Morphology and Crossing Ability of Tetraploid Species Closely Related to Sweetpotato

Jpn. J. Trop. Agr. 43 (1) : 42-48,1999

Katsumi KOMAKI

National Agriculture Research Center, 3-1-1 Kannondai, Tsukuba, Ibaraki 305-8666, Japan

Abstract Twenty five accessions of tetraploid Ipomoea species that are closely related to sweetpotato were used for the analysis of morphological variation and evaluation of crossing ability. Based on the principal component analysis of 47 characters, the accessions were morphologically classified into four groups. One of the groups consisted of five accessions which had small, thick and leathery or membranous leaves and markedly different from other three groups. However, crossing rates were not significantly different in inter- and intra-group cross combinations, suggesting that there was no significant biological isolation. Morphological variation in the progeny resulting from inter-group crossing, covered almost all range of the variations of parental accessions. All the tetraploid accessions used in this study were considered to belong to one taxon, as indicated in the taxonomical studies carried out in U. S. A. Therefore these accessions should be designated as I, batatas. Key words Crossing ability, Ecological variation , Ipomoea species, Tetraploid

四倍体のサツマイモ近縁野生植物の形態と交雑性小巻克巳農業研究センター〒305-8666茨城県つくば市観音台 3-1-1

要約四倍体のサツマイモ近縁野生植物25種類を供試して,花器,萼片,及び茎葉に関する57形質を調査し,変異の認められた47形質について主成分分析法によりその変動様相を明らかにした.供試した25種類はこれにより四つのグループに分類することができ,その一つは葉が小さく,厚く,膜質あるいは革質であるという特徴をもっており,他の3つのグループとは著しく異なっていた.しかし,グループ内あるいはグループ問で行った交配実験の結果,いずれのグループとの交雑においても交雑率に有意な差が認められないことが明らかとなった.これは形態的に差があったとしても生物学的な隔離は十分に進んでいないことを示唆するものであった.また,グループ問の交雑の後代の形態は両親の中間的な特徴を示し,変異は連続的になった.これにより,サツマイモと交雑が可能な四倍体近縁野生植物は分類学的には一つの種に属すると判断された.サツマイモ近縁野生植物の形態分類を精力的に行ってきた米国の研究グループによる研究蓄積と今回得られた形態変異及び交雑性に関する知見から,わが国でこれまでI. trifidaであるとしてきたこれらの植物はI. batatasとするのが妥当であると結論した. キーワード形態,交雑性,サツマイモ近縁野生植物,四倍体

I. batatas6,7). Introduction Morphological variation and crossing Ipomoea trifida (H. B. K.) G. DON. is a ability of tetraploid Ipomoea species have species most closely related species to sweet- not yet been analysed in detail. Thus, this potato. It is principally distributed in the study aimed at analyzing various aspects of Carribian region and may consist of both morphological variation in the tetraploids diploid and tetraploid races4). Japanese scien- and classifying them based on multivariate tists10,16)have recorded diploid, triploid, and analysis. Crossing experiments were conducted hexaploid types. The morphological charac- to detect reproductive isolation among the teristics of the tetraploid types are highly groups classified based on the morphological distinctive, in terms of leaf size and thickness characteristics. Morphological and crossing or plant type16). This type of tetraploid is rep- studies were also carried out in progenies resented by K 233 collected at Veracruz, from the cross of the tetraploids. Mexico, which has small, thick and leathery Materials and methods or membranous leaves. K233 and other morphologically identical Twenty five tetraploid Ipomoea accessions accessions were designated as I, littoralis.20), were used for the analysis of morphological I. gracilis.8,13), a hybrid between sweetpotato variation and evaluation of crossing ability and diploid species1,2), I. trifida9, 10,15, 16, 18, 19) or (Table 1). The accessions were grafted onto Received Aug. 28, 1998 a dwarf type morning glory (I. nil cv. Kidachi) Accepted Nov. 13, 1998 grown in 24 cm clay pots because only a KOMAKI: Variation of tetraploid Ipomoea species 43

Table 1. Tetraploid Ipomoea species used for morphological analysis and crossing

*,**: renamed I . trifida by KOBAYASHI 9,10) and SHIOTANT 16), respectively. small number of flowers were formed under sis (PCA)processed by SPSS Base 7.5 J natural conditions. The plants were kept in a (SPSS Inc.,Chicago, Illinois,U.S.A.). green house at Ibusuki Branch, Kyushu Na- Crossing was mainly performed for 25 tional Agricultural Experiment Station, flowers in each cross combination. Seed set-

Kagoshima, Japan. ting was calculated by the formula(No. of Data were gathered for 57 characters re- mature seeds×100)/(No. of pollinations× lated to corolla, sepal, leaf, vine, and others 4)and expressed in percentage. A one-way

(Table 2). Measurements were based on 3 to analysis of variance(One-way ANOVA)was 5 samples per accession. Qualitative charac- employed to detect differences in the seed ters involving color, pubescence, shape or setting among the types of cross combina- texture were rated on a numerical scale ac- ti ons based on the classification of the acces- cording to their levels. Two ratings were sions by PCA and testing of the homogeneity adopted for the characters, one for presence of variance within the type of cross combina- and zero for absence. Since no variations tion by the Levene test. Mature seeds ob- among the accessions were observed among tamed from 16 cross combinations were the 10 characters such as: presence of star grown in the greenhouse and the plants were shape inside of corolla tube bottom and ex- grafted to the dwarf type of morning glory ternal nectary, corolla tube shape, color of to induce flowering as described above(Ta- stigma, style, and anther, apex shape of ble 3). Morphological data were collected in outer and inner sepal, vine twining, and pres- the same way as in the parents. Each plant ence of adventitious root primordia at node, was crossed with the parents or other plants data matrix of 25 accessions×47 characters and crossing rate was also calculated. was used for the principal component analy- 44 Jpn. J. Trop. Agr. 43 (1) 1999

Table 2. Characters measured or observed in this study

leaf thickness (-0.850), leaf lobing (-0.717), Results and adaxial pubescence of leaf (0.752). The Morphological classification of tetraploid second principal component (Component II) accessions had high loading values for the pedicel Around 25 and 12% of total morphologi- length (0.784), longest stamen length (0.802), cal variation of 47 characters in 25 acces- and shortest stamen length (0.753). There- sions could be explained by the first and sec- fore, the Component I mainly explained the ond principal components, respectively. In combination of variation among whitish the first principal component (Component I), flowers, small sepals, large, round, thin and high factor loading values (<-0.7 or >0.7) hairy leaves, and thin pedicel vs. pinkish were observed for the corolla limb color (- flowers, large sepals, small, lobed, thick and 0.881), corolla tube color (-0.791), stamen glabrous leaves, and thick pedicel. On the pubescence (0.713), outer sepal width (- other hand the Component II mainly ex- 0.731), inner sepal length (-0.720), inner se- plained the variation of stamen length and pal width (-0.748), pedicel diameter (- arrangement of the inflorescence. 0.772), leaf length (0.864), leaf width (0.787), The scatter diagram of the first and sec- KOMAKI: Variation of tetraploid Ipomoea species 45

ond principal component scores showed that One-way ANOVA was applied on the accessions fell into four different groups. basis of the Levene test, which did not reject The first group (Group A) which had a the hypothesis of equal variances across the smaller Component I score (<-1.5) and in- 14 types of cross combinations, and it did not termediate Component II score (around 0) any difference in the means among the type consisted of 5 accessions including K 233. of cross combination between the different The second group (Group B) included 2 ac- groups classified by morphological analysis cessions, the third group (Group C) had 5 ac- (Table 3). Cross incompatibility was ob- cessions including 7928, and the last group served among accessions belonging not only (Group D) had 13 accessions (Fig. 1). As de- to the same group (Samples No. 1, 23 and 24 scribed above, Group A was characterized in Group A ; 12, 14 and 21 in Group D, etc.) by the presence of pinkish flowers, small se- but also to different groups [Samples No. 3 pals, small, lobed, thick and glabrous leaves, (C), 6 (D) and 7 (B), etc.]. and a thick pedicel. On the other hand, All the progenies from crosses among Group C consisted of accessions with large different morphological groups were mor- and whitish flowers ; large sepals ; large, phologically normal. Even the variation of round, thin and hairy leaves, and a thin leaf size and thickness and sepal size, which pedicel. Group D was characterized by rela- distinctively enable to separate Group A tively small and whitish flowers ; large se- from the other Groups, became continuous pals ; large, round, thin and hairy leaves, because the crosses between K233 and K500 and a thin pedicel. Accessions belonging to or 7948 produced intermediate types of par- Group B were intermediate types between ents and looked similar to the accessions of those of Group A and C or D. Group B (Fig. 2). Variations of the characters extracted by PCA for the classification Crossing rate among tetraploid accessions of the accessions were also continuous due to and morphological variation in the progenies wide variations observed in the progeny (Fig. Mean value of seed setting in the inter- 2 and Table 4). group type of cross combinations was 34.5%, Female fertility of the progenies evalu- ranging from 25.0 to 50.7%. In the individual ated by polycross pollination ranged from 4.2 crosses, the lowest seed setting value was to 89.3 % which was as high as, or relatively 2.8%, and the highest was 90.0%. In the intra- higher than that of original tetraploids, sug- group type of cross combinations the mean gesting that the parents had a similar genetic value was 41.6%, ranging from 41.4 to 41.8%. constitution (Table 3). In the individual crosses, seed setting value Discussion ranged from 1.3 to 91.7% (Table 3). Tetraploids, such as K 233, K 300-1, K 500-1 etc., were reported to be very close in the genus Ipomoea12). However, among the tetraploids, K233 and almost identical accessions formed a separate group (Group A) characterized by small, lobed, thick and glabrous, and darker corolla, resulting in various taxonomic designations for the same accessions (Fig. 1). The accessions of Group A have been designated as I. littoralis20) and I. gracilisg8). These materials were collected from Veracruz, Mexico (Table 1). KOBAYASHI9,10) SHIOTANI16,17),SHIOTANI and KAWASE18,19), and ORACIONet al.15)renamed these accessions and Fig. 1. Scatter diagram of the first two principal other tetraploids I. trifida based on morpho- component scores, I and II. Numbers in logical and cytological observations. However, the figure indicate genotypes, as in Table 1. BOHAC et al5)., HE et al.6) and JARRET et al.7) 46 Jon. J. Trop. Agr. 43 (1) 1999

Table 3. Crossing rates among or within morphologically classified groups

One way ANOVA

*: Mean (Min .-Max.)

Fig. 2. Variation of leaf size (a), sepal size (b), stamen length (c) and pedicel length and diameter (d) in the tetraploid accessions and the their progeny.

◆: Group A,■:Group B,▲:Group C,●:Group D,○:K233-1×79480r 7948×K233-1, ■: K233-1×K500-1 or K500-1×K233-1,〓: K233-1×7928 or 7928×K233-1,

◇: K233-1×K300-1 or K300-1×K233-1,△: K233-1×K510 or K510×K233-1, ×: K233-1×7947 or 7947×K233-1,+: K300-1×K500-1,〓: K500-1×K510,〓 : K500-1×7928 or 7928×K500-1 KOMAKI : Variation of tetraploid Ipomoea species 47

Table 4. Means and ranges of the characters extracted by PCA in tetraploid species and the progenies

identified them as I. batatas, and AUSTIN 1,2) spective of their morphological differences. as a hybrid between I, batatas and diploid I. Moreover, progeny between accessions rep- trifida. resenting the different morphological groups Accessions belonging to Group B, which was found to be intermediate between the were intermediate types between Group A groups and morphological variation became and Group C or D, were collected at Veracruz, continuous (Fig. 2 and Table 4). Female fer- Mexico, and Cali, Colombia (Table 1), sug- tility of the progeny was almost as high as gesting that the gene controlling the morpho- that of the parents (Table 3). Therefore, all logical habit similar to that of K233 had the tetraploids that can be crossed with spread to the South American continent, and sweetpotato seem to belong to one taxon, I. was not limited to Veracruz. SHIOTANI17) batatas or I. trifida. also concluded that the sweetpotato and Tetraploids collected in Ecuador and Co- polyploid I. trifida including K233 were lo mbia14),7947 and 7948, belonged to Group D autopolyploid, consisting of the genome B of and Group B, respectively,and were classified diploid I. trifida. Thus, Group A represented as I. batatas5)or hybrids between I. batatas by K233 is considered to be an ecotype and diploid. I.trifida 1). 7928 belonging to Group adapted to a coastal environment such as in C was identified as I. trifidaby KOBAYASHI Veracruz. et al.11),but it was also designated as I. batatas Crossing experiments between or within by BOHAC et al 5).Therefore, all the represen- groups based on PCA did not reveal significant tatives of the morphological groups were differences in the crossing ability among the identified as I. batatas by the American re- types of cross combinations (Table 3), sug- search group who carried out extensive stud- gesting that no or a very weak biological ies on the taxonomy of the species in the ge- barrier existed among the tetraploids irre- nus Ipomoea section Batatas2,3,4,5) 48 Jpn. J. Trop. Agr. 43 (1) 1999

These results indicate that tetraploid ac- tal differentiation. Recent Advance of Breeding cessions that can be crossed with sweetpo- (Ikushugaku saikin no shinpo) 22: 107-113. tato belong to I. batatas, and not to I. trifida, 10. •\1984 .The Ipomoea trifida complex closely related to sweet potato. Proceeding of a taxonomy generally adopted by the Japanese Symposium of the International Society of scientists. Tropical Root Crops. Lima, Peru, February 21-

26, 1983. Edited by S. F. SHIDELER and H. RINCON. Acknowledgements International Potato Center (Lima). 561-568. The author thanks Dr. M. KOBAYASHI . •\, H. MURATA and K. KOMAKI 1980 A wild and Dr. I. SHIOTANI for providing the seeds species of section Batatas genus Ipomoea col lected in Venezuela. Japan. J. Breed. 30 (suppl, and plants of Ipomoea species and for their 2): 114-115. valuable suggestions. The author expresses 12. KOMAKI, K., H. N. REGMI, K. KATAYAMA and S. his appreciation to Prof. A. M. MARISCAL for TAMIYA 1998 Morphological and RAPD pattern his critical reading of the manuscript. variations in sweetpotato and its closely related species. Breed. Sci. 48: 281-286. Literature cited 13. MARTIN, F. W. and A. JONES 1972 The species of Ipomoea closely related to the sweet potato. 1. AUSTIN D. F. 1977 Hybrid polyploids in Ipomoea Econ. Bot. 26: 201-205. section Batatas. Jour. Hered. 68: 259-260. 14. •\,•\and R. M. RUBERTE 1974 A 2. •\1978 The Ipomoea batatas complex. I. wild Ipomoea species closely related to the sweet Taxonomy. Bull. Torrey Bot. Club 105: 114-129. potato. Econ. Bot. 28: 287-292. 3. •\1983 Variability in sweet potatoes in 15. ORACION,M. Z., K. NIWA and I. SHIOTANI1990 Cy- America. Proc. Amer. Soc. Hort. Sci., Tropical tological analysis of tetraploid hybrids between Region. 27 (B): 15-27. sweet potato and diploid Ipomoea trifida (H. B. 4. •\1987 The taxonomy, evolution and ge- K.) G. DON. Theor. Appl. Genet. 80: 617-624. netic diversity of sweet potatoes and related wild 16. SHIOTANI,I. 1983 A survey of habitats of Ipomoea species. In •eExploration, maintenance, and utili- trifida, a closely related species to sweet potato. zation of sweet potato genetic resources•f Rep. 1 Rep. Plant Germ-plasm Inst. Kyoto Univ. 6: 9- st Sweet Potato Planning Conf., CIP (Lima). 27- 27. 59. 17. •\1988 Genomic structure and the gene 5. BOHAC, J. R., D. F. AUSTIN and A. JONES 1993 Dis- flow in sweet potato and related species. In •eEx- covery of wild tetraploid sweetpotato. Econ. Bot. 47:193-201. ploration, maintenance, and utilization of sweet 6. HE, G., C. S. PRAKASHand R. L. JARRET 1993 potato genetic resources•f Rep. 1st Sweet Potato Planning Conf., CIP (Lima). 61-73. Analysis of genetic diversity in a sweetpotato 18. •\and T. KAWASE 1981 Origin and differ- (Ipomoea batatas) germplasm collection using entiation of the sweet potato. 2. Genomic struc- DNA amplification fingerprinting. Genome 38: ture and domestication. Recent Advance of 938-945. Breeding (Ikushugaku saikin no shinpo) 22: 114- 7. JARRET, R. L., N. GAWEL and A. WHITTEMORE 134. 1992 Phylogenetic relationships of the sweetpo- 19. •\and•\1987 Synthetic hexaploids tato [Ipomoea batatas (L.) LAM.] J. Amer. Soc. derived from wild species related to sweet po- Hort. Sci. 117: 633-637. tato. Japan. J. Breed. 37 : 367-376. 8. JONES, A. 1970 Asynapsis in Ipomoea gracilis. 20. TERAMURA, T. 1979 Phylogenetic study of Ipo- Journ. Heredity 61:151-152. moea species in the section Batatas. Mem. Coll. 9. KOBAYASHI, M. 1981 Origin and differentiation of Agr. Kyoto Univ. 114: 29-48. the sweet potato. 1. Geographic origin and varie-