploid species
Less than one third of the possible crossing combinations between diploid species have been attempted and reported (Fig. 1.5). Of the seven diploids involved in interspecific crossability studies, only F. dalioniana J .Gay has not 15 successfully produced progeny with other species (Evans, 1964). Fragaria iinumae
Makino, F. nilgenensis, F.nipponica Makino, F. nubicola Hook. , F. vesca, and F.
viridis Duchesne have been successfully hybridized to at least one other diploid species, and several resulting hybrids were fertile (Fadeeva, 1966; Evans and
Jones, 1967; Sebastiarnpillia and Jones, 1976; Davis et al., 1996) showing potential for gene transfer at the diploid level with these species.
Diploid crossability of F. nilgerrensis, F. nubicola, F. vesca, and F. virids has
been studied by several researchers (Tables 1.1 and 1.4). Fragaria nilgenensis was the most dificult to hybridize, confiming cataplastic DNA analysis (Harrison et
al., 1993, 1997) suggesting this diploid was distantly related to other Fragana
species. The other three widely used diploids, F. nubicola, F. vesca, and F. viridis,
have been intercrossed to produce fertile hybrids. This suggests that F. nubicola,
F. vesca, and F. vindis are more closely related to each other than to F.nilgerensis.
Differences exist in crossability of these three species to F. daltoniana, F. nipponica
and F. nilgenensis (Fig. 1.5). It is difficult to make conclusions regarding
crossability of F. daltoniana, F.iinumae and F. nipponica since there has been little
research to document their crossability (Tables 1.1 and 1.2).
While several researchers have focused on the introgression of diploid
Fragaria species into cultivars (Scott, 1951 ; Fadeeva, 1966; Bringhurst and Gill,
1970; Sebastiampillia and Jones, 1976; Bauer, 1976, 1993; Evans, 1977;
Trajkovski, 1990,1993) it is surprising that prebreeding at the diploid level between
species has not been mentioned, since fertile diploid hybrids are possible. Studies
involving breeding of F, interspecific hybrids have had the goal of understanding Figure 1.5. Crossability of diploid Fragaria species. This shows the best results obtained by researchers as outlined in Tables 1.1 and 1.2. Arrows originate at males and teminate at females. Lines with two arrow heads indicate similar results for reciprocal crosses.
F. pentap hyi/a
fertile progeny created m
progeny created -,---,,-,-
no viable progeny 1 Ul--IIIHIYll----- C Oself-compati ble self-incompatible unknown compatibility 17 genetic relationships but not improvement of diploid Fragaria (Evans and Jones,
1967; Davis et al., 1996). Diploid level prebreeding would have advantages over breeding at higher ploidy levels for combining desirable and, breaking undesirable, genetic linkages. Diploids have fewer alleles than polyploids, producing simpler segregation ratios and making the selection process easier, especially for recessive traits such as dayneutrality and fruit firmness.
Incornpaübility mechanisms in diploid Fragaria
Similar to other fruit crops in the Rosaceae (Lapins, l983), F.mandschunca,
F-nipponka,F.nubicola, and F. vindis possess gametophytic self-incompatibility (SI) alleles that prevented selfing but allow crossing to genotypes with different SI alleles
(Evans, 1964; Evans and Jones, 1967;Staudt, 1967a, 1989). Fragaria daltoniana.
F.iinumae, Enilgenensis, and F. vesca are self-compatible (Evans, 1964; Staudt,
1989) while the compatibility statuses of Egracilis and F.pentaphy/la were not reported. Incompatibility mechanisms in Fragaria were due to inhibition of pollen tube growth in the styles, are garnetophytic in nature (Evans and Jones, l967), and corresponded with Lewis and Crowe's (1958) descriptions of unilateral self- incompatibility. These incompatibility relationships are summarized in Table 1.5.
Variation in style length was not a factor effecting success of interspecific hybridization of Fragaria species (Evans, 1964).
Self-incompatibility mechanisms have been shown to break down on occasion when self-incompatible F. vindis occasionally sets seeds with self- compatible pollen from F. vexa(Williams, 1959; Fadeeva. 1966). It is questionable Table 15. Gametophytic system of unilateral interspecificincornpatibility of Fragaia species, based on Evans and Jones. 1967.
lncompatibility relationships:
Fernale Male Outcome cornpatibility compatibility type t~Pe normal pollen tube growth nonal pollen tube growth pollen tube growth arrested pollen tube growth depends on proper combination of SI alleles of gametes
Examples of SI x SI combinations:
Fernale Male Outcome SI alleles Y SI alleles SI,S2 SI,S2 pollen tube growth arrested
SI,S2 SI$3 pollen tubes with SI alleles have arrested growth those with S3 alleles grow norrnally SI,S2 S3,S4 normal pollen tube growth
': SC = self-compatible species, SI = self-incompatible species Y: S1, S2, S3,S4 = different self-incompatibility alleles 19 if these were true hybrids since F. vesca and F.vindis have similar leaf morphology
(Staudt 1989) and the studies did not mention how they determined the resulting progeny were hybrids. Mutations are a plausible explanation for seeds from SI x SC crosses and for selfing of self-incompatible species (Lapins, 1983).
Seif-incompatible alleles have neither been specifically identified nor categorized for Fragana species. It is not known if different species contain the same SI alleles or loci, which could have had an impact on success of interspecific crosses. There is no indication of how many SI alleles may be operating within
Fragada species. Therefore the use of many accessions is recomrnended for crosses between self-incompatible species. As a self-compatible species, F. vexa has advantages over SI diploids, such as F.nubicola and F.viridis, for use in interspecific crosses. Since compatibility barriers do not operate when SC species are used as fernales, Evesca could be especially useful when lirnited accessions of SI species are available. Backcrossing SC x SI hybrids to SC species could eliminate SI alleles and make it easy to create isogenic lines and aid the isolation and transference of specific genes. As Evesca has the best record of SC species for interspecific hybriditation (Tables 1.1 -1.4), Evesca has clear potential for use as a bridge species.
Crossability between polyploids
Polyploid species are more likely to produce interspecific progeny that are fertile when the parents are at the same ploidy level (Fig. 1.6). All tetraploid Fragaria species have been hybridized and fertile progenies have been produced (Staudt, 20
Fig. 1.6. lnterspecific crossability of polyploid Fragana. Hybrids resulting from crosses of species with the same ploidy level are generally inter-fertile.
Hybridization between species with different ploidy levels has been less successful than species with the same ploidy levels. Arrows originate at males and terminate at females. Lines with two arrow heads indicate similar results for reciprocal crosses. Based on the best results of crosses listed in Tables 1.3 and 1.4. Not al1 crosses have been attempted as in the case of F.iturpensis.
fertile progeny created
1 pmgeny created -----O--. * no viable progeny -) 2 1
1959). Crosses between three of the four octoploid species, F. virginiana,
F.chiloensis, and F. x ananassa, also result in fertile progeny (Evans, 1964; Darrow,
1966; Staudt, 1989; Hancock et al., 1996) but no reports were found regarding crossability of F. iturpensis (8x).
Crosses between polyploid species were more likely to produce viable seed when the higher ploidy species were used as the female parent (Evans,1974). In
such crosses, the resulting embryo : endosperm chromosome ratio in progeny is
closer to a normal ratio, and thus is more likely to survive than if the lower ploidy
parent was used as the female. Unreduced gametes rnay have better survival
potential than reduced gametes, particularly if a normal 2:3 embryo : endosperm
ratio occurs (Evans, 1974). In such crosses, progeny frequently have higher ploidy
levels than expected. Crosses resulting in odd numbers of genomes are usually
sterile (Darlington, 1973; Evans, 1974; Sanford, 1983) although sterility of F. x
ananassa (8x) X F. moschata (6x) hybrids was overcorne by applying the chernical
mutagens H-nitrosoethylurea and 1,4-bis-diazoacetlybutane to seedlings (Kantor,
1984). It was suggeçted that the mutagens altered genes involved in meiosis and
that odd numbers of chromosomes were not a factor causing sterility in Fragana
hybrids.
The ability of polyploid Fragaria to hybridize and produce fertile offspring
suggested that polyploids were closely related (Federova, 1946; Fadeeva, 1966;
Bringhurst and Senanayake, 1966; Bringhurst 1WO), through common genomes,
which is surprising because of their morphological differences (Fig. 1.1 and 1.2). 22
Outcrossing mechanisms in polyploids
In the first half of the 19th century, al1 F. x ananassa (8x) cultivars were dioecious, requiring growers to grow staminate plants to pollinate pistillate varieties.
Pistillate varieties were considered superior in yields to hermaphrodites by early breeders (Roe, 1881). With the discovery and incorporation of productive hemaphrodites into breeding programs, pistillate varieties were rapid ly replaced during the late 1800's (Roe, 1881) and virtually eliminated in modern times (Darrow,
1966). Cross-pollination was not required for fruit set of cultivars, but was important for breeding programs to obtain hybrid vigour since octoploid cultivars are subject to inbreeding depression (Spangelo et al., 1971). Successive generations of inbred lines have lower vigour and fertility than parental lines (Scott and Lawrence, 1975).
There were three major alleles that control sex expression: female (F), male
(M) and hermaphrodite (H), which express dominance in the order of F > M > H in
F. onentalis Losinsk. (4x), F. moschata (6x), F. chiioensis (8X) and F.virginiana (8x)
(Staudt, 1968). Fragana orientalis and F. moschata were found to have tetrasomic and hexasomic inheritance ratios, respectively, for sex determination. Sex ratios in octoploids were not as clear. Staudt (1968) theorized that genes controlling female and male expression were similar in tetraploids and hexaploids but suggested octoploid species may have different sex-detenining genes. Further evidence to support Staudt's theory that sex inheritance differed in octoploids was provided when octoploid species were crossed to the diploid F. vesca and diploid Potentilla
glandulosa (Ahmed and Bringhurst, 1991). Sex was controlled by octoploid
inheritance in the order of F > H > M. The three sex genes were allelic in 2 3 octoploids but environmental conditions could influence hermaphroditic expression toward predominantly male or female expression (Ahmed and Bringhurst, 1991).
Environmental influences were discussed as a plausible explanation for unclear sex ratios in octoploids. It has been difficult to differentiate visually between males and hermaphrodites as some males have pseudo-pistils. A method to differentiate between simiiar phenotypes was to treat emasculated flowers with phytohormones, such as NAA, whereby only female flowers set fruit (Staudt, 1968).
Dioecious forms promoted outcrossing in polyploid Fragaria species (Staudt,
1989). It may be that separate sexes evolved in Fragana polyploids as an alternative rnechanism to self-incornpatibiiity to maintain heterozygosity. Many diploid Fragaria species were self-incompatible and were likely to have been involved in the evolution of polyploids (Staudt, 1989). However, if polyploid species have self-incornpatibility alleles, they are probably inactive. Self-incompatibility mechanisms broke down in synthetic tetraploids derived from self-incompatible diploid species (Evans and Jones, 1967) and hermaphrodite forms of polyploid species were self-compatible (Darrow, 1966). Of the diploid species, only Evesca subspecies bracteata had female flowers (Ahmedi and Bringhurst, 1991). As
F. vesca ssp. bracteata was located in Western North Arnerica, it is unlikely to be the source of genes determining sex expression in Asian or European polyploids.
Perhaps, this F.vesca subspecies and polyploid species share a common dioecious diploid ancestor or dioecy evolved separately in polyploids and diploids. 24
Crossability between diploids and polyploids
Crosses between diploid and polyploid species often gave endosperm that failed to develop properly (Allard, 1960). It has been suggested that the irnbalances of chromosomes (Stephens, 1942) or gene dosages (Allard, 1960) were responsible for difficulties in obtaining hybrids behrveen diploids and polyploids. In most plant species, the genetic material of the endosperm was two parts fernale parent and one part male parent (North, 1979), thus, the chromosome ratio between endosperm and embryo was 3:2 for crosses between parents with the same number of chromosomes. This ratio becomes altered when crosses occur between plants of different ploidy levels. For example, diploid x tetraploid and tetraploid x diploid crosses have endosperm / embryo chromosome ratios of 4:3 and 5:3 respectively.
It was suggested that endospem:embryo chromosome ratios were responsible for the failure of many diploid x polyploid crosses in Fragaria, and recommended that polyploid parents be used as females when crossed to diploids
(Evans, 1974). Nevertheless, diploids species have often been hybridized as females to polyploid Fragana (Tables 1.1 to 1.4). A notable exception to this recommendation was the tetraploid F. moupinensis that çuccessfully crossed as a male to two diploid species. It is surprising that F. moupinensis and F.nilgenensis did not hybridize. These two species have similar morphology which has led to the theory that F. moupinensis may be a polyploid form of F. nilgerensis (Staudt, 1989).
Limited numbers of accessions may have been responsible for the failure of these two species to hybridize or F.nilgerrensis and F. moupinensis are not related. As
F.nilgemnsis is SC, it is doubfful that self-incompatibility alleles were involved in the failure to hybridize these species.
Crossability data supported the theory that F.vesca was a progenitor to polyploid Fragaria (Federova, 1946; Bringhurst and Gill, 1970; Bringhurst, 1990) but many other diploid species have been untested (Tables 1.1-1.4). Fragaria vesca
(Zr) has often been hybridized to octoploid species by breeders (Darrow, 1966;
Bauer, 1976; 1993; Trajkovski. 1990, 1993, Ahmadi and Bringhurst, l992), and hybrids between F.vesca and F-chiloensis (8x) have beei: iound in the wild
(Bringhurst and Khan, 1963; Bringhurst and Senanayake, 1966). Fragana vesca and F. vindis have been the only non-octoploid species to have produced progeny when used as females in crosses with F. x ananassa. Thus, these two species may have potential for contributing cytoplasmic DNA to 8x cultivars. Some F. vesca x
F. x ananassa hybrids have been partially fertile while only sterile hybrids have been reported with F. viridis x F. x ananassa. Crossability studies indicate that F. vesca may have the greatest potential of the diploid species to act as a bridge species to octoploid cultivars.
Although not mentioned in the literature, it is likely that recessive detrimental or lethal alleles present in polyploids may be a factor that lirnits the success of creating polyploid x diploid hybrids. As polyploid Fragana species were susceptible to inbreeding depression (Spangelo et al., 1971; Scott and Lawrence, 1975) polyploid x diploid crosses may have reduced vigour since heterozygosity would be decreased by the reduction of the number of genomes.
The mechanism of self-incompatibility promotes heterozygosity, which may obscure the presence of detrimental or lethal alleles. Conversely, self-compatible 26 species, such as F. vesca, tend to be more homozygous and less likely to harbour lethal alleles. Thus, crossing polyploid species with self-compatible species may have a greater chance of success than crossing polyploid species with self- incompatible species.
Summary of interspecific crossability
Based on current Fragaria literature, F. vesca may have the greatest potential of the diploid species for acting as a bridge species to cultivars. Fragana vesca alone has successfully crossed as a male and female with F. x ananassa producing semi-fertile progeny and may offer the possibility to transfer unique cytoplasm to cultivars. As F.vesca is self-compatible, it can be used as a female in crosses with self-incompatible species without the interference of self-incornpatibility mechanisms.
As previous research has not used an extensive collection of Fragana species and most had only one or two accessions for each species studied, crossing studies have been unable to elucidate the evolution of Fragaria. Since several Fragana at both the diploid and polyploid levels can be hybridized to produce progeny, it would seem that many species in Fragan'a are closely related.
This could facilitate the introgression of the wild species of Fragafia into cultivars.
GENOMIC INVESTIGATIONS
Genomic investigations in Fragana may offer insight into evolutionary relationships and aid in developing introgression strategies. Studies involving 27 chromosomes, cytoplasrnic DNA, nuclear DNA, and isozymes have been loosely defined as 'genornic investigation' and included in this section, as these studies are useful in discerning relationships between various Fragaria species. The genus of
Fragana is divided into 2x, 4x, 6x, and 8x species. The diploids species are likely progenitors of higher ploidy species and may have contributed different genomes, complicating investigation of evolutionary relationships. Much of the genomic research in Fragana has focused on discovering progenitors of the commercial strawberry, F.x ananassa. As evolution is an ongoing process, the discovery of progenitor or intermediate species may not be possible if they no longer exist
(Bringhurst and Gill, 1970). The search for a species similar or less divergent to the progenitor is perhaps a more realistic goal. Although genomic investigations of
Fragaria do not offer conclusive evidence for identification of a progenitor species, the information is beneficial for developing an introgression strategy.
Karyotyping
Fragana chromosomes were very srnall, ranging in size from 0.9 to 1.7 microns (Yarnell, 1929) making differences between chromosomes difficult to discem with light microscopy. Chromosome banding techniques would be difficult to do with such small chromosomes, and has not been reported for Fragana.
Karyotypes were developed for some diploid species. Fragana vesca, F. nipponica,
F. nubicola and F. daltoniana were very similar in karyotype morphology (Iwatsubo and Naruhashi, 1989,1991). Fragana iinumae differed from other diploids because
it had more chromosomes with median centromeres and a large satellite on 28 chromosome seven. F. yezoensis and F. nipponica chromosomes were so similar it was recommended that F. yezoensis be reclassified as a variety of F. nipponica
(Iwatsubo and Naruhashi, 1989).
Investigation of chloroplast DNA
Investigation of chloroplast DNA (cpDNA) has limited use for determining evolutionary relationships since cpDNA is inherited rnaternally. Chloroplast DNA may be highly conserved in Fragaia but some differences existed. The cpDNA of nine Fragana species had "strikingly little cpDNA variability" (Harrison et al., 1993,
1997). In these studies it was determined that F. iinumae, F. nilgenensis, F. nubicola, F. vesca, and F.vidis were not materna1 ancestors of octoploid species.
Fragana virginiana and F. chiloensis had no detectable differences in cpDNA and s hared four unique restriction fragment length polymorp hism (RFLP) bands not present in other Fragada species. Some species, which were widely separated geographically, were found to have similar cpDNA. Fragaria nubicola (from India), and F. vesca (from North American) and had no detectable differences in cpDNA.
These two species had more (RFLP) bands in common with polyploid species than other diploid species. Fragana nubicola diverged from F. viridis (from Europe) by one RFLP band, F. vesca (from Europe) by eight bands, F. nilgerrensis by 11 bands and F. iinumae by 21 bands. These results compliment crossing studies (Tables
1.1 -1.4), morphology (Fig 1-1 and 1.2; Reed, 1966;Staudt, 1989) and karyotyping
(Iwatsubo and Naruhashi 1989, 1991) which suggest F.nilgerrensis and F.iinumae are divergent from other Fragana species. 2 9
Evesca accessions displayed a wider range of diversity in cytoplasrn than other Fragaria species (Harrison et al. 1993, 1997). The octoploid species, F. X ananassa, F. chiloensis and F. virginiana d iffered f rom Ame rican F. vesca s pecies by only four mutations, and eight mutations differentiated Arnerican and European
F. vesca. This could support a theory of F.vesca as a progenitor species. Little is known, however, about diversity of cytoplasm within other diploid species in the study since they were each represented by only one or two accessions.
Unfortunately, F.daltoniana, F.gracilis, F. mandschuica, Fmpponica, F.pentaphylla, were not included in the studies by Harrison et al. (1993, 1997). Perhaps one of these species has a cytoplasm similar to that of octoploid species.
Investigations of nuclear DNA
Most investigations of nuclear DNA in Fragaria have been concerned with fingerprinting octoploid cultivars, estimating relatedness of cultivars, or using marker assisted selection (Davis, 1996a). Only the study of nuclear DNA by Davis et a1.(1 996b) had implications for Fragaria evolution. When progenies of the cross (F. vexa x F. vindis) x Evesca were investigated, only four linkage groups were found instead of the expected seven (Davis et al., 1996b). It seems likely that a self- incompatibility allele from Eviridis may have been responsible for the 16 markers in Magegroup IV that had no recombination since the (F. vesca x F. vindis) hybrid was used as the female in crosses (see Table 1.5). The female gametes containing self-incompatibility alleies would have been selected against since these gametes would have prevented growth of SC pollen tubes from F.vesca. Despite 30 difficulties with linkage group IV, evidence provided indicated chromosomal translocations have occurred in the divergence of F. vesca and F. vindis.
lsozyme studies
Glucose phosphate isomerase -2 (GPI-2) isozymes were studied in many accessions of F.chiloensis, F. virginiana, F.x ananassa and in a few accessions of
F. vesca, F. vindis, F.nubicoia, F.nilgemnsis, F.iinumae and F.moschata (Arulseker and Bringhunt,1983) but not al1 Fragana species were investigated. Each genorne canied genes that encoded for synthesis of GPI-2 isozymes. Thus, polyploid accessions could have more isozyme bands than diploid accessions. Since GPI-2 isozymes were expressed as dimers, three isozymes bands were possible in diploid accessions. Fifteen bands were isolated which proved useful for fingerprinting and inheritance studies. The diversity of GPI-2 isozymes in octoploids showed broader biochemical diversity that may be related to adaptations evolved by octoploids
(Arulseker and Bringhurst, 1983) but implications concerning Fragada evolution were not fully discussed. If hybrid dimer bands are excluded, F. chiloensis had the greatest diversity followed by F.vesca, F. virginiana, F. viridis , Emoschata and
F.nilgenensis with 6, 4, 3, 2, 2, and 1 GPI-2 bands, respectively. Octoploid accessions had GPI-2 bands corresponding to bands found in several diploid species, the exception being band #25 that was unique to some Echiloensis accessions. Thus, it is possible that F.chiloensis was derived in part from another species not present in the study. Fragana daltoniana (2x) would be an excellent candidate for further investigation of band #25 since leaf morphology suggests it 3 l may have been a progenitor to F.chiloensis (Fig. 1.1, Staudt, 1989). Since Fragana viridis had three GPI-2 bands (one being a dimer hybrid) that were unique, it seems unlikely it was involved in evolution of octoploid species. Conversely, F.vesca,
Ç.iinumae, F.nubicola, and Fmoschata had GPI-2 bands that corresponded to bands in octoptoid Fragana, so these four species may be considered as possible progenitors of octoploids. Fragana iinumae and F. nubicola had a GPI-2 bands that corresponded to F. vesca ssp. califomica and F. vexassp. vexa respectively, which suggests a degree of divergence in some F.vesca subspecies.
It has been suggested that F. x ananassa was highly diploidized. based on isozymes studies (Arulsekar et al., 1981. Arulseker and Bringhurst, 1983). The monohybrid and dihybrid segregation of GPI isozymes indicated that chromosomes carrying GPI genes are diploidized, but such results do not show that al1 chromosomes were diploidized. Conclusive proof of diploidization would require genetic markers for each chromosome that make up Fragana genomes. Genetic control was suggested as the cause of diploidization in Fragana octoploids (Byrne and Jalenkov, 1976; Arulsekar et al.. 1981; Bringhurst, 1990). An alternative explanation is octoploids are allopolyploids derived from several diploid species with
homologous pairing occurring preferentially to homeologous pairing.
Glucose phosphate isomerase-one (GPI-1) bands were also studied by
Anilseker and Bringhurst (1983). Only two different GPI-1 bands were found in
Fragana species; F.nilgemnsis had one unique GPI-1 band while al1 other species
had the other GPI-1 band. This finding showed further evidence of the divergence
of F.nilgerrensis from other species in its genus. 32
Chromosome pairing in diploid hybrids
The ability of homeologous chromosomes to pair during meiosis is, with few exceptions, a prerequisite for fertility of interspecific hybrids. While interspecific hybridization between di ploid species may be difficult, chromosome pairing in meiosis was normal for interspecific hybrids of Fragada diploids (Staudt, 1959;
Jones, 1976). Pairing of homeologous chromosomes occured in hybrids derived from crossing remotely related Evesca and Enilgenensis (Jones, 1976). Jones suggests that little differentiation has occurred in the homology of chromosome sets in Fragana, thus preventing any simple analysis of evolutionary relations.
Chromosome pairing in tetraploid hybrids
Fragaria orientalis (4x) formed rnultivalents in diakinesis for 50% of cells studied, but by anaphase 1bivalent formation with late separation of one bivalent was noted for 15% of the cells (Staudt. 1952). Some chromosomes tend to associate as quadrivalents more ofien than others in autotetraploids derived from four diploid Fragarfa species (Bhanthumnavin, 1965) indicating that diploidization was probably not under genetic control in these species.
Evans and Jones (1967) observed 9 to 14% meiotic quadrivalent chromosome associations for three 4x (F. vesca x F. virids) hybrids and 26 to 37% quadrivalents for two 4x (F. nilgerensis x F. vindis) hybrids. In these putative allotetraploids there was tetrasomic inheritance of self-incompatibility alleles.
Quadrivalent formation in F. nilgerrensisx F. vinds hybrids was especially surprising since the parental species were thought to be distantly related. These two species 33 differed in geographical location (Reed, 1966), morphological characteristics
(Staudt, 1989). chloroplast DNA mutations (Harrison et al., 1993, 1997) and isozyme banding patterns (Arulsekar and Bringhurst, 1983).
In another study (Sebastiampillia and Jones, 1977) an average of 10.4 bivalents in diakinesis and 11.5 bivalents in metaphase I were found in eight tetraploid forms of F-vesca, Enipponica and Eiinumae. Thus, it was shown that diploidization may be only partial in autotetraploids. Perhaps small chromosome size (Darlington and Ammal, 1932; White, 1961) or low chiasmatic frequency
(Upcott. 1938) found in Fragaria were responsible for the majority of these chromosomes pairing as diploids.
Chromosome pairing in octoploid cultivars
Examination of nine octoploid cultivars found on average between four and seven chromosomes involved in multivalent formation in diakinesis but the remainder of the cell cycle appeared normal (Mok and Evans, 1971). It was concluded that tetrasomic inheritance could occur in octoploid cultivars. Other studies detenined chromosomes in cultivars paired as bivalents (Byrne and
Jelenkovic, 1976; Ibrahim et al., 1981). It was suggested that genetic control causes preferential pairing within genomes but if homologues were not present, pairing could occur with homoeologous chromosomes (Byrne and Jelenkovic,
1976). As pointed out by Galletta and Maas (1990), whatever the cause of diploidization, 'selection by breeders for high fertility types probably autornatically results in a correlated selection for regular bivalent pairing and disjunction'. If 34 pairing in octoploid species is indeed under genetic control, then introgression of other species should be easy.
Genornic designations proposed for Çragaria species
The following genomic relationships have been proposed, based on homology of pairing in interspecific crosses. with each genome represented by a capital letter: F.nipponica = BB, F.vesca = CC. Eorientaiis = AAAA, Fmoschata =
AAAABB, and F. x ananassa = AAAABBCC (Federova, 1946). The designation for F. nipponica was not based on pairing studies, but on its ability to hybridize with
F. moschata to produce fertile tetraploids (Federova, 1946). The Federova study had the disadvantage of using hybrid species F. x ananassa (8x) rather than its progenitor species F. chiloensis (8x) and F. virginiana (8x). lt was suggested that
F. chiloensis (8x) and F. virginiana (8x) could be classified as AAAABBCC since
Fragana octoploids easily intercross and have fertile progeny (Fadeeva, 1966).
Inferring that F. virginiana and modern F.x ananassa have similar genomic constitution may be reasonable since F. x ananassa is more closely related to F. virginiana than F. chiloensis. Fragana virginiana was extensively used in early breeding programs of F. x ananassa cultivars and F.x ananassa x F.chiloensis hybrids display heterosis while F.x ananassa x F.virginiana hybrids do not (Darrow,
1966). However, it may be erroneous to assume F.chiloensis had the same genomic constitution as other octoploid species.
Recent reviews (Scott and Lawrence, 1975; Hancock et. al, 1990,1996) accepted that F. chiloensis, F. virginiana, and F. xananassa = AAA'A'BBBB, F. 35 vesca = AA, and F. vindis = AA designations suggested by Senanayake and
Bringhurst (1967) but do not discuss Federova (1946) or Fadeeva (1966).
Bringhurst (1990) modified his earlier hypothesis based on evidence that octoploid
Fragada species are highly diploidized (Byrne and Jalen kovic, 1976; Arulseker and
Bringhurst, 1981, 1983)and concluded that octoploid Fragaria genomes should be designated as AAA'A'BBB'B'. These designations were based an limited
interspecific crosses between diploid and tetraploid forms of F.vexa with both F.
chiloensis and F. virginiana as well as F. chiloensis x Potentilla glandulosa and F.
chiloensis x F. viridis. While Senanayake and Bringhurst (1 967) discuss Federova's
(1946) genomic designations (erroneously altering Federova's AAAABBCC to
become AABBBBCC) at length to present evidence to re-designate CC to A'A', they
do not discuss the bulk of Federova's work which designated possible origins for
each of the genomes in F. x ananassa. Their suggestion that the A' genorne
originated from an extinct species and B genomes originated from an undiscovered
species is not well substantiated since only two diploids, F.vesca and F-vindiswere
included in their study.
Research on karyotyping and chromosome pairing of diploids seerned at
variance with the above octoploid genomic designations. Thus far, only F.inumae
genomes were noticeably divergent from other fragada genomes, and it has not
been established or negated that F.iinumae genomes were present in octoploids.
Genomic investigations and introgression strategy
Fragana chromosomes exhibited high hornology with a strong tendency 3 6 towards diploidization at al1 ploidy levels. The diploidization tendency could be due to small chromosome size, low chiasma frequency, or genetic control. Morphology and isozyme studies indicate octoploid species rnay share some common as well as unique diploid progenitors. This possibility will be discussed in more detail in the
pivotai genome section.
Hornoeologous pairing and chromosome substitutions could have occurred
at the diploid, tetraploid or octoploid levels during the evolution of F.chiioensis and
Evirginiana so there is no guarantee that genomes in these species can be
identified with diploid progenitors. If F.chiloensis and F.virginiana descended in part
from different species, the hybrid Exananassa could have recombined genomes
derived from two or more diploid species. While the similarity of Fragaria genomes
may obscure evolutionary relationships, octoploid Fragaria species may have the
capacity to integrate genomes from other species in the genus. Thus, there may
be great potential for broadening the germplasm base of F. x ananassa by
integrating genomes from species that were not involved in the evolution of
octoploid species
No clear strategy for integration of 2x, 4x. and 6x species into octoploids is
indicated by previous genomic studies in Fragaria. It seems likely a number of
integration strategies may be possible (Jones. 1966). While chromosome pairing
is not likely to be difficult, factors such as crossability and genetic differences could
play important rotes in developing an introgression strategy. While F.vesca has
been designated as an A genome and is considered by many to be a progenitor to
the octoploid species, it seems rnost diploid species in Fragana could also be 37 designated as A genomes. The choice to investigate Evesca in this thesis is made with the knowledge that F. vesca genomes are probably present in octoploid species but that genomes from other diploids may also be present. While genomic differences between species can cause serious barriers for introgression strategies, this is not the case in Fragaria.
Pivotal Genome Theory
The Pivotal Genome Theory proposed that allopolyploid species may result from crosses between polyploid species that shared at least one genome in common (i.e. pivota1genomes), yet differed by at least one genome (Le.differential genomes) (Zohary and Feldman, 1961). In polyploid interspecific hybrids, pivota1 genomes helped maintain fertility so that recombination could occur between differential genomes. Cytological, morphological, and taxonomic evidence from studies of Aegilops and Tdticurn and interspecific hybrids provided the basis for the theory (Zohary, 1965). Although several studies suggested that evolution of new species in nature through the mechanism of some pivotal-differential genomes was probably rare (Zhang and Dvorak, 1992; Zhang et al., 1992; Talbert et al., 1993;
Dubcovsky and Dvorak, 1995), the Pivota1 Genome Theory has been quite useful for breeden involved with interspecific hybridization of polyploid grain crops. This theory has shaped introgression strategies and allowed chromosomes from distantly related species to be recombined and introgressed (Gustafson and Dera 1989;
Armstrong et al., 1992; Gustafson and Sears, 1993; Lelley et. al,1 995). In wheat breeding the use of the Pivotal Genome Theory led to many new varieties with 38 increased yield, quality and adaptability because related çpecies could be used as sources of new genes (Feldrnan and Sears, 1981).
The Pivotal Genorne theory could be used to enhance the introgression of chromosomes from other Fragada species into F.x ananassa cultivars. If genomes similar to those in F. x ananassa, were used in interspecific hybridization perhaps crossability and fertility would be enhanced during the introgression process. The most likely diploid species to have been involved in the creation of both F.virginiana and Ç.chiloensis is Evesca (Bringhurst and Senanayake, 1966; Bringhurst, 1990).
Fragana vesca is the only diploid species that shared the same geographic range
as the octoploid species (Evans, 1964; Reed, 1966; Staudt, 1989). It also
hybridized with F. virginiana and F.chiloensis and often resulted in fertile progeny
when ploidy levels of hybrids were doubled (Yarnell, 1931a; Bringhurst and Khan,
1963; Evans, 1964; Senanayake and Bringhurst, 1967; Bauer, l976,l993; Ahmadi
and Bringhurst, 1992). In addition to F.vesca, two other species have been shown
to have common genornes with the octoploid species. Chromosome pairing studies
suggested Eorientalis (4x) and Emoschata (6x) share genomes with F.x ananassa
(Federova, 1946). These latter two species rnay also contain F. vesca genomes
(Federova, 1946; Staudt, 1959; Darrow, 1966). If F.vesca is present in 4x, 6x and
8x species, it may have been a pivotal genome in the evolution of polyploid Fragana
species . 3 9 ADVANTAGES OF USlNG Fragaria vesca AS A BRIDGE SPECIES
Introduction
An important element to any interspecific introgression program is the proper knowledge and use of germplasrn. Of al1 the species in the genus Fragana, F. vesca may have the greatest potential for use as a bridge to introgress lower ploidy species into octoploid cultivars. In a broader sense, a bridge species is defined as one which allows the combining of genetic material from species which cannot directly hybridize. In regards to the SO system a bridge species could one that crosses with several other species and could allow the introgression of dificult to hybridize species into synthetic octoploids. This section will review the unique attributes of F.vesca and its potential as a bridge species for both geneflow and the
SO system.
F.vesca is widely adapted and rnay be a progenitor species
Fragaria vesca is widely distributed and partially overlaps geog rap hically with al1 of the other Fragaria species (Figs. 1.3 and 1.4) which has led several researchers to conclude that it rnay be the oldest Fragaba species and progenitor of the genus (Duchesne in Darrow, 1966; Staudt, 1953; Nurnberg-Kruger;l958;
Longley in Darrow 1966). Morphological traits have been used to suggest that
Evesca is closely related to, or a progenitor of other species (Federova, 1946;
Darrow, 1966; Reed, 1966; Staudt , 1959, 1989, Ahmed and Bringhurst, 1991).
Since hybrids can be made between Evesca and polyploid species, several researchers have suggested F. vesca is at least a progenitor to polyploid species 4 O (Darrow, 1949, 1966; Federova, 1946; Ellis, 1958; Staudt, 1959, 1984; Bringhunt and Senanayake, 1966; Bringhurst and Gill, IWO; Bringhurst, 1990; Ahmed and
Bringhunt, 1991). If F.vesca is closely related to other Fragaria species, it may have the greatest potential of al1 diploid species for use as a bridge species.
A factor contributing to F. vesca's widespread distribution was its ability to photosynthesize at low light levels, which helped it to adapt to forest ecosysterns
(Chabot and Chabot, 1977). It may be better adapted to habitats in cooler climates since it is found primarily in northern areas, and at higher altitudes in equatorial locations (Staudt, 1989). Adaptability of F. vesca was a major reason for attempting to introgress it into cultivars (Darrow, 1966). Decaploids (called F. x vescana) derived from crosses between F. vesca var. sempeflorens and F. x ananassa were noted to possess broader climatic adaptation than F. x ananassa cultivars (Bauer,
1976). These hybrids showed increased vegetative growth during long daylengths compared to pure F. x ananassa cultivars. These hybrids conti nued vegetative growth later in the fall and had flower initiation at 5 - 10 C in the field rather than entering dormancy at the same time as F. x ananassa cultivars (Bauer, 1976). This attribute could be especially valuable at northern latitudes where low temperatures limit the duration of flower bud initiation and reduce yield potential (Chercuitte et al.,
1992). Delayed dormancy was attributed to the day neutral gene of F. vesca var. sempedlorens (Bauer, 1976) although wild types of F. vesca without the day neutral gene were not tested. As the day neutral gene of F. vesca was recessive (Darrow,
1966; Ahmadi and Bringhurst, 1990) it seems unlikely that this gene was responsible for delayed dormancy. Fragaria vesca's ability to carry out 4 1 photosynthesis under low light levels (Chabot and Chabot, 1977) rnay have contributed to increased flower bud initiation during the shorter day lengths and low light levels in autumn. As F. vesca seemed well adapted to cooler climates, a variety of other genetic factors could be involved in F. x vescana's improved climatic adaptation.
F. vesca is self-compatible
Evans and Jones (1 967) found diploid Fragada species had a gametophytic system of unilateral interspecific incompatibility as described by Lewis and Crowe
(1958). Whiie F. vesca was rarely successful when pollinating diploid species (Table
1.1 and 1.2), it can be used as a female in crosses with self-incompatible species to circurnvent self-incornpatibility mechanisms. Only four of the1 0 diploid Fragana species were self-corn patible: F. vesca, F. daltoniana, F.iinumae and F. nilgemnsis.
Of these, little data was available on crossing F. daltoniana and F.iinumae with other species and F.nilgenensis has rarely crossed with other species or has produced stunted interspecific hybrids (Reed, 1966). In contrast, F. vesca has been hybridized with several Fragana species (Mangelsdorf and East, 1927; Yarnell,
1931; Scott, 1951; Bringhurst and Khan, 1963; Evans, 1964; Jones, 1966; Fadeeva,
1966; Evans, 1974; Bauer, 1976; Sebastiampillia and Jones, 1976; Hancock et al., l99O,'i996; Ahmadi and Bringhurst, 1992; Bauer, 1993; Trajkovski, 1993) and the resulting hybrids are often viable (Tables 1.1-1 -4). Thus, the self-compatibility trait of F.vesca could be of assistance in diploid hybridization. 4 2 Some forms of F. vesca are adapted to cultivation
Fragaria vesca, also known as the Alpine Strawberry, has been cultivated for
at least 500 years in Europe (Darrow, 1966;Wilhelm and Sagen,1974). More than three hundred years ago the everbearing non-runnering form, F. vesca var.
sempemorens, was discovered in the Alps which formed the basis for modern F.
vesca cultivars. (Darrow, 1966). As alpine strawberries were propagated primarily
from seed and need to be replanted every few years, it is possible Evesca cultivars
have had approximately 100 generations of active andlor passive selection for
adaptation to cultivation.
Fragaria vesca var. sempedloiens has useful traits that facilitate breeding
Fragaria vesca var. sempedorens is both day neutral (continuously
blooming) and non-runnering. No other diploid species in Fragada was known to
carry non-runnering or day neutral genes, although a dominant day-neutral gene
existed in some octoploid cultivars (Bringhurst and Voth, 1984). These traits were
recessive, and governed by independent genes (Darrow, 1966;Ahmadi et al., 1990)
making them idealiy suited for use as genetic markers to verify hybridization has
taken place. Fragaia vesca, F. vindis, F.nipponica, and F.nubicola have similar
morphology (Reed, 1966; Staudt, 1989; Hancock et al., 1990; Figure 1.l) and
hybrids between these species could be difficult to identify visually.
The day neutral trait of F. vesca var. sempeflorens could be especially useful
logistically when working with other species. As species derived from various
latitudes and altitudes are very likely to bloorn at different times, everblooming 4 3 F.vesca cultivars could be continuously available for hybridization.
Fruit quality
The aroma and flavour of Evesca is considered superior to other Fragana species and several breeding programs have attempted to introgress these two attributes into F. x ananassa cultivars (Darrow,1 949, 1966; Jones, 1966; Ahmadi and Bringhurst, 1992; Trajkovski, 1993). The pleasing aroma from F. vesca was expressed in decaploids derived from F. vesca and F. x ananassa (Darrow, 1949;
Bauer, 1993). Some characteristics of F.vesca fruits were undesirable. Small, very soft fruit with large intercellular air spaces (Darrow, 1966) couid make hawesting both delicate and labour intensive.
Lack of inbreeding depression
Unlike octoploid cultivars (Morrow and Darrow, 1952; Spangelo et al., 1971;
Niemirowicz-Szczytt, 1989), diploid F. vesca cultivars did not have inbreeding depression and were true from seed (Darrow, 1966). It is, therefore, unlikely that undetected deleterious recessive traits would be introduced from F. vesca gennplasm. Even at the autotetraploid level, F. vesca was fertile (Yarnell, 1931b;
Scott, 1951; Evans, 1964; Bumagina, 1974; Bauer, 1976; Trajkovski, 1993;
Sebastiampillia and Jones, 1976,1977; Silva and Jones, 1996). These factors may make F. vesca more fit at higher ploidy levels than other Fragaria diploids, which rnay be important in introgression strategies. 4 4 Fmvesca is amenable to chromosome doubling
Fragaria vesca was not only more responsive to colchicine's chromosome doubling action but it was less sensitive to colchicine toxicity than other species.
Chromosome doubling occurred more readily for F. vesca than for F.nubicola,
Eiinumae, Enilgerrensis, F. vindis, F. moschata, or F. x ananassa (Fadeeva, 1966;
Sebastiampillia and Jones. 1976) and had a higher survival rate after colchicine treatment (Sebastiampillia and Jones , 1976). The superiority of Evesca seemed to be due to bath genetic and cytoplasrnic factors (Fadeeva. 1966). This peculiarity may be due in part to phenolics or biochemical adaptations of different species.
Porebski et al. (1997) found it necessary to modify CTAB DNA extraction protocols for Fragana species because of high polysaccharide, tannins and polyphenol components. It seems likely that concentrations of these compounds differ among
Fragana species and could interfere with the alkaloid activity of colchicine or perhaps be connected with increasing the toxic effects of colchicine. Whatever the mechanism, Evesca's cytoplasrn and genomes may transmit ease of chromosome doubling to hybrid progeny. Thus, the use of F.vesca as a female parent would be particularly beneficial for introgression strategies that require chromosome doubling.
F. vesca cytoplasm
Cytoplasmic differences have been important in the success of interspecific hybridization (North, 1979; Stoskopf et al., 1993). Too few synthetic octoploids have
been created to judge how important cytoplasmic differences are for synthetic
octoploid production, but fertile synthetic octoploids were created that had F. vesca 4 5 cytoplasm (Ellis, in Darrow, 1966; Sebastiarnpillia and Jones, 1976; Evans, 1982b).
Synthetic octoploids have also been created with F. moupinensis and F. moschata cytoplasm (Sebastiampillia and Jones, 1976; Evans, 1977). Although rnost of
Fadeeva's (1966) interspecific crosses were unbalanced between species and hybrids of differing ploidy level, good seed set was achieved when F. vesca was the female parent.
Investigations of RFLPs from chloroplast genomes revealed cytoplasmic variation was greater among three subspecies of F. vexa than among six subspecies of F.virginiana and F.chiloensis (Harrison et al., 1993, 1997). While it is not known if different cytoplasm would be of benefit to cultivars, the use of
F. vesca in introgression strategies could offer researchers an opportunity to explore this possibility.
F.vesca as a bridge species
As will be seen in the section that follows, Evesca has been used successfully as a bridge species in the synthetic octoploid system. However, such research did not emp hasize F. vesca, so the potential of F. vesca as a bridge species in the synthetic octoploid system has not been fully investigated. 4 6 INTROGRESSION OF FRAGARIA SPECIES USiNG SYNTHETIC OCTOPLOID
SYSTEMS
Only a few accessions of F. vesca, F. vindis, F-nubicola,Fmoupinensis, and
Fmoschata have been introgressed into octoploid cultivars (Darrow, 1966; Evans,
1976; Kantor, 1984; Ahmadi and Bringhurst, 1992; Bauer, 1993; Sangiacomo and
Sullivan, 1994). There is no current evidence to suggest that the nine other non- octoploid species have been introgressed into 8x cultivars. While fertile heptaploids and decaploids resulted from crosses between F. x ananassa and lower ploidy species, these groups were reproductively isolated from octoploid varieties because of differences in ploidy levels (Kantor, 1984; Bauer, 1976, 1993; Bringhurst and
Voth, 1984; Ahmadi and Bringhurst, 1992; Noguchi et al., 1997). It was proposed that lower ploidy species (2, 4, and 6x) be intercrossed and have ploidy levels doubled with colchicine to create synthetic octoploids (SOS) (Evans, 1974,1977).
This strategy would overcome ploidy level barriers and facilitate introgression of lower ploidy species into octoploid cultivars. While creation of synthetic octoploids may be diffkult, once created they would not require specialized cytogenetic techniques, such as doubling or counting chromosomes, ta be used in strawberry breeding programs (Evans 1977,1982~).
Despite potential benefits, SO production had been abandoned for more than twenty years. The SOScreated by Sebastiampillia and Jones (1976) were the rnost recent attempts in this area. Evans had several papers in the 1980's on the synthetic octoploid system but he last created SOS in 1972 (Evans, 1982~).Guelph
SOI, and Guelph S02 have been the only SOS released for use by breeders 4 7 (Evans, 1982bc), and two breeding programs, one at Guelph and one at Sweden, have reported using them (Sangiacomo, 1989; Sangiacomo and Sullivan, 1994;
Trajkovski; 1990. 1993).
lmproving upon the SO system requires elucidation of reasons for difficulties in obtaining SOS. A critical examination of SO literature must consider the level of technology in past investigations and new techniques that have become available in the last twenty years.
Crossing strategies to create SOS
Several researchers have attempted to create SOS by crossing lower ploidy species directly ta octoploid cultivars (Federova. 1946; Ellis, 1958; Bhanthumnavin,
1965; Jones, 1966; Ellis, in Darrow 1966; Kantor, 1984). Such strategies often relied on colchicine or unreduced gametes and required several generations of crosses between different ploidy levels to restore hybrids to the octoploid level
(Fig. 1.5). This type of strategy is designated 'Unbalanced Ploidy Strategy' in further discussion. An alternative strategy will be designated the 'Balanced Ploidy
Strategy' in further discussion as almost al1 crosses leading to SO creation were
between plants of the same ploidy. The Balanced Ploidy Strategy was adopted by
Evans (1977, l982a, l982b) and Sebastiampillia and Jones (1976) (Fig.l.6). They intercrossed lower ploidy species and applied colchicine to increase chromosome
numbers and created SOS, which could then be crossed into octoploid cultivars. 4 8 Fig. 1.5. Unbalanced ploidy strategies for creating synthetic octoploids. Octoploid cultivars were used in initial crosses, followed by crosses with other species to restore ploidy level to 8x. The diagrams are based on Ellis (1958), Bhanthumnavin
(1965), Darrow (1966), and Kantor (1984).
unreduced ametes
mutagenic chemicals
unreduced 5x gametes
8x 2x / colchicine
-8x 16x colchicine colchicine -a le)8x colchicine 4 9 Figure 1.6. Balanced ploidy strategy for introgression of lower ploidy species into octoploid cultivars. Lower ploidy species are used in initial crosses, and the resulting synthetic octoploid is crossed to cultivars as the last step. Except for crosses using hexaploid species, al1 crosses are between plants having the same ploidy level.
Diagrams are based on Sebastiampillia and Jones (1976) and Evans (1976).
--4x 8x colchicine
4~ / colchicine
4x / colchicine *'> 4x 8x colchicine
-8x colchicine 52%unreduced
-2x 4x -8x colchicine colchicine 2x 4x -8x =chicine colchicine
2~ 4~ / colchicine colchicine 50 Germination rates ranged from O to 4.4% for unbalanced ploidy crosses of ten researchers (Evans, 1974). When Evans made diploid x hexaploid and diploid x octoploid crosses, set was 2 seeds / pollination, germination was 25%, but seedlings that resulted did not appear to be hybrids. It was suggested chromosome imbalances between the zygote and endosperm occur in unbalanced ploidy crosses resulted in low seed set and poor germination. Using the parent with the higher ploidy level as the female in crosses was recommended (Evans. 1974). Reciprocal crosses were not done in the Evan's study (1974), but diploid and tetraploid foms of (F.vesca x F.vindis) were crossed as females to F.chiloensis, F.virginiana, and
F. x ananassa. Only the combination (F.vesca x F.vindis) 4x X (Enubicola x
F.moschata) 8x produced hybrids while similar crosses using diploid (Evesca x
F.viridis) as females were not successful. The tetraploids were crossed to 14 octoploid accessions while diploids were crossed to only seven octoploid accessions, so the variation between these two ploidy levels rnight be due to too few accessions in the diploid segment of the study. Despite difficulties, Unbalanced
Ploidy Strategies have resulted in a limited number of fertile synthetic octoploids
(Table 1.6). Using a unique approach, Kantor (1984) used mutagenic chemicals (H- nitrosoethylurea and l,4-bis-diazoacetlybutane) to overcome sterility of 7x hybrids produced by crossing F-moschata (6x) to F. x ananassa (8x). He was attempting to transfer desirable flavour from F.moschata to F. x ananassa., but this flavour disappeared during backcrossing so Kantor abandoned introgression in favour of developing 7x iines that were F, hybrids of F. x ananassa X F. moschata. 5 1 Table 1.6. Combinations of Fragaria species that have resulted in synthetic octoploids with different fertility levels.
Sterile:
F. moupinensis x F. moupinensis (Evans, 1964, 1977) F. vesca x F. moschata (Ellis, in Darrow, 1966) (F. nilgenensis x F. virids) 4x x F. moupinensis (Evans, 1977)
Ferülity unknown:
F. moschata X F. viridis (Bhanthumnavin, 1965) F. vesca X (F. vexa 4x x F. x ananassa) 6x (Ellis, in Darrow 1966) F. moupinensis x F. corymbosa (Sebastiampillia and Jones, 1976) (F. rnoschata X F. vindis) X F. corymbosa (Sebastiampillia and Jones, 1976) F. vesca 4x X (Ç. moschata X F. vindis) (Sebastiampillia and Jones, 1976)
Partial Fertility :
(F. x ananassa X F. moschata) 7x , selfed and backcrossed to Ex ananassa (Federova, 1946; Kantor, 1984) F. moschata X F. nubicola (Bhanthumnavin, 1965; Evans, 1977)
(F. x ananassa x Ç. vesca)lUx X F. moschata (Nicholson, in Jones, 1966) ( F. vesca 4x x F. x ananassa)6x X(4x F. vesca X 76x F.x ananassa) 70x (Ellis, in Darrow, 1966) F. vesca 8x (Dermen, in Darrow ,1966) (F. vesca x F. vindis)4x x (F. moupinensis) (Evans, 1977) 52 Balanced Ploidy Strategy usually has tetraploid crossing as the final step prior to chromosome doubling to create octoploids. Tables 1.7 and 1.8 show results of balanced ploidy crosses among tetraploid species and hybrids. Note that germination rates for balanced ploidy crosses are much higher in these tables than the O - 4.4 % germination range reported for unbalanced ploidy crosses (Evans,
1964). All three tetraploid species and seven 'synthetic' tetraploids have been used in crosses at the tetraploid level. Of these, F.vesca (4x), (F.vesca x F. vindis) 4x and (F.nilgenensis x F. vindis) 4x are the only synthetic tetraploids derived solely from diploid species. Clearly, further research is warranted regarding use of tetraploids derived from diploid species. Strategies to create tetraploids from diploid species include: creation of auto- and allotetraploids, and crossing diploids to
F.moschata (6x). Many. but not all, combinations of tetraploid species and hybrids have been hybridized to one another. Besides yielding higher numbers of seeds, the Balanced Ploidy Strategy required only 1-2 generations to achieve an octoploid, while two to four generations are required for an Unbalanced Ploidy Strategy. Using a Balanced Ploidy Strategy, Evans (1982~) successfully introgressed three SOS into octoploid cultivars; no reports were published on the eight SOS created by
Sebastiampillia and Jones (1976). Only Evans (1 977, 1982a, l98Zb, 1982~)has given a full account of creation, fertility and introgression of synthetic octoploids.
When the two synthetic octoploids, Guelph SOI and Guelph S02, were backcroçsed into F.x ananassa it was demonstrated that important SO traits could be introgressed into cultivars and that fertility was rapidly restored in two or three crosses to cultivars (Sangiacomo and Sullivan, 1994). Thus, it has been 53 Table 1.7. Results of studies on hybridization of Fragaia tetraploids. These studies did not atternpt to create synthetic octoploids, but are included since tetraploid hybridization is part of Balanced Ploidy Strategy for synthetic octoploid production. Evans,l964:
poilin- combin- seeds % Fernales' Males ations ations Y Ipo11. gem.
F-moupinensis (1) * F.nilgemnsis x F. viridis (3) 91 F.moupinensis (7) F. vexa x F.viridis (2) da
F.nilgemnsis x F. vitidis (4) F.moupinensis (7) 48
F.nilgemnsis x F. viridis (3) F.orientalis (7) 83
F.nilgemnsis x F. vindis (3) F.vesca x F. viridis (4) 72 F.orientalis (7) F.moupinensis (1) da F-orientalis (1) F.nilgenensis x F. vindis (1) nia F-orientalis (7) F.vexa x F. vindis (3) nia
F. vesca x F.vindis (5) F.moupinensis (1) 54
F. vesca x F.vindis (5) F.nilgenensis x F.viridis (3) 28
F. vesca x F. vindis (5) F.orientalis (1) II
Females Males seedibeny % germination
F. vesca (4x1 F.viridis x F.moschata 2 1 30
F.vesca (4x) F.moschata x F.viridis 58 28
Females Males Progeny F.orientalis F-corymbosa 765
F. vesca (4x1 F.onentalis 67
F. vesca (4x) F. vesca (4x) X F. orientalis 44 F. vesca (4x1 X F.orientalis F.orientalis 499
2: Except for F.moschata (6x1 x F-nubicola (24 from Evans 19ï7, al1 female and male parents in this table are tetraploids Y: combinations are the number of crosses with dierent accessions as parents. X: number in ( ) indicates number of accessions available 54 Table 1.8. Results of attempts to create synthetic octoploids (SOS) from 2x, 4x and 6x Fragana species. The resulting progeny from these crosses were treated with colchicine to create synthetic octoploids which could eventually be hybridized with 8x cultivars of F. x ananassa. Except for the Emoschata x F.nubicola crosses of Evans (1977) the final crosses made were between tetraploids.
Females Males seedlings survivors SOS Fertile reference after SOS colchicine
F.moupinensis (4x) F. corymbosa (4x) 6 5 2 Sebastiampillia and
F. onentalis (4x) [F.moschata (6x) x F.nubicola (2x11 4x 16 13 O Jones, 1976
IF.vesca (2x) x F.viridis (2x)] 4x [F.moschata (6x) x F.nubicola (2x11 4x 16 14 O
IF.moschata (ex) x F.viridis (2x)] 4x F.orientalis (4x1 8 4 O
[F.moscheta (6x) x F. vindis (2x)]4x F. corymbosa (4x) 16 13 5
F.vesce (4x) [Emoschata (6x) x F. viridis (2x11 4x 4 3 2
F ,moschata (6x) F.nubicola (2x) 312 42 2 2 Evans, 1977
[F.moschata (6x) x F.nubicola (2x11 4x F.orienta/is(4x) 2600 196 O O
[F. moschata (6x) x F.nubicola (2x11 4x [F. vesca (2x) x F. vindis (2x11 4x 600 47 O O
F.moupinensis (4x) [F.nilgerrensis (2x) x F.viridis (2x)] 4x 2120 216 O O
F. moupinensis (4x) F.moupinensis (4x) 42 2 1 O
If.ni/gemnss (2x1 x F.viridis (2x11 4x F.moupinensis (4x) 230 4 2 O
/F. vesca (2%) x F. vindis (2x11 4x F.moupinensis (4x) 466 60 1 1
[F. vesca (2x) x F. vindis (2x)]4x [F.vesca (2x) x F.viridis (Zx)] 4x 194 25 O O 5 5 demonstrated that the synthetic octoploid system can be used to introgress traits from lower ploidy species into octoploid cultivars.
The group lead by J.K.Jones at the University of Reading (Ellis,
Bhanthumnavin, Evans. and Sebastiampillia) probably used the same group of accessions for their research. Thus, synthetic octoploids produced by this group may have been derived from a very narrow germplasm base. Evans' (1964) thesis lists the available accessions as follows: F. vesca (13), F.nubicola (2), F. vindis (1),
F.nilgerrensis (1), F.daitoniana (1), F.orientalis (1), F.moupinensis (2) and
F.moschata (4). This group originally used Unbalanced Ploidy Strategy (Fig. 1.5) but later abandoned it in favour of Balanced Ploidy Strategy (Fig. 1.6). While Balanced
Ploidy Strategy rnay have been a more successful approach, research did not continue beyond a few attempts. Only a few of the possible combinations of species have been investigated for creation of SOS. With ten diploids, three tetraploids and one hexaploid species, theoretically 12,769 combinations of species could result in SOS within two generations. A simplification of these possibilities, including creation of tetrahaploids is presented in Figure 1.7. This figure is similar to the crossing strategy for this thesis except that tetrahaploids derived from octoploid species (tetra-haploids) will not be investigated.
lmproving SO production
While sorne researchers developed techniques that potentially could improve
SO production, there has not been an effort to bring these techniques together for
SO production. For instance, Sebastiarnpillia and Jones (1W6), developed a 56 Fig. 1.7. A simplified Balanced Ploidy Strategy for synthetic octoploid production.
This diagram simplifies crossing strategies depicted in Fig 1.6 but is broader in scope. Breeding at diploid and tetraploid levels as well as creation of tetrahaploids is incorporated into this strategy. Diagrams show ploidy levels of species and hybrids involved in crosses. Parents are on left and progeny on right.
Tetraploid creation
Diploid chromosome doubling Tetraploid Octoploid breeding breed ing creation --4x 8x chromosome doubling
anther culture androgenesis chr. elimination 57 superior colchicine application technique that was not used by Evans (1977,
1982~).Test crosses to discover combinations of accessions with high seed set was likely used by Evans (1977) who produced 6564 hybrid tetraploid seed by using the successful combinations of parents identified in an earlier study (Evans, 1964).
A wider germplasm base increased the likelihood of successful interspecific hybridization (Burbank ,1921; Galletta and Maas, 1990; Stoskopf et al., 1993) and is an obvious way to improve SO production. In addition to test crossing, pollination of the same flowers on different days has increased seed set (Evans, 1964). lmproved germination methods (Jonkers, 1958; Scott and Draper, 1967; Wilson et al., 1973; Miller et ai., 1992) were also not employed in SO research. If al1 these techniques were incorporated into one rnethodology, it seems likely that the efficiency of the SO system would be greatly improved.
lmproved strategy for SO production
Previous research showed that a Balanced Ploidy Strategy was more likely to be successful in the creation of synthetic octoploids than an Unbalanced Ploidy
Strategy. Such a strategy requires fewer generations and gives higher seed production than an Unbalanced Ploidy Strategy but also requires the sometimes difficult step of chromosome doubling. Previous investigations of SO production have been hampered by lirnited availability of gennplasrn, particularly diploid species. As more species become available through increasing holdings of genebanks, intercrossing of al1 available accessions becomes less feasible.
There has not been an attempt to focus on specific species to improve SO 58 production. As mentioned earlier, Fragana vesca not only possesses traits that would be beneficial to introgress into cultivars, but has several unique attributes that could improve introgression strategies. Its ability to hybridize with octoploid cultivars has been shown but it has not been used as a bridge to aid introgression of other species into cultivars. It is hypothesized that a SO strategy focusing on use of
Evesca as a bridge species would be an improvement over earlier attempts to create SOS. 59 Chapter 2
General materials and methods
Introduction
This chapter details the general materials and methods used throughout the thesis. Most of these techniques were adapted for this study and represent technology not used in earlier attempts to create synthetic octoploids (SOS) in
Fragaria. Synthetic octoploid production has been abandoned for more than 20 years, largely because the system was inefficient. Difficulties previously encountered such as poor fruit set, low germination rates, chromosome doubling and small chromosomes that were difficult to count, have been addressed by the methodology presented in this chapter. In this study, several modern techniques have been applied simultaneously to improve the SO system.
ln vitro germination
The in vitro germination technique Of Miller et al. (1992) was modified for use in this research. This technique was originally developed for use with F.x ananassa seed, but was adapted for seeds resulting frorn interspecific hybridizations.
Murshige and Skoog medium (Sigma-Aldrich Canada Ltd., Oakville, ON.) was prepared with no hormones as descrÎbed by Miller et al. (1992) but Gellan gurn agar
(Schweizerhall, South Plainfield, N.J.) at 2.5gi1 was substituted for agar. Acid washed, activated charcoal (Gibco Laboratories 1 Life Technologies Inc., Grand
Island, NY) was added at 3.0 g/l to darken the medium. In a previous study, shoots 60 of seedlings germinated on clear medium often grew upside down or laterally.
Shoots in darkened media had a higher frequency of upright growth, which is an important characteristic for colchicine treatment. Medium (7.5mls) was placed in
30ml glass French squares, autoclaved (mode! 3021, AMSCO, Erie, Pa) at 121OC for 20 minutes and aliowed to solidify in a slanted position on racks.
For surface sterilization, achenes were wrapped in cheese cloth held by a paper clip, dipped in a 0.5% (vlv) sodium hypochlorite (Lilo products, Hamilton, ON) solution containing tween 20 (2~111) and placed on an orbital shaker (Labline
Instruments, Melrose Park, III.) for 20-30 mins. Agitation continued through three transfers into vials of sterile deionized water to remove the sodium hypochlorite solution. Achenes were placed on moistened sterilized filter paper to prevent desiccation, and the distal third of each achene was removed with a scalpel and discarded. Cutting occurred under a dissecting microscope (AusJENA, Gei-many) in a larninar flow hood (Canadian Cabinets Co. Ltd., Ottawa, ON). Cut achenes were placed in vials on the surface of the medium described above. These vials were placed on racks and in a tissue culture growth room maintained at 20°C,30cm below 40 watt cool white flourescent lights (Sylvania, Mississauga, ON) at 70 pmol m-2- s*~.Seeds usually germinated and had fully expanded cotyledons within 10 days of being cut and placed on the media.
Colchicine treatrnent for chromosome doubling
Colchicine (SigrnaAldrich Canada Ltd., Oakville, ON.) was dissolved in 95% 61 ethanol and diluted with distilledideionized water for final concentration of 50 gm colchicine / litre. This solution was applied to seedlings 10-20 days after placement of cut achenes on media, which coincided with full expansion of cotyledons and before expansion of the first true leaf. Colchicine solution was applied as drops
(10ullseedling) with a micropipettor to the meristematic region between cotyledons of in vitro seedlings (Fig. 2.1). The sterile environment was not maintained for colchicine treatment since seedlings were to be removed from tissue culture within
20 hours. Vials were sealed to rnaintain humidity, and returned to the growth room.
Vials were filled with deionized water to provide one quick rinse after 18-20 hours of colchicine treatment.
Acclimatization of seedlings
ARer in vitro germination or colchicine treatrnent, seedlings were transplanted to plug trays (72 plugs / tray, Kord Products Ltd., Blarnalea, ON) for acclimatization.
The plug trays contained soilless mix (Promix BX, Premier Horticulture Inc., Red
Hill, Pa.). Plug trays were placed for 3-4 weeks in a growth chamber (Model EY8M,
Controlled Environrnents Ltd., Winnipeg, Manitoba) with continuous light provided by 40 watt cool white flourescent lights (Sylvania, Mississauga, ON) at 15-17C before being moved to the greenhouse. Plants were bottorn watered with deionized water. When plants grew larger, they were transplanted into larger pots containing
Promix BX. Seedlings were raised in the greenhouse until planted into the field.
Greenhouse conditions consisted of : 18/14°C daylnight temperature; 16 hour daylength provided by 400W high pressure sodium supplemental lighting (PL 62
Figure 2.1. In vitro treatment of Fragaria vexa seedlings with colchicine solution.
Note the droplets of colchicine solution placed on cotyledons. 63
Lighting, Grimsby, ON); and 60% relative humidity during growth stage. Plantings into the field occurred in either early June or late August of 1995, 1996,and 1997.
Plants were field grown at Cambridge Research Station, Cambridge, ON in Fox sandy loam soil.
Handling of parent plants for crossing
In early November, dormant plants were dug from the field and stored bare
rooted in a freezer at -1C. From late December to early March, plants were potted
with a soilless mix (Promix BX, Premier Horticulture Inc., Red Hill, Pa.) in either 3
or 6 litre pots (Plant Products, Brampton, ON) and grown in the greenhouse at
Guelph, ON. Plants were watered as required with deionized water and fertilized
with an all-purpose fertilizer solution [20N - 8P - 20K (Plant Products, Brampton,
ON ) used in the Guelph greenhouse at a concentration of 267mgllitre solution that
had been brought to a pH of 6.0 with phosphoric acid].
Floral induction
F.nubicola, F.pentaphy//a, F.daltoniana, F.iinurnae, F. orientalis, and some
hybrids derived from these species did not bloom under the greenhouse conditions
described above. They required additional short day and temperature treatments
(four weeks, 10 hr photoperiod, 18C day, 15C night) (Jonkers, 1958) in a growth
chamber (Model EY8M, Controlled Environments Ltd., Winnipeg, Manitoba) to
induce bloom. The flower induction treatment was applied in late winter or early
spring to greenhouse plants that showed no signs of blooming. 64
Pollination
Emasculation was carried out according to Scott and Lawrence (1975). Each moming, anthers and petals were removed with sharp tweezers when buds were in the "popcorn" stage (i.e., buds were in the early stages of opening with white petals emerging). Anthers were placed on petri dishes in the dark at 20-22 C and allowed to dry and dehisce overnight. Pollen was stored according to the protocol shown in Fig. 2.2. Microcentrifuge tubes (1.%?.O mls.) containing pollen were placed in a Magenta box (#GA7-3. Magenta Corp., Chicago, III.) half filled with self- indicating desiccant (#07-577 & 07-578 Drierite, Fisher Scientific. Nepean, ON).
Magenta boxes were stored in styrofoam boxes and placed in a refrigerator at 3 to
4 C.
Often, dried anthers were crus hed to release pollen within microcentrifuge tubes using the handle end of paint brushes with an action similar to a rnortar and pestle. Flowers were emasculated and pollinated the same day. Camel hair brushes were used to spread pollen ont0 stigmas of emasculated fiowers. For diploid crosses, only one primary bud was pollinated per truss. As tetraploid flowen were larger than diploid fiowers, primary, secondary, and occasionally tertiary fiowers were also used, if receptacles were greater than 3 mm in diameter after emasculation. Small buds often showed signs of wilting on sunny days and were not used. High humidity (80-90%) in the greenhouse. and removal of fully opened flowers reduced chances of selfing. Flowers were not bagged after emasculation. 65
Fig. 2.2. Pollen storage method based on procedures of MacFarlane Smith and
Jones (1989). Pollen was protected from light by placing the storage container in a box kept in a refrigerator at 3C.
Air tight
Container ---
u-- - '-C -+- % - --' Desiccant
Hole in top Microcentrifuge Non-absorbant cotton
Anthers and Pollen 66
Organization of crosses
Crosses were done over a period of time as different genotypes flowered.
Within each group of species or hybrids, pollen from various genotypes was
randomized each day and used in crosses. An attempt was made to pollinate each female with equal number of the different species used as pollinizerswhen possible.
Parents with common ancestry were not crossed together, thereby fostering greater
heterozygosity in offspring. Choice of parents was made to maximize the number
of male/female combinations and, thus, sample a greater amount of diversity.
Pollen from genotypes that had never been used was given prîority over previously
used genotypes.
Seed collection and storage
Ripe berries were either crushed on petri dishes or placed intact into airtight jars containing desiccant. Crushed berries were air-dried at room temperature.
Once dry, achenes were rubbed off. counted and stored until use. The conventional
method of extracting seed in a blender was not used to avoid damage to achenes
which might allow penetration of bleach into embryos during the in vitro sterilization
step. Only large plump seed were collected and stored. Intermediate and small-
sized seeds contained no embryos in as determined in previous investigations.
Seeds were stored at room temperature or in a refrigerator at 3 to 5 C.
Data collection and analysis
Variables studied included % fruit set, seedslflower, % embryos, and % 67 embryo germination. Percent set referred to the number of flowers that produced at least one seed divided by the number of flowers pollinated. Large. plump seeds were counted for each flower to provide seed numbers. Percent ernbryos was the percentage of seeds that contained fully developed embryos with a healthy appearance. These data were obtained when achenes were cut in half for in vitro germination. Only seeds containing white coloured embryos and cotyledons were considered healthy. As semi-filled seed with white interiors were capable of germination, they were classified as developed ernbryos. Previous results had shown that achenes with yellowish or light brown interiors were not viable and were categorized as dead. Emb~yogermination was the ratio of healthy seedlings 1 embryos. Although almost al1 healthy embryos grew when placed on MS medium, only those that developed into normal green seedlings were counted. Abnormal seedlings that were albinos, lacked hypocotyls or roots, or failed to develop true leaves were occasionally observed but were not counted as geninated. Data were analyzed with the GLM program of PC SAS (Sas system for Windows V.6.12. Cary.
N.C.) and means separation was accomplished using the LS means function.
Nomality of data was checked with SAS and arc-sine transformations were done on those data which did not appear to have normal distribution.
Visual screening of plants following colchicine treatment
Visual screening was used to identify hybrid progeny which showed morphological evidence of chromosome doubling at four to six months after colchicine treatment. Hybrids that had slower rates of development (see Fig. 2.3) 68 and larger, thicker, darker leaves with more pronounced serrations (Fig. 2.4) compared to their parents and siblings were set aside for flow cytometry testing as described in the next section.
Flow cytometry protocol
Flow cytometry has been used to estimate ranges of 8x to 16x for F x ananassa accessions derived from protoplasts (Nyman and Wallin, 1992), but a flow cytometry protocol has not been developed for Fragaha with ploidy levels lower than 8x. Nyrnan and Wallin's (1992) flow cytometry protocol required creation of strawberry protoplasts as a first step. This step would have been quite difficult to replicate on a variety of Fragana species and would have increased the time required to obtain ploidy level estimates. A protocol being used at the University of
Guelph for analysis of Lycopersicon esculentum (tomato) was adapted for use with
Fragana species. The nuclei isolation solutions (Table 2.1) and nuclei isolation protocol (Table 2.2) were derived from Arumuganthan and Earle (1991) and Bino et al. (1992) as modified by Shawn Rogers (unpublished). Sample size, chopping time, centriiugation tirne. propidium iodide concentration, and standards were refined for use with Fragaria species in this study and have been included in Table
2.2. The Coulter Epics Elite ESP Row cytometer, manufactured in 1994, was used to estimate ploidy levels. Flow cytometer settings are provided in Table 2.3. The flow cytometer was set to read a maximum of 5000 cells for each sample. When intemal standards were used 10,000 cells were counted. Often, distinct peaks were 69
Figure 2.3. Diploid (left) and tetraploid (right) forms of the "Alexandria" variety of
F. vesca ssp. vesca var. sempeflorens at identical ages. The diploid has ripe fruit
(indicated with arrows) and greater number of leaves, indicative of a faster growth rate. The tetraploid plant has just begun to bloom. 70
Figure 2.4. Leaf morphology of interspecific hybrids of Fragaria species. Diploids, tetraploids and octoploids are located on the lower, middle and upper rows, respectively. Leaf serrations along leaf edges and leaf sire increase at higher ploidy levels. Table 2.1. Nuclei isolation solutions. These solutions are used during chopping, staining, and running of samples.
Solution A:
15 mM HEPES (H-3375 Sigma, Oakville, ON) 1 mM disodiurn EDTA (BP-120-500 Fisher Scientific, Fairlawn, N.J.) 80 mM KCI (3040 J.T.Baker, Phillipsburg, N.J.) 20 mM NaCl (S-9625 Sigma) 300 mM Sucrose (Redpath, Toronto, ON.) 0.2% Triton X-1 O0 (T-9284 Sigma) 0.5% Spermine tetrahydrochloride (S-2876 Sigma) 1.O% PVP (MW=40,000) (PVP-40Sigma) pH adjusted to 7.5 store in aliquots at -20C add 0.1% 2-mercapto-ethanol (R-4875 Sigma) prior to use
Solution B:
2.5 ul RNAaseI ml of Solution A (10mglml stock RNAase) (R-4875 Sigma) 10 ul Propidium lodide Solution per sample (P-3566 Molecular Probes, Eugene, N.J.) Note: solution is 1.0 rnglrnl stock) Table 2.2. Nuclei isolation procedure. 1. Leaf tissue (4 cm2 per plant) was harvested, placed in a in petri dish and put on ice. Fully expanded young leaves were preferred but old leaves were occasionally used.
2. During maceration, petri dishes containing the leaf sample, centrifuge tubes and filters were on top of ice. Solution A (1 .O ml) was added to leaf samples that were then chopped with a razor blade until leaf tissue attained a liquid consistancy and the suspension started momentarily sticking to the razor blade foming strings. After 'string' fornation was noted, chopping continued for about 15 seconds. Often, chopping lasted 1.5 - 2 minutes per sample. but this varied according to speed of chopping and species. Blades were used on a maximum of 5 samples.
3. Homogenate was filtered through 100 Fm and then a 30 pm nitride mesh into a microcentrifuge tube.
4. Optional step:
Interna1 standard: Diploid trout red blood cell solution (Ten cytornetry control, #IOOï, Biosure, Grass Valley, California) was diluted 30 MIper Iml of solution B and filtered through a 30 pm nitride mesh.
External standard: Desiccated chicken red blood cells (CRBC) (#R0504, Sigma, Oakville, Ontario) were suspended in distilled HZ0 at 25mglml. This suspension could be stored for a few months if refrigerated. CRBC suspension was mixed at a rate of 20 pl 1500 pl solution B.
5. Samples (from step 3) were vortexed for 5 seconds and then centrifuged for four to five seconds (time from start, not from peak speed). Supernatant was discarded.
6. Solution B (200 pl) was added to each sample.
7. Optional step: 20 pl of interna1 standard solution (step 4) was to each sample.
8. For extemal standards, 20 pl of intemal standard stock solution (step 4) were added to 200 pl of solution B.
9. Samples and exterml standards were vortexed and incubated at 37' C in darkness. After 15 minutes, they were removed from the incubator and placed in the darkness at room temperature. Sarnples were used within three houn and vortexed immediately before nins through the Row cytometer. Table 2.3. Settings for the Coulter Epics Elite ESP fiow cytometer when running Fragana nuclei with trout red blood cells (TRBC) as an interna1 standard. For the PMT3 sensor a red FI filter was used. The 488 nm argon laser was used as the light source.
PROTOCOL: STRMJBERRY NUCLeI
srnmom FS PHT1 PlIl2 PHT3 PHT4 PM6 AüXl AUX2 Uoltm 889 340 7f0 610 60e 409 1Q.h 1. 7.1 8.1 10.0 6.0 t.e a f.0 POIin 1.0 6.8 6.e L.0 1. O p--P 1.0 1.0 oœly LOU LOU LOU LOU LOU LOU LOU LOU Flwrercrnci Conpmnmat ion mtmd ~mp Si-1 out (Y> Y - XX PARAPI A PHT~LOG y X~~lPMI mf3 PHT~ PP~TE QUXL ISUXZ PC~RA~?I P~TSLOO Pm1 0.0 0.9 C3WOi.c OFF PM7 4.8 1.8 fr Sourc FS PEAK PPnr 0.0 9s 0 Clock S. 0 nt4 O. 0 1. O Un UIdth 25.0 PHTE B. 0 1.0 Un Omlru 60.0 AUX1 8.0 0.0 U T Oimc 09 RW a.0 O. B tr Omin 8 Sq Olhy 20 ui Lao Lack OFF Scmpm Trmcm CnbiOibl OFF Pluidici (psi) tlist811an~our f.iph Shmath arnctwidtk LOU 11.a t2. OB 0i.c 9rt ~xt6.0- Timiûamm La.@ us
FLR(CT1OHS Ckting: ON nutonmlyria: OFF Eurnt Colar: OFF S topTimm t OPf ¶ortSmttingr: OFF Expart: NoSaum Lfmhadi: NoSauo Cytokttlngm: OfP 74 observed before maximum cell count was achieved and a run could be terminated early. Examples of flow cytometry output cmbe seen in Figures 2.5 and 2.6.
Flow cytometry standards and the estimation of ploidy level
For most of this thesis the flow cytometer protocol was used with external standards consisting of known 2x, 4x, 6x. and 8x Fragaria species that were run at the beginning and end of each session. Later, interna1 and external standards were adopted which simplified estimations of ploidy levels. Calculations used to estirnate ploidy levels of hybrids are presented in Table 2.4. These calculations were used in conjunction with standard channel numbers of Fragana species (Chapter 3) to estirnate ploidy levels. Figure 2.5. Example of flow cytometer output for a 4x-8x mixiploid Fragana hybrid with an internal standard. Peak 'A' is the trout red blood cell internal standard peak. Peaks 'B' and 'C' correspond to tetraploid and octoploid peaks of the Fragana hybrid, respectively. Data below 50 on the X axis were not recorded because background noise increases geometrically as the x axis approached zero. Numerical output is presented below the graph. The mean value under the data column 'x channel' was used for estimation of ploidy levels.
SXNQLE PARRMETER STATISTICS
.O*.roPmmk+* O. ..t..o...... X Channml....+...... ID Pmt Amr Position Hmiaht Hœrn 90 FulLCü HmlfCU Min Mmx CI 22.6 988 821 19 819.7 27.1 3.31 4 73% a81 8 19.3 TI8 146 38 137.6 1 11 4.07 107 173 C 9.8 397 278 21 267.6 16.8 8-29 0.316 230 387 Figure 2.6. Example of flow cytometer output for a hexaploid Fragaha plant. Peak 'A' is the trout red blood cell infernal standard peak. Peak '8'is the hexaploid peak from the plant sample. Data below 50 on the X axis were not recorded because background noise increases geornetrically as the x axis approached zero. ~umericaloutput iç presented below the graph.
SINQLE PARA?iET€R STRTISTICS- ...... Pmak...... X Chamml...... 10 Pcnt Wrr Padtion Hright Mian 50 FullCU HalfCV Min Max CI 15.7 461 812 X0 088.2 27.8 3.34 0.096 742 87f 8 26.8 717 209 34 281.7 16.1 7.9s 1.18 lai 246
R Lou Chrnnri = 742, Hiph Chmnnrl = 871 B B Low Channal = 161, High Chrnnmi = 205 8 Table 2.4. Calculations used to determine chromosome numbers for Fragana hybrids from Row cytometry channel numbers.
samples with multiple external standards
Sarnple's channel number Standards Correction Standards' XED'A contents x = sample pg DNA C channel numbers from table 2.5
sarnples with intemal standards Standard's Sarnple's channel number DNA content Correction = çample ~CJ DNA Standard's channel number from table 2.5 factor
expected DNA level
Add together the DNAlgenome values from Table 2.5 according to species in lineage of hybrid king tested.
chromosome number estimate
Sam~leDNA ExpeCted Sample X chromosome = chromosome Expected number number
Z The correction factor for 2,4.6, and 8 x samples is 1.000. 1.030, 1.045, and 1.060, respectively. 78 Chapter 3
Fragaria species differ in DNA content
ABSTRACT
Flow cytometry was used to detenine DNA content of diploid ( F. daltoniana,
F.gracilis, F.Nnumae, F.nilgenensis, F.nipponica, Enubicola, F.pentaphylla, F. vindis,
F. vesca), tetraploid (F.onentalis), hexaploid (F.moschata) and octoploid (F.
chiloensis, F. virginiana) Fragana species to provide a baseline for determining
ploidy level of interspecific hybrids and colchiploids. Fragana species ranged frorn
0.62 pg (octoploid species and F.nubicola) to 0.82 pg DNNgenome (F.daltoniana).
This variability among species indicates that ploidy levels of interspecific tetraploids
and octoploids need to be based on a cornparison for DNA levels with their parental
species rather than natural tetraploids or octoploids. Cornparison of 242 samples
having primary (GA period cells) and secondary (G2 period plus mitotic cells) peaks
indicated that a doubling in ploidy results in flow cytometry readings being
approximately 3% lower than expected. This discrepancy should be taken into
account when estimating ploidy levels of colchiploids. The flow cytometry protocol
developed was successfully used to differentiate ploidy levels of interspecific hybrids
and colchiploids. INTRODUCTION
Understanding DNA content of Fragaria species is important for the development of synthetic polyploids. Differences in DNA content among species would be important to consider in estimating ploidy levels of hybrids and may also provide insight into evolution of Fragana species.
Although flow cytometry has been used to estimate ploidy of 8x and 16x
Fragana x ananassa protoplasts (Nyman and Wallin, 1992) this technique has not been used to rneasure nuclear DNA content of other Fragana species.
Chromosome counts using root tip squashes have been used by many researchers for ploidy verification in Fragah but the number of cells counted was not included
in their materials and methods (Mangelsdorf and East, 1927; Scott, 1951;
Niemirowicz-Szczytt, 1987; Sayeg h and Hennerty,1989; Rose et al., 1993). Other
researchers have published chromosome counts based on 16 to 26 cells (Evans
and Jones, 1967) or 83 to 253 cells per accession (Mok and Evans, 1971). A flow
cytometer can estimate DNA levels of thousands of cells in a few minutes and is an
efficient way to estimate ploidy levels; it can also be used to estimate genome size.
Quantification of Fragaria genome size with flow cytornetry has not been reported.
Species of Malus (Dickson et al., 1992). Honleum (Kankanpaa et al., 1996) and
Eucalyptus (Grattapaglia and Bradshaw, 1994) have been shown to differ in their
DNA contentlgenome.
The objective of this study was to establish DNA levels of several Fragana
species and determine if flow cytometry output was linear as ploidy level increases, 80
(Le. if the channel readings of a tetraploid nuclei are twice the channel readings of a diploid nuclei). These data would be needed to estimate ploidy levels of interspecific hybrids.
MATERIALS AND METHODS
Plant material was grown in the greenhouse at the University of Guelph according to procedures described in Chapter 2. Table 3.1 lists the accessions used in the experirnent.
Isolation of nuclei and measurement of DNA content were done with the procedure and flow cytometry settings described in Chapter 2.
The linearity of DNA content was tested using channel readings of primary and secondary peaks of 242 samples of Fragana nuclei. These samples were obtained from various hybrids and species with different ploidy levels produced at the University of Guelph. In fiow cytometry output, primary peaks are larger than
secondary peaks and represent nuclei from cells in a resting stage. Secondary
peaks occur for nuclei which have replicated their DNA but have not yet divided
(Dickson et al., 1992). Cells which have only partially replicated their DNA would
have fiow cytometry readings between the values of primary and secondary peaks.
An example of a secondary peak can be found in Figure 3.1. To calculate linearity
of flow cytometry readings, the mean channel number of the pnmary peak was
plotted as the independent variable and secondary peaks were plotted as the 81
Table 3.1. Gennplasrn used for fiow cytometry testing of Fragana species.
Species Guelph #Identifier used by source SourceZ
F.daltoniana J. Gay da12 dal-2 RBG Edinburg h F.gracilis Losinsk. gra 1 Pl551576 NCGR gra2 CFRA 1199.000 NCGR F.iinumae Makino ii3 CFRAI OO8.OOO NCGR F.nilgenensis Schltd. ni1 1 CFRA 1188.000 NCGR ex J. Gay ni12 Mt. Omei, frch059 Forest Farms ni14 CFRA 1224.001 NCGR ni15 CFRA 1383.001 NCGR ni16 CFRA 1358.001 NCGR F.nipponica Makino nip4 CFRA 1009.001 NCGR F.nubicola Hook. nubl PI 551851 NCGR nub2 PI 551853 NCGR F.pentaphy/la Losinsk. penl 19881143 RBG Edinburgh pen2 19892408 RBG Edinburgh F. viridis Duchesne virl PI 551741 NCGR vir2 PI 551742 NCGR vir5 56.01 23 RBG Edinburgh F. vesca L. vcvl 1 Ruegen Richters vcv10 Alexandria Thompson and Morgan vw12 PI 551909 NCGR vw39 CFW 988 NCGR vw53 Newcastle, Ontario collected by author Eorientalis Losinsk. ori ? 7947 x 4940 Gunter Staudt F.moschata Duchesne mcvl PI 551 528 NCGR mcv2 PI 551 549 NCGR rnwl PI 551750 NCGR F. chiloensis L., BCy sm366 Fra 366 Ag Canada, Harrow sm777 Fra 777 Ag Canada, Harrow sm883 Fra 883 Ag Canada. Harrow F. chiloensis, SAX cl077 CFRA 1077 NCGR clO89 CFRA 1089 NCGR cl110 CFRA 1110 NCGR F. virginiana Mill. vg BRB Blind River Beach, Ontariocollected by author vg4 Spanish, Ontario collected by author v~7Manitoulin Island. Ontario collected by author 2: details regarding sources of gennplasm can be found in appendix 1. Y: F.chiloensis from British Columbia, Canada X: F.chiloensis from South Arnenca Fig. 3.1. Example of a secondary peak in fiow cytometer output. The peak designated 'A' is the TRBC interna1 standard peak. 'B' is the primary peak while
'C' is the secondary peak. 83 dependant variable. Regression analysis was done with Microsoft ExceIl97 SR-1.
To determine if Fragana species Vary in amount of DNA, nuclei from the accessions listed in Table 3.1 were isolated and analyzed by flow cytometry.
Samples of the accessions were run as a group on three separate occasions and treated as three replications. A minimum of 5 x 103 nuclei were analyzed per sample. Calculations converting channel numbers into pgDNA were based on chicken and trout red blood cells as external standards as described in Chapter 2.
Also, DNA estimates were adjusted to account for the distortion in flow cytometry output detemined by comparing primary and secondary peaks. The GLM prograrn in SAS (release 6.12, SAS lnstitute Inc., Cary, N.C., USA) was used for data analysis with means separation done with LS means at a 95% confidence level.
RESULTS AND DISCUSSION
Although fiow cytometry channel numbers were significantly linear when comparing prirnary to secondary peaks (Figure 3.2), the value derived for the slope was less than expected. Since the y-intercept value of 0.9982 is negligible when channel numbers are in the range of 100-400,it would be reasonable to expect secondary peaks to have twice the channel numbers of primary peaks, or a dope of 2.00. Channel numbers of secondary peaks would be expected to be twice amount of primary peaks, however, the x coefficient is 1.9412 with a standard error of 0.0057. Thus, the channel nurnbers of secondary peaks were 3.0% +1- 0.3% less than expected. This distortion could be particularly important when calculating expected channel numbers for polyploid hybrids. The standard error of the y 84
Figure 3.2. Regression of channel numbers from secondary peaks ont0 channel numbers of primary peaks for Fragada nuclei. Channel readings of 242 samples were used in the calculation of this regression.
Channel numbers of primary peaks 85 estimate was 17.98. A possible explanation for this phenomenon lies in the dynamics of a sphere, and light passing through, or reflecting upon a suspension within it. Two spheres will reflect more light than a larger sphere that has the same volume and concentration of a suspension. In a similar manner, tetraploid nuclei rnay contain the same amount of DNA as two diploid nuclei but its surface area would be less, and thus would be less efficient at reflecting or absorbing laser beams from the flow cytometer. Nuclei moving througn a suspension in a Row cytometer are probably not exactly spherical, nor is it likely tetraploid nuclei have exactly twice the volume of two diploid nuctei, so it would be impractical to derive a mathematical model describing this phenomenon until more data become available.
To adjust for the 3% distortion, channel numbers of 4x, 6x, and 8x species were multiplied by 1.03, 1.O45 and 1.O6 when calculating pgDNNgenome for Table
3.2. More study is required to determine if this 3% distortion is a universal phenomenon with flow cytornetry studies or if this is specifically applicable to
Fragana nuclei or the flow cytometer used in this study. it might be suggested that the multiple peaks of preparations of chicken red blood cells do not show this distortion, but it should be kept in mind that such multiple peaks are created by the dumping of individual cells. A clump of unifon individual cells is not the same phenornena as smaller and larger sized nuclei with variable DNA content. While a
3% distortion in channel numbers when ploidy levels are increased may not be important for many flow cytometry applications, it could be important in Fragana research. In particular, an attempt to create synthetic octoploids from diploid species would result in ploidy bels being doubled twice, which could result in a 6% Table 3.2. Variation in DNA content of various Fragaria species, accessions and blood cell standards. DNA content (pg DNA) / genome
Accession Species means Ploidy S pecies Ploidy Accession means SEZ mean F. daltoniana 2x da12 0.82 0.02 0.82 abdY 0.70 F.gracilis 2x gra 1 0.74 0.02 0.71 b,d-f,g-i q ra2 0.68 0.04 Eiinumae 2x ii3 0.66 0.09 0.66 cd,f-l F. nilgerrensis 2x ni11 0.83 0.06 0.75 c-f
ni16 0.71 0.04 Fnpponica 2x nip4 0.78 0.18 0.78 a-f F.nubicola 2x nubl 0.59 0.04 0.62 i-l nub2 0.65 0.05 F.pen tap h ylla 2x penl 0.73 0.04 0.74 b-h
F. vesca 2~ vcv 1 0.69 0.02 0.67 f-k vcvl O 0+68 0.04 vw12 0.64 0.02 vw39 0.66 0.03 vw53 0.69 0.04 F.vindis 2x virl 0.67 0.02 0.64 d,g-l
vir5 0.66 0.04 F. orientalis 4x oril 0.74 0.04 0.74 b-e,gi 0.74 F-moschata 6x mcvl 0.69 0.04 0.69 e,g-j 0.69
mwl 0.68 0.05 F.chiloensis 8x cl077 0.61 0.02 0.62 i-l 9.62
sm883 0.64 0.03 F.virginiana 8x '44 0.62 0.02 0.62 i-l vg7 0.60 0.02 vg BRB 0.64 0.05 mean 0.68 0.05 Blood cell standards Chicken red blood celts, reconstituted 0.58 Chicken red blood cells, Biosure 2.50 Trout red blood cells, Biosure 6.13 ': SE based on three samples letters are LS means groupings at 0.05 level ': DNA values derived by the author *: DNA values frcm Vinogradov (1998) 87 distortion.
Flow cytometry results indicate some Fragaria accessions (ie. sri777 and da12) differ by as much as 42% in amount of nuclear DNAIgenome (Table 3.2). As
DNA content varies in Fragaria species, calculations of expected DNA Row cytometry readings of Fragana hybrids levels should be based on DNA levels of species in the lineage of hybrids. For example. a synthetic polyploid derived from the cross F-moschata x F.vidis should not be compared to the 8x species
Evirginiana to determine if it is an octoploid, rather the DNA levels of Emoschata and Evindis should be added to derive an expected value for an 8x hybrid.
Octoploid Fragana and the diploid Fmbicola have the lowest DNA/genome of Fragaria species. Fragana octoploids may have lost DNA in their evolution.
Perhaps at the octoploid level. eight copies of some alleles are disadvantageous and a genotype with deletions of certain alleles rnay have a survival advantage. It has been proposed that smaller sized chromosomes rnay have evolutionary advantages for polyploids when it was observed with microscopy that in Dianthus,
Chrysanthemum, Narcissus, and Tulipa genera polyploid species have smaller chromosomes than diploid species (Darlington, 1973). Conversely, perhaps there is an advantage for lower ploidy species having larger genomes. Fragana daltoniana is native to elevation of 5000 meter above sea level in the Himalayan mountains (Staudt, 1989) which may be the harshest environment where Fragana species exist. The high DNA content of this species may be indicative of mutations acquired that have allowed it to adapt to such an environment. Perhaps the inability of many researchers to produce tetrahaploids from octoploid cultivars (Hughes and 88
Janick, 1974; Predieri et al., l989b; Sayegh and Hennerty, 1989, 1993; Jelenkovic et al., 1983; Quarta et al., 1991; Rose et al., 1993; Svensson and Johansson, 1994) could be due to having insufficient doses of some alleles when ploidy levels are reduced.
Among the diploid species in the study there is considerable overlap of LS means groupings (Table 3.2). Since six of the nine diploid species in the study were represented by Mo or fewer accessions, conclusions that can be drawn regarding the evolution of DNA content within diploids is speculative. Within the two species having five accessions, F.nilgerrensis, and F. vesca had ranges of 0.12 and
0.05 pg DNAIgenome, respectively. Presumably, such variation would be synonymous with genetic variation, if indeed the extra genetic material encodes active genes. The 21 diploid and 9 octoploid accessions have ranges of 0.24 and
0.13 pgDNAIgenorne, respectively. This fact parallels studies of chloroplast DNA
(Harrison et al., 1993, 1997) which showed more variability among diploid species than among octoploid species.
The mean DNA content of F.onentalis (4x) and Fmoschata (6x) is closer to that of diploid species than octoploid species. Perhaps at 4x and 6x levels there is less selection pressure for reduced genome site. Fragana rnoschata is alleged to be a polyploid hybrid between F.vesca and F.viridis (Staudt, 1959; Ahmed and
Bringhurst, 1991). The data of this experiment supports this theory since the DNA
content of F.moschafa is in the range of what could occur if diploid accessions were
corn bined.
DNA content can Vary among samples of the same accession. While the 89 accessions of ni15, nip4 and cl1 10 had rather large SE values of 0.1 1, 0.1 8,and
0.14, respectively, other accessions had SE values in the range of 0.02 to 0.06 with a mean SE of .05. On average, the mean SE was 7% of the mean for pg
DNAlgenorne which gives a reasonable estimate of the precision of the fiow cytometry technique. Put in terms of the 56 chromosomes found in octoploid
Fragana species, the SE would account for approximately +/- four chromosomes.
This degree of precision is adequate for identihing differences among ploidy levels such as 4x, 6x and €lx, but would not be precise enough to identify additions or deletions of a few chromosomes. If greater precision is required additional flow cytometry runs could be performed, but even one sample run provides information on 1000s of cells compared to 10s of cell through root tip squashes.
For the purposes of synthetic octoploid identification, the flow cytometry technique outlined offers an efficient way to screen many accessions for ploidy levels. As Fragana chromosomes are extremely small, from 0.9 to 1.7 microns
(Yarnell, 1929; lwatsubo and Naruhashi, 1989, 1991), the flow cytornetry method would be much easier to use than root tip squashes.
CONCLUSION
Fragana species Vary in nuclear DNA per genome. Ploidy levels of intenpecific hybrids should be calculated using DNA levels of individual species in their lineage. Also, the flow cytorneter underestimated DNA content by 3% when an increase in ploidy occurred, and such distortion should be accounted for when calculating DNA content of polyploid Fragana. It is not known if this underestimation 90 is universal among al1 types of cells and al[ flow cytometers, but a comparison of primary and secondary peaks may be useful in other situations. The octoploid species have a lower DNA contentlgenome than most other Fragana species, which suggests DNA has been lost in their evolution. Diploid species are more variable in their DNA content/ genome than octoploid species but more accessions are needed to study differences among diploids. The above factors of flow cytometry linearity and differences of DNAfgenome in Fragaria species can be used to interpret flow cytornetry results and identify ploidy levels of interspecific hybrids and colchiploids. 91
Chapter 4
Hybridization of Fragaria vesca subspecies as female parents
w it h FMgerrensis, F.nubicola, Epentaphylla and F. viridis
ABSTRACT
The potential of using F.vesca as a bridge species to F.nilgenensis,
F.nubicola, F.pentaphylla, and F. vindis was investigated using a wide gerrnplasm
base of 40 F.vesca accessions. This study was successful in producing many
hybrids between F.vesca and other diploid species. Of the species used as
pollenizers, F.nubicola, F.pentaphylla, and F. viridis accessions were more
successful, averaging 85% to 100% fruit set and 12 to 25 seedslflower. It was
most dificult to obtain hybrids with Fragada nilgerrensis, which had only 38% fruit
set and 1.2 seedslflower. Differences among pollenizers were minimal when hybrid
seeds were germinated in vitro. For different species combinations, 75 to 99% of
seeds had embryos and 77% to 85% of these embryos geninated. The lack of
significant differences in crossability variables among the four types of F. vesca
studied (F. vesca subspecies americana. bracteata, vexa and vesca var.
sempemorens) demonstrated that no F.vesca subspecies was superior for
interspecific hybridization with any of the other diploid species used in this study.
As European and North American F.vesca subspecies are not sufficiently
divergent to differ in interspecific hybridization, it seems most likely that F-vesca is
a young species rather than an old progenitor species. The high crossability of
Evesca indicates that strong potential exists for geneflow between F.vesca and other diploid species.
INTRODUCTION
The synthetic octoploid (SO) system was developed to incorporate germplasm of 2x, 4x and 6x Fragaria into commercial 8x cultivars of F. x ananassa.
This bypasses ploidy level differences and eases introgression of 2x. 4x and 6x species (Evans, 1977). The first step of a synthetic octoploid system is the intercrossing of diploid species to create diploid hybrids (Fig. 1.7).
The use of a bridge (or pivotal genome) to facilitate interspecific crosses has been useful in introgressing diploid species into polyploid cereals (Feldman and
Sears, 1981; Gustafson and Dera, 1989; Armstrong et al., 1992; Gustafson and
Sears, 1993; Lelley et. al, 1995) but no suggestions for bridge species have been mentioned in previous investigations of SO systems with Fragana (Sebastiampillia and Jones, 1976; Evans, 1977). Fragana vesca is a logical choice to use as a bridge species for other diploid Fragada in the diploid step of the SO system because it has been successfully hybridized with several Fragana species including octoploid cultivars (Yarnell, 1931a; Mandelsdorf and East, 1927; Federova, 1946;
Williams, 1959; Staudt, 1959, 1967b, 4989; Evans, 1964, 1974, 1977; Fadeeva,
1966; Evans and Jones, 1967; Senanayake & Bringhunt, 1967; Sebastiampillia &
Jones, 1976; Ahrnadi and Bringhurst, 1992; Trajkovski, 1993). Fragah vesca may be progenitor of the genus Fragana (Duchesne in Darrow, 1966; Staudt, 1953;
Numberg-Kruger, 1958; Longley in Darrow, 1966) and rnay, therefore, be closely related to other diploid species. This close relationship rnay be exploited to facilitate 93 interspecific crosses. The use of F. vesca subspecies in interspecific crosses in this study may also aid in understanding divergence and evolution in Fragaria. Since
F. vesca is distributed across five continents (see Figure 1.3),crossability differences among F.vesca subspecies could also be exploited to optimize an SO system.
Advantages of using F.vesca as a bridge species
The primary importance of using F.vesca as a bridge species is its known ability to hybridize with other species. Table 4.1 provided details on crosses beheen F. vexa as a female parent with three of the pollenizer species also used in this study. No data were available regarding the cross F. vesca x F. pentaphylla.
The crossability of /=.vexawith other species can be seen in Table 1.1.1.3 and 1.4. in Chapter 1.
In many species, using several accessions increased the probabiiity of success that interspecific hybridization would occur (Burbank, 1921; Galletta and
Maas, 1990; Stoskopf et al., 1993). However, very few accessions of self- incompatible Fragaria species were available for this experiment. Of al1 diploid species, the most accessions were available for F. vesca (ie. approximately 120).
In corn panson, when this study began, only 20 accessions of diploid species (other than F.vesca) were listed at various genebanks and most of these either were unavailable, incorrectly labeled or would not germinate.
Fragaria vesca's adaptation to low light levels (Chabot and Chabot ,1977) and cool temperatures (Bauer, 1976) may be especially useful in northem areas Table 4.1. Results of previous research using Fragaria vexa as a female in crosses with F. vindis, F. nubicola, and F. nilgenensis. All subspecies rnentioned refer to subspecies of F. vesca.
Species combinations Reference
- - - - F. vesca x F. viridis F. vesca x F. nubicola F. vesca x F. nilgenensis 16 plants partially ssp. vesca: 13 pollinations, Yarnell, 1931a fertile 6 seed, 4 germinated, al1 dwarfs ssp. bracteata: 90% germinated, 19 plants dwarf, al1 died F. vesca from Hawaii: 50 seeds, 18 plants, vigourous full seed set, plants full seed set,plants full seed set, viable hybrids Williams, produced produced only with eastern European 1959 ssp. vesca. Most F. vesca accessions were unsuccessful ssp. vesca: 17 ssp. vesca: 21 ssp. vesca: 18 pollinations, Evans, 1964 pollinations, 90 pollinations, 201 seed, O seed seed, 62 germinated 152 germinated accession #1: Only stunted hybrids Fadeeva, 25 seedlberry, obtained 1966 383 seed, 231 germinated accession #2: 7 seed/berry, 337 seed, 200 germinated viable seed viable seed produced viable seed produced Evans and produced Jones, 1967 95 and could enhance late season growth (Bauer, 1976), fall Rower bud initiation, and yield potential if these adaptations were successfully transferred into cultivars. Its worldwide distribution shows broad adaptation to diverse conditions (Darrow, 1966;
Fig. 4.1). Fragaria vesca also has a very desirable aroma that could be used to improve fruit quality of cultivars (Darrow, 1949, 1966; Jones, 1966; Ahmadi and
Bringhurst, 1992; Trajkovski, 1993).
Advantages of using F.vesca as a female parent
Fragaria vesca is more successfully used as a female parent in crosses with other diploid species. When F.vesca is used as a male in crosses with self- incompatible species, such crosses often produce no seed (Evans and Jones,
1967). However, when the self-compatible F. vesca is used as a female in crosses with self-incompatible diploid species (ie. F. vindis, F. nubicola and F. penfaphylia)
(Evans, 1964; Staudt, 1989),incompatibility mechanisms are bypassed (Lewis and
Crowe, 1958; Evans and Jones, 1967). Cornpared to other Fragaria species,
F. vesca has more variable cytoplasm (Harrison et al., 1993;1997) which could be important to the success of interspecific hybridization (Stoskopf et al., 1993). This variability can be exploited if F.vesca is the female parent. Also, F. vesca cytoplasm and gemmes are more amenable than other Fragafia species to chromosome doubling by colchicine (Fadeeva, 1966;Sebastiampillia and Jones, 1976). Thus, F. vesca could be of special benefît to the Synthetic Octoploid system which requires two stages of chromosome doubling. Accessions of Evesca ssp. vesca var. 96
Figure 4.1. Distribution of Fragana vesca subspecies (Evans, 1964; Reed. 1966;
Staudt, 1989).
ssp. vexa var.
ssp. 97 sempeflorens, when used as a female in crosses, have recessive everblooming and non-runnering traits (Ahmadi et al., 1990) that can be used as genetic markers to facilitate sorting of interspecific hybrids from selfed progeny. This everbearing trait also simplifies coordinating the timing of pollination with other species and could be used to breed multiple generations per year provided selfing or backcrossing is used to restore the homozygous condition to the recessive alleles that govern the everblooming trait.
Evidence that F.vesca subspecies have diverged
If F. vesca is the progenitor species to other diploids (Duchesne in Darrow,
1966; Staudt, 1953; Nurnberg-Kruger;1958; Longley in Darrow, 1966), then F. vesca subspecies may differ in relatedness and hence crossability with other diploid species. With a range of distribution over five continents (see Fig 4.1). F. vesca subspecies could have become geographically isolated and diverged sufficiently to differ in interspecific crossability. Although it has been suggested that F.vesca is
not highly variable genetically (Reed, 1966),there have been several studies that
have highlighted morphological differences of plants, fruit, leaves and flowers of
F. vesca subspecies (Williams, 1959; Staudt, 1989; Ahmadi et al., 1990; Harrison et al., 1993, 1997). Fragana vexa subspecies were also found to differ in
chloroplast DNA RFLPs (Harrison et al., 1997), and the number of genes goveming
photosensitivity (Ahmadi and Bringhurst, 1990). 98
Goals of this study
In this study it is hypothesized that F. vesca subspecies have diverged sufficiently to cause differences in interspecific crossability. In this experiment, divergence among F. vexa su bspecies amencana, bracteata, vesca and ssp. vesca var. sempeflorens is examined. The latter group, var. sempeflorens, is the cultivated form of F.vesca, which rnay have diverged through artificial selection.
The objective of this study is to detenine which of these four Evesca types is best suited for interspecific hybridization with the six accessions of other diploid species. This information could be important for developing a crossing strategy for early stages of the SO system and may provide insight into the evolution of Fragana species.
MATERIAL AND METHODS
General material and methods including induction of flowering, pollination methods, seed storage and germination are presented in Chapter 2. Additional details for this experiment are covered in the remainder of this section.
A total of 40 accessions of Evesca (Table 4.2) were hybridized with seven pollenizers (Table 4.3). Crosses were with Evesca as a female pollinated with either F.nilgenensis, Enubicola, F-pentaphylla,F. vindis, or F.vesca. Fragana vesca subspecies amencana, bracteata and vesca were represented by 12, 10 and 8 accessions, respectively. To maximize time available to facilitate crossing, one accession of each of these three subspecies was placed in the greenhouse in early Table 4.2. Fragada vesca accessions used as female parents in crosses with F.nilgen-ensis, F.nubicola, F.pentaphylla, F.viridis and F. vesca. Accessions are grouped by subspecies. Page 1 of 2.
Guelph id Identifier used by source SourceL
F. vesca ssp. vesca var. sempemorens (dayneutral cultivars) vcvO2 PI 551517, Alpine NCGR vcvO4 PI 551827, Yellow Wonder NCGR vcv06 CFRA1185.001, Golden Alpine NCGR vcv07 Pineapple Crush Park Seed vcvl O Alexand ria Thompson & Morgan vcvl 1 Ruegen Richters vcvl3 Mignonette Park Seed vcvl4 Golden Sprite Ornamental Edibles vcv20 Alpine Strawberry White Flower Fams vcv22 FRA 2193 IPK Genbank
F. vesca spp. vesca (wild type) vw 07 Pl 551792 NCGR vw 09 Pl 551890 NCGR vwl O Pi 551892 NCGR vwl 1 PI 551893 NCGR vwl2 PI 551909 NCGR vwl3 PI 552273 NCGR vwl4 PI 552274 NCGR wu16 PI 552239 NCGR vw22 FRA 13197 IPK Genbank vw38 PI 552242 NCGR
F. vesca spp. bracteata (wiM type) vw 02 PI 551519 NCGR vw 06 PI 51 1791 NCGR vw23 PI 551524 NCGR vw24 PI 551551 NCGR vw25 PI 551644 NCGR vw26 PI 551645 NCGR vw57 PI 148 C.C.G. wu58 PI 418 C.C.G. 2: full narnes and addresses for germplasm sources can be found in Appendix 1. Table 4.2. continued.
Guelph id Identifier used bv source Source
F. vesca ssp. americana (wild type) vw17 Pl 552246 NCGR vw29 PI 552241 NCGR vw30 PI 552247 NCGR vw32 PI 552286 NCGR vw33 Grand River, Cambridge, ON Spencer Murch vw34 Cambridge, ON collected by author vw35 Pl 552243 NCGR vw36 Pi 552244 NCGR vw47 PI 551898 NCGR vw48 PI 551908 NCGR vw49 Srnithfield, ON collected by author vw53 Newcastle, ON collected by author Table 4.3. Fragaria accessions used as male parents in crosses with Evesca. Accessions are grouped by species.
Guelph id Identifier used by source SourceL F.nilgerrensis niIl CFRA 1188.000 NCGR
F.nubicola nubl Pi 551851 NCGR nub2 PI 551853 NCGR
F.pen taph ylla penl PI 881143 RBG Edinburgh
NCGR NCGR
F. vesca (control ) vw69 Fra 18193 IPK Genbank Z: full names and addresses for gemplasm sources can be found in Appendix 1. 102
January and another in early February. Three plants each of 10 cultivars of
F-vesca ssp. vesca var. sempeflorens were also included. Since sempeflorens accessions bloom continuously, they were brought out of cold storage only in
January. The recessive everbearing and non-runnering traits of sempeflorens cultivars were also useful in this study because they provided easily identifiable morphological markers to identify true hybrids from selfs.
Accessions used as males were removed from cold storage in early
Decernber and placed in the greenhouse. Initially, accessions of F. nubicoia did not bloom in the greenhouse although they received the same growing conditions as other plants in the study. However, they were induced to bloom after being subjected to a shorter day length and cooler temperatures in a growth chamber (see
Chapter 2).
Experimental design and data analysis
The female parents were grouped into four F. vesca su bspecies: amencana, bracteata, vesca, or vexa var. sempeflorens. There were six male parents for interspecific crosses: nubl, nub2, penl, virl, vie, and Nil1 and one F.vesca accession used as a pollen source for control crosses. Ten F.vesca var. sempeflorens cultivars were assigned to each of the three blocks but accessions of the three wild subspecies (ie amerkana, bracteata, vesca) were randomly distnbuted among the blocks.
Control crosses with F.vesca pollen were done to ver@ that emasculation 1O3 and pollen storage techniques were correct and for comparison with interspecific crosses. VW69 was used for control crosses because it was native to Asia (unlike other F.vesca accessions in the study) and produced abundant pollen. Data from test crosses were discussed in results but were not included in the data set of interspecific crosses.
Pollinations for interspecific crosses were done to maximize the number of parental combinations. Pollination was randomized each day according to available pollen but attempts were made to equalize the various combinations of species.
Details of pollination methods are in Chapter 2.
Fruit set (%), seeds/flower, seeds with ernbryos (%) and germination (%) were measured. Where the same combination of parents occurred in the same block, data were pooled for that combination before statistical analysis. Data were analyzed with the GLM program of PC SAS (Sas system for Windows V.6.12, Cary,
N.C.). Mean separation was accomplished using the LS means function of PC
SAS. Analysis of fruit set and seedslflower was based on each combination of parents crossed, while seeds with embryos (%) and germination (%) was based on a subset of those cornbinations that received in vitro germination.
RESULTS
Flowering time influenced the number of potential combinations of parents.
There were 191 different cornbinations of parents achieved by 360 interspecific pollinations. The males, nill, nubl, nub2, penl, virl and vir2 were used as pollenizers in 37, 38, 28, 27, 35 and 36 hybrid combinations, respectively. Pen1 1O4 produced trusses with only one to three flowers and was used in fewer combinations. Virl and vir2 were the first pollenizer species to bloom and were involved in more crosses. While nill bloomed about three weeks after virl and vir2, its total blooming period was about two weeks longer than that of any of the other pollenizers. It was noted that ssp. bracteata plants had fewer fiowers per plant than other F. vesca subspecies in the study so low nurnbers of crosses occurred with this group.
Fruit set (Oh) and seedslflower
Pollenizer accessions were a significant source of variation for fruit set and
seedslflower but Evesca subspecies and the interaction sources of variation were
not significant (see ANOVAs in Appendix 2). The F. nilgerrensis accession, nill,
had the lowest flower set, 38%, while cther pollenizers averaged between 76% and
100% (Table 4.4). Crosses having the nill accession as a pollenizer also had the
lowest seedslfiower with an average of 1.2. Pollenizers nub2, penl virl and viR
produced similar seedslfiower averaging from 1 1.6 to 16.9 while nub 1 was
significantly higher with 24.7 seedslflower (Table. 4.5).
The two North American subspecies, amencana and bracteata were similar
with 69 and 65% fruit set, respectively. However, these averages were not
statistically different from the European su bspecies, vesca (wild type) and vesca
var. semperflorens, which had 85 and 83% fruit set, respectively. Means of
seedsmower for Evesca subspecies varied by less than two seeds, having a range Table 4.4. Fruit set for crosses among Fragaria vesca subspecies when pollinated with F. nilgenensis (1 accession), F.nubicola (2).F.pentaphylla (1) and Eviridis (2) and F.vesca (1). lnterspecific crosses were analyzed separately from the control crosses and means separation was done with LS means at p = 0.05. F. vesca ssp. Species used as male parents (accessions) Control potlenizer & F.nilgenensis F.nubicola F.~8nta~h~//a . F. viridis Mean F. vesca accessions ) - inii (nubi) (nub2) (~enl) (virl) (vir2) (Mg) used as fernales N Fruit N Fruit N Fruit N Fruit N Fruit N Fruit N Fruit N Fruit set (74) set {%) set (9%) set (Yo) set (Oh) set ("/O) set (Oh) set (%) ssp. americana VW17 2 O 1 IO0 1 O 1 100 4 100 3 100 12 67 1 1O0 VW30 2 O 1 100 1 O 1 100 3 100 1 O 9 60 4 100 VW33 1 O 1 1O0 2 100 1 100 5 75 1 1O0 VW34 3 100 2 100 3 O 2 100 10 75 2 100 VW35 3 O 1 100 1 100 2 O 1 O 8 40 1 1O0 VW36 3 O 2 100 2 100 1 100 4 O 1 100 13 67 2 1O0 w47 4 100 1 100 2 100 3 100 1 100 11 100 2 100 VW48 1 O 1 IO0 2 100 3 IO0 1 100 8 60 2 1O0 VW49 3 O 1 100 1 100 6 100 1 100 12 80 1 1O0 VW53 4 O 1 100 1 100 2 100 8 75 1 100 Mean 26 20ns 8 1OOns 10 711-1s 7 lOOns 31 70ns 14 7711s 96 69ns 17 1OOns ssp. vesca VW07 4 50 1 100 1 100 1 100 1 100 1 100 9 92 1 1O0 Table 4.4. Continued.
F. vesca ssp. Species used as male parents (accessions) Control ~ollenizer & F.nilgenensis F. nubicola F.pentaph ylla F. vjridjs Mean F. vesca - . - accessions (ni11 ) (nubl) (nu b2) (pen 1 (virl ) (vir2) (M9) used as females N Fruit N Fruit N Fruit N Fruit N Fruit N Fruit N Fruit N Fruit . - . . - -- . - - set (%) set (%) set (%) set [%) set (%) set (%) set (%) set (%) ssp. vesca var. sempeflorens VCV02 3 33 2 100 3 IO0 4 100 12 80 4 67 vcv04 VCVO6 vcv07 VCVI 0 VCVI 1 VCVI 3 vcv14 VCV20 ssp. bracteata VW02 1 O 1 100 1 O 1 IO0 1 100 5 60 1 O
Overall 110 384 34 1OOab 40 76bc 33 93abc 75 88abc 68 9labc 360 78 83 87 Table 4.5. Seeds/flower for crosses among Fragaria vesca subspecies w hen pollinated with F, nilgenensis (1 accession), F. nubicola (2), F.pentaphyl/a (1) and F.vjridis (2) and Evesca (1). lnterspecifc crosses were analyzed separately from the control crosses and means separation was done with LS means at p = 0.05. F. vesca ssp. Species used as male parents (accessions) Control pollenizer F.nilgerrensis F. nubicola F.pentaphylla F. viridis Mean F. vesca accessions (ni11 ) (nubl) (nub2) (~en1) (virl ) (viR) (vw69) used as fernales N Seeds N Seedsl N Seedsl N Seedsl N Seedsl N Seedsl N Seedsf N Seedsl / flower flower flower flower flower flower flower flower ssp, americana WVI7 2 O 1 50 1 O 1 3 4 3 3 11 12 11.2 1 62.0 VW30 2 O 1 5 1 O 1 2 3 2 1 O 9 1.8 4 46.5 VW33 1 O 1 12 2 25 1 5 5 9.5 1 1.O VW34 3 5 2 14 3 O 2 6.5 10 6.4 2 7.0 WU35 3 0.0 1 19.0 1 16.0 2 0.0 1 0.0 8 7.0 1 42.0 VW36 3 0.0 2 22.0 2 6.0 1 13.0 4 0.0 1 10.0 13 8.5 2 33.5 VW47 4 7.3 1 33.0 2 24.0 3 19.0 1 8.0 11 18.3 2 54.5 VW48 1 0.0 1 25.0 2 15.5 3 8.0 1 O. O 8 9.7 2 34.5 VW49 3 0.0 1 10.0 1 43.0 6 37.0 1 39.0 12 25.8 1 11.0 VW53 4 0.0 1 57.0 1 65.0 2 51.5 8 43.4 1 39.0 Mean 26 1.2ns 8 27.1ns 10 11.2ns 7 16.8ns 31 13.5ns 14 16.8~s 96 14.4ns 17 33.1ns ssp. vesca VW07 4 1.O 1 24.0 1 44.0 1 20.0 1 16.0 1 17.5 9 20.4 1 27.0 VW09 2 1.0 1 5.0 1 23.0 2 19.0 1 19.0 1 27.0 8 15.7 1 44.0 VWIO 4 0.8 2 15.5 1 21.0 1 1.O 1 1.0 9 7.7 1 34.0 VWI 1 1 1.0 1 39.0 1 22.0 3 6.0 1 13.5 7 16.3 1 31.O VW12 4 0.5 2 27.0 1 20.0 1 O. 0 1 1.0 2 13.0 11 30.3 2 34.5 W13 4 0.5 1 26.0 2 30. 1 7.0 8 15.9 3 38.3 W14 1 11. 2 13.0 2 6.0 1 35.0 1 35.0 7 20.0 1 18.0 VW16 3 0.0 2 50.0 2 3.0 1 12.0 1 8.0 1 1.0 10 12.3 5 33.4 VW22 1 0.0 1 9.0 1 7.0 1 2.0 1 1.0 5 3.8 1 4.0 VW38 2 0.0 1 21.0 1 15.0 1 12.0 1 0.0 2 3.0 8 8.5 2 0.0 Mean 25 0.5 ns 11 23.6 ns 11 19.4 ns 12 14.1 ns 11 9.8 ns 12 11.8 ns 82 13.2ns 18 26.4ns 99 0 =? a &O0 CVCV - CC)
Y- Nrr
Naei PNN 1O9 of 13.2 to 14.7 seedsMower (Table 4.4).
Although fruit set for control crosses was 9% higher than the overall mean for interspecific crosses, four of the six pollenizers had between 1 and 13% higher fruit set than controls. Control crosses averaged twice as many seeds/flower than interspecific crosses and al1 interspecific pollenizers had lower numbers for this variable.
Seeds with embryos and embryo germination
InsufFicient numbers of hybrid seeds were produced with Evesca ssp. bracteata fernales to allow meaningful ANOVA analysis of differences among
F.vesca subspecies for the proportion of seeds with embryos and percent embryo germination. Therefore, only the effect of pollenizer accessions was incorporated
into ANOVAs of these two variables (Appendix 2). Pollenizer accessions were a significant source of variation for percent of seeds with embryos but not for
germination (Table 4.6, ANOVAs in Appendix 2). For percent of seeds with
ernbryos, ni11 had the lowest numbers but this was not significantly different from
vir2. Other pollenizers were at least 13% higher then nill or vir2 for percent of
seeds with embryos (Table 4.6). Percent embryo germination was similar for al1
pollenizen, with only a 12% difference between the lowest (vir2) and highest (virl)
pollenizer.
Differences in intraspecific crosses
Percent flower set did not differ significantly among F. vesca subspecies Table 4.6. Seeds with ernbryos (%) and ernbryo genination (%) for interspecific crosses arnong Fragaria vesca accessions as females and six di ploid accessions as males.
Pollinizer Accession Number of Total no. of Seeds In vitro embryo species female seeds with embryos germination accessions germinated (%) (%) in vitro - -- - F. nilgerrensis ni1 1 15 108 75b" 85ns
F. nubicola nubl 12 324 97a 81 ns nub2 17 397 99a Wns F. pentaphylla penl 21 490 92a 81 ns
F. vindis virl 11 24 1 99a 89ns vi R 6 308 79ab 77ns
------
82 Y 1868 Y 90 ' 82 ' Means separation with LS means at p = 0.05.
y Sums. Means 111 when crossed as fernales to vw69 (control). F.vesca ssp. amencana had the highest values, which averaged 43% higher than F. vesca ssp. bracteata (Table
4.4). Fragana vesca subspecies d id not differ significantly for seedslflower with averages within a 27 seed range and the lowest and highest values occurring for
F. vesca ssp. bracteata and F.vesca ssp. vesca var. sempefiorens, respectively.
Surprisingly, some accessions of F. vesca (~02,vw24, vw25 and vw38) did not set fruit when pollinated with vw69. However, each of these four accessions did
produce seed in interspecific crosses. Vw26 was the only F.vesca accession that
produced seeds with the control pollenizer but was not successful when crossed
with other species (Table 4.5). However, it was involved in only five interspecific
crosses.
Differences among Evesca accessions
Althoug h variability existed within F. vesca subspecies, this study was not
designed to allow for statistical analysis of crossability of individual F.vesca clones.
Further pollinations would be required to insure replication for each F.vesca clone
x pollenizer combination. Superior combinations of F.vesca accessions and
pollenizen for interspecific hybridization can be found in Tables 4.4 and 4.5. Such
data could be useful for future investigation to produce interspecific hybrids. For
example, superior accessions for hybridizing with nill were vcv07, vw 23 and vw47
(Table 4.4). Some accessions of F-vesca had superior crossability with most of the
pollenizers in this study. Of the 15 Evesca accessions pollinated with al1 six -Il2 interspecific pollenizers,vw32, vw07, vcv10, vcvl3 and vw09 were very successful ranging between 15 and 22 seeds/flower. Other notable accessions were vw53, w49, vw14, and vw25, although these were not crossed with al1 pollenizers. The superior genotypes mentioned in this paragraph are fairly evenly distributed amongst the F.vesca groups in this study. Each group had three superior genotypes except for F.vesca ssp. vesca var. sempeflorens which had only two.
DISCUSSION
This study used 39 accessions of F.vesca in interspecific hybridizations, a
number fagreater than those used in other reported studies, and it is likely that this study provides a better representation of the diversity within F.vesca compared to those earlier studies. Despite isolation in widely separated areas of North America
and Europe as well as the isolation that occurred when Evesca varsempeflorens was domesticated, F. vesca subspecies did not differ sig nificantly in interspecific
crossability in this study. although considerable variation was present within
subspecies. The interactions among F. vesca subspecies and pollenizers were not
statistically different for any of the variables investigated. The hypothesis that
F-vesca subspecies differ in interspecific crossability (Williams, 1959; Fadeeva,
1966) was not supported by the results of this study. Since a few superior
genotypes were found within each of the F-vesca subspecies. it is quite possible
that smaller collections of F.vesca subspecies in previous studies might be skewed
resulting in some su bspecies being found superior. For example, observations that 113 indicated cultivars of F.vesca var. sempemorens were superior over wild types for interspecific crossability was based on only two accessions of F.vesca var. sempeflorens and an undisclosed number of wild accessions of F.vesca (Fadeeva.
1966).
The ability of F. vesca to hybridize with four other diploid species validates the hypothesis that F.vesca could be very useful as a bridge species for the first steps of the synthetic octoploid system. Fragana breeders wishing to use F. vesca as a bridge species could use any subspecies of Evesca with a high likelihood of success. Since most F.vesca accessions hybridized with most pollenizers. with the exception of F.niigenensis, it may be advantageous to focus on F. vesca accessions with superior horticultural qualities when introgressingother species. Qualities such as larger fruit size or disease resistance may make an accession desirable to use, even if only a few seeds were produced in interspecific hybridization. Fadeeva
(1966) observed a correlation between fruit size of F.vesca lines and fruit size of intenpecific hybrids. king a locally adapted subspecies would also be a recommended strategy. The fiexibility to choose among many genotypes of F. vesca would be especially useful if prebreeding were to occur at the diploid level as part of the synthetic octoploid system.
The data from this experiment can neither support nor refute the theory
(Duchesne in Darrow, 1966; Staudt, 1953; Numberg-Kruger, 1958; Longley in
Darrow, 1966) that F. vesca is the progenitor species of the genus Fragana. Trying to elucidate evolution in Fragana is very problematic since many species in the genus are closely related (Jones, 1966). The lack of significant differences among Il4
F.vesca subspecies suggests F.vesca is a younger species rather than an ancestral species undergoing differentiation into other species. However, F.vesca successfully hybridized with four other diploid species in this study, which supports the progenitor theory. Until more is known about the crossability among diploid species, determining Evesca's role in the evolution of its genus is dificult. It is not known if F.vesca is the most easily intercrossed of the diploid species. Even if
F.vesca is not the progenitor of diploid species, it could be an ancestor of some species. The ability of F.vesca to hybridize with other diploid species in this study tends to support the theory (Darrow, 1949. 1966; Federova. 1946; Ellis, 1958;
Staudt, 1959, 1984; Bringhurst and Senanayake, 1967;Bringhurst and Gill, 1970;
Bringhurst, 1990; Ahmadi and Bringhurst. 1991) that Evesca could have been involved in the formation of polyploid species.
A theory that could explain the similarities among F.vesca subspecies is that
Evesca's adaptation to low light levels, which enables it to survive in forest ecosystems (Chabot and Chabot, 1977), is responsible for its wide distribution
(Reed, 1966; Staudt, 1989), despite being a young species. As F.vesca is widespread, particularly throughout the northern continents (Reed, 1966; Staudt,
1989), it could have rnigrated during the Miocene (23 - 5.3 million years ago) with numerous forest species across intercontinental land bridges connecting Asia,
North America and Europe (Stebbins, 1950; Hara, 1956, 1972; Constance, 1972;
Li, 1972; Wood, 1972; Lowery and Jones, 1984). This would explain the morphological similarities between F.vesca ssp. vesca of Europe and Evesca ssp. arnericana of eastern North America noted by Fletcher (1917) and Staudt (1989). 115
It would also explain why North American and European subspecies of F. vesca did not differ in interspecific crossability in this study. Fragana species that were not adapted to northern latitudes would not have been able to migrate across the northern land bridges. Thus. the presence of F. vexa in North America may be due to its specialized adaptations to forest ecosystems rather than the species being ancient.
This study shows that F. pentaphylla. F.nubicola. and F. vidis could be closely related since rnost accessions formed interspecific hybrids with F-vesca.
However, intercrossing of F. pentaphylla, F.nubicola, and F. vindis would provide more information regarding the relatedness of these three species. Morphology
(Reed, 1966; Staudt. 1989). and chloroplast DNA analysis (Harrison et al., 1993,
1996) also suggest F. vesca, F. nubicola and F. vindis are closely related. Fragana vexax F. viridis and F. vexa x F.nubicola crosses prod uced similar results to those of other researchers (Table 4.1 ) but F vesca x F.pentaphylla crosses have not been previously reported. It was surprising that F. pentaphylla had similar crossing results to that of F. vindis and F. nubicola as this species has unique leaf (Fig 1.l) and fruit (Fig 1.2) morphology suggesting at least some divergence.
The results obtained in this study concur with that other research (Williams,
1959; Evans, 1964), that Evesca x F. nilgemnsis hybrids are difficult to obtain. An explanation for these findings is that F. nilgerrensis is divergent from other diploid species (Harrison et al., 1993,1997). Since F. vesca accessions produced few seeds when pollinated with F.nilgemnsis, averaging only 1.2 seedslflower, it may Il6 be of benefit to use the more successful F.vesca accessions in Table 4.5 to cross with other F.nilgerrensis accessions. Earlier studies identified only three F.vesca accessions with potential to produce healthy hybrids with F.nilgenensis (Yarnell,
1931a; Williams, 1959; Evans, 1964) but in this study, 19 accessions were found that produced hybrid seeds and three superior accessions that produced greater than five seeds per flower. While stunting (Yarnell, 1931a; Fadeeva, 1966) and lethal seedlings (Williams, 1959) have been observed in F. vexa x F. nilgenensis hybrids, the lack of these phenornena in this study indicates variability in the species of F.nilgenensis and perhaps that nill is superior for interçpecific hybridization with F.vesca. While it has been suggested that F.nilgerrensis cannot be introgressed into the genepool of cultivated strawberries (Hancock et al., 1W6), the current study shows encouraging progress toward this goal.
A few other differences existed among this study and earlier studies. While fruit set was not reported in previous studies, seedstflower and germination rates were reported. The seedslflower produced in this study were higher than the average of other researchers (Table 4.1). Averages for F.vesca x F. vindis, F. vesca x F.nubicola, and F-vesca x F-nilgerrensis were 2, 7, and 1 seedsMower higher in this study, respectively. The results of Evesca x F.niigenensis crosses were particularly noteworthy in this study since very few successful crosses between these two species had been reported previously. If percent seeds with embryos is rnultiplied with percent embryo germination (Table 4.6), the resulting numbers can be compared to germination rates in Table 4.1. For the above three combinations, this study had germination rates 13, 5, and 0% higher, respectively, than earlier 117 studies. While the use of in vitro germination did not dramatically increase germination rates compared to traditional rnethods, it provided additional information regarding the germination of interspecific hybrids. Sig nificant differences among the various combinations of species (Table 4.6) were due to ernbryo abortion during seed formation (ie. seeds with embryos) and not germination rates of fully formed embryos (ie. embryo germination).
CONCLUSION
This study was successful in producing many hybrids between Evesca and other d iploid species, including the difficult to obtain F. vesca x F.nilgerensis hybrids. The lack of significant differences in crossability variables arnong the four types of F. vesca demonstrated that no F.vesca subspecies was superior for interspecific hybridization with any of the pollenizers of this study. As European and
North American Evesca subspecies are not divergent enough to differ in interspecific hybridization, it seems more likely that F.vesca is a young species rather than a progenitor species. An explanation for the global distribution of
F.vesca is that specialized adaptations have allowed F.vesca to spread in forest ecosysterns. This theory is counter to previous theories of F. vesca evolution
(Duchesne in Darrow, 1966; Staudt. 1953; Nurnberg-Kruger, 1958; Longley in
Darrow, 1966).
Using a wide gemplasrn base of F.vesca was significant for the success of this investigation cornpared to previous research. Crossability of F. vesca indicates that strong potential exists for geneflow between F.vesca and other diploid species. 118
Although the number of accessions of other diploid Fragana species was limited,
Evesca hybridized with the four other diploid species used in this study, indicating good potential as a bridge species. Limitations of gerrnplasm make it impossible to conclude that F.vesca is the best bridge species available, but certainly F. vexa has potential value in initial steps of creating of synthetic octoploids. CHAPTER 5
Interspecific crossability of nine diploid Fragaria species
ABSTRACT
Accessions of the diploid species F.daltoniana, F.iinumae, F.nilgerrensis,
F. vesca, F.gracilis, F.nipponica, F.nubicola, F.pentaphylla and F. viridis were crossed in 36 interspecific cornbinations. Of the 20 combinations of species that resulted in viable F, plants, 13 bloomed and produced seeds and seven did not bloom. Seven combinations of species failed to produce seeds and two additional combinations produced seeds that would not geminate.
With the exception of F.iinumae, al1 species in the study produced fertile F, hybrids with at least one other species. This demonstrated the significant potential for geneflow at the diploid level. Fragana pentaphylla was the most successful species for interspecific hybridization followed by F. vesca. Fragana pentaphylla formed hybrids with seven species in the study, and five of the seven hybrid types were fertile. Fragada vesca foned fertile hybrids with five other species, but fomed non-viable hybrids with three species. The superiority of Epentaphylla and
F.vesca for interspecific hybridization indicates they have the greatest potential as bridge species for diploid Fragaia.
Hybrids were readily obtained when intercrossing self-incompatible species fie. F.gracilis, F.nipponica, Fmbicola, Fpentaphylla amd F. vindis), but were vety difficult to obtain when intercrossing self-compatible species fie. Edaltoniana,
Ç.iinumae, F.nilgerrensis, F. vesca) . In contrast to previous research which showed 120
F. vesca was the most likely progenitor of the genus Fragaria, this study indicates
F. pentaphyiia rnay be the progenitor. It is also likely that self-incompatible
Fragana species are more closely related and ancestral to self-compatible species.
lNTRODUCTlON
Previous research on interspecific hybridization with Fragatia diploids has
been based on a limited number of accessions and only 28 of the approximately 90
possible combinations of diploid species have been reported (Table 5.1). For
example, no reports have been made regarding interspecific crossability of
F.pentaphylia, Ç.gracilis, or F.manchunka while interspecific hybridization involving
F.iinumae (Sebastiampillia and Jones, 1976), Enipponica (Williams, 1959) and
Edaltoniana (Evans, 1974) has received only limited attention. In contrast, the
diploid interspecific crossability of F.nilgerrensis, F.nubicola, F. vesca, and F. vitidis
has been investigated by many researchers in several reports (Table 5.1 ).
An early investigation (Chapter 4) focussed on an introgression strategy to
broaden the germplasm base of the cultivated strawberry that used Evesca as a
bridge species with F.niigenensis, F.nubicola, F.pentaphylla and F.vindis. That
study cast some doubt on a theory of Fragana evolution (Duchesne in Darrow,
1966; Staudt, 1953; Nurnberg-Kruger, 1958; Longley in Darrow, 1966) that
suggested F.vesca was the progenitor species of the genus. Following that study.
Evesca was crossed with F.iinumae and Egracilis but the hybrid seedlings failed
to develop beyond the cotyledon stage despite the use of 15 Evesca accessions
and in vitro (Miller et al., 1992) germination. Since F.vesca may not be sufficient as Table 5.1. Nurnber of reports for interspecific hybridization of diploid Fragana species, listed by crossability categories. Based on Yarnell, 4931a; Mandelsdorf and East, 1927; Federova, 1946; Williams, 1959; Staudt, 1959, 1967, 1989; Evans, 1964,1974,1977; Fadeeva, 1966; Evans and Jones, 1967; Bumagina and Mesaros, 1969; Sebastiampillia and Jones, 1976; and Trajkovski 1993.
Self-compatible males Self-incompatible males
F.daltoniana F.iinumae F.nilgerrensis F.vesca F.nipponica F.nubicola F.viriciis Fernales ~ornpatibility~~'~~~~~ABCDEF ABCDEF ABCDE F ABCDEF ABCDEF ABCDE F F.daltoniana SC 1 1 1 F.nilgerrensis SC 1 1 3 111 1 3 1 2 311 F.vesca SC 111 12523 1 3 1 14 4 F.nipponica SI 1 1 1 1 F.nubicola SI 1 3 3 1 1 11 F.viridis SI 1 3 113 3 131 1 12 21 =:SC= self compatible Crossability categories: SI = Self incompatible A = no set 6 = seed, no germination C = death after germination D = sterile plants E = plants produced, fertility not reported F = fertile plants 122 a bridge for al1 Fragana diploids, this study was initiated to investigate other diploid species in Fragana that may have potential as a bridge species. Although investigation continued using colchi-tetraploid F. vesca x diploid species hybrids as parents in tetraploid crosses (Chapter 7), this study was undertaken to determine which species combinations may be most useful for breeding at the diploid level and to gain an insight into the evolution of Fragana species. The synthetic octoploid system originally proposed by Evans (1977) required crossing amongst diploid species as the first step. Identification of bridge species would greatly facilitate hybridization and broaden the range of germplasm advanced to the octoploid level.
This study examines the crossability of nine diploid Fragana species including multiple accessions of some species. Thus, this study includes more species and a broader genetic base than previous studies. it was hypothesised that if another species was similar to the progenitor species, it would cross more readily to other species than F.vesca. Such a species could also have potential as a genetic bridge ai the diploid level.
MATERIALS AND METHODS
Details regarding handling of plants for crosses, pollination, in vitro germination, and growing methods are provided in Chapter 2. Over a period of three years, Fragana vesca, F. viridis, F.nubicola, F. nipponica, F. nilgerrensis, and
F. penfaphylla were crossed in the greenhouse and field in most pair-wise combinations. Fragaria dalloniana, Egracilis and F.iinumae produced only a few flowers each and were included in only a partial set of crosses. Many species used --- 1 L 3 in this study were represented by only a few accessions (Table 5.2). Fragaria vesca was represented by the greatest number of accessions. Forty F.vesca accessions were crossed to F.viridis, Fmbicola, Epentaphylla and F.ni/gerrensis, in a related study (chapter 4) but other species were crossed to at least 10 F. vesca accessions. During bloom, species were intercrossed at random using fres h pollen but some pollen was stored (MacFarlane Smith et al., 1989) for use with species not in bloom. Self-compatible species were not used to pollinate self-incompatible species. As the compatibility status of F.pentaphylia and F.gracilis was unknown, these species were allowed to self pollinate under greenhouse conditions. Crossing strategy was infuenced by time of bloorn and availability of stored pollen. Not all species survived in the field each year, thus limiting field crosses. Preference was given to combinations of species that had not been hybridized or had been unsuccessful in previous studies. Most seeds were germinated with the in vitm rnethod (Miller et al., 1992) while some crosses with good seed set were germinated in the greenhouse. Progenies were compared to both parents to confirm that the hybridization was successful. Hybrid progenies were planted at Cam bridge
Research Station, Ontario where female fertility was judged based on fruit and seed set under open-pollinated conditions.
The results of interspecific crosses were categorised into six groups: A = no seeds from cross, B = seeds produced but no germination, C = seedlings died after germination, D = F, plants bioomed but had no seeds, E = F, plants have not bloomed, F = F, plants bloomed and produced seeds. Group E included those plants that have not bloomed or did not survive field conditions. As many of the 124
Table 5.2. Diploid Fragaria germplasm used in interspecific crosses.
Species Guelph # Identifier used by Sourcez source F.daltoniana da12 19861075 RBG Edinburgh NCGR gra2 CFRA 1199.000 NCGR F.iinumae ii3 CFRAI 008.000 NCGR F.nilge rensis ni11 CFRA II88.000 NCGR ni12 Mt. Omei, frch059 Forest Farm nip4 CFRA 1009.001 NCGR nubl PI 551851 NCGR nub2 PI 551853 NCGR F.pentaphylla penl 19881143 RBG Edinburgh pen2 19892408 RBG Edinburgh virl PI 551741 NCGR vir2 PI 551742 NCGR vir3 Oberau 2 IPK Genebank vir5 56.0123 RBG Edinburgh F. vesca 40 see Table 4.2 accessions Cha~ter4
' : See Appendix 1 for full names and addresses of germplasm sources 125 species used in this study have not bloomed consistently at this latitude, further observation may be required to judge fertility of hybrids which have not yet bloomed
(ie. Group E). Each species combination was assigned to the group that showed the greatest potential for geneflow displayed by its hybrid progeny. For example, if some crosses between two species produced no seeds but other crosses yielded fertile F, progeny, that combination of species was categorized as 'FI = F, plants bloomed and produced seeds. Also, general observations were made concerning general health and vigour of F, hybrid progeny grown in the field. Some species combinations were judged only by the qualitative index mentioned above. Data were recorded for number of seedslflower, % seeds with embryos and % embryo germination for species combinations treated with the in vitro method of germination. Data were analyzed with the GLM program of PC SAS (SAS systern for Windows V.6.12, Cary, N.C.). Mean separation was accomplished using the LS rneans function of PC SAS.
RESULTS
The crossability categories of 36 combinations of species are presented in
Table 5.3. F, plants were produced from 20 combinations of species, of which 13 bloorned and produced seeds (Group F) and seven did not bloom (Group E). The other 16 combinations of species failed to result in viable progeny (Groups A. B, or
C). No combinations were categorized Group D (i.e., blooming but producing no seed).
Wlh the exception of F.iinumae, al1 species in the study produced fertile F, 126
Table 5.3. Crossability categories for interspecific crosses among several diploid
Fragada species. Self-incompatible (SI) females were not poliinated with self- compatible (SC) males as this type of cross is unlikely to produce seeds.
Females Compat- SC species as males ibility F. dalloniana F. iinumae F.n~lqenensis F. vesca F.daitoniana SC E A F. iinumae SC A F.nilgenensis SC A~ A
SI species as males F.qraciiIs F.nipponIca F.nubicoia F.~eniaphylla Evindis F.daltoniana SC F.iinumae SC F.nilgemnsis SC F. vesca SC C C F F F F.gracilis SI E F F.nipponica S 1 C B F. nubicola SI A C E F F.pentaphyila SI F F F F F. viridis S 1 E E F F
Crossability categories A = no seeds from cross B = seeds produced but no germination C = seedlings died after germination O = F, bloorned but had no seeds under open-pollinated conditions E = F, plants have not bloomed F = F, bloomed and produced seeds under open-pollinated conditions 127 hybrids with at least one other species. Fragaria pentaphylla, and F-vexaformed fertile F, (Group F) hybrids with five out of seven and five out of eight species, respectively. However, Fragaria pentaphylla was more successful than F. vesca for interspecific hybridization if other groups of F, hybrids were considered. Two additional species, F. daltoniana and F.nilgerrensis, hybridized with F. pentaphylla forming viable piants which did not bloom (Group E). When F. vesca was pollinated with F.iinumae, F.nipponica, orF.gracilis, it resulted in unviable seedlings (Group C).
When Evesca was used as a male parent with the other three self-incompatible species no seed set occurred. Unlike F.pentaphy//a,F.vesca was not a parent in any Group E hybrids. Fragaria viridis was almost as successful as F.vesca for producing interspecific hybrids. It produced Group F hybrids with four other species and Group E hybrids with one other species. The next best results were obtained with F. nubicola, F.gracilis, F.nipponica and F.daltoniana which had Group F hybrids with three, two, one and one species. respectively. Besides being the most successful at interspecific hybridization, Epentaphylla, F.vesca, F. vindis and
Enubicola, when intercrossed, resulted in fertile progeny. Other species included in this study were only successful in hybridizing with two or fewer species.
Detailed information on those interspecific crosses subjected to in vitro germination are shown in Table 5.4. Of the three variables studied (Le. seeds~ower, % seeds with embryos, % embryos developing into plants) seedsMower was most variable, having a standard error approximately the same magnitude as the mean. SeedsMower ranged from 3 to 96 for the various species cornbinations, most of which had greater than 50% of seeds with embryos.
129
Notable exceptions were crosses involving Edaltoniana as a female and the combination F-nubicola x F.nipponica, which had less than 23% seeds with embryos. In 89% of the species combinations that produced seeds, hybrid plants were obtained through in vitro germination. Hybrid seedlings failed to develop from two crosses: F.nilgenensis x F.vindis and F. vesca x Enipponica.
It was noted that vegetative growth of most interspecific hybrids was very vigourous. Some of the crosses involving F.nubicola and F.daltoniana, the smallest and least vigourous species in this study, were particularly vigourous. When these two species were crossed with other species, hybrid progeny had larger leaves and
more vigourous plants than the rnost vigourous parent (Fig. 5.1). In the field, F,
hybrids were usually vigourous and healthy (Fig. 5.2). The exceptions were hybrids
of F.daltoniana x F. vindis, F.nilgerrensis x F-nubicola and F-nubicolax Enipponica, which were stunted and only lived for several months before dying. Fruit set of
most hybrids typically varied within the range shown in Figure 5.3. Notable
exceptions were hybrids resulting from the cross F.vesca x F.daltoniana, which
produced only one to five seeds on a small percentage of flowers. It is too early to
categorize non-blooming hybrids as sterile since most have had only one year's
growth in the field. Fragada iinumae, Fdaltoniana, Egracilis, and F.nubicola have
not bloomed consistently at Cambridge Research station, so hybrids with these
species in their lineage may not be well adapted for Rower initiation at this location.
Fraganapentaphylla and F. gracilis accessions did not set fruit under isolated
greenhouse conditions and were deemed self-incompatible. The few flowers of
F.iinumae allowed to self-pollinate did not set seed. Pollen from F.iinumae (ii3) was Figure 5.1. Hybrid vigour for vegetative growth of Evesca x F.daltoniana F, hybrids. The hybrid is depicted with selfed seedlings of its parents. All seedlings are three months ald. Note: F-vesca and F.daltoniana are self-compatible and not subject to inbreeding depression, so these seedlings are indicative of vigour present in the parents. Figure 5.2. Diploid hybrids shown one year after planting. Hybrids resulting from these combinations of species have not been previously reported. A = F.vesca x F.pentaphyiia, B = F.pentaphyiia x F.nipponica, C = F.vesca x F.daltoniana and D = F.daltoniana x F.pentaphylla. Figure 5.2 continued. E = Enubicola x Epentaphylla, F = F.pentaphylla x Enubicola, G = F.pentaphyila x F.viridis, and H = F.vjridis x F.pentaphyl/a. Figure 5.3. Variation in fruit size and yield of interspecific diploid hybrids. The photo shows variability among lines arising from hybridization of different accessions of Fragaria pentaphylla (P 1 & P2) and F. viridis (V2 & V5). 134 viable because seed set occurred when ii3 pollen was used to pollinate Evesca accessions. Self-cornpatibility status of al! other species was consistent with Table
5.4.
Reciprocal combinations differed for seed set arnong self-compatible (SC) species but were relatively less important among self-incompatible (SI) species
(Table 5.3). Crosses among F.vesca and other SC species produced seeds and plants when F.vesca was used as a female parent, but produced no seeds when used as a male parent. Also, crosses between Fdaltoniana and F.nilgerrensis produced plants when Fdaltoniana was the female but did not produce seeds when
F.nilgenensis was the female. Reciprocal combinations were identical for three combinations of SI species (F.vindis and Epentaphylla, F.vindis and Fmbicola, and F.nubicola and Enipponica) while other cornbinations of SI species (ie. F. viridis x F.graciik and Enubicola x F.pentaphylla) were classified into group E with reciprocal combinations classified into group F. One combination involving SI species, F. vindis x Enipponica produced healthy plants but reciprocal crosses produced seeds that did not geminate.
Table 5.5 combines data from reciprocal crosses showing those combinations of species where geneflow has potential. SI species have the greatest potential for gene flow as 60% of the combinations resulted in fertile FI hybrids.
Although fertile FI hybrids were produced by 50% of SC combinations, many different F.vesca accessions were used as parents to produce a few seeds of
F. vesca x F. daltoniana and F. vesca x F-nilgerrensis. As noted earlier, one of these combinations, Evesca x F.daltoniana, was observed to have the lowest fertility of Table 5.5. Results of interspecific crosses among several diploid Fragaria species, showing differences among SCZ x SC, SC x SI, and SI x SI combinations of species. Reciprocal combinations from Table 5.3 are combined into one value for each pair of species.
SC x SC F.daltoniana F.iinumae F.nilgen-ensis F.vexa F.gracilis F.nipponica F.nubicola F.pentaphylla F.iinumae F.nilgen-ensis EY F.vesca F C F
SC x SI SI x SI F.gracilis C F.nipponica C C E F.nubicola C A C F A C F.penlaphylla E E F F F F F.viridis C A B F F E F F
= Self-compatible species = Self-incompatible species
no seeds from cross seeds produced but no germination seedlings died after germination F, bloomed but had no seeds under open-pollinated conditions F, plants have not bloomed F, bloomed and produced seeds under open-pollinated conditions 136
any hybrid in Group F. Although seed set occurred for rnost combinations among
SC and SI species, 43% of the combinations produced seedlings that died after germination (Group C). SC x SI hybrids which developed into plants had either
Evesca or Epentaphylla as one of their parents. Combinations between SC and
SI species produced fertile hybrids only 21 % of the time, and al1 fertile combinations
had F. vesca as a female parent. Hybrids of F. daltoniana x Epentaphylla and
F.ni/gerrensis x Epentaphylla were produced but have not bloomed, but six other
combinations of SC and SI species produced unhealthy seedlings that died .
Fragaria vesca was the cornmon denorninator for producing fertile hybrids
between SI and SC species, but F.vesca was not able to provide a bridge to
F.iinumae, F.gracilis, or F.nipponica. However, F.pentaphylla can produce fertile
hybrids with al1 other SI species (which includes F.graci/is and F.nipponica) as well
as the SC species F.vesca. Thus. potential exists for geneflow at the diploid level
among eight diploid species, if Evesca and F.pentaphy/la are used as genetic
bridges. In this study, no single species was identified with the potential to provide
a bridge to F.iinumae, but this study was limited by having only one accession of
Einumae that rarely produced flowers. Fragaria pentaphylla was superior to
F. vesca for interspecific hybridization since it formed viable hybrids with eight other
species in the study, compared to five with F. vesca. This is particularly surprising
since far greater numbers of Evesca accessions were available for crossing and
only two accessions of Epentaphylla were available. DISCUSSION
With the discovery that octoploid strawberry cultivars have a very narrow
germplasm base (Sjulin and Dale, 1987), research in low ploidy species may be
particuiarly beneficial for broadening the germplasm base in Fragaria. Researchers
have suggested that tremendous advances could be made if strawberries could be
bred at the tetraploid level instead of the octoploid level (Barrientos and Bringhurst,
1973; Niemirowicz-Szczytt, 1987; Owen and Miller,1996). The arguments advanced for breeding with tetraploids instead of octoploids included simpler inheritance
patterns, ease of selecting recessive traits, and the ability to create homozygous
lines w hen chromosome dou bling occurs. Breeding and selecting of diploids would
be even simpler than tetraploids or octoploids. Such breeding would require use of
the SO systern (Evans, 1977) to facilitate geneflow between low and high ploidy
Jevels.
This study has a bearing on investigations to improve the synthetic octoploid
(SO) system (Evans, 1977) by using F-vesca as a bridge to diploid species.
Fragana vesca showed potential to act as a bridge byforming fertile hybrids with five
diploid species but formed only lethal hybrids with three other species (Table 5.5).
In addition, Fragana pentaphylla had greater potential as a bridge species than
Evesca. It also formed fertile hybrids with five species, but in addition, viable hybrids were formed with two other species.
It is interesting to note that viable progeny resulted from SC x SI crosses only
when F.vesca or F.pentaphylla was one of the parents. The abilrty to serve as a
genetic bridge among groups with different compatibility mechanisrns is indicative 138 of potential to assist breeding at the diploid level. Both F. vesca and F.pentaphylla are required to transfer genes among eight diploid species since only the former species formed fertile hybrids with Edaltoniana and F-nilgenensisand only the latter species formed fertile hybrids with F.graciiis and F.nipponica.
The identification of 11 combinations of species (13 if reciprocal
combinations are counted) that can produce fertile offspring, could be used for pre-
breeding of wiid species prior to use in the SO system. Pre-breeding could
concentrate desirable traits and greatly increase the value of wild germplasm prior to introgression into commercial cultivars and is a strategy employed with polyploid
species such as wheat (Gill et al.. 1995), soybeans (Lewers et al., 1998) and
potatoes (Jacobsen and Jansky, 1989). Since chromosome doubling could restore fertility of interspecific hybrids (Eigsti and Dustin, 1955), fertility of F, hybrids at the diploid level is not an absolute requirement for the SO system. Thus, al1 20
combinations of species listed in Table 5.3 that produced viable plants could
potentially be used for SO production. If al1 tetraploid hybrids were fertile, several
diploid species could be used as genetic bridges. For example, F.pentaphyiia could
substitute for F. vesca as a bridge to F. daltoniana or F. nilgerrensis. Similarly,
F. vindis could replace F.pentaphylla as a bridge to F.nipponica. This strategy would significantly increase genetic diversrty in germplasm derived from the SO
system.
Previous studies (Table 5.1) attempted 15 combinations (28 counting
reciprocals) of diploid species but only eight combinations (14 with reciprocals)
produced viable plants. Of these, only three combinations of species (five with 135 reciprocals) produced fertile interspecific hybrids. This study investigated 28 combinations of species (38 with reciprocals) and found approximately three tirnes as many combinations that could produce viable plants and more than three times
as many fertile combinations. This success was primarily due to having a greater
number of species and accessions. Fragana pentaphylla had the highest level of
crossability in this study but had not been previously investigated. Crossability of
F.graci/îs had also not been studied previously. Using a large number of Evesca
accessions to obtain a few rare seeds and then using an in vitro germination
technique (Miller et. al., 1992) was important to obtain interspecific hybrids from SC
x SC crosses. As many of the species in this (Table 5.2) and previous studies were
represented by only a few accessions it seems likely that additional successful
combinations will be found in the future, if more accessions become available.
Certainly, differences among accessions may be partially responsible for variation
of results obtained by earlier researchers (Table 5.2). In this study, accession
differences may have contributed to the large standard errors for traits such as
seeds I flower (Table 5.4).
Of the 34 combinations of species in this study, 19 combinations had not
been previously reported by other researchers. The results of previous studies
(Tables 5.1) and this study (Table 5.3) are cornbined to show successful
combinations in Figure 5.5, and those combinations which have not produced viable
progeny are presented in Figure 5.6. The combined data indicates more
possibilities for geneflow at the tetraploid level if hybrids become fertile when
chromosome numbers are doubled. Figure 5.5. Geneflow potential among diploid Fragana species, showing results of previous investigators combined with this study. Note that only F.inumae has not produced fertile progeny with other species. AH other species have produced fertile progeny with F.vesca andfor F.pentaphy//a. The interspecific progenies that have not been shown to be fertile may yet have genefiow potential if chromosome numbers are doubled, or after a longer period of observation. Based on Tables 5.1 and 5.3.
Legend O self-compatible self-incompatible fertile progeny -..II.-****. progeny created, fertility not yet demonstrated arrows go from males to females Figure 5.6. Combinations of diploid Fragana species that have not resulted in viable progeny, but might be successful if more accessions were investigated. Combinations that have not been investigated or have been unsuccessful are depicted. Since self-compatible species cannot usually pollinate self-incompatible species, this combination of parents is not recommended. Based on Tables 5.1 and 5.3.
F. viridis a
Legend O self-compatible self-incompatible no viable progeny -....-..-HI---* cross not attempted barrows go from males to females 142
Two combinations of species from previous research are worth mentioning.
Plants had been created with combinations of F.nilgerrensis x Eiinumae
(Sebastiampillia and Jones, 1976) and F-nilgerrensis x F. viridis (Evans, 1967,
1977), thus, indicating a possible bridge to F.inumae and an additional bridge to
F.niigerrensis. In neither of these combinations was fertility of F, hybrids reported at the diploid level, but the latter combination was fertile at the tetraploid level.
Figure 5.6 shows additional combinations of species that should be further investigated if more accessions become available, since increased numbers of accessions improve the likelihood of creating interspecific hybrids (Burbank, 1921;
Hermsen, 1992). While nine diploid species were investigated in this study, more combinations of species could be crossed if F.manchunca (Staudt, 1989) or newly discovered species are made available.
Another factor in the success of this study was that one type of cross was deliberately avoided, and is not recommended in Figure 5.6. Self-compatible (SC) species were not used to pollinate self-incompatible (SI) species. This type of cross is extremely unlikely to be successful (Evans and Jones, 1967). However, in rare instances where SI x SC crosses have resulted in progeny (Yarnell, 1931a;
Williams, 1959; Fadeeva , 1966),mutations involving self-incompatibility alleles are a plausible explanation for success (Lapins, 1983). Since SC x SI crosses can be quite successful (Evans and Jones, 1967; Lapins, 1983), this type of cross was perfonned in this study while SI x SC crosses were avoided.
Differences among SC x SC, SI X SI and SC X SI hybrids (Table 5.5, Figures
5.5, 5.6) may have implications for evolutionary theory of Fragaria. These data 143 suggest SI species are easier to intercross than SC species and that SI species are closely related while SC species are distantly related. Of the 15 SI x SI combinations attempted, 15 have resulted in hybrids and seven were fertile to date.
Of the nine SC x SC combinations attempted, only four have resulted in progeny and only two of these four combinations have been fertile. It has been speculated that self-incompatibility arose from self-compatibility in Fragana species (Darlington,
1973) and that the widespread self-compatible F.vesca is a progenitor to other
diploid species (Staudt, 1953; Nurnberg-Kruger, 1958; Darrow, 1966). However,
these two theories are contrary to classic studies (Lewis and Crowe, 1958) that
proposed SI mechanisrns orig inated early in the establishment of angiospems to
further promote cross-fertilization and that most SC species have SI ancestors.
Lewis and Crowe (1958) speculated that two types of SC species existed in plants.
one ancient, that could pollinate styles of SI species and one more recent, derived
from SI species, which would not pollinate SI species (Lewis and Crowe, 1958).
Self-compatible species F.nilgerrensis and F. vesca would not pollinate self-
incompatible species but reciprocal crosses were successful (Evans and
Jones.1967). Although no assertions were made regarding evolution in Fragaria,
the research by Evans and Jones (1967) supports the theory that F.nilgemnsis and
F. vexa were likely derived from SI species.
Geographical isolation not only leads to formation of new species but may
cause SC to arise from SI species in order to continue seed production (Stebbins,
1950; Lewis and Crowe, 1958; Darlington, 1973). The four self-compatible species
occupy unique ecological niches that may have lead to isolation and speciation: i44
F.vesca is adapted to low light levels of forest ecosysterns (Chabot and Chabot,
1977; Angevine, 1983); Enilgerrensis has the rnost southern range of diploid
Fragaria (Evans, 1964); Edaltoniana is found at the highest elevations (ie.
Himalayas) for diploid Fragaria, (Reed, 1966; Staudt, 1989) and Eiinumae is found in the isolated mountain regions of northern Japan (Reed, 1966; Staudt, 1989). As these self-compatible species, F vesca, F. nilgenensis, F. iinumae and Fdaltoniana, occupy different ecological niches. have divergent morphology (Fig. 1.1, Reed,
1966; Staudt. 1989) and are difficult to intercross, they probably do not originate from a common self-compatible ancestor. It is more likely that mutations arose independently in each of these species during isolation which broke down SI mechanisrns, thereby becoming SC, in a manner similar to that discussed for other species by Lewis and Crowe (1958). It is noted that F.pentaphylla does not have the wide geographical distribution of Evesca. It may be that the progenitor species was restricted in its distribution and that new species were formed through adaptation to new environrnents.
It was suggested that F.vesca rnight not be the progenitor species of the
Fragada genus and that intercrossing of diploid species would be needed to provide additional insight into the identification of the progenitor species (Chapter 4). It was hypothesized that the progenitor species would cross more readily to other species,
The results of this study indicate that the SI species, F.pentaphylla, rnay be more similar to the progenitor species of the Fragana genus than F.vesca. It is conceivable that F.vesca could have evolved from Epentaphylla or that bath species are intermediate steps in the evolution of other diploid species. Since fertile 145 interspecific hybrids can occur among many diploid species, an alternative theory is that F.penfaphylla and F.vesca are descendants of two or more species, which has resulted in improved crossability.
Although F. pentaphylla may be superior to other diploids for interspecific hybridization, the SO system could have enhanced flexibility by using two species as a bridge to other species. For example, if F.pentaphyila is narrowly adapted. it may be preferential to use F-vexa as a bridge species whenever possible.
Alternatively, attributes may be discovered in Epentaphylla (eg . pest resistance, cold hardiness, etc) that could make it preferable to use as a bridge species.
In light of the earlier discussion of SC species evolving from SI species, it is interesting that the SC F.vesca crossed readily with other species. This suggests
F.vesca has diverged more recently from SI species than other SC species. More similarities (ie. leaf morphology, flavours, chloroplast DNA) exist among F. vesca and the SI species than with other self-compatible species (Fig . 1.1, Evans, 1964;
Darrow, 1966; Reed. 1966; Staudt. 1989; Harrison et al.. 1997). Fragaria vesca also produces more seeds when pollinated with SI than with SC species (Chapter
4; Table 5.4).
While previous crossing studies revealed limited information on fertility of interspecific hybrids (Table 5.1), this study revealed that many combinations of hybrids were, in fact. fertile (Table 5.3). This supports other studies involving karyotyping (Iwatsubo and Naruhashi, 1989, 1991). chromosome pairing (Staudt,
1959; Jones,I 976) and DNA analysis (Harrison et al., 1993, 1997) that suggested
Fragaria species are closely related. Except for F.iinumae which has one 146 noticeably different chromosome (Iwatsubo and Naruhashi, 1989), and has not produced progeny when crossed with other species, it seems likely that similartypes of genornes exist among the other eight species in the study. It has been suggested that F-vesca and F.vindis have A genomes while octoploid Çragaria has
AAA'A'BBBB or AAA'A'BBB'B' genomes (Senanayake and Bringhurst, 1967;
Bringhurst, 1990). The assignment of genomic designations in these two studies was mainly based on the ability to hybridize octoploids with F-vesca and Evindis.
The data of this study suggests that diploid Fragana are very closely related and, therefore, most would possess A genomes. Without a confirmed B genome species at the diploid level, perhaps a genomic designation of AAA'A'A"A"A"'Anl would be more appropriate to explain genomic makeup of octoploid Fragana. Thus, it may be less important that cornmon, or pivotal, genomes be used in polyploid crosses for SO production. There may already be enough genomic homology among species to make this precaution unnecessary. It may be more important to insure that diverse genotypes are used in crossing so that multivalent pairing does not occur, particularly when chromosome doubling is used.
Almost 50% of the potential combinations of species (Figure 5.6) have not resulted in viable offspring. About 20% of the total combinations have not been investigated while the remaining 30% did not result in progeny, emphasizing that crossability differences do exist among Fragada species. Certain genetic combinations may be lethai. This would seem to be the case in those combinations where seeds gerrninated but did not develop, or had embryos that did not geminate. However, only a few accessions for most species have been available 147 in this and previous studies. It is possible that additional successful combinations will be found if a wide gerrnplasm base (ie. more accessions) of these rare species is used.
SUMMARY
While the germplasm base of octoploid Fragaria cultivars is narrow , there is great potential for broadening the germplasm base at the diploid level. This study
provides additional evidence suggesting diploid Fragaria species are closely related,
and is the first study to show that geneflow could occur among most diploid Fragaria
species. While only five combinations of species were previously shown to have
fertile F, hybrids, this study has expanded that number to 14 combinations. Among
the nine diploid species studied, F. vesca and F.pentaphyl/a are the most promising
species to use as bridges, at the diploid level. With these two species geneflow
could theoretically occur among al1 the diploid species in this study, except for
F.iinumae. The successful combinations identified in this study could serve as an
outline for prebreeding and improving diploid germplasm prior to use in the synthetic
octoploid system. As this study had only one or two accessions for many species,
it is quite possible that more successful combinations of species will be found as
more accessions become available. The similarities among diploid species could
become a factor in creating synthetic octoploids from diploid species. It may be not
be important to design crossing strategies with common, or pivotal, genomes since
the diploid species may already be closely related.
This study also has implications for the evolutionary theory of Fragaria i48 species. While Evesca produces interspecific progeny more readily than other SC species, the results of this study cast doubt on the assertion that it is the progenitor species of the genus. Instead, it is more likely that the progenitor species was similar to F.pentaphyila and that SC species evolved from SI species in Fragana. 149
Chapter 6
lnterspecific hybridization of Fragaria moschata (6x) with
Enubicola (2x) and Eviridis (2x)
ABSTRACT
The crosses Fragana rnoschata x F.nubicola, Emoschata x F.vindis, and their reciprocal combinations were done to create tetraploids for eventual introgression into octoploid cultivars of Ex ananassa via the synthetic octoploid system. The combination F.nubicola x F.moschata averaged 3.3 healthy plantslpollination, which was 2.3 times more than the next best combination,
Fmoschata x F.vindis. Fragaria viridis x Fmoschata crosses averaged only 0.1 heaithy plantslpollinationand no plants were obtained from F.moschata x Enubicola
hybridizations. The success of the Fmbicola x Fmoschata crosses in this study
indicate that embryo 1 endospen balance ratios were not as important a factor in
producing hybrids with F.moschata x diploids species, as previously suggested.
Although 90% fruit set and 19 seeds/pollination occurred for the experiment, only 15% of the seeds contained healthy, white embryos and only 38% of these developed into healthy seedlings. The remaining 62% of embryos lacked pigment,
had short hypocotyls or did not continue to develop after slight expansion out of the
seed coat. Only 39% of the crosses resulted in viable progenies but al1 six diploid
and six of the seven hexaploid accessions were successfully incorporated into 89
hybrids. After one year, 27% of these hybrids bloomed and 71% of the blooming hybrids were tetraploids.
WTRODUCTION
This experiment contributes to the Synthetic Octoploid (SO) system (Evans,
1977) by focusing on creating tetraploids from the hexaploid Çragaria moschata for eventual introgression of this species into octoploid cultivars of F.x ananassa. Since
F. rnoschata may be a naturally occurring hybrid of F.vesca and either F.viridis or
Enubicola (Federova, 1946; Staudt, 1959; Darrow, 1966),the creation of hybrids in this experiment is useful for later research focusing on the use of Evesca to create synthetic octoploids (Chapter 7).
Of the 15 SOS created by Sebastiampillia and Jones (1976) and Evans
(1 977),nine had F. moschata in their lineage. The two strategies for incorporating hexaploid F. moschata into SOS are depicted in Figure 6.1. Only a very limited amount of Fmoschata germplasm was introgressed into cultivars. A fertile SO released by Evans was created by crossing F.moschata (6x) x F.nubico/a (2x) and applying colchicine to seeds to create an octoploid hybrid (Evans 1982a, 1982~).
Guelph SOI was semi-fertile and was used in breeding programs in Guelph
(Sangiacomo and Sullivan, 1994) and Sweden (Trajkovski, 1990, 1993). Kantor
(1984) introgressed F.moschata into F. x ananassa by crossing Emoschata directly to cultivars and using rnutagens to overcome sterility in the 7x hybrids. Kantor abandoned this line of research because restoration to the 8x level required several Fig. 6.1. Strategies used by Sebastiampillia and Jones (1 976) and Evans (1977) to create synthetic octoploids with the hexaploid Fragaria moschata. Numbers represent ploidy levels of species and hybrids. Parents are on the left and progenies are on the right. Strategy A involved applying colchicine directly to hybrid seedlings. Strategies B,C and D used F.moschata x diploids hybrids in crosses with other tetraploids. 6x 8x 'Ti->*'colchicine
/ colchicine
2x 4x / colchicine colchicine 152 generations of backcrossing, after which the backcrossed progeny no longer possessed the desirable traits from F. moschata. Several desirable traits have been identified in F. moschata that have potential for introgression into cultivars. These include resistance to leaf diseases (Evans, 1982~;Kantor, 1984; Trajkovski, 1993;
Maas et al., 1995), resistance to spider mites (Gimenez-Ferrer, 1993), cold hardiness (Reed, 1966; Kantor, 1984), large plants more vigorous than octoploid species (Reed, l966), unique, highly aromatic Ravour (Reed, 1966; Kantor, 1984), upright flower stalks that hold fruit above the canopy (Evans, 1982; Kantor, 1983) and unifom ripening (Reed. 1966).
For SO production, the hexaploid Fmoschata can be crossed to a diploid species to create tetraploid hybrids. Table 6.1 summarizes investigations involving crosses among F.moschata and diploid species. Crosses between Fdalfoniana,
F.nilgerensis, F.nipponica, or F.vesca, and accessions of F.moschata were unsuccessful but fertile hybrids were produced when F.moschata was crossed with
Eviridis (2x) or Enobicola (2x) (Evans, 1964, 1977; Bhanthurnnavin, 1965;
Fadeeva, 1966; Bumagima and Mesaros. 1969). Thus, this study focused on using
F. vindis and Fmbicola. Althoug h F.nubicoia x F.moschata crosses have not been successful (Table 6.1), this combination of species was included in this experirnent, since the reciprocal combination was successful. This experiment was done with increased numben of accessions (compared to earlier studies) to improve the likelihood of creating Table 6.1. Outcornes of interspecific crosses between Fragana moschata and diploid species. Species combination Reference F. moschata x F. vesca F. vesca x F. moschata Mangelsdorf no set good set. 600 seed, 4 germinated, al1 and East, 1927 hybrids were weak and died within 2 years Federova, no seedlings 5430 seed, 15 plants, 1 1 materna1 1934 diploids, 2 tetraploid hybrids, 2 pentaploid hybrids
Evans, 1964, 15 pollinations, 1 seed, O 6 pollinations, O seed 1974 gerrninated Fadeeva, 1966 no germination or lethal sterile plants and seedlings that died seediings shortly after germination Bumagima and 0.04% set, 2 seedlings Mesaros, 1969
Ç. moschata x F. viridis F. viridis x F. moschata
Evans, 19 pollinations, 18 seed, 3 7 pollinations, 17 seed, 2 germinated but 1964,1974 germinated died soon after Fadeeva, 1966 3.1 seedlpol., 38 seed, 2 5.7 seedlpol., 64 seed, 4 germinated, germinated, hybrids were hybrids were fertile fertile Bhanthum- obtained hybrid plants navin, 1965 Bumagima and 3241Oh set, S. 1-3% gem. 5 hybrids Mesaros, 1969 F. moschata x F. nubicola F. nubicola x F. moschata Evans, 1964, 28 pollinations, 85 seed, 26 3 pollinations,l4 seed, 1974 germinated O germination Bhanthum- obtained hybrid plants navin, 1965 Evans, 1977 obtained fertile 4x and 8x hybrids Table 6.1. continued.
Species combination
Reference F. moschata x F. nipponica F. nipponica x F. moschata Fadeeva, sterile plants 1966
Menfield, fertile hybrids 273 seed, 1 sterile plant 1933
F. moschata x F. nilgerrensis F. nilgerrensis x F. moschata
Evans, 1964 8 pollinations, no set 6 pollinations, no set
F. rnoschata x F. daltoniana F. daltoniana x F. moschata -- - - - . ------Evans, 1964 7 pollinations, no set 2 pollinations, no set 155
interspecific hybrids (Burbank, 1921; Hermsen, 1992).
The objective of this study was to examine crossability of a larger number of accessions and to determine optimum combinations of species to create tetraploids with Fmoschata parentage using the germplasm available. It was hypothesized that either Fmbicola or F. vindis would be superior for crossing with F.moschata.
MATERIALS AND METHODS
The three species used in this study are depicted in Fig. 6.2. and sources of germplasm are listed in Table 6.2. The Fmoschata accessions originate from diverse regions, in France, Italy, Germany and Russia. The F.nubicola accessions are from Pakistan, while three of the four F.viridis accessions are from Germany.
The fourth F.vjridis accession (vir-5) was obtained from a botanical garden but its geographical origin is unknown. Plants were field grown at Cambridge Research
Station, Cambridge, Ontario, dug when dormant in late fall, and forced in the
University of Guelph's greenhouse during winter. Fragarfa nubicola accessions
required short day treatment in a growth chamber (i.e. four weeks at 10 hr. day
length, 1811 5 C daylnight temperature) to encourage bloom.
A total of 127 pollinations were made including 47 different combinations of
parents. An effort was made to have similar nurnbers of crosses for each species
combination. For many combinations of parents, one or two pollinations were made.
Additional crosses were made for those accessions producing abundant fiowers.
As Fragana moschata is triecious with plants being either male, female, or (rarely) 156
Figure 6.2. The three Fragaria species used in this study: Emoschata, F. vindis and
F.nubicola. Table 6.2. Accessions of Fragana moschata (6x), F.nubico/a (2x) and F.vindis (2x)used in crossing program for tetraploid production.
-- - Species Guelph # Identifier used by SourceY Se? accession source t~PeS Fmoschata mcvl "Capron" NCGR h clone PI 551 528 "Profumata di NCGR f clone Tortona" PI 551549 NCGR f clone NCGR f+m family
FRA 9193 IPK f clone PI 551550 NCGR m clone mw5- #2 "Cottan IPK f+m family abcdefik F.nubicola nub 1 PI 551851 NCGR h clone Pl 551853 NCGR h clone F. viridis virl PI 551741 NCGR h clone Pl 551742 NCGR h clone #2 "Oberau 2" IPK h clone 56-0123 RBGS h clone
': mcv = Fmoschata cultivars nub = Fmbicola mw = F.moschata wild vir = F. viridis Y: See Appendix A for full names and addresses of germplasm sources.
X: f = female m = male h= hermaphrodite
W: Letten listed after numbers are individuals of a family. For example, four members are in the mw-2 family. 158 hermaphrodite (Staudt, 1989). reciprocal crosses cannot be done with most F. moschata accessions. The only hermaphrodite F-moschaia in the study. mcvl, was included in additional crosses since it was perceived to be valuable germplasm. As
F.nubicola required forcing to bloom, it flowered later than many F.moschata accessions and consequently participated in only 10 crosses as a male with
Emoschata. Since Fmoschaia pollen was stored, Enubicola could be pollinated with earlier blooming F-moschataaccessions. Reciprocal crosses were not possible with Fmoschata accessions except for the hermaphrodite clone mcvl . Fragana nubicola and F.vindis accessions are hermaphroditic and were used as both male and female parents.
Seeds were genninated in vitro according to Miller et al. (1992) with slight modification. Rather than cutting cotyledons in half. only 30% was removed.
Observations were made during dissection of achenes and only white healthy embryos were placed on media for germination. Small white embryos that did not completely fil1 were included in the healthy category since they were found to be capable of geninating in vitro. Seeds were discarded if embryos were brown, off- white or yellowish. Previous research had shown that these three types of embryos would not germinate. Further details regarding pollination and in vitro germination of seedlings have been presented in Chapter 2.
Five dependant variables were studied: percent fruit set, seedslpollination, embryoslpollination, heathy plantslpollination and one year old hybrids that bloomed/pollination. Descriptions of the first four variables are contained in Chapter 159
2. Ploidy levels of hybrids that bloorned after one year were estimated with fiow cytometry (see Chapter 3 for details). Means for each combination of parents were used in statistical analysis of differences among species. Data were analyzed with the GLM program of PC SAS (SAS System for Windows V.6.12, Cary, N.C.). Mean separation was accomplished using the LS means function at the 5% level of significance. Statistical analysis was used to determine differences among species combinations and to determine if a species was more successful as a male or female parent for interspecific crosses.
RESULTS
Means for species combinations are presented in Table 6.3 whiie data for individual crosses and ANOVAs are presented in Appendix 3. Percent fruit set averaged 90% and seed production averaged 19 seedslpollination for the experiment. From a total of 2032 seeds that were dissected for in vitro germination,
296 healthy, white embryos were obtained. Of the remaining seeds, 1493 and 243 contained brown or discoloured embryos, respectively, and were considered nonviable. Alrnost al1 healthy embryos showed signs of growth when placed in vitro but only 38% developed into healthy seedlings. The remaining 62% of in vitro embryos had lethal deformities such as lack of pigment (albinos), lack of hypocotyls, and arrested development after slight expansion out of the seed coat. In total, 89 healthy hybrids were produced, 24 of these bloomed when approximately one year old, and 17 of the blooming hybrids were tetraploids. The plants that were not 160 tetraploids consisted of a pentaploid, a 4x16~mixaploid, two hexaploids from 2x x
6x crosses and a diploid also from a 2x x 6x cross. Plant morphology of al1 hybrids, except a diploid resulting from nub2 x mwZd, was indistinguishable from
F.moschata, regardless of ploidy level. This exception had leaves similar in width and pubescence to F.nubico/a and was intermediate in length and shape when corn pared to Fmbicola and Fmoschata.
Means of % fruit set. seedslpollination, embryoslpollination and healthy plants/pollination, and one year old hybrids that bloomedlpollination were calculated for four combinations of species: Emoschafax F.nubicola, F-nubicolax Fmoschata,
Fmoschata x F. virids and F.vindis x Emoschata (see Table 6.3). Only the means of embryosfpollination and healthy plantslpollination were significantly different among the four species combinations used in crosses. The combination Fmbicola x Fmoschata produced significantly larger numbers of healthy embryos and healthy plants than other species combinations. This combination produced almost three times as many healthy embryos and 2.3 times more healthy plants than the next best combination of Fmoschata x F.vindis. Although fruit set and seeds were produced, no healthy plants were obtained from the combination of F-moschata x
F.nubicola. Although F. vindis males produced 1.3 more healthy plantsfpollination than F. vindis females in crosses with F.moschata, this difference was not significant.
While 90% of various combinations of parents used in Fmbicola x F.moschata crosses resulted in healthy plants, only 25% and 16% of combinations of parents used in F-moschata x F.vindis and F-vindis x F.moschata crosses. respectively, produced any healthy plants.
102
There were only a few combinations of accessions that were superior in creating hybrids. It is interesting to note the best three combinations of accessions for production of healthy plants were crosses arnong nub2 and three accessions in the mw5 family (ie. mw5d, mw5f and mw5i). These three combinations averaged seven to 10 healthy plants per pollination. The crosses mcvl x vir2, mcv2 x virl , mw2c x viR and nubl x mw2d were the second most successful, producing five to six healthy plants per pollination. All other combinations of accessions produced on average one or less progeny per pollination. Although vir5 x mw5f and mw5k x nubl produced the most seeds, (ie. 65 and 62 seeds per pollination, respectively), neither combination produced healthy plants.
Although only 18 of 46 combinations of accessions were successful in creating viable progenies, al1 of the diploid species and most of the Fmoschata accessions were successfully incorporated into hybrids. The Emoschata accessions that were not incorporated into hybrids included mw3b and some members of the mw2 and mw5 families. Most of these unsuccessful accessions were only used in one or two crosses.
DISCUSSION
The methodology and hybrids resulting from this study greatly expands the genepool of Fmoschata that could be used for introgression into strawberry cultivars. Although, several authors have created tetraploids with F.moschata, none
of the hybrids mentioned in Table 6.1 were listed in genebanks contacted (see
Appendix l),and the tetraploids that Evans had created, no longer existed at the 163
University of Guelph. Only two F-moschaia accessions have been introgressed into cultivars (Evans, 1982c; Kantor, 1984). The 89 hybrids in this study were derived from five clones and two open-pollinated families of F.moschata (Table 6.1)
Compared to previous crossing (Table 6.1), this study used a broader collection of
Emoschata and created more interspecific hybrids. While Evans (1964) obtained
31 hybrids between F.moschatû and diploid species, al1 other reports either did not show how many hybrids were created or have reported zero to seven hybrids. Much of the success of this study may be due to adopting a crossing strategy of maximizing the number of combinations of parents. Having a wide genetic base is especially important for interspecific crosses (Herrnsen, 1992). To increase success of wide crosses, using many parental genotypes for a few interspecific hybrids is superior to using a few parents for many crosses (Burbank, 1921; Galletta and
Maas, 1990).
An in vitro technique for improved germination (Miller et al., 1992) was
important for obtaining hybrids. Previous research involving Emoschata hybrids
probably germinated whole seed on soil-less mix. When used on F. x ananassa
seeds, the whole seed method had 27% germination but the in vitro method had
97% germination (Miller et al. 1992).
The use of the in vitro germination (Miller et a1.J 992) technique in this study
provided information not reported by previous researchers. This study s howed that
embryo abortion is a primary cause of low germination rates with seed produced by
crossing F.moschafa to either F.nubicola or F-vindis. The prevalence of normal
sized seeds that contained brown shriveled embryos, indicates embryos aborted at 104 a stage sometime after the outer seedcoat had reached maximum size. Discoloured embryos which did not develop were likely to have aborted in the later stages of seed development. Disruption of normal development was obsewed beyond the seed development stage. During in vitro germination a number of aberrations were observed including albinism, lack of hypocotyls and arrested development that could have prevented germination with traditional methods. It would appear there is no specific developmental stage in which Emoschata x diploid hybrids are likely to abort. Rather, a number of developmental events may be affected. As fruit set averaged 90% for the experirnent, there apparently is little or no influence of self- incompatibility rnechanisms.
Ideas regarding interspecific crossability often change as more accessions become available or as new techniques such as embryo rescue are used
(Hermsen, 1992). In this study, a diploid x hexaploid combination, Enubicola x
Fmoschata, resulted in the highest numbers of embryos and healthy plants. Evans
(1974) suggested embryolendosperm balance was responsible for difficulties in obtaining diploid x hexaploid hybrids and recommended that the hexaploid species be used as a female in crosses with diploid species. Although, Evans (1974) based his recommendation on several combinations of species, including octoploids and tetraploid hybrids, he had used only one combination of parents for each of
Enubicola x Fmoschata and F.viridis x Emoschata crosses. While Evans was not successful in obtaining diploid x Fmoschata hybrids, other researchers were successful with F.vjrids x F.moschata crosses (Fadeeva,l966; Bumagima and
Mesaros, 1969). Researchers crossing parents with different ploidy levels often use 165 the higher ploidy parent as the female parent (Stoskopf et al., 1993),but a notable exception is in Helianthus species where accessions of the lower ploidy species can be the most effective female (Georgieva-Todorova, 1984).
Other factors could be more important than ernbryo/endosperrn ratios when
Emoschata is crossed with F. vindis or F.nubicola. An explanation for embryo abortion and malformed hybrid seedlings in this study may be chromosome instability or chromosome elimination. Chromosome elimination likely occurred with the diploid hybrid that had some characteristics of F.moschata (Table 6.4). A combination of chromosome elimination and spontaneous chromosome doubling may have occurred with the 4x16~mixaploid and the two hexaploids derived from diploid x hexaploid crosses. The pentaploid hybrid could have been derived from an unreduced gamete of the diploid parent that fused with a 3x gamete from the hexaploid parent similar to hexaploids produced when F. vesca was hybridized with
Fmoschata in an earlier study (Federova, 1934).
Fragana moschata rnay also harbour lethal or sub-lethal alleles. The occurrence of lethal and semi-lethal genes at high frequency in obligate outcrossen is well known to geneticists (Stebbins,l950). As F.moschata is polyploid and an obligate outcrosser (except for the rare hermaphrodite forms), recessive lethal alleles could easily accumulate in natural populations of this species. Song et al.
(1995) showed that rapid genome change occurs in derived polyploids of Brassica and suggested that polyploid species can generate extensive genetic diversity in a short period. If deletions or mutations have occurred in F.moschata, a reduction in ploidy level from 6x to 4x would reduce the buffering capacity offered by the 106 additional two sets of chromosome. Differences in cytoplasm or interactions between cytoplasm and nuclear DNA could be involved in obtaining hybrids
(Stoskopf et al., 1993) between F.moschata and diploid species.
Unlike previous attempts (Table 6. l),the F. nubicola accessions in this study were particularly suited as female parents when crossed to Fmoschata.
Conversely, no hybrids were obtained from Fmoschata x F.nubicola crosses, althoug h other researchers were successful with that combination (Evans, 1964,
1974; Bhanthumnavin, 1965). Both this and Evans' (1964,1974) studies used only two accessions of F.nubicola, so it is not surprising that results would Vary among these studies.
The 1.4 plantslpollinationfor Fmoschata x F.vifidis crosses in this study were much higher than the 0.16 and 0.05 plantslpollination obtained by Evans (1964) and
Fadeeva (1966). The reciprocal combination, F.vitidk x F+moschata, had somewhat similar results to previous research with 0.1 plantslpollinationin this study compared to earlier studies averaging O (Evans, 1964), 0.36 (Fadeeva, 1966) and
0.07 (Bumagima and Mesaros, 1969) plantslpollination.
The putative diploid ancestors, F.nubicola, F. vindis or F. vesca (Staudt, 1959,
1984, 1989), may not be fully compatible with F. rnoschata if the latter has undergone genomic changes. Recombination among different genomes may have occurred in Emoschata since pairing readily occurç in diploid interspecific hybrids
(Jones, 1976) and the three putative ancestors are similar enough to create fertile hybrids (Chapter 5). Fragaria moschata accessions may be highly heterozygous so that interspecific crossability varies greatly among accessions. 167
If it is accepted that Fmoschata has a genomic constitution of AAAABB
(Federova, 1946; Fadeeva, 1966), it seems likely that the B genome in Fmoschata is similar to F.nubicoia or F-viridis genomes, since this study and others
(Evans,1 974, 1977; Fadeeva,1 966) obtained fertile tetraploid hybrids when
Emoschata was crossed with F-vindis or F-nubicola. These resulting tetraploid hybrids would be fertile because they have two corn plete sets of different genomes
(je. AABB).
Hybrids with F.moshata in their lineage may be reflecting the low germination inherent in Fmoshata. The accessions of mw2, mw3 and mw5 were originally obtained from seed that had in vitro germination rates of 16%, 1.3% and 8%, respectively (unpu blis hed data by author). Mean germination rate of these accessions was 6.0% while the germination rate of hybrids in this study was 5.8%.
The germination rates of the original F.moschata parents was much lower than the
21 other accessions of various Fragaria species from the same genebanks, which ranged from 12 to 96% with an average of 58% germination (unpublished data by author). It is unlikely that detrimental alleles were introduced into hybrids from either
F.nubicola or F.vindis. Malformations in seedlings did not occur when F.nubicola and F.viridis were crossed to diploids in other experiments (Chapters 4 and 5).
Although this study used more combinations of accessions than previous studies, far too few accessions were used to make generalizations regarding
interspecific relationships. Of the accessions used in this study, the most productive
crosses were male F.moschata plants crossed ont0 F.nubicola and female
F.moschata plants pollinated with F.vindis. The data of this study and earliet 10s research combined indicates F.moschata can be crossed both as a male and as a female with Enubicola and F.viridis.
CONCLUSION
This study was successful in obtaining more Fmoschata x diploid hybrids with a larger gemplasm base than previously reported. In particular, this study is the first to show that viable hybrids of F.nubicola x F.moschata can be created.
While low germination of F, seeds was noted in previous research, it was not known that aborted embryos and malformations in seedling progeny were major factors
limiting Fmoschata x diploid hybrid production. The success of the Enubicola x
F.moschata crosses in this study showed that embryo I endospem balance ratios were not as important a factor in F.moschata x diploids crosses as previousiy
suggested by Evans (1974) and that there does not seem to be any advantage in
using Fmoschata as a female parent when crossing to Ç.nubicola. Chromosome
elimination, presence of lethal or sub-lethal alleles in F.moschata, and a reduction
in buffering capacity associated with a decrease in ploidy from 6x to 4x may be
important factors in disrupting growth of hybrid embryos and germinating seedlings.
A total of 18 of the 46 combinations of parents were identified as capable of
creating hybrid progeny. While many combinations of accessions did not create
viable offsprhg, most available germplasm was successfully incorporated into at
least one tetraploid progeny. Thus, this study demonstrated the importance of
attempting many different crosses and using a wide gemplasm base during
intenpecific hybridization. The diversity of hybrids created in this study could be 169 especially beneficial for research into the final stages of the SO system (ie. intercrossing of tetraploids with colchicine treatment of progeny) since earlier attempts of intercrossing Fragada tetraploids had a narrow genetic base (Chapter
1). In particular, the tetraploids created in this study are allopolyploids and, thus, differ from autoploids and naturally occurring tetraploids, which will be used for tetraploid breeding in the next chapter. 170 Chapter 7
The use of Evesca, tetraploid and hexaploid Fragaria species to
incorporate diploid Fragaria species into synthetic octoploids
ABSTRACT
The synthetic octoploid (SO) system is a method of combining diploid, tetraploid and hexaploid Fragaria species into hybrid octoploids. The SOS
produced could then be introgressed into 8x cultivars of the commercial strawberv,
F.x ananassa. This study used F-vesca, Eonentalis and Emoschata as genetic
bridges, incorporated the pivotai genome theory in its crossing strategy, used a
wide gerrnplasrn base, maximized heterozygosity in the crossing design, and used
advanced techniques for germination and colchicine delivery to improve the SO
system. In this study 192 SOSwere created from 25 combinations of species, with
11 fertile combinations. Of the 98 SO's planted in 1997,28produced fruit in 1998.
The number of SOScreated in this study represents a significant improvement over
previous attempts to create SOS.
This strategy used colchi-tetrapioids derived from F. vesca crossed with
F.nilgerrensis, F.nubicola, Epentaphylla. and F. vindis for crosses at the tetraploid
Ievel. These tetraploids produced, on average, only 37% fruit set and three
seedsMower when intercrossed. When the colchiploids were pollinated with
tetraploids derived from F.orientaiis or F.moschata, 52% fruit set and 10
seedslflower were obtained. Tetraploids containing two genomes of F.vesca were
not as fertile as tetraploids without any Evesca genomes, but F.vesca was useful 171 in introgressing four diploid species into SOS. The fact that so many combinations of species were capable of producing progeny at the tetraploid level suggests that the species involved in this study are closely related and that there may be great potential for cornbining many species and breeding at the tetraploid level in
Fragana .
INTRODUCTION
The commercial strawberry, Fragada x ananassa, is an octoploid species.
Within the genus of Fragana there are ten diploid, three tetraploid and one hexaploid species known, which are generally not used by breeders because crosses among species with different ploidy levels result in poor seed set, poor germination andfor sterile progeny (Evans, 1976; Kantor, 1984). By crossing lower ploidy species and applying colchicine, synthetic octoploids (SOS) can be created which can be introgressed into cultivars (Evans, 1977,1982a, 1982b, 1982~). There are 12,769 combinations of Fragana species which could be investigated to create
SOS in two generations. Previously, SOS were created from available accessions, without attention to species combinations that might have a high rate of success.
Rather than attempt al1 possible combinations of species, this study focused on the use of F. vesca, F-moschata, and F.onentalis in SO production as bridges to incorporate some of the d iploid Fragana species (F. nilgerrensis, Enubicola,
F.pentaphyila, and F. vindis) into synthetic octoploids. 172
Previous crossing strategies to create SOS
One strategy to create SOS was to cross 2x. 4x. or 6x species directly to octoploid cultivars (Figure 1.5). This strategy relied on unreduced garnetes, colchicine, or required several generations of crosses among different ploidy levels to restore hybrids to the octoploid level. These unbalanced ploidy crosses rarely produced viable seed (Evans, 1974) or resulted in progeny with odd numbers of chromosomes which had dysfunctional chromosome pairing in meiosis and sterility
(Darrow, 1966; Kantar, 1984).
The Synthetic Octoploid (SO) method involves creating tetraploids from 2x,
4x, and 6x species and treating tetraploid hybrids with colchicine to double chromosome numbers (Evans, 1976; Figure 1.6). Advantages to this approach include: parents have the same ploidy level, embryolendosperm ratios are the same as intraspecific hybrids, rare unreduced gametes are not required , hybrids have even numbers of chromosomes, and only one or two generations of crosses are required .
Tetraploid breeding in Fragaria
Previous studies investigated tetraploid breeding (Table 7.1) while others attempted to create SOS from tetraploid crosses (Table 7.2). In this latter group,
only three SOS were introgressed into octoploid cultivars (Evans, 1982~)and two
Sots were released for use by breeders (Evans, 1982a.b). There is no further report on the eight SOS created by Sebastiampillia and Jones (1976).
The University of Reading germplasm used by Sebastiampillia and Jones
Table 7.2. Studies that created Synthetic Octoploids (SOS)from crosses among tetraploid Fragana species and hybrids. Note that Evans (1977) reported on fertility of SOS but Sebastiampillia and Jones (1976) did not.
# of # of sun/ivors # of SOS # of fertile Female Male seedlings after colchicine SOS Reference F. moupinensis F.corymbosa 6 Sebastiarnpillia
F. orientalis F.moschata x F.nubicola 16 and Jones, 1976 F.(vesca x viridis) F.moschata x F.nubicola 16 F. (moschata x viridis) F.orientalis 8
F,(moschata x viridis) F.corymbosa 16 F. vesca (4x) F.moschata x F.viridis 4
------F.moschata F.nubicola 312 42 2 2 Evans, 1977 F. (moschata x nubicola) F.orientalis 2600 196 O O
F,(moschata x nubicola) F.vesca x F. viridis 600 47 O O
F.moupinensis F.nilgerrensis x F. vindis 2120 216 O O
Fmoupinensis F. moupinensis 42 2 1 O F.(nilgerrensis x viridis) F.moupinensis 230 4 2 O F,(vesca x viridis) F.moupinensis 466 60 1 1
F. (vesca x viridis) F. vesca x F.viridis 194 25 O O 176
(1976) and Evans (1964, 1977) was derived from the Max Planck Institute in
Gerrnany (Evans, l964), where Staudt (1959) researched. Thus, it would appear that previous studies involving tetraploid crosses are in fact based on closely related if not identical germplasm. Evans (1964) lists 13 accessions of Evesca, four of
Fmoschata, two of F.moupinensis, two of Enubicola, and one each of F. vindis,
F.niigenensis and F-orientalis as being the founders of his hybrids.
The hybrid tetraploid material created by previous research was not available for use in this study. It most likely no longer exists, or at least was not listed at genebanks contacted in the U.S., Canada, U.K., or Russia. Thus, it was necessary to create tetraploids for this study (Chapters 2,4 and 6).
Emphasis on F. vesca, F. orientalis and Emoschata in crossing strategy
The relationship among crossing strategies of Chapters 4, 5, 6 and this experiment is shown in Figure 7.1. Those three chapters involved diploid breeding
and tetraploid creation while this study focused on tetraploid breeding and octoploid
creation. Figure 7.1 . also encompasses the strategies presented by Evans (1977
; Figure 1.6) ). Although this and earlier studies are similar in the way ploidy levels
are combined, this study is unique in emphasizing F.vesca, Eorientalis and
F.moschafa in crossing strategy.
Fragana vesca possesses many worthwhile attributes (Chapter 1) that rnay
be useful to improve SO production, particularly if F.vesca could act as a bridge
species to facilitate gene fiow. As a diploid, tetraploid or interspecific tetraploid
hybrid Fragaria. vesca has hybridized with many species including octoploid 177
Figure 7.1. Crossing strategy: a simplified balanced ploidy strategy for Synthetic
Octoploid production. Diagrams show ploidy levels of species and hybrids involved in crosses. Parents are on left and progeny on rig ht.
Tetraploid creation Diploid Tetraploid Octoploid breeding 2x 4x breeding creation chromosome dou bling chromosome doubling 178 cultivars (Yarnell, 1931a; Federova, 1946; Bringhurst and Khan, 1963; Evans, 1964;
Darrow. 1966; Senanayake and Bringhurst, 1967;Bauer, 1976,1993; Ahmadi and
Bringhurst, 1992). Fragada vesca was more responsivethan other Fragana species to chromosome doubling with colchicine (Sebastiarnpillia and Jones, 1976) and
both nuclear and cytoplasmic inheritance were involved (Fadeeva, 1966). The use
of F.vesca as a bridge species in SO production might be enhanced if it were used
as a pivotal genome in crosses at the tetraploid level [ie. (F.vesca x diploid) (4x) x
(F-vescax diploid) (4x)I. A pivotal genome is one shared by polyploid species that
enhances interspecific crossability in the presence of uncommon genomes, (Zohary
and Feldman, 1961). While the pivota1 genome theory has been beneficial for
introgression of wild species in grain crops (Feldman and Sears. 1981; Gustafson
and Dera, 1989; Gustafson and Sears, 1993) it has not been exploited for fruit
crops.
The (F.vesca x diploid) tetraploids used in this experiment were colchiploids.
Colchiploids of fruit species often have reduced fertility and may require crossing
with d issimilar genotypes to maximize heterozygosity and restore fertility (Sanford,
1983). Thus, it may not be feasible to use colchiploids as both the female and male
parents in a cross since fertility problems would be compounded. Instead, it may
be advantageous to cross colchi-tetraploids with (hexaploid x diploid) hybrids or
naturally occurring tetraploid species so that at least one of the parents will be highly
heterozygous and fertile. For this reason, tetraploids derived from Emoschata x
diploids crosses (Chapter 6) and the naturally occurring tetraploid, F.onenta/is,were
included to cross with the (Evesca x diploid) colchi-tetraploids. Objectives and hypothesis
The choice to emphasize Evesca, F.orientalis, and F-moschatain this study limits the possible combinations of species that could be investigated, but further explores Evesca's potential as a bridge species and increases the potential for production of fertile progeny. The objective of this study is to determine the potential of using Evesca in the SO system in combination with F-orientalis (4x) or tetraploid hybrids of Fmoschata x diploid species.
In this study it was hypothesized that colchiploid hybrids derived from F. vesca x diploid species crosses could be used as bridges for diploids species in the SO system. It was also hypothesized that crossing these colchiploids to F-onentalis or
Emoschata x diploid (4x) accessions will be more successful than intercrossing colchiploid accessions.
MATERIALS AND METHODS
Gerrnplasm
The 46 accessions listed in Table 7.3 were used to create 104 tetraploids for this experiment (Tables 7.4,7.5). Five types of tetraploids were used in this study:
2x x 2x hybrids (Chapters 4 and 5)treated with colchicine, 6x x 2x hybrids (Chapter
6),4x x 4x hybrids, colchiploid Evesca (4x). and F-orientalis (4x). The ploidy level of each parent used in the study was verified by fiow cytometry (Chapter 3). Table 7.3. Fragaria accessions that were founders of tetraploid gennplasm for this experiment. This table can be used to trace the lineage of tetraploids in Tables 7.4 and 7.5. Note that many accessions of Fragana vesca were used but other species had limited representation. Continued on next page.
Species Ploidy Guelph Source identifier Source identifier Fmoschata 6x mcvl Capron,PI551528 NCGR mcv2 Profumata di NCGR Tortona,P1551549 mw2c,dY PI 551869 NCGR mw4 PI 551550 NCGR mw5e,f Cotta #2 IPK F.nilgerensis 2x ni1 1 CFRA 1 188.000 NCGR ni12 Mt. Omei Forest Farm F.nubicola 2x nubl PI 551 851 NCGR nub2 PI 551853 NCGR F.orientalis 4x oril ,2,13, 4947 x 4940 Dr. Gunter Staudt 20,a,b,k F.pentaphylla 2x pen 1 881 143 RBG Edinburgh pen2 892408 RBG Edinburgh F. vesca 2x vcv2 Alpine, PI 551 517 NCGR vcv6 Golden Alpine, NCGR CFRA 1185.001 vcv7 Pineapple crush Park Seed vcvl O Alexand ria Thompson & Morgan vcvl 1 Ruegen R ickters vcv13 Mignonette Park Seed vcv15 Crimson Sprite Ornamental edibles vcv20 A02 alpine White Flower Farm Strawberry Baron Solemacher U. of N.H. FRA 21 93 IPK Berry Sweet Henry F. Michel1 Co. Reins des Vallees SAPM Pl 551519 NCGR Pi 551523 NCGR PI 551792 NCGR PI 551890 NCGR PI 552273 NCGR PI 552274 NCGR PI 548865 NCGR PI 552239 NCGR wvl7 Pl 552246 NCGR Table 7.3. Continued.
Species Ploidy Gueip h Source identifier Source identifier F. vesca 2x vw19 East Malling F. vesca U. of Guelph vw22 FRA 13191 IPK vw25 PI 551644 NCGR vw34 Cambridge, ON collected by author vw35 PI 552243 NCGR vw39 CFRA 988 NCGR vw47 PI 551898 NCGR vw50 Rockwood, ON collected by author vw53 Newcastle, ON collected by author vw6 1 Niagara Falls, ON collected by author F. viridis 2x virl PI 551741 NCGR vir2 PI 551742 NCGR vir5 56-0123 RBGS ': Full names and addresses of germplasm resources are listed in Appendix 1.
Letters following numbers indicate members of a family. For example, mw2c and mw2d are derived from the sarne seed lot. Table 7.4. Tetraploid Fragana germplasm derived from diploid species used for synthetic octoploid production. All tetraploids in this table are colchiploids. Accessions are grouped by species combination. Tetraploid accessions and their parents are listed with Guelph identifiers. Additional information on parents of these tetraploids can be found in Table 7.3.
Tetraploid Female parent Male parent accession species accession species accession tl5-2 F. vesca vcvl5 F.vesca vcvl5
41 95 vcv7 x vw2 vcv7 x vw2 7 F. vesca vcv2 F.nubicola nub2 139 vcv6 nubl 138 vcv7 nubl 155 vcvl O nub2 11 vcvl 1 nub2 184 vcv22 nubl 9 vcv23 nub2 12 vw7 nub2 149 vw7 nub2 170 vw9 nub2 120 vwl3 nubl 133 vwl3 nub2 1O0 vw?6 nubl 59 vw34 nub2 135 vw39 nubl 108 vw47 nub2 157 vw47 nub2 168 vw47 nub2 175 vw47 nub2 177 vw47 nub2 137 vw53 nubl Table 7.4. Continued. Tetraploid Female parent Male parent accession species accession species accession 41 1 F. vesca vcv7 x vw2 F.pentaphyl/a pen2 vcvl O pen 1 vcv20 x vw3 pen2 vcv22 x vw34 penl vcv23 penl vw22 penl vw25 pen l wu25 pen1 vw25 penl vw35 penl vw39 pen2 vw47 pen 1 vw50 pen 1 187 Ml penl 421 F.vesca vcv20 x vw3 F. vindis vir5 vir5 vir2 vir2 virl virl virl virl 15 vw33 viR 45 F. vesca vcvl3 F. nilgerrensis niIl 427 vcv20 x vwl7 nil2 2 vcv23 ni11 151 wu15 niIl 4 vw47 niIl 46 vw47 nill 130 vw47 nil 1 329 F. viridis virl F-nubicola nub2 41 16 virl nubl Table 7.5. Tetraploid Fragana germplasm derived from hexaploid, tetraploid and diploid species without the use of colchicine. Accessions are grouped by species combination with ploidy levels in brackets. Except where noted, tetraploid accessions and their parents are listed with Guelph identifies. Additional information on parents is in Table 7.3.
Tetraploid Female parent Male parent accession s pecies accession species accession 190 F.nubicola(2x) nubl Fmoschata(6x) mcvl 192 nub? mcvl 110 nubl mw2dz 131 nubl mw2d 169 nubl mw2d 182 nubl mw2d 186 nubl mw4 17 nub2 mw2d
47 1 F.moschata(6x) mw5e F.nubicola(2x) nub2 n4 mb F.pentaphylla (2x) pen2 F. rnoschata (6%) bul k F. rnoschata
F.moschata (6x) mcvl F. vindis (2x) vir2 mcvl v1r2 mcvl v1r2 mcvl v1r2 mcvl v1r2 mcv2 virl mcv2 vir? mcv2 vi rl mcv2 virl mcv2 v1r2 mw2c v1r2 mw2c v1r2 77 mw2c vir2 38 F. vnidis (2x) vir 1 Emoschata (6x) mw2d virl vit2 vir5 Table 7.5. Continued.
Tetraploid Female parent Male parent accession s pecies accession species accession 'oril ,2,13,20,F. orientalis (4xj 4947 F.onentalis (4x) 4940 a,U 877 F.orientalis (4x) ori b F. vindis (2x) x virl x mw4 F-moschata (6x1 81 08 F.orientaiis(4x) orib F-moschata mcvl x vir2 (ex) x F.vindis Px) Z*Letters following numbers indicate members of a family. For example, mw2c and mw2d are full sibs. All F.onentalis accessions are full sibs. The parents of these accession (ie. 4947 and 4940) are accessions numbers of Dr. Gunter Staudt. He provided the author with seeds resulting from 4947 x 4940 crosses. 186
Crosses
A total of 464 different combinations of parents were crossed. Additional crosses were done for some combinations of parents with 647 pollinations in total.
Crosses provided a variable num ber of F. vexa genomes in the resulting hybrids.
Tetraploid parents had either zero, MO,or four Evesca genomes and will be referred as O-ves, 2-ves or 4-ves, respectively. The O-ves and 4-ves groups were mostly pollinated with O-ves, although a few were pollinated with 2-ves. The 2-ves plants were pollinated with both O-ves and 2-ves pollen. No groups were pollinated with 4-ves. The 2-ves plants were hermaphrodites and could be used as either
males or females in crosses. However, the O-ves group was monecious (except for
110, a hermaphrodite) so individual accessions could be crossed in only one
direction.
Pollination was randomized each day (see Chapter 2) according to available
supply of pollen with the following qualifications: half or full sibs were not
intercrossed and new combinations of parents were emphasized to increase the
number of crosses and diversity of potential hybrids. An attempt was made to
pollinate each female parent with equal numbers from the various combinations of
species, but this was not always possible due to different flowering times, different
numbers of accessions and limited numbers of Rowers per accessions.
Techniques
Hybridizations were done from February to April in 7996 and 1997. Plants
were brought into the greenhouse in two groups, three weeks apart for both 1996 187 and 1997. General procedures for handling of plants, emasculation, pollination, raising seedlings, colchicine application, and verification of ploidy level are described in Chapter 2. Pollen was collected during the emasculation procedure, categorized according to species combination, dried and stored. Most flowers were pollinated twice in this study with the second pollination occurring 24 hours after the first pollination.
A total of 8403 seeds were harvested of which 5846 were germinated in vitro
(Miller et al., 1992; see Chapter 2) and the remainder were saved for future experiments. The resulting hybrid seedlings were treated with a 5% colchicine treatment for 16 to18 hours as outlined in Chapter 2. Hybrids with morphological attributes of higher ploidy level than their parents (ie. thicker leaves and stems, wider leaf angles, larger plant size, slower rate of development) were verified with flow cytometry (Chapter 3). Hybrids identified as octoploids were planted
(Cambridge Research Station, Cambridge, Ontario) in close proximity to other octoploids (ie. F x ananassa, Evirginiana, and F.chiloensis) and allowed to set fruit under open pollinated conditions. SOS which set fruit in 1998 were noted for future study. The other SO's produced by this study were not planted in the field until
1998, so fertility data for these hybrids were not available.
Data analysis
When more than one pollination occurred for the same combination of parents, results were averaged prior to statistical analysis. Fruit set (%), seedsflower, % germination and % SOS (ie. SOs/seedlings treated with colchicine 188 x 100) were measured. Means for each combination of parents were used in statistical analysis of the various species combinations. Parents with reciprocal lineage (ie F. vindis x Fmoschata and Fmoschata x F. vindis) were grouped together for data analysis. The influence of female and male parents and their interaction were analyzed with the GLM program of PC SAS (SAS System for Windows V.6.12,
Cary, N.C.). Mean separation was accomplished using the LS means function at the 5% level of significance. Fertility of hybrids was not measured due to lack of time in the field although SOS with fruit set were noted.
RESULTS
Ali hybrids described, for exarnple F.vesca x F.nilgenensis, are tetraploids unless othenivise stated.
A total of 192 Sois were created in this study, and F. vesca, F. vindis, F. nubicola, F. pentaphylla, F. nilgerrensis, F. orientalis, and F. moschata were successfully incorporated into 101, 71, 105, 12, 39, 95, and 139 synthetic octoploids, respectively. Of the crosses attempted, 51 O/O produced fruit with an average of 24 seeds per fruit (ie. 12 seeds per fiower pollinated). Examples of tetraploid parents with fruit set are shown in Figure 7.2. Of the seeds that received in vitro treatment, 65% germinated, and 4.1% of geminated seedlings treated with colchicine were verified as synthetic octoploids. Female and male parents were important sources of variation for % fruit set and seedslflower (see Appendix 5).
Male parents were a significant source of variation for germination, but female parents were not significant (P = 0.0574). Female and male parents were not Figure 7.2. Examples of tetraploid hybrids and fruit set resulting from interspecific hybridization. Tetraploid plants were vigourous and readily produced fruit for many combinations of parents. From lefi to right: T70 (Fmoschata x Evindis), Tl70 (F.vesca x F.nubicola) , and T4 (F.vesca x F.nilgerrensis) . 190 significantly different in SO production and there was no interaction among females and males for any of the characters studied. The data for individual crosses are presented in Appendix 4 while ANOVAs are presented in Appendix 5.
Differences among female parents
The O-ves and 4-ves females had 20% more fruit set than 2-ves females
(Table 7.6). The only naturally occurring tetraploid in the study, F. orientalis, had the highest fruit set at 86%. The 2-ves type derived from self-compatible (SC) species
(ie. F.vesca x Ç.ni/gerrensis) had 70% fruit set which was within 2% of F.vesca x
F. vesca, and F.moschata x F.vMis female parents. Among the O-ves females,
F.moschata x F.nubicola had the lowest fruit set (41%) which was very similar to those 2-ves types derived from F-vesca and self-incompatible (SI) species. These
latter mentioned 2-ves types were F. vesca x F. vindis, F.vesca x F.pentaphylla, and
F.vesca x Fmbicola with 37%. 43%, and 41% fruit set, respectively.
For seedsmower O-ves and Cves produced 3.5 times more seedslflower than
2-ves. The highest seedslflower occurred for F. onentalis, F moschata x F. vindis
and F.vesca x F-vesca with 38, 30 and 24 seedslflower, respectively. Again,
Emoschata x F.nubicola females had the lowest numbers (six seedslflower) of the
O-ves types, which was similar to 2-ves fernales. Means were closely grouped
among 2-ves females ranging from F-vesca x F.pen@hy/iawith four seedsMower to
F. vesca x F.nilgerrensis with 1 0 seedslflower.
Although in vitm germination of embryos for O-ves females ranged from 82 5 3 O Ecn m Q) 2 $ ;'C $9 u C .C +2 .'Fc s 8 c c O u. 8-c ccal n 2 & g9 c Q, c ca C E E r z ou u g: E L g .r cn:Q) ' 192 to 88% this was not statistically different from Zves (range 53 to 65%) or 4-ves
(53%) fernales. There were no significant differences among fernales for % SOS.
Fragana vexa x F-pentaphylla, F.vesca x Enilgerrensis and F.orienta/is had the highest proportions with 6.2, 5.5, and 5.4% SOS produced, respectively.
6
Differences among male parents
Overall, O-ves males were superior to 2-ves males in every character measured (Table 7.7). The O-ves males had 23% more fruit set, five times more seedslflower, 17% higher genination and almost four times more % SOS than 2- ves males. Among O-ves types, Fmoschata x F.nubico/a,F.moschata x F. vindis,
F. pentaphylia x F.moschata, and Eorientalis were the best males if al1 four characters are considered. These aforementioned O-ves types had 53% to 73% fruit set surpassed only by Evesca x F.vindis males with 82% fruit set. These four species combinations also had the highest means for seeddfiower and were among the best for genination. For percent SOS, Emoschata x Enubicola and Eonentalis x (F-maschata x F. vindis) were exceptional with 11.7% and 8.8%, respectively, followed by F. vesca x Fmbicola, Epentaphylla x F.moschata, F.orienta/is, and
Emoschata x F. vindis with 3.7%, 3.1 %, 2.3% and 2.0%, respectively. Other species combinations used as males had O to 1.1% SOS. Despite the fecundity of the O-ves
males already mentioned, some O-ves males were also the poorest parents used.
The O-ves males derived from two diploid species, F.vindis x F.nubico/a and the
male derived from three species, F. onentalis x (F. moschata x F. vindis)),had the Table 7.7. Effect of number of Fragana vexa genomes and male parentage on % fruit set, seeds/flower, % germination, and % synthetic octoploids (SOS) for crosses arnong tetraploid Fragana hybrids.
-- -- -. ------Evesca genomes Male lineage NZ Fruit set Seeds/flower N Germination N SOS (%) (%) ('w 2 F. vesca x F.viridis 30 82 abY 3 b-f 24 61 a-c 17 0.2 ns
F. vesca x F.nubicola 56 38 bd-f 6 b-f 35 40 b-e IO 3.7ns F.vexa x F. pentaphylla 56 Il e-f 0.5 d-f 10 80 a-c 9 1.1ns
F. vesca x F.nilgerrensts 16 36 bd-g 4 bd-f 7 14 c-e 3 O ns
F.viridis x F.nubicola 14 7e-g 0.2 bd-f 1 33 a-e 1 O ns F.moschata x F.viridis ' 80 73 ab 17 a-d 47 74 a-c 44 2.0ns F.nubicola x F.moschata " 112 55bc 18 a-c 39 67 a-c 35 11.7ns Fpntaphylla x F.moschata 17 53 a-ce 14 a-e 3 58 a-d 3 3.1 ns
F.orientalis x (F.moschata x F.viridis) 18 29 d-g 3 d-f 4 50 a-e 2 8.8 ns F.orientalis 65 68 ab 19 a-c 36 75 a-c 35 2.311s mean 306 59 16 131 70 120 5.0 N is the number of unique combinations of parents that were crossed, N was the same for % fruit set and seedslflower but differed for other variables. Letters following means denote Ismeans groupings at 5%. lncludes reciprocal combination 194 lowest values for each character when compared to other O-ves.
In most cases, there were no significant differences within the group of 2-ves males. Each combination of species tended to have the highest value for at least one of the characters measured. Fragana vesca x F.viridis had 44% more fruit set.
F. vesca x F.nubicola had 50% more seeds/flower, F. vesca x F .pentaphylla had 39% higher germination and F-vescax Enubicola had Z.60h more SOS than the next best 2-ves males. Fragaria vesca x F.ni/gerensis had the poorest overall record with only 14% germination and no SO production.
Interaction among males and females
In this study, 52 of the 66 (79%) combinations of species were succesçful in producing viable tetraploid progeny, and 25 of these combinations resulted in SOS
(Table 7.8). The interaction among males and fernales was not significant (Appendix
5) for any of the characters in the study. Thus, the greatest values for each trait were obtained when the best females were pollinated with the best males. For example, F.onentalis accessions were among the best of the female parents (Table
7.6) while F.moschata x F.viridis and Enubicoia x Fmoschata accessions were good male parents (Table 7.7) When Ç.orientalis was hybridized with these two groups of males, % fruit set, seedsMower, % germination, and % SOS were much higher than the average for the experiment (See Table 7.8). Table 7.8. Fruit set, seedsl flower, germination and synthetic octoploids (SOS) resulting from interspecific crosses arnong tetraploid Fragana hybrids with different numbers of F.vesca genornes. Y Female parent Male parent Seeds No, of Species No. of Species No. of NZ Fruit set Seeds receiving N Germ. N SOS (%) flowers F. vesca F. vesca (Oh) lflower invitro (Oh) genomes genornes pollinated treatment
4 F. vesca 2 F. vesca x F. viridis 1 1 100 6.0 6 183.3 1 O F. vesca x F. nubicola 4 3 33 5.7 34 1 14.7 1 20.0 F. vesca x F. pentaphylla 6 4 O 0.0 O O nla nla F. vesca x F. nilgerrensis 2 2 O O.0 O O nla nla Total N & rneans 13 70 20 2 40 2 49 2 IO
F. vesca O f.moschata x F. viridis Y 6 5 100 20.7 73 3 67.7 3 0.0 F.nubic01a x F.moschata Y 16 9 89 42.6 759 6 42.3 6 4.0 F.pentaphylla x Fmoschata 4 2 100 20.0 69 2 59.7 2 0.0 F. orientalis x 3 3 67 8.7 1 1 100.0 1 0.0 (F. rnoschata x F. viridis) F. orientalis 8 7 100 39.3 314 8 54.4 8 0.0 Total N & means 37 26 92 32 1216 20 53 20 1.3
: N = number of combinations of accessions used in crosses. N is the same for fruit set and seedslflower but differs for other variables. lncludes reciprocal combination Table 7.8. Continued. 196
Female parent Male parent Seeds No. of Species No. of Species No. of N Fruitset Seeds receiving N Gerrn. N SOS (%) F. vesca F. vesca flowers (%) / flower in vitro (%) ,cienornes qenomes poliinated treatment 2 F. vesca x F. viridis 2 F. vesce x F. viridis 5 5 100 5.4 27 5 38.7 3 0.0 F. vesca x F. nubicola 13 IO 20 1.3 25 2 4.2 1 0.0 F. vesca x F. pentaphylla 25 15 19 0.5 13 5 100.05 0.0
F. vesca x F. nubicola F. vesca x F. viridis 7 5 80 1.1 10 4 75.0 3 0.0 F. vesca x F. nubicola 24 14 39 11.7 27 2 71.4 2 8.3 F. vesca x F. pentaphy//a 31 21 7 O.7 25 2 50.0 1 0.0 F. vesca x F. nilgerrensis 7 5 40 9.1 83 2 40.1 2 0.0
F, vesca x F. pentaphyila F. vesca x F. viridis 19 12 75 2.6 51 10 55.0 6 0.0 F. vesca x F. nubicola 21 14 27 0.8 9 4 25.0 1 0.0 F. vesca x F. pentaphylla 15 10 5 0.1 1 1 100.0 1 0.0 F. vesca x F. nilgerrensis 3 3 67 2.3 7 2 0.0 n/a
F. vesca x F. nilgenensis F. vesca x F. virjdis II 7 79 4.5 44 4 84.3 4 0.9 F. vexax F. nubicola 15 10 52 3.3 18 5 52.5 4 0.0 F. vesca x F. pentaphylla 13 5 28 1.1 19 2 51.7 2 5.0 F. vesca x F. nilqerrensis 9 4 44 2.4 29 3 5.6 1 0.0 total N & means 218 140 37 3 388 53 53 36 0.8 Table 7.8. Continued. 3 97
Female parent Male parent Seeds No. of Species No. of Species No. of N Fruitset Seeds receiving N Germ. N SOS (%) F.vesca F.vesca flowers (%) l flower in vitro ("10 genornes qenomes pollinated treatment 2 F. vesca x F. viridis O F. viridis x F. nubicola Y 220 0.0 O nla nla F. moschata x F. viridis 4 4 50 8.8 1 1100.01 0.0 F. nubicola x F.moschata Y 8 8 63 27.5 134 3 40.2 2 6.3 F. pentaphylla x F.moschata 2 2 50 39.0 78 1 55.1 1 9.3 F. orientalis x 4 3 17 0.8 5 1 0.0 nla (F.moschata x F. viridis) F. orientalis 3 3 33 4.3 13 7 38.5 1 0.0 F. vesca x F. nubicola F. viridis x F. nubicola 2 1 O 0.0 O n/a nla F. moschata x F. viridis Y 34 23 61 10.2 222 9 66.5 8 2.2 F.nubicola x F.moschata y 50 41 41 10.5 226 7 70.5 7 6.9 F.pentaphylla x Emoschata 8 7 57 12.5 O nla nla F, orientalis x 6 6 O 0.0 O nia nla (F. moschata x F. viridis) F. orientalis 24 19 53 14.8 225 7 59.9 6 4.7 F. vesca x F. pentaphylla F. viridis x F. nubicola Y 6 6 17 0.5 3 1 33.3 1 0.0 F. moschata x F. v~ridis y 21 13 44 7.7 32 4 50.5 3 0.0 F. nubicola x F.moschata 28 24 43 4.3 19 5 80.0 4 31.3 F-pentaphylla x F. moschata 1 2 700 1.0 O nla nla F. orientalis x 2 2 O 0.0 O nla nla (F. moschata x F. viridis) F. orientalis 16 12 71 8.0 76 5 82.0 5 0.9 F. vesca x F. nilgerrensis F. viridis x F. nubicola 4 3 O O. O O nla nia F. moschata x F. viridis Y 16 12 100 9.7 138 11 69.3 10 1.9 F.nubicola x F.moschata Y 23 11 80 24.5 281 7 58.1 6 22.1 F. orientalis x 4 2 83 1.2 1 1 0.0 nia (F. moschata x F. viridis) F. orientalis 16 9 89 19.3 279 6 89.3 6 3.0 total N & means 284 215 52 10 1733 70 65 61 6.8 J?$2 CCC
322 CCC Table 7.8. Continued. 7 99
Fernale parent Male parent Seeds No. of Species No. of Species No. of N Fruitset Seeds receiving N Germ. N SOS (Oh) F. vesca F.vesca flowers (%) 1 fiower in vitro (NI genomes clenornes potlinated treatment O F. moschata x F. viridis O F. moschata x F. viridis Y 20 9 89 36.9 801 8 86.3 8 2.2 F.nubicola x F.moschata Y 8.2 Epentaphylla x F.moschata nla F. orientalis x 17.6 (F. moschata x F. viridis) F. orientalis 1.2
F.nubicola x F.moschata F. viridis x F. nubicola O nla nla F. rnoschata x F. viridis Y 21 2 70.0 2 0.0 F.nubicola x F.moschata Y 29 1 75.9 1 0.0 F.pentaphylla x F.moschata O nla n/a F. orientalis x O nla nla (F. moschata x F. viridis) F. orientalis 7.3
F. orientalis F. viridis x F, nubicola nla F. moschaia x F. viridis Y 4.5 F.nubicola x F.moschata Y 12 9 89 43.2 528 8 86.6 8 7.4 total N & means 100 65 69 27 2442 40 87 40 4.1
. - summary for experiment 662 464 51 12 5846 186 65 159 4.1 200
Influence of number of Evesca genomes
The 4-ves x O-ves crosses resulted in the highest fruit set (92%) and seedsiflower (32). When 4-ves females were pollinated with 2-ves males, fruit set was 20% lower than with O-ves males and only two seedsiflower were produced.
A similar decrease was noted with 2-ves females. When pollinated with O-ves, fruit set and seedsMower were 52% and 10 respectively, but when pollinated with 2-ves the result was 37% and 3, respectively. O-ves x O-ves had similar numbers of seeds/flower (27) to 4-ves x O-ves crosses, although fruit set was only 69%. The O-
ves x 2-ves and 2-ves x O-ves crosses produced similar results with 44% fruit set
and 10 seeds per flower.
Too few seeds were obtained from 4-ves x 2-ves and O-ves x 2-ves crosses
to make germination numbers rneaningful for these two cornbinations. The hybrid
combinations with a total of four F.vesca genomes (ie. 4-ves x O-ves or 2-ves x 2-
ves) had 53% germination. Crosses involving zero Evesca genomes had a much
higher rate of germination (87%) while crosses involving two F.vesca genomes (ie.
2-ves x O-ves) were intermediate with 65% germination.
The highest and lowest % SOS were produced with Cves x Zves and O-ves
x 2-ves crosses, 10% and 0% SOS, respectively. The data of these two groups
were based on in vitro treatment of only 40 and 27 seeds, respectively. The next
highest SO production occurred with 2-ves x O-ves with 6.8% followed by O-ves x O-
ves with 4.1 % which were based on a much larger arnount of seeds, 1733 and 2442
respectively. The 4-ves x O-ves crosses and 2-ves x 2-ves crosses were similar with
1.3% and 0.8% SOS, respectively. 201
Within many combinations of species there were differences in seedsfiower for certain combinations of accessions. For individual crosses, only 21 5 of the 464 combinations of accessions (ie. 46%) resulted in seed production (Appendix 4). An extreme examp le of varia bility for d ifferent accessions was (F.vexa x F.nilgerrensis) x (F.nubico/ax Emoschata) crosses, which had a range of O to 131 seedsMower for different combinations of accessions (Appendix 4). Most of the 464 combinations of accessions were based on only one pollinated flower. However, number of flowers did not appear to have a major confounding effect. When 139 accession combinations involving two or more pollinated flowers (Appendix 4) were examined, adding more flowers did not affect fruit set in 107 (ie. 77%) crosses.
Lineage and fertility of SOS
The most productive combinations of accessions for SO production are shown in Table 7.9. These 14 crosses represent only 3% of the combinations of accessions crossed, yet they resulted in 128 of the 198 (ie. 67%) SOS produced.
The most common species in the lineage of superior fernales were, F.vesca,
F.orientalis, F.vindis, and F.nubico/a, which were present in 72, 39, 31 and 24 SOS, respectively. In the male lineage of the superior combinations, F. moschata was the most common, being present in 105 SOS. Fragaria nubicola was present in male lineage of 91 SOS in the combination F.nubicola x Emoschata. None of the 2-ves male parents were present in this group of productive crosses.
Twenty-five combinations of species are represented in the 192 synthetic Table 7.9. Details of the 14 most productive crosses among tetraploid Fragaria which resulted in 128 synthetic octoploids (SOS). Crosses are grouped by the nurnber of F.vesca genomes and species combinations of the parents. Each cross is shown with numbers of flowers pollinated (N), seeds/flower, percent germination in vitro, percent SOS and total SOS produced. Female Parent Male Parent N Seeds Germ.' SOS Total F.vexa Species corn bination Acc. Evesca Species com bination Acc. /flower (%) (%) SOS genomes Id? genomes Id. -. 4 F. vesca x F. vesca 4181 O F.nubicola x F.rnoschata 110 2 85 44 13 10 -- 2 F. vesca x F. viridis 1 06 O F.nubicola x F.moschata 18 1 126 63 13 10
106 F. pentaphylla x F. moschata n4mb 1 78 55 9 4 F. vesca x F. nubicola 177 F.nubicola x F.moschata 169 1 34 88 37 11
182 2 33 94 10 6
184 F. orientalis ori2 2 46 76 10 7
F. vesca x F. ntlgerrensis 15 1 F.nubicola x F.moschata 110 2 38 59 i8 8 151 F. orientalis ori2 3 53 93 11 16
O F. moschata x F. viridis 70 O F. rnoschata x F, viridis 22 5 47 75 6 10
36 F.nubicola x F.moschata 169 2 51 84 8 7 F. orientalis oril 3 F. viridis x F. moschata 449 3 80 96 3 6
oril 3 F.nubicola x F.moschata 18 1 88 86 14 11 ori20 110 2 78 92 10 15
ori20 182 1 82 100 9 7 -- Acc. Id. = Accession identification, see Tables 7.4 and 7.5 for more details on individual accessions. Y Gerrn. = Germination 203 octoploids produced in this study (Table 7.10) with eight different combinations of ploidy levels (Figure 7.3). The resulting genepool of SOS created includes al1 accessions of F.moschata, F.nilgerrensis, F.nubicola, F.orientalis, F.pentaphylla, and F-vin'dis and IO of the F.vesca accessions listed in Table 7.3. The successfully incorporated F. vesca accessions encompassed three subspecies, ssp. vesca var. semperflorens (vcv 20,22.23,24), ssp. bracieata (vw 3), and ssp. amencana (vw17,34,47,50,61),and an accession from Ecuador (~15).Each of the various types of tetraploids, except F. viridis x F.nubicola, were incorporated into
SO's. Only four SO's were created with 2-ves pollen while 190 SO 's were created with O-ves pollen. The female lineage of 106 SOS contained F.vesca in the tetraploid form or in combination with F.nilgerrensis, F.nubicola, Epentaphylla, or
F.viiîdis.
Of the 97 SOS planted in 1997, 28 fruited in 1998. Fruits from two haivests of open pollinated SOS are shown in Figure 7.4. All species in the study except
Epentaphylla were incorporated into SOS capable of setting fruit. There are however 11 SO's with F.peniaphylla lineage which were not planted until 1998.
Fertility data is considered preliminary since most of the SOS were not planted until
1998, and fruit production is an indication of female fertility and not male fertiliity.
Full study of the fertility of these SOS was not undertaken as part of this study due
to tirne constraints.
DISCUSSION
A need to expand the narrow germplasm base of octoploid strawberry Table 7.10. Combinations of synthetic and natural Fragaia tetraploids used to produce synthetic octoploids (SOS)
Female parent Male parent No. SOS No. with No. of No. of of fruit in F. vesca Species combination F. vesca Species combination SOS 1998 ~enomes qenomes 4 F.vesca(4x) 2 (F.vesca x F.nubicola) Total 1 O
4 F. vesca (4x) O (F.nubicola x F.moschata) Total 1 3 3
2 (F.vesca x F.nilgerrensis) 2 (F.vesca x F.nubicola) 1 (F. vesca x F.nilgenensis) (F.vesca x F.vinais) 1 1 (F.vesca x F.nubicola) (F. vesca x F.nubico/a) 1 Total 3 1
2 (F.vesca x F. nilgenensis) O (F.moschata x F. vindis) 4 (F. vesca x F.nilgenensis) (F. viridis x F.moschata) 1 (F.vesca x F.ndgenensis) (F.nubicola x F. moschata) 13 2 (F. vesca x F.nilgemnsis) F.onenfalis 19 (F.vesca x F.nubicola) (F. nubicola x Fmoschata) 18 (F.vesca x F.nubicola) (F. vindis x Emoschata) 2 2 (F.vesca x Fmbicola) F.orientalis S (F.vesca x F.pentaphyila) (F.nubicola x F.rnoschata) 3 (F.vesca x F-pentaphylla) F.orientalis 1 (F.vesca x F. vindis) (F.nubicola x Fmoschata) 1 O 1 (F.vesca x F.vindis) (F.pentaphylla x F.moschata) 4 Total 84 5
O (F.moschata x F. viridis) O (F.moschata x F. viridis) (F.moschata x F. vinüis) (F. viridis x F.moschata) (Fmoschata x F. viridis) (Fmbicola x Fmoschata) (F.moschata x F. vin'ds) F.orientalis (F.moschata x F. viridis) F. orien talis x (F.moschata x F. viridis) (Enubicola x F.moschata) F. orientalis F. orientalis (F.moschata x F. viridis) F. orientalis (F.viridis x F. moschata) F-orientalis (F.nubicola x F.moschata) Total
Overall Total 192 28 Figure 7 .3. Crossing plans using Fragana species that were successful in creating synthetic octoploids in this study. Ploidy levels of parents and colchicine application for doubling of chromosomes are shown. Numbers In parenthesis indicate synthetic octoploids produced.
zx 4x / colchicine colchicine
(3) 25.- (3) 2x colchicine
2x 4x Bx (29) 4x colchicine colchicine -
2x 4x / colchicine \ I colchicine
207 cultivars (Sjulin and Dale, 1987; Daubney, 1990; Galletta and Maas, 1990; Hancock et al.. 1990, 1 996; Shaw, 1991; Sullivan, 1991; Dale et al., 1993; Harrison et al.,
1993; McNichol and Graham. 1992; Sangiacorno and Sullivan, 1994; Davidson,
1995) prompted this investigation into the creation of SOS. Previous reviews of strawberry breeding (Darrow, 1966; Scott and Lawrence, 1975; Hancock et al., 1990,
1996) have indicated limited investigation has occurred on interspecific hybridization
in Fragaria. The 192 SOS produced in this study represent a much larger number
of interspecific hybrids than al1 previous attempts combined (Table 7.1). While this
and Evans' (1977) studies produced similar nurnbers of tetraploid seeds, 5846 vs.
6564 respectively. this study produced 25 times more synthetic octoploids from a
wide genetic base. After five years of observations only three male fertile SOS were
identified by Evans (1982a,b,c) but after only one season in the field 28 SOS were
identified as female fertile in this study. Furthermore, it is likely that additional SOS
will be identified as fertile when the second planting of SOS has a full season in the
field and when male fertility is investigated. Previously, SOS have been created from
just seven combinations of species, with only two combinations producing fertile
plants (Table 7.2) but this study created SOS from 25 combinations of species, with
11 combinations producing plants identified, to date, as fertile. As in Chapters 4, 5
and 6, this study used a very wide germplasm base. Thus, the many SOS created
in this study have the potential to greatly expand the genetic base of Fragana
available to breeders.
This study demonstrated that F. vesca could be used to introgress the diploid
species F. nilgerrensis, F. nubicola, F-pentaphylla, and F.vindis into synthetic 208 octoploids. Although F. vexa has been used to create synthetic octoploids
(Sebastiampillia and Jones, 1976; Evans, 1977) and has much potential as a bridge species (Chapters 1 and 4) previous research had not used the concept of a bridge species or F. vexa as that bridge species. This study investigated alternative ways for combining Evesca genomes when creating SOS. When considering the results, it is important to focus upon crosses having 2-ves parents as these have excellent potential to transfer genes from other diploid species. The optimum combinations involving 2-ves parents was 2-ves x the best O-ves males (either F.odentalis or
Emoschata x diploids), which gave the highest values for % fruit set, seedslflower,
% gemination and % SO (Table 7.8). The O-ves x 2-ves crosses may also have potential as they averaged the same number of seeddflower but not enough seeds were germinated to detenine germination rate and SO production.
There was a dosage effect whereby increasing the number of genomes derived from F.vesca and diploid species decreased fruit set and seedslflower. For example, O-ves x O-ves, O-ves x 2-ves, 2-ves x O-ves, 2-ves x 2-ves, and Cves x 2- ves had 69%. 52%, 44%, 37%, and 20% fruit set and 27, 10,10,3,2, seedsflower, respectively. This effect could be due to decreased heterozygosity (ie. hybrid vigour) in the gametes from 2-ves and 4-ves plants. The 4-ves x 2-ves combination would have had less heterozygosity than other combinations and it had lower numbers than other combinations. It had been suggested that pivota1 genome crosses (ie. 2-ves x 2-ves) would be more productive than other crosses (Chapter 1, Zohary and
Feldman, 1961; Zohary, l965), but this does not seem to be universal for the
Fragaria tetraploids used in this study. Fragana genomes may be so similar (Jones, 209
1977; lwatsubo and Naruhashi, 1989, 1991) that a strategy using pivotal genomes might not be beneficial for tetraploid breeding. In Fragaia, the exact genomic constitution of polyploid species is unknown. As polyploid species were derived from diploid species, some tetraploid parents may have shared common or pivota1 genomes. Only 2 of the 31 combinations of tetraploids reported by previous researchers (listed in Tables 7.1 and 7.2) had common genomes [ie. (F.vesca x
Eviridis) x (F.nilge~ensisx F.vindis) and the reciprocal] which had similar seed production(2.9 and 1.8 seeds/flower) to the 2-ves x 2-ves crosses in this study. Also, since the 2-ves hybrids were colchiploids, there may be a need to maximize
heterozygosity for interspecific crosses (Sanford, 1983). In Aegilops and Tnticum, where the species have distinctly different genomes, it is very important for interspecific crosses to have parents that share at least one common genome
(Feldman and Sears, 1981). While it is likely that similar genomes are important for producing interspecific hybrids in Fragaria, it may be that there are not many different genornes in the genus.
The natural tetraploid, Fragana onentalis, and (6x x 2x) hybrids (F. moschata x diploids) were very important in this study. One of these was present in 98% of the
SOS produced (Figure 7.3). In previous studies (Tables 7.1 and 7.2),F. orientalis
and (F. moschata x diploids) have been successful in tetraploid crosses. However, this study was the first to incorporate F.orientalis and F.pentaphylla x Fmoschata into
SOS (Table 7.10). These types of O-ves parents may have been superior to 2-ves
parents since the latter were colchiploids. Colchiploids are highly homozygous
(EingstJ959) and are known to be subject to fertility problems especially in fruit 21O species (Sanford, 1983). As both F.orientalis and Fmoschata are dioecious and obligate outcrossers (Staudt, 1989) they would have been more heterozygous than
2-ves parents, and would have produced genetically variable gametes. The garnetes from 2-ves and Cves colchiploids would have had much less genetic variability, and variability is very important for interspecific hybridization (Burbank, 1929; Galetta and
Maas,1990). Fragana orientalis and Fmoschata rnay be most genetically fit for high ploidy levels. It was noted that 6x and 8x Fragana tend to have less DNNgenorne than 2x Fragana (Chapter 3). Perhaps in polyploids, multiple copies of some genes are detrimental, and have been selected against during evolution. Thus, it may beneficial to hybridize colchi-tetraploids derived from diploid species with tetraploids derived from higher ploidy species to mask deleterious genes and maximize heterozygosity.
Fragana moschata (6x) was identified as a bridge for three diploid species (ie.
Fmbicola, F.pentaphylla, and F.vin'dis) to be introgressed into SOS. However, recombination among the three Emoschata genomes and the one diploid genome in the tetraploid gametes likely provided only a few chromosomes from the diploid species into SOS. The strategy of using F.vesca to cross with other diploids has the advantage of delivering an intact genome of the other diploid into an SO. An alternative use of F.moschata would be to treat F1 (F.moschatax diploid) hybrids (4x) with colchicine (Evans, 1977) to produce an octoploid and bypass tetraploid crossing.
This method may be very difficult because of the low success rate of crossing
Emoschata with diploids compounded with low chromosome doubling rates.
However, the strategy couid be improved by simply using the best combinations of 21 1 accessions (Chapter 6) in the crossing program.
At the tetraploid level, most combinations of species can intercross, particularly if severai combinations of accessions are tested. Only 14 combinations of species did not produce seeds in this study but nine of these involved only one combination of accessions for parents. The value of having many accessions has been a recurring theme at other ploidy levels (Chapters 4, 5, and 6). In previous studies, 88% of 25 combinations of tetraploid hybrids resulted in progeny (Tables 7.1 and 7.2). This study was similar to previous studies when 79% of 66 combinations of species produced seeds and 90% of the combinations germinated in vitro resulted in viable offspring (Table 7.8). This was much higher than crosses at the diploid level in which 55% of 36 combinations of species resulted in progeny (Chapter 5).
With so many combinations of tetraploids possible, there is excellent potential to breed at the tetraploid level prior to making synthetic octoploids. Although, the two accessions of Eodentalis x (Fmoschata x F. vindis) averaged only three seedsflower
(Table 73,they demonstrated that tetraploids derived from three species could be at least partially fertile. The successful intercrossing of the tetraploids verifies that self-incompatibility mechanisms begin to break down at the tetraploid level in
Fragaria because of tetrasomic segregation of self-incompatibility alleles (Evans and
Jones,1967). A partial breakdown could explain why the colchiploid fernales derived from self-compatible species (ie. F. vesca x F. vexa and F. vesca x F.niigerrensis) had the highest fruit set and seedslflower (Table 7.6). These two types would have presented no incompatibilitybarriers while the other 2-ves types would have reduced crossability. Conversely, self-incompatibility alleles could have been responsible for 212 reduced crossability when the F.vesca x F.ni/genensis hybrids were used as males
(Table 7.7).
The current study compliments cytogenetic evidence (Staudt, 1959; Jones,
1976; lwatsubo and Naruhashi, 1989, 1991) and DNA analysis (Harrison et a1.J 993,
1997) that suggests Fragaria species are closely related. Since many combinations of species were used to create fertile SOS, it is diffîcult to suggest which species might have been involved in the evolution of natural occurring octoploid species. The results of this study tend to expand rather than limit the number of possibilities for progenitors of the polyploid species. The two polyploid species used in this study,
F.orienta/is and (Fmoschata x diploid) accessions sften had similar results
(Table7.8, Appendix 4), which supports the theory that Emoschata and Eonentalis may have been derived from the same diploid species (Federova, 1946; Staudt,
1959, 1989). The F.vesca x F. vindis and F-vesca x F-nubicola tetraploids bore a strong resemblance to F.moschata while the F.vindis x F.nubicola hybrids most closely resem bled F.orientalis. As the geograp hical location of F-moschataoverlaps with Evesca and F.viridis but not with F.nubicola (Figures 1.3 and 1.4) it is more likely that F.vesca and F.vinüis fomed F.moschata. Although the main habitat of
F.odentalis lies to the east of F.vindis and Enubicola, they cannot be ruled out as possible progenitors of F.odentalis since the exact locations of Fragana species in
Asia requires further research (Staudt, 1989).
Difficuities encountered in creating tetraploid hybrids from diploid or hexaploid species may not be present when these hybrids are used as parents. For example,
Evesca (2x) x F.nilgemnsis (2x) and F-moschata(6x) x diploid hybnds were difficult 213 to obtain because of poor seed production of the former (Chapter 4) and poor germination of the latter (Chapter 6). At the diploid level, only 1.2 seeds/flower were obtained for F.vesca x Enilgerensis (2x). while F.vesca pollinated with either
F.nubicola, Epentaphylla, or F. viridis averaged at least 10 times more seeds/flower
(Table 4.4, Chapter 4). At the tetraploid level, Evesca x F.nilgenensis (4x) females had the highest numbers of 2-ves females with 10 seedsMower (Tables 7.6). This, and the occurrence of fertile F. vexa x Enilgenensis diploids (Chapter 5) indicates
F. vesca and F.nilgerrensis are genetically closer than previous research suggested.
When Emoschata x diploid (4x) hybrids were intercrossed germination rate was 79%
(Table 7.8). This is considerably higher than the 6% germination from seeds obtained by intercrossing F-moschata (6x) and diploid species (Chapter 6). It was suggested that Fmoschata could harbour lethal alleles that surfaced when crossed to diploids (Chapter 6). If so, such alleles may not be present in viable F.moschata x diploid hybrids (ie. parents used in this study) which could explain the higher germination rates and the lack of albinos or stunted seedlings at the tetraploid level.
Endosperm balance may also be an important factor (Evans,?977) in the improved germination of tetraploid crosses compared to hexaploid x diploid crosses.
Data analysis indicated that males and females were important sources of variation but that the interaction among males and females was not significant
(Appendix 5). This would be similar to stating that general combining ability is much more important than specific cornbining ability for interspecific hybridization of
Fragaria tetraploids. It wouid, therefore, be more important to identify good male and females parents for crossing rather than attempt to intercross many inferior 214 tetraploids in the hopes of finding a good combination. As F. orientalis performed well as a male and female, it might be valuable for use in test crosses to identify other superior tetraploids. While this study shows that some combinations of species are
more successful as tetraploid parents, it may also be true that certain accessions are
superior parents. Among the 14 superior crosses identified in this study (Table 7.9),
50% of the parents appear more than once. Tetraploid '1 10' was particularly
noticeable as it appeared in the lineage of three of the best crosses. Further
investigation revealed that nine of the 14 best crosses resulted in 95 SOS with the
Emoschata accession 'mw2dPin their lineage via the tetraploids 18, 1 10, 169, and
182 (Tables 7.8 and 7.4). The 2-ves accessions 106, 151, and 171 appeared twice
in Table 7.8, but each of these originated from a different source of F. vesca. With
these superior crosses identified, it may be possible to do similar crosses to introduce
new gerrnplasm into the SO collection. For example, mw2d could be crossed with
a new F.nubicola accession and the resulting tetraploid could be used to pollinate
ori20. Again. including a large variety of accessions in this type of research is very
important to its success or failure (Burbank, 1921, Galletta, 1990).
Cornparison of % fruit set, seedslflower, % germination and Oh SOS data
indicated that chromosome doubling was the most limiting step for synthetic
octoploid production in this study. The in vitro colchicine method of this study created
4.1% SOS per treated seedling, which was higher than the 0.1 % SOS obtained with
the immersion method (Evans, 1977) but less than the 7% SOS obtained by the
dropper method (Sebastiampillia and Jones,l976). However, al1 but two of the most
productive crosses (Table 7.9) had higher chromosome doubling rates than the 21 5
Sebastiampillia and Jones study (1976). The evidence suggesting F. vesca was more amenable to chromosome doubling than other Fragana species (Fadeeva, 1966;
Sebastiampillia and Jones, 1976) was one of the considerations for emphasizing
F.vesca in this SO system. As males and fernales did not significantly influence percent SOS (Appendix 5) it would seern that F.vesca genomes had little bearing on chromosome doubling at the tetraploid level. Too few O-ves x 2-ves seedlings were produced to make a meaningful cornparison with 2-ves x O-ves seedlings or to draw conclusions regarding Evesca cytoplasm. It may be that other factors such as heterozygosity were more important factors influencing the survival of colchicine treated plants. The success of colchicine treatment that could be improved by treating several runners from mature plants so chromosome doubling could be repeated many times for the same genotype.
SUMMARY
The 192 SOS created in this study represent a tremendous improvement over previous techniques and considerable potential to broaden the gemplasm base of the cultivated strawberry. While tetraploids containing two genomes of F. vesca did not produce as many hybrids as those tetraploids without any F-vesca genomes, this does not diminish the usefulness of using F.vesca to introgress other diploid species into SOS. This study showed that tetraploid hybrids resulting from crosses among
Evesca and either F.nilgerrensis, F.nubicola, F.pentaphy/la, or F.vindis are fertile, and that such hybrids could be used to create SOS through additional crosses with other tetraploids. Rather than intercrossing 2-ves tetraploids, a better strategy would 216 be to cross Z-ves tetraploids with tetraploids derived from Fmoschata x diploids of
F.orientalis. Heterozygosity, presence of lethal alleles, and genetic fitness of hybrids derived from polyploid species are important factors involved in crossability of tetraploid hybrids. The fact that so many combinations of species were capable of producing progeny at the tetraploid level suggests that the species involved in this study are closely related with similar genomes and that there may be great potential for cornbining many species and breeding at the tetraploid level in Fragada. While many combinations of accessions can intercross, it is important to use a wide gemplasm base to obtain accessions with the highest potential success rates.
Screening tetraploids by crossing to highly fertile accessions is recommended to identify those accessions that are superior male or fernale parents. 217
Chapter 8
General discussion & summary
The need for a wider genetic base for breeding of octoploid cultivars of strawberries (Sjulin and Dale, 1987) prompted this investigation of introgression of wild Fragada species using the synthetic octoploid system. By hybridizing 2x, 4x and 6x species and using colchicine to create synthetic octoploids, interspecific barriers due to differences of ploidy level were overcome and introgression into octoploid cultivars was facilitated (Evans, 1976). There have only been a few reports regarding the creation of synthetic octoploids (Evans, 1976; Sebastiampillia and Jones, 1976; Jones 1977) and only two fertile SOS were released (Evans,
1982ab). In previous reports, crossing strategies have been outlined to combine species of various ploidy levels to produce octoploids (Darrow, 1966: Evans. 1976) but actual investigation of a planned crossing strategy had not been done. With 10 diploid, three tetraploid and one hexaploid Fragana species identified (Staudt, 1989;
Hummer, 1996), there are over 10.000 combinations of species that could be
investigated for creation of SOS. Rather than attempt ail possible combinations of
species, this investigation focused on a strategy of using F.vesca as a bridge or
pivotal genome to bring other diploid species to the tetraploid level. This was followed by intercrossing of tetraploids including Eonentalis (4x) and F.moschata
(6x) x diploid species. Thus, diploid, tetraploid and hexaploid species were
incorporated into the crossing strategy used in this study. The crossing strategy
also increased heterozygosity by including as many different combinations of 218 parents as possible and by avoiding crosses between full or half sibs. This aspect of the crossing strategy was especially recommended for interspecific crosses where it is important to have as wide a germplasrn base as possible (Burbank.
192 1; Galletta, 1990).
The decision to ernphasize F.vesca as a bridge to diploid species in this crossing strategy was based on several factors. Fragaria vexa was alleged to be the progenitor species of the genus of Fragana (Staudt, 1953; Nurnberg-Kruger;
Darrow, 1966) or at least the progenitor of polyploid species (Darrow, 1966; Ellis,
1958; Staudt, 1984; Bringhurst and Senanayake, 1967; Bringhurst, 1990) and has been hybridized with many other species (Tables 1.1, 1.2, 1.3, 1.4). Also F.vesca is self-compatible (Staudt, 1989), has a desirable fiavour and aroma (Darrow, 1966), is adapted over a wide geographical area (Reed, 1966; Staudt, 1989) and many accessions were available from genebanks.
In addition to crossing strategies. this study adapted advanced techniques and obtained germplasm which had not been available during earlier research into
SO production (Evans, 1976; Sebastiampillia and Jones, 1976). These techniques included flow cytometry for ploidy verification, in vitro germination. and in vitm colchicine application. Genebanks that were not in existence in the 1970's were used in this study. providing higher number of accessions than in previous studies.
The results of interspecific crosses between diploid species in this study cast doubt on F.vesca as the progenitor of its genus. Fragana vesca subspecies from
Europe and North America did not significantiy differ in crossability with 219
F.nilgerrensis, F.nubicola, F.pentaphyl/a or F.viridis indicating that F. vesca may be younger than previously supposed. Fragana vesca and F-pentaphylla were found to be highly crossable and each able to fonn fertile hybrids with five other diploid species, but F. pentaphylla had a better crossing record than Evesca. Fragana pentaphylla formed non-blooming hybrids with two other species (F.daltoniana and
F.nilgemensis) while F.vesca formed letha1 hybrids with three other species
(F.iinumae, Egracilis, and /=.nipponka). The superior crossability of F.pentaphy/la rnay indicate it is the progenitor of the genus of Fragana. As self-incompatible species were more readily intercrossed than self-compatible species and are located in the centre of Fragaria's Asian centre of diversity, it was theorized that self-incompatible species are ancestral to self-compatible species in Fragana. Self- compatible species have often arisen frorn self-incompatible species when isolation restricted opportunities for cross pollination (Stebbins, 1950; Lewis and Crowe,
1958). Thus, F.pentaphyl/ats self-incompatibility, crossability with other species, and central location in Fragana's centre of diversity in central Asia, further support the theory that it is the progenitor of the Fragana genus, and not the self-compatible
F. vesca.
Previously, only five combinations of diploid species were reported as fertile but this study increased the number of known fertile combinations to 13. All diploid species, except Eiinumae, formed fertile hybrids with at least one other diploid species indicating favourable potential of interspecific breeding at the diploid level.
Hybridization between diploid species could be further improved if more accessions 220 of some species were available.
The results of diploid crosses indicated that F.vesca is valuable for the SO system, particularly as a bridge for self-compatible species F-nilgenensis and
Fdaltoniana. The availability of many accessions of Evesca was an important factor in obtaining hybrids with these two species. Fragaria vesca probably is not the progenitor of the genus Fragana, but it could be a progenitor of polyploid
Fragada. With its widespread range (Staudt, 1989) there would have been opportunity for Evesca to hybridize with other species and form polyploid species.
In this study it was noted that F.vesca x F-viridis and Evesca x F.nubicola tetraploids resemble Fmoschata (6x). The successful integration of F.vesca into many SOS in this study suggests that F.vesca has potential to form polyploids in nature,
To incorporate F.moschata (6x) into the SO system it was hybridized with the diploid species F.nubicola and F.vindis to create tetraploids. Fruit set (90%) and seeds/pollination (19) were quite good for these combinations, but embryo abortions and malfoned seedlings reduced the outcome to only 1.1 plants/pollination. The best combinations for viable plants were found to be Fmbicola x Emoschata followed by Emoschata x F-vindis. This was contrary to earlier investigations that did not obtain any F.nubicola x F.moschata hybrids (Evans, 1964, 1974). These results contradict the idea that the higher ploidy species should be used as the female parent (Evans, 1974). As most Emoschata accessions are dioecious
(Staudt, 1989), they cannot be used as both male and females in crosses so it was 221 impossible to do reciprocal crosses. It was suggested that the early findings on crossability may have been biased by use of limited germplasm. It was also noted that having many accessions was important for incorporating the F.moschata germplasm into tetraploid hybrids. A new theory was proposed that Emoschata harbours lethal alleles that become exposed when crossing to lower ploidy species.
The resulting tetraploids created from crosses of Emoschata with diploids may be more genetically fit, which explains why embryo abortion and malformed seedlings were rare when F.moschata x diploid hybrids (4x) were intercrossed with other tetraploids.
At the tetraploid level, 52 out of 66 hybrid combinations of species resulted in viable progeny. A total of 192 SOS were created from 25 different combinations of species and at least 28 of these SOS were fertile. With so many combinations resulting in progeny, there appears to be great potential for breeding at the tetraploid level when using the crossing strategy of this study. Each of the four species which were hybridized with F. vesca at the diploid level were fertile at the tetraploid level and successfully incorporated into SOS. However, F. vesca x diploid colchi-tetraploids have reduced fertility and best results were obtained when these hybrids were crossed with highly fertile F. orientalis (4x) or Fmoschata x diploid species (4x). The results of this study show that certain combinations of species and accessions are good as either males or females but that the interaction between males and female was not significant. Thus, it would be more important to identify tetraploid accessions with good general crossability to serve as either 222 males or females rather than attempt to identify specific combinations of parents that are successful. A recommended strategy for future use of this system is to identify the best parents by test crossing with highly fertile F.odentalis andlor
F.moschata x diploid accessions.
The success of tetraploid crosses in this study makes it difftcult to speculate which species rnay have been involved in the creation of naturally occurring polyploids. This study broadens rather than narrows the number of species that could have been involved in creation of the polyploid species. Certainly, F. vesca could have been involved in evolution of octoploid species and evidently many diploid species have potential to make octoploids when hybridized with F.vesca.
The success of F. moschata x diploid tetraploids in crosses indicates that
F.moschata could be used as a genetic bridge to incorporate F-nubicola,
F.pentaphylla or F.vindis into the SO system. However, the Fmoschata x diploid
(Le. 6x x 2x) strategy may not be as desirable as using F.vesca as a genetic bridge to diploids as recombination between the three F. moschata and one diploid genornes in the tetraploid hybrid rnay allow only incomplete genomes of the diploid species to be transmitted into SOS, while the latter would likely transmit intact genomes of the component diploids.
The crossing strategy, wide germplasm base, and techniques developed each contributed to the overall success of this study. These results indicate great potential for breeding at the diploid and tetraploid levels and success of the synthetic octoploid system for widening the genetic base of octoploid cultivars. REFERENCES
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Yarnell, S.H. 1929. Notes on the somatic chromosomes of the seven-chromosome group of Fragana. Genetics 14:78-84.
Yarnell, S.H. 1931a. Genetic and cytological studies on Fragana. Genetics l6:422- 454.
Yarnell, S.H. 1931b. A study of certain polyploid and aneuploid forms in Fragana. Genetics 16:455-489.
Zhang, H-B., J. Dvorak, and J.G. Waines. 1992. Diploid ancestry and evolution of Tnticum kotschyi and T. peregrinum exarnined using variation in repeated nucleotide sequences. Genome 35:182-191.
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Zohary, D., and M. Feldman. 1961. Hybridization between amphidiploids and the evolution of polyploids in the wheat (aegilops-tnticum) group. Evolution 16:44-61.
Zohary, D. 1965. Colonizer species in the wheat group, p. 403419. In: HG. Baker and G.L. Stebbins (eds.). The genetics of colonizing species. Academic press, New York. Appendix 1: Abbreviations and addresses of germplasm sources.
C.C.G.: Canadian Clonal Genebank, Agriculture and Agri-Food Canada Harrow, Ontario NOR 1GO
Forest Farm 990 Tetherow Road Williams, Oregon 97544-9599 USA
Fox Hollow Herb & Heirloorn Seed Co. P.O. Box 148 McGrann, Pa. 16236 USA
Ornamental Edibles 3622 Weeding Court. San Jose, CA 95132 USA
Genebank OBST lnstitute fur Pflanzengenetik und Kulturpflanzenrofschung -Gatersleben Dresden - Pillnitz Dorfplatz 2 D-01326, Dresden Germany
IPK: Institute fur Pflanzengenetik und Kulturpflanzenrofschung- Genbank D-06466 Gatersleben, Germany
MicheIl's: Henry F. Michell Co. P.O. Box 60160 King of Prussia, PA 19406-0160 USA
NCGR: National Clonal Genplasm Repository 33447 Peoria Road Corvallis, Oregon 97333 USA
Ornamental Edibles 3622 Weedlin Court San Jose, California, 951 32 USA Park Seed: Ge0.W. Park Seed Co. lnc. Cokesbury Road P.O.BOX46 Greenwood, S.C. 29648-0001 USA
RBG Edinburgh: Royal Botanical Garden Edinburgh Edinburgh, Scotland EH3 5LR
Richters Gocdwood, ON LOC IAO
The N. I .Vavilov Ali-Russian Scientific Research Institute of Plant Genetic Resources 44 Bolshaya Morskaya St. St. Petersburg, 190000 Russia
The Gourmet Gardener 8650 College Blvd Overland Park, Kansas 6621 0 USA
Thompson and Morgan Inc. P.O. Box 1308 Jackson, N.J. 08527-0308 USA
U. of N.H.: University of New Hampshire, Tom Davis Appendix 2: ANOVAs from Chapter 4
Table A2.1. ANOVA for fruit set (%) of interspecific crosses with F. vesca subspecies as female parents and six accession of other diploid species.
Source DF Type III SS Mean Square F Value Pr > F
VESCA SSP. 3 O. 77932965 0.25977655 2.21 O. 0883 MALE 5 10.90520839 2.18104168 18.52 O. O001 VESCA SSP.* MALE 15 1.37977030 0.09198469 0.78 0.6978 BLOCK 2 0.11001001 0.05500500 0.47 O. 6274 Error 2 17 25.55077538 O. 11774551 Corrected Total 242 40.06532922
Table A2.2.ANOVA for seedsfflower of interspecific crosses with F. vesca subspecies as female parents and six accession of other diploid species. Source DF Type III SS Mean Square F Value Pr > F' VESCA SSP. 3 211.880457 37.293486 0.24 O. 8694 MALE 5 10440.605602 2088.121120 13.36 0.0001 VESCA SSP. *MALE 15 1230.139025 82.009268 0.52 0.9254 BLOCK 2 1792.287512 896.143756 5.73 O. 0038 Error 217 33925.163610 156.337159 Corrected Total 242 49570.592428
Table A25 ANOVA for fruit set (%) of intraspecific crosses with F-vesca subspecies as female parents and the control pollinizer w69.
Source Di? Type III SS Mean Square F Value Pr > F
Vesca ssp. 3 0.79834609 0.2661 1536 2.43 0.0764 BLOCK 2 0.02929847 0.01464924 0.13 O. 8750 Error 4 8 5.251 65391 O. 10940946 Corrected Total 53 6.09259259
Table A2.6. ANOVA for seedslflower of intraspecific crosses with F.vesca subspecies as female parents and the control pollinizer w69.
Sum of Mean Source Squares Square F Value P r > 1;'
F.vesca ssp. 3 4601.5266963 1533.8422321 2.64 O. O602 BLOCK 2 2843.2899450 1421.6449725 2.44 0.0575 Error 4 8 27918.4514148 581.6344670 Corrected Total 53 34857.6325926 Appendix 3: ANOVAs and data for Chapter 6.
Table A3.1. ANOVA for fruit set (%) of intraspecific crosses comparing (Emoschata x F.nubicola), (F.moschata x F.viMs), (Enubicola x F.moschata) and (F.vindis x F.moschata).
Sum of Mean Source DF Squares Square F Value Pr > F
Error 4 2 15490.8777778 368.8304233
Corrected Total 45 18114.9782609
Table A3.2. ANOVA for seeds per pollinated flower of intraspecific crosses comparing (Emoschata x F.nubicola), (F.moschata x F.vindis), (F.nubicola x F.rnoschata) and (F.vindis x F.moschata).
Sum of Mean Source Squares Square F Value Pr > F
Error 42 10851.-75150000 258.37503571
Corrected Total 45 11483.20869565 zahk OOkO wf:wu Table A35 ANOVA for percent of hybrids that bloomed the following year resulting from intraspecific crosses comparing (Emoschata x F.nubicola), (F.moschata x F.vindis), (F.nubicola x F.moschata) and (F.vindis x F.moschata).
Sum of Mean Source DF Squares Square F Value Pr > F
Corrected Total 45 35.90325082 Table A3.6. Fruit set, seeds, embryos, healthy plants, and one year old hybrids that bloomed, for crosses among accessions of Fragaria moschata and F.nubico/a or F.viridis. Means are calculated for each species combination.
Accessions Healthy 1 yr. old hybrids Ploidy of F.moschata F.nubicola # of Seedsl Ernbryos/ plants1 that bloomedl btooming fernale male pollinations % Fruit set pollination pollination pollination pollination hybrids mcv2 nub2 1 1 O0 3 O O O mwl nubl 4 1 O0 24 O.3 O O mw7 nub2 1 1O0 5 0 O O mw5ez nub2 2 100 42 5 O O mw5e nu b 1 1 1 O0 12 O O O mw5k nubl 1 100 62 --O O O - Mean 100 ns 25 ns 0.9b Ob O ns
F. nubicola F. moschata females males nubl mcvl nub2 mcvl nubl mw2d nub2 mw2d nubl mw4 nub2 mw4 nub2 mw5a nub2 mw5d nub2 mw5f
': letters in the accession identifier signify individuals of an open-pollinated family Table A3.6. continued.
Accessions Heaithy 1 yr. old hybrids Ploidy of F.moschata F.viridis # of Seedsl Embryosl plants1 that bloomedl blooming fernale male pollinations O! fruit set pollination pollination pollination pollination hy brids mcvl vif2 1 100 12 5 5 3 4x mcvl vir3 rncv2 virl mcv2 vie rnwl virl mwl vir2 mwl vir5 mw2a virl mw2a vir2 mw2c vir2 mw3 virl
': 416x = mixaploid having 4x and 6x sectors.
Appendix 4. Data from tetraploid crosses in Chapter 7. Table A4. Fruit set, seedsl flower, germination and synthetic octoploids (SOS) resulting from interspecific crosses between tetraploid Fragana accessions.
Female parent Male parent Seeds No. species IDL No. species ID No. of Ny Fruit set Seeds l receiving N Germination N SOS F. vesca F. vesca flowers (%) flower iti vitro (%) (%) genomes clenornes pollinated - treatment
4 F. vexa 4187 2 F. vesca x 1 06 1 1 100 6.0 6 1 83.3 0.0
4187 F. vesca x 1 84 2 100 17.0 34 14.7 20.0 F. nubicola 4192 184 1 O O.0 O nla nla t 1 5-2 160 1 O 0.0 O nla nla mean 4 3 33 5.7 34 1 14.7 1 20.0
F. vesca x 118 2 O 0.0 O n/a n/a F. pentaphylla 114 1 O 0.0 O nla n/a 118 1 O 0.0 O nla nla 41 87 114 2 O 0.0 O nia nla rnean 6 4 O 0.0 O O n/a nla
F. vesca x 4 1 O O 0 O nla nla F. nilgenensis 4192 4 1 O 0.0 O nla nla mean 2 2 O O.0 O nla n/a
ID = Guelph identifier, see table 7.4for lineage of each accession. Y N = number of combinations of accessions used in crosses. N is the same for fruit set and seedslfiower 247 Table A4 continued. Female parent Male parent Seeds No. species IDL No. species ID No. of N' Fruit set Seeds 1 receiving N Germination N SOS F.vesca F.vesca flowers (%) flower in vifro (%) (%) genornes genomes pollinated treatment
4 Evesca 426 O F. moschata x 22 1 100 26.0 26 96.2 0.0 F. viridis 426 24 2 100 22.0 44 6.8 0.0 4182 24 2 1O0 1.5 3 100.0 0.0 mean 5 3 100 16.5 73 3 67.7 3 0.0
4182 F. viridis x 449 1 100 51.0 O nla nla F. moschata tl5-2 449 1 100 3.0 O nla nla mean 7 2 100 27.0 73 nla nla
F.nubicola x 186 1 nla F.moschata 192 3 24.6 6.7 186 2 71.1 0.0 110 2 44.4 13.3 110 2 43.1 0.0 186 2 27.7 O.0 110 2 42.7 4.0 1 92 1 nla nla 131 -- 1 nla nla mean 16 6 42.3 6 4.0
426 F.pentaphylla x n4mb 2 1 O0 4.5 9 77.8 0.0 F.moschata 4192 n4mb 2 100 35.5 60 41.7 0.0 mean 4 2 100 20.0 69 2 59.7 2 0.0
Table A4 continued. Çernale parent Male parent Seeds No. species I DL No. species ID No. of Ny Fruit set Seeds l receiving N Germination N SOS F. vesca F.vesca flowers (%) flower invitro (%) ("/.) genomes clenornes pollinated treatment
2 F. vesca x 149 2 F. vesca x 114 nla nla F. nubicola 149 F. pentaphylla 118 0.0 149 121 nla nla 155 4122 nla nla 157 Il3 nla nla 157 118 n/a nla 168 43 nla nla 170 43 nla nla 175 113 nla rita 175 118 100.0 0.0
.- .- nia nla 2 50.0 1 0.0
F. vesca x F, 2 3 100 18.7 56 35.7 O. O nilgerrensis 45 1 100 27.0 27 44.4 0.0 46 1 O 0.0 O n/a nla 51 1 O 0.0 O n/a nla 175 4 1 O 0.0 O nla nla mean 7 5 40 9.1 83 2 40.1 2 0.0
168 O F. viridis x 329 2 1 O 0.0 O nla nla F. nubicola Table A4 continued. Fernate parent Male parent Seeds No. species IDL No. species ID No. of Ny Fruit set Seeds l receiving N Germination N SOS F. vesca F.vesca flowers (%) flower in vitro (%) (%) genomes clenornes pollinated treatment
2 F. vesca x 120 O F. moschata x 21 63.6 0.0 F. nubicola 120 F. viridis 22 55.3 0.0 135 22 nla nla 135 24 nla nla 137 72 76.9 0.0 149 22 nla nla 149 24 nla nla 168 22 nla nla 1?'O 22 nla nla 175 22 nla nla 175 24 0.0 nla 184 22 nla nla 184 24 2 O 0.0 O nla nla mean 22 13 69 13.0 133 4 49.0 3 0.0
F. viridis x 38 100.0 0.0 F. moschata 62 71.4 0.0 449 n/a nla 487 nla nla 38 44.0 0.0 62 87.0 5.0 487 nla nla 449 nla nla 487 nla nla
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Table A4 continued. Female parent Male parent Seeds No. species IDL No. species ID No. of NYFruit set Seeds l receiving N Germination N SOS F.vesca F.vexa flowers (Oh) flower in vitro (%) (%) genomes clenornes pollinated treatment
2 F. vesca x F. 1 13 O F. pentaphylla x n4mb 1 100 1 .O O nla nla
pentaphylla. - F.moschata 118 n4mb 3 O 0.0 O nia nfa mean 4 2 50 O.5 O nla nla
113 F. orientalis x(F. 877 1 O 0.0 O nla nla moschata x F. vkdis) il8 877 1 O 0.0 O nla nla mean 2 2 O 0.O O nla nla
F. orientalis 01 nla nla ok nia nla 01 nla nia 02 100.0 o.0 ok nla nla 02 100.0 0.0 oa nia da 01 nla nla oa nla nla 01 50.0 0.0 02 85.7 0.0
Table A4 continued. Female .aren nt Male parent Seeds No. species IDZ No. species ID No. of Ny Fruit set Seeds 1 receiving N Germination N SOS F.vesca F. vesca flowers (%) flower in vitro (%) (%) genomes clenornes pollinated treatment
2 F. vesca x F. 4 2 F. vesca x F. 43 2 O 0.0 O n/a nla nilgerrensis pentaphy//a 4 114 3 67 2.7 8 12.5 O. O 4 118 4 75 2.8 11 90.9 10.0 130 43 2 O 0.0 O nla n/a 151 114 2 O 0.0 O nla nla mean 13 5 28 11 19 2 51.7 2 5.0
F. vexa x F. 151 4 75 5.0 20 0.0 nla nilgerrensis 427 1 O O O O nia nla 151 2 50 3.0 6 16 7 O.O 151 4 2 50 1.5 3 0.0 nla mean 9 4 44 2.4 29 3 5.6 1 0.0
4 O F. viridis x F. 329 2 O 0.0 O nla nla nubicola 4 41 16 1 O 0.0 O nla n/a 130 41 16 1 O 0.0 O nla nla mean 4 3 O 0.0 O nla nla
F. moschata x 21 1 100 10.0 10 50.0 0.0 F. viridis 22 1 100 5.0 5 80.O 0.0 21 1 100 37.0 37 97.3 8.3 22 3 100 15.3 33 93.9 3.2 21 1 100 4.0 4 75.O 0.0 Table A4 continued. Female parent Male parent Seeds No. species IDZ No. species ID No. of Ny Fruit set Seeds 1 receiving N Germination N SOS F.vesca F.vexa fiowers (%) flower invitro (%) (%) penomes clenornes pollinated treatment
2 F. vesca x F. 2 O F. viridis x 62 1 100 2.0 2 0.0 nla nilgerrensis F.moschata 4 38 1 100 15.0 15 93.3 7.1 4 449 1 100 5.0 O nla nla 45 38 2 100 2.5 5 100.0 0.0 45 62 2 100 15.0 30 23.3 O. 0 46 62 1 1O0 4.O 4 50.O 0.0 mean 8 6 100 7.3 51 5 53.3 4 1.8
F.nubicola x 110 96.4 7.4 F.moschata 131 nla nla 169 nla nla 182 nla nla 186 100.0 O.O 192 0.0 nla 471 nla nla 110 50.0 0.0 186 100.0 7.1 110 59.2 17.8 0.8 100.0 58.1 6 22.1
2 F. vesca x 4 O F. orientalis x 877 3 67 1.3 O nla n/a F. nilgerrensis (F. moschata x 130 F. viridis) 877 1 1O0 1 .O 7 0.0 nla mean 4 2 83 1.2 1 1 O. O nla Table A4 continued. Female parent Male parent Seeds No. species IDL No. species ID No. of Ny Fruit set Seeds 1 receiving N Germination N SOS f.vesca F. vesca flowers (%) flower in vitro (%) (w genomes ~enomes pollinated treatment
2 F. vesca x 2 81.3 2.6 F. nilgerrensis 4 nla nla 4 93.1 10.8 4 97.8 4.4 4 n/a nla 45 75.0 0.0 45 100.0 0.0 46 88.9 0.0 46 og 1 O 0.0 O nfa nfa mean 16 9 89 19.3 279 6 89.3 6 3.0
O F. moschata x 30 2 F. vexa x 139 1 100 27.0 27 70.4 O. O F. viridis 30 F. nubicola 160 2 50 17.5 O nla nla mean 3 2 75 22.3 27 1 70.4 0.0 nia 36 O F. moschata x 22 2 IO0 38.0 76 92.1 0.O 70 F. viridis 21 2 100 50.0 100 61 .O 1.6 70 22 5 100 46.6 233 74.7 5.7 71 21 3 100 36.3 109 89.9 2.0 mean 12 4 100 42.7 518 4 79.4 6 1.6
30 O F. viridis x 449 1 100 49.0 49 95.9 6.4 30 F.moschata 487 1 O 0.0 O nla nla 68 62 2 100 47.5 95 90.5 0.0 70 62 3 100 37.3 112 92.0 1.9
O F. moschata x 24 O F.nubicola x 131 1 O 0.0 O nla nla
Table A4 continued. 2 7 O
O F. orientalis 01 3 O F. viridis x 329 1 1 O 0.0 O nla nla F. nubicola
012 F. moschata x 24 1 100 16.0 O nla nla ob F. viridis 21 1 100 10.0 10 90.0 0.0 ob 22 1 100 80.0 80 92.5 4.1 OC 22 1 100 61.0 61 95.1 1.7 mean 4 4 100 41.8 151 3 92.5 3 1.9
01 3 O F. viridis x 74 1 100 100 1O 70.0 14.3 013 F. moschata 449 3 100 80.3 241 96.3 2.6 ob 38 1 100 27.0 27 74.1 5.0 ob 62 1 100 55.0 55 96.4 0.0 OC 62 1 100 59.0 59 98.3 5.2 oe 62 1 100 3 0 3 66.7 0.0 mean 8 6 100 39.1 395 6 83.6 6 4.5
O F. orientalis 01 3 O F.nubicola x 17 nla nla 01 3 F.moschata 18 86.4 14.5 01 3 169 90.9 10.0 01 3 190 90.0 11.1 020 110 91.7 10.5 020 169 100.0 2.2 020 182 100.0 8.5 020 186 73.7 0.0 Appendix 5. ANOVAs for Chapter 7.
Table A5.1. ANOVA for fruit set (%) of tetraploid crosses for data in Chapter 7.
Source OF Type XII SS Mean Square F Value Pr > F
Females 7 29125.12282 4160.73183 2.41 O. 0202 Males 9 124959.26367 13884.36263 8.03 O. 0001 Fernales*Males 4 9 84186.86770 1718.09934 0.99 0.4898 Error 398 688259.64813 1729.29560 Corrected Total 463 1078139.26612
Table A5.2. ANOVA for seeds per pollinated flower of tetraploid crosses for data in Chapter 7.
Source DF Type III SS Mean Square F Value Fr > F
Fema les 7 4890.866413 698.695202 2.30 0.0262 Males 9 13444.835192 1493.870577 4.92 0.0001 Females*Males 4 9 16865.800948 344.200019 1.13 0.2589 Error 398 120926.277986 303.834869 Corrected Total 463 192031.847220 Table A5.3. ANOVA for germination (%) of tetraploid crosses for data in Chapter 7.
Source DF Type III: SS Mean Square F Value Pr > F
Females 7 15264.320452 2180.617207 2.01 O. 0574 Males 9 26697.223311 2966.358146 2.74 0.0056 Females*Males 31 40199.709190 1296.764813 1.20 0.2383 Error 138 149374.27031 1082.42225 Corrected Total 185 250669.83333
Table A5.4. ANOVA for synthetic octoploid production (%) of tetraploid crosses for data in Chapter 7.
Source DF Type III SS Mean Square F' Value Pr > F
Females 7 234.9656825 33.5665261 0.23 O. 9783 Males 9 1604.6145081 178.2905009 1.20 O. 3000 Females*Males 28 3334.6749596 119.0955343 0.80 0.7432 Error 114 16895.0216151 148.2019440 Corrected Total 158 23617.5358491