Heredity (1980), 44, 201-209 0018-067X/80/01 57020 l$02.00 1980The Genetical Society of Great Britain

MITOTICAND MEIOTIC CHROMOSOME BEHAVIOUR IN NEWHYBRIDSOF WITH TR!TICUM AND SECALE

R. A. FINCH and M. D. BENNETT Breeding Institute, Maria Lone, Trumpington, Cambridge CB2 2LQ Received7.ix.79

SUMMARY First metaphase in pollen mother cells (pmc's) is described in the new hybrids, 2x x 6x Triticum aestivum (2n =28),2x H. chilense x 2x Secale cereale (2n =14),4x H. jubatum sap. breviaristatum x 2x S. africanum (2n =21) and 2x H. vulgare x 6x H. murinurn ssp. simulans (2n =28),and for the first time in 6x H. murinum ssp. simulans x 2x H. vulgare (2n =28)and 6x H. procerum x 2x H. vulgare (2n =28).The intergeneric hybrids had no chiasmata at meta- phase I except those between H. jubatum chromosomes in the hybrid with S. africanum. Multivalents were rare or absent and mean chiasma frequencies per euploid pmc (non-doubled) were 255, 250, 225 and 150 in H. jubatum x S. africanum, H. vulgare x H. murinum, and in H. murinum and H. rocerum x H. vulgare, respectively. In hybrids with metaphase I chiasmata, 33-93 per cent of pmc's were aneuploid (or rarely polyploid) and in H. vulgare hybrids, somatic instability also occurred. No hybrid set seed. Mitotic chromosomes (2n =14)of the new hybrids 2x H. chilense x 2x S. africanum, 2x S. montanum and 2x S. vavilovil, and the hybrid, 2x H. vulgare x 2x S. africanum, are described for the first time. These hybrids were vigorous but have not flowered, probably through lack of vernalisation.

1. INTRODUCTION WIDE crosses in cereals are usually difficult to achieve, but have obvious potential in crop improvement by the introduction of alien variation (Riley and Kimber, 1966). Embryo culture, though not always essential (Kimber and Sallee, 1976) usually facilitates hybrid production greatly (Davies, 1960) and has recently been used in many new crosses involving Horcleum, Triticum and Secale (Subrahmanyam, 1977; Martin and Chapman, 1977; Cauderon et al., 1978; Fedak, 1978). Wide crosses involving Hordeum have recently been of unique use in haploid breeding programmes (Kasha and Reinbergs, 1976; Finch and Simpson, 1978) and research in genetics (Snape et al., 1979), chromosome pairing (Finch and Kasha, 1976; Miller and Chap- man, 1976) and chromosome elimination (Subrahmanyam and Kasha, 1973; Bennett et al., 1976). The present paper describes seven new combina- tions all involving Hordeu,n, five of which may be of particular use for study- ing interspecific crossability and chromosome elimination. It also presents the results for three other Hordeum crosses producing additional material of general cytogenetic interest. 201 202 R. A. FINCH AND M. D. BENNETT

2. MATERtALS AND METHODS (i) The chromosome numbers and ploidy levels of the plants used are given in table 1. All material came from stocks at the Plant Breeding Institute, Cambridge except for H. chilense, H. jubatum ssp. breviaristatum, H. murinum ssp. simulans (= H. leporinum var. simulans), H. procerum, and H. pusillum (from Dr W. Lange, Wageningen, The Netherlands), S. cereale cv. Petkus Somro (from Dr K. V. Cooper, Edinburgh, U.K.) and line UC9O (from Dr J. P. Gustafson, Manitoba, Canada) and S. africanum line 2D127 (from Prof. E. N. Larter, Manitoba, Canada).

TABLE 1 Chromosome number (2n) and ploidy level of parent plants

Plant 2n Ploidy level Hordeum vulgare cv. Sultan 14 2x H. chilense 14 2x H. jubatum ssp. breviaristatum 28 4x H. murjnum ssp. simulans( H. leporinum var. simulans) 42 6x H. procerum 42 6x H. pusillum 14 2x Triticum aestivum selection from cv. Chinese Spring 42 6x Secale cereale cv. Petkus Somro and line UC9O 14 2x S. africanum lines Karoo, R102 and 2D127 14 2x S. montanum line R15 14 2x S. vavilovii line R30 14 2x

(ii) Plant culture All parents were grown from seed, and all except H. vulgare were verna- lised as germinating seeds or juvenile plants. Plants were grown in pots of soil-less or John Innes No. 2 compost in a variety of conditions in frost-free glasshouses throughout the year. Supplementary artificial lighting was given when needed to ensure long day conditions after vernalisation.

(iii) Crossing Spikes were emasculated and pollinated 1-5 days later. On day 1 or 2 after pollination, spikes were sprayed with aqueous gibberellic acid solution (75 ppm GA8 from I,C.I. Berelex tablets) and protected with brown paper bags. Embryos were excised in sterile conditions 12-23 days after pollina- tion and grown on" Difco" bacto orchid agar (29 g/l) at 20°C in the dark. When shoots appeared, embryos were moved into diffuse and eventually strong light at 20°C. Young plants were potted in soil-less compost and grown in glasshouses.

(iv) ytological preparations Root tips were pretreated in water at 1°C for 24 hours, or saturated aqueous monobromonaphthalene at room temperature for 4 hours. Pre- NEW HYBRIDS OF HORDEUM 203 treated roots and meiotic spikes were fixed in Carnoy's solution for 2 hours or more. Fixed root tips and excised primary and secondary florets were stained by the Feulgen method, and roots and anthers squashed in aceto- carmine, propionic-orcein or 45 per cent acetic acid.

3. RESULTS (i) Morpho1oy Table 2 shows the numbers of embryos and plants obtained from 10 crosses. At the time of embryo excision, endosperm was scanty or absent except in some H. procerum x H. vulgare seeds. Progeny of H. vulgare x S. africanum and H. chilense x S. africanum, S. montanum and S. vavilo vii crosses were not vernalised and were still vegetative at the time of writing. All progeny

TABLE 2 JsIumbers offlorets pollinated, embryos cultured, plants obtained and their chromosome numbers in inter- specific combinations 2n chromosome number Florets Embryos Plants (no. of plants Combination pollinated cultured obtained in brackets) H. pusillum x I aestivum 44 4 2 28 (2) H. vulgare x S. africanum 283 73 26 14 (16) H. vulgare x H. murinum ssp. simulans 82 31 29 28 (26) 26 (1) H. murinum ssp. simulansxH. vulgare 20 7 2 28 (1) H. procerum x H. vulgare 126 26 18 28 (8) 21(4) 30 (2) H. chilense x S. cereale (2 lines) 101 46 7 14 (7) H. chilense x S. africanum 21 11 8 14 (8) H. chilense x S. montanum 62 18 5 14 (5) H. c/zilense x S. vavilovii 63 8 2 14 (2) H. jubatum ssp. breviaristatum x 44 4 1 21(1) S. africanum R102 tillered profusely and were vigorous except for H. vielgare x S. africanum hybrids, which were stunted and subviable, some H. murinum ssp. simulans hybrids which were subviable and H. pusillum x T. aestivum which tillered relatively sparsely. Hybrids were morphologically intermediate between parents, resembling more the parent with the higher chromosome number if parents differed in number. Voucher specimens are kept at the Plant Breeding Institute, Cambridge. Meiosis was irregular (see Results section iii) and pollen abortive and all anthers were indehiscent. Seedset on open pollination was nil.

(ii) Root tip chromosomes Table 2 gives the chromosome numbers of progeny of crosses. All karyotypes were clearly hybrid, except those of plants with 21 chromosomes from H. procerum x H. vulgare crosses which were probably haploid H. procerum. 204 R. A. FINCH AND M. D. BENNETT Most chromosomes in hybrids could not be identified as to except in Hordeum x Secale hybrids, where all the Secale chromosomes were distinctly larger than the Hordeum ones (fig. 1). In Hordeum x Secale hybrids, secondary constrictions at the nucleolar organisers were clearly visible in Hordeum chromosomes but not expressed in Secale chromosomes (fig. 1). However, nucleolar organiser constrictions of both parents were expressed in Hordeum x Hordeum and Hordeum x Triticum hybrids (table 3).

TABLE 3 Chromosome number (2n) and species (where known) of satellite chromosomes expressed in cells of parents and ,'zybrids No. of satellites (species in Hybrid (parent sat. nos. in brackets) (2n) brackets) H. pusillum (4) x T. aestivum (4) 28 4 (both parents) H. vulgare (4) x S. africanum (2) 14 2 (vulgare) H. vulgare (4) x H. murinum spp. simulans (8) 28 6 (probably both parents) H. procerum (6) x H. vulgare (4) 28 5 (both parents) 30 6 H. c/zilense (4) x S. cereale (2) 14 2 (chilense) H. hilense (4) x S. africanum (2) 14 2 (chilense) H. chjlen.se (4) x S. montanum (2) 14 2 (chilense) H. chilense (4) x S. caribou (2) 14 2 (chilense)

Aneuploid cells with one or two chromosomes above or below the euploid number were seen in all hybrid types except H. pusillum x T. aestitum which was stable, and H. chilense x S. vavilovii and H. jubaturn ssp. breviarista- turn x S. africanurn which were not scored.

(iii) Jvleiosis in hybrid pollen mother cells (pmc's) In hybrids, the chromosome number in many pmc's (euploid) was the sum of the parental gametic chromosome numbers. However, in most hybrids, some pmc's (hypoploid) had 21-25 per cent fewer, others (hyper- ploid) 4-52 per cent more, and a few (" approximately doubled ") 68-100 per cent more than the gametic sum. Table 4 gives the percentage fre- quencies and ranges of chromosome numbers of these different pmc types at metaphase I in hybrids. In nearly all hypoploid pmc's, all the chromo- somes behaved normally, but in hyperploid pmc's, some chromosomes were clumped together, often at the pmc periphery, or differently condensed from the others, or both (fig. 2). Approximately doubled pmc's arose spontaneously in the H. procerum hybrid (fig. 3) and occurred also in H. murinurn ssp. simulans hybrids (fig. 4). The H. murinum ssp. simulans hybrids were treated 7 months before fixation with 005 per cent colchicine in 15 per cent aqueous dimethyl sulfoxide for 10 hours at 20°C in an attempt to double their chromosome numbers. H. chilense x S. cereale and H. pusillum x T. aestivum were given the same treatment (but 3 and 8 months before fixation, respectively) without any apparent doubling effect in the shoots. Thus, doubled pmc's in H. murinum ssp. simulans hybrids probably also arose spontaneously as in the untreated H. procerum hybrid. Table 5 gives the mean chiasma and maximum bivalent frequencies in the pmc's included in table 4. The data in tables 4 and 5 are for single plants except for H. TABLE 4 .Wumbers ofpmc's and percentages ofdflerent types ofpmc in samplesfrom hybrids scored at metaphase I

Type of pmc1 ______t1 Not doubled

Hyperploid —, Approximately Some doubled Number Chromosomes chromosomes (chromosomes Hybrid ofpmc's Hypoploid Euploid normal abnormal normal) o 'Tj H. pusillumx T. aestivum 20 00 1000 (28) 00 00 00 H. c/zilensexS. cereale 40 00 1000 (14) 00 Q0 00 H. jubatum ssp. breviaristatumxS. africanum 30 00 667 (21) l67 (22-32) l33 (21) 00 H. vulgarexH. murinum ssp. .simulans 39 74.4 (22-27) 103 (28) lO3 (29-41) 26 (28) 26 (47) H. murinum ssp. simulansxH. vulgare 51 745 (21-27) 78 (28) 98 (29, 30) 20 (29) 59 (50-56) H. procerumxH. vulgare 21 810 (21-27) 95 (28) 48 (33) 00 48 (54) Chromosomenumbers in brackets. 2 Including one cell with 27 normal chromosomes and an unknown number of abnormal chromosomes. 206 R. A. FINCH AND M. D. BENNETT

chilense x S. cereale, where data for 20 pmc's from a hybrid from each S. cereale line are pooled. Meiotic chromosomes were identifiable as to species only in Secale hybrids, where all the Secale chromosomes were distinctly larger than others (figs. 2, 5 and 6). For example, in H. jubatum ssp. breviaristaturn x S. africanum, only the Hordeum chromosomes formed chiasmata at metaphase I (figs. 2 and 5). The chiasma frequencies in table 5 exclude numerous doubt- ful associations which were probably achiasmate. At metaphase I, all hybrids had many achiasmate pmc's (fig. 6) and chiasma frequencies were

TABLE 5 Mean c/ziasma and maximum bivalent and trivalent frequencies per MI pmc formed by normal chromosomes in different hybrid pmc types Type of pmc Not doubled -A- Hyperploid Some chromo- Approxi- Chromosomes somes mately Hypoploid Euploid normal abnormal doubled

Hybrid Xta. biv. Xta. biv. Xta. biv.triv. Xta.' biv. Xta. biv. H. pusillum x Y. aestivum — — 0000 — H.chilense x S. cereale — — 0.000 — — — — — — — H.jubatum ssp. breviarist. x — — 255 6 460 5 — 1O03 — — S.africanum H. vulgarexH. snurinum ssp. 1.59 5 250 4 600 13 — 3002 8'OO 8 simulans H. murinum ssp. simulansx 268 5 225 3 680 8 — 8'OO4 4633 28 H. vulgare H. procerumxH. vulgare 441 10 1'50 2 2700 13 1 — — 500027

1Innormal bivalents.

variable but generally low (fig. 7) except in hyperploid or approximately doubled pmc's which often had many closed bivalents (figs. 3 and 4). H. procerum x H. vulgare was particularly variable: at metaphase I, about 40 per cent of pmc's in this hybrid were achiasmate, but 10 and 13 bivalents (4 and 12 closed) occurred in two pmc's with 27 and 33 chromosomes, res- pectively. Rare associations of three chromosomes which may have been fully chiasmate were seen in this hybrid and in H. jubatum ssp. breviaristatum x S. africanum.

4. Discussioi (i) .New intergeneric and interspecific crosses Hordeum pusillum x Triticuin aestivum, H. chilense x Secale cereale, S. africanuin, S. montanum and S. vavilovii and H. jubatuin ssp. breviaristatum x S. africanum are new hybrids. Plants have not previously been reported from H. vulgare x H. murinum ssp. simulans though they have from the reciprocal (Barclay, NEW HYBRIDS OF HORDEUM 207 1976) and several workers have obtained plants from crosses between H. vulgare arid H. murinum at other ploidy levels (e.g. Barclay, 1976; Rajhathy et al., 1964). Descriptions of the H. vulgare x S. africanum karyotype and meiosis in hybrids of H. murinuin ssp. simulans and H. procerum with H. vulgare are also new. Hybrids of Hordeum with Triticum or Secale are becoming well known, but the highest production rates previously reported were 310 per cent of fiorets giving hybrids in H. vulgare x T. aestivum (Islam et al., 1976) and 7.7 per cent in H. vulgare x S. cereale (Thomas and Pickering, 1979). Our results of 4.55 per cent in H. pusillum x T. aestivum and a mean of 1051 per cent for Hordeum x Secale are a clear advance on these, and our success rates with Hordeum x Hordeum crosses also exceed those previously published (Barclay, 1976; Subrahmanyam, 1977). It is unclear whether this is due to the techniques or genotypes used, or even to some other unknown cause. Since H. chilense crosses so well with other species, it may contain a cross- ability gene or genes similar to those in T. aestivum cv. Chinese Spring (Snape et al., 1979). This possibility is being investigated using some of the above hybrids.

(ii) J"fuclear instability and chromosome elimination Variation in chromosome number occurred in 7 of 10 hybrid types (Results section 2) and in the pmc's of four of the six types seen at meiosis (table 4). Such nuclear instability is well known and may be general, at least in small degree, in interspecific hybrids within the Triticineae. Thus, variation in chromosome number was noted in roots or pmc's in reciprocal hybrids of H. nulgare with T. aestivum and I (Bates et al., 1974; Islam et al., 1976; Mujeeb et al., 1978) and in hybrids of H. vulgare, H. depressum and H. jubatum with S. cereale (Morrison and Rajhathy, 1959; Wagenaar, 1959; Kruse, 1969). Such nuclear instability may be an in- complete expression of the complete preferential chromosome elimination leading to haploid formation which occurs in many wide Hordeum crosses (e.g. Barclay, 1976; Subrahmanyam, 1977; Fedak, 1978).

(iii) IVleiotic pairing at metaphase I The present results broadly agree with those previously published for similar hybrids. We found no convincing evidence of chiasmata between Hordeum and Secale chromosomes and except in H. jubatum ssp. breviaristatum x S. africanum, where up to six bivalents were formed by H. jubatum chromo- somes, pairing was low in euploid pmc's (table 5). The interpretation of meiotic figures in low-pairing hybrid meiocytes is subjective since achiasmate figures intergrade in appearance with chiasmate ones. As we ignored all doubtful associations, the absence of chiasmata in our relatively small samples of pmc's of H. pusillum x T. aestivum and H. chilense x S. cereale agrees with the very low chiasma frequencies in non-doubled euploid pmc's reported in H. chilense x I aestivum (Martin and Chapman, 1977), H. vulgarex T. aestivum (Islam et al., 1976), T. durum (Mujeeb et al., 1978) and T. timopheevi (Cauderon et al., 1978), and T. timopheevi x H. bogdanii (Kimber and Sallee, 1976) and H. vulgarexS. cereale (Kruse, 1969). Wagenaar (1959, 1960) found about 56-94 chiasmata per cell in H. jubatum x S. cereale 208 R. A. FINCH AND M. D. BENNETT where below 2 per cent of associations were intergeneric. Rajhathy and Symko (1974) found a mean of 2.70 (maximum 5) bivalents (all rods) per pmc in haploid H. jubatum but did not give chiasma frequencies. Thus, this result probably agrees with the H. jubatum pairing in our hybrid and supports the conclusion of Starks and Tai (1974), which was based on H. jubatum x H. compressum and derivatives, that H. jubatum is a segmental allopolyploid with partial homology between its two types of genome. In non-doubled euploid pmc's of H. murinum and H. procerum hybrids with H. oulgare, maximum bivalent numbers per pmc were 4 and 2, respec- tively and mean chiasma frequencies were 250 or 225 and l50 (table 5). Such low frequencies either indicate great intergenomic differences within these hexaploid species and between them and H. vulgare or suggest suppres- sion of homoeologous pairing. Evidence from H. vulgare hybrids with H. parodii (Subrahmanyam, 1978), H. lechieri (Rajhathy and Symko, 1974) and other species (Rajhathy et al., 1964) suggests that the H. vulgare genome may depress homoeologous chiasma formation when homoeologous genomes are in hybrids instead of haploids. Both hypoploid and hyperploid pmc's showed higher chiasma frequencies than non-doubled euploid pmc's (table 5). This is probably due to duplication of homologues in hyperploid pmc's and perhaps also in hypoploid pmc's. However, if homoeologous pairing is suppressed in hexaploid Hordeum species by a "hemizygous ineffective" locus (Subrahmanyam, 1978) or one like the Ph locus (Riley and Chapman, 1958), elimination of relevant chromosomes may remove, or duplication of others overcome, the suppression of homoeologous pairing. This possibility, itself, justifies further study of the present inter- specific hybrids since removal of this obstacle may open the way for the transfer of genes between Hordeum, Triticum and Secale by meiotic recombina- tion.

5. REFERENCES BARCLAY, I. R. 1976. A study of the genetics and mechanism of genome and chromosome loss in cereals. Ph.D. Thesis, Camb. Univ., 149 pp. BATES, L. S., CAMPOS, V. A., RODRIGUEZ, R. E., AND ANDERSON, R. n. 1974. Progress towards novel cereal grains. Cereal Sci. Today, 19, 283-286. BENNETT, M. D., FINCH, K. A., AND BARCLAY, 5. R. 1976. The time, rate and mechanism of chromosome elimination in Hordeum hybrids. Chromosonm, 54, 175-200. CAUDERON, Y., TEMPLE, J., AND GAY, G. 1978. Creation et analyse cytogénetique d'un nouvel hybride Hordeuni vulgare ssp. distichon x Triticum tirnopheevi. C.r. hebd. Séanc. Acad. Sci., Paris D, 286, 1687-1690. DAVIES, D. K. 1960. The embryo culture of inter-specific hybrids of Hordeum. J'few Phytol., 59, 9-14. FEDAK, Cs. 1978. monoploids and hybrids from barley x rye crosses. In "Inter- specific hybridization in plant breeding ",eds.E. Sanchez-Monge and F. Garcia- Olmedo, pp. 269-273. Proc. 8th Eucarpia Cong. Madrid, 1977. FINCH, R. A., AND KA5HA, K. j.1976.Meiotic associations in barley lines with eight pairs of chromosomes and their haploids. Can. J. Genet. Cytol., 18, 753-761. FINCST, K. A. AND SIMPSON, E. 1978. Haploid production in barley. Rep. P1. Breed. Inst., 1977, 116-117. ISLAM, A. K. M. R., SHEPHERD, K. W., AND SPARROW, IS. H. B. 1976. Addition of individual barley chromosomes to wheat. In Barley Genetics III, ed. H. Gaul, pp. 260-270. Proc. 3rd mt. Barley Genet. Symp., Garching, 1975. Thiemig, Munchen. KAIHA, K. J., AND REINBEEGS, E. 1976. Haploidy and and its application in breeding techniques. In Barley Genetics III, ed. H. Gaul, pp. 307-3 15. Proc. 3rd mt. Barley Genet. Sy,np. Garching, 1975. Thiemig, Munchen. NEW HYBRIDS OF HORDEUM 209

KIMBER, C., AND SALLEE, i'. j. 1976. A hybrid between Triticum timopheevi and Hordeum bogdanii. Cereal Res. Communs, 4, 33-37. KRTJSE, A. 1969. Observations on some interspecific and intergeneric hybrids in Gramineae. Hereditas, 63, 459 (Abstr.). MARTIN, A., AND CHAPMAN, V. 1977. A hybrid between Hordeum chilense and Triticum aesti- mm. Cereal Res. Comrnuns, 5, 365-368. MILLER, T. E., AND CHAPMAN, V. 1976. Aneuhaploids in bread wheat. Genet. Res., 28, 37-45. MORRISON, J. W., AND RAJHATHY, T. 1959. Cytogenetic studies in the genus Hordeum. III. Pairing in some interspecific and intergeneric hybrids. Can. j. Genet. Cytol., 1, 65-77. MUJEEB, K. A., THOMAS, J. B., RODRIGUEZ, R., WATERS, R. F., AND BATES, L. s. 1978. Chromo- some instability in hybrids of Hordeum vulgare L. with Triticuni turgidum and T. aestivum. j. Hered., 69, 179-182. RAJHATHY, T., MORRISON, j. W., AND SVMKO, s. 1964. Interspecific and intergeneric hybrids in Hordeum. In Barley Genetics I, eds. S. Broekhuizen, G. Dantuma, H. Lamberts and W. Lange, pp. 195-213. 1st mt. Barley Genet. Symp., Wageningen, 1963. Cent. agric. Pubis. Documn, Wageningen. RAJHATHY, T., AND 5yMKO, s. 1974. High frequency of haploids from crosses of Hordeum lechieri (6x) x H. uulgare (2x) and H. jubatum (4x) x H. bulbosum (2x). Can. 3.Genet. C.ytol., 16, 468-472. RILEY, R., AND CHAPMAN, V. 1958. Genetic control of the cytologically diploid behaviour of hexaploid wheat. Nature (Lond.), 182, 713-715. RILEY, K., AND lUMBER, &. 1966. The transfer of alien genetic variation to wheat. Rep. Fl. Breed. Inst., 1964-65, 6-36. SNAPE, J. W., CHAPMAN, V., MOSS, J., aLANCHARD, C. K., AND MILLER, T. E. 1979. The cross- abilities of wheat varieties with Hordeum bulbosum. Heredity, 42, 291-298. 8TARKs, 0. D., AND TAS, w. 1974. Genome analysis of and H. compressum. Can. 3.Genet.Cytol., 16, 663-668. SUBRAHMANYAM, N. C. 1977. Haploidy from Hordeum interspecific crosses. 1. Polyhaploids of H. parodii and H. procerum. Theor. Appi. Genet., 49, 209-2 17. SUBRAHMANYAM, N. C. 1978. Meiosis in polyhaploid Hordeum: hemizygous ineffective con- trol of diploid-like behaviour in a hexaploid? Chroinosoma, 66, 185-192. SUBRAHMANYAM, N. C., AND KASHA, K. j. 1973. Selective chromosoinal elimination during haploid formation in barley following interspecific hybridization. Chromosoma, 42, 111-125. THOMAS, H. M., AND PICKERING, R. A. 1979. Barley x rye crosses. The morphology and cytology of the hybrids and the amphidiploids. 2. FfiZucht., 82, 193-200. WAGENAAR, E. a. 1959. Intergeneric hybrids between Hordeumjubatum L. and Secale cereale L. 3.Hered.,50, 194-202. WAGENAAR, E. B. 1960. The cytology of three hybrids involving Hordeum jubatum L.: the chiasma distributions and the occurrence of pseudo ring-bivalents in genetically induced asynapsis. Can. 3.Bot.,38, 69-85. Fin. 1 .—Hordeurz vulgare x Secale africanum (Karoo)—root tip metaphase with 7 JIordeum chromosomes (2 satellited) and 7 larger Secale chromosomes,

FIGS 2-7:metaphaseI pmc's Fin. 2.—H. jubatutn ssp. breviaristaturn x S. africanum—3 Hôrdeu,n bivalents (2 closed+ 1 open) -F 8 .Hordeum and 7 larger Secale univalents-1-- fragment (small arrow) -I- clumped chromosomes (large arrow). Fso. 3.—H. vulgare x H. procerum—2n =54pine (left) with 27 bivalents, some out of focus; 2n =28pmc (right) with 1 trivalent (double arrow) + 1 closed bivalent (arrow) + 23 univalents. Fin. 4.—H. rnurinam ssp. sirnulans xH.vulgare— 25 closed bivalents + univalent (arrow). Fin. 5.—H. jithatum ssp. bre'jiaristatum xS. ofricannm—6 open Herdewn bivalents-4- 2 Hordeuni and 7 larger Secale univalents. Fin. 6.— H. chilense x S. cereale (UC9O)—7 Hordeu'm-I-- 7 larger Secale univalents. Fin. 7.—H. vulgare x H. tnurinum ssp. sisnulans—4 bivalents (1 closed + 3 open) + 20 univalents. All figs at same magnification: bar =5sm. Plate I

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