Crosses between H. vulgare cv. Vada and two genotypes of tetraploid H. bulbosum, produced after colchicine treatment of diploid H. bulbosum, have been described previously (Pickering, 1987). Over 80 triploid hybrids, denoted VBcBc, have since been obtained from these crosses, combining 7 chromosomes from H. vulgare (male) and 14 from autotetraploid H. bulbosum (female). The barley cultivars used were Emir, Golden Promise, Vada, and the homozygous male sterile lines of Domen and Vada (stock nos. 15 and 440 respectively, both with indehiscent anthers). The autotetraploid H. bulbosum genotypes used were Cb 2920/4/Colch, Cb2929/l/Colch and selections from the cross between them (27/n). Emir and Golden Promise were also pollinated with several accessions of wild tetraploid H. bulbosum collected by the author on the Greek islands of Crete and Tinos. The hybrids from these crosses will be referred to as VB+B+.
Many of the plants from crosses involving Cb 2929/1/Colch and 27/n as pollinator were stunted and chlorotic. Their anthers were either indehiscent or a mixture of dehiscent and indehiscent on the same spike. All the vigorous VBcBc hybrids involving Cb 2920/4/Colch possessed fully dehiscent anthers, including those which had the male sterile gene from Domen and Vada. This was contrary to expectations as most VBB hybrids have previously been reported as being completely sterile (Davies, 1960; Kasha and Sadasivaiah, 1971; Lange, 1971; Morrison and Rajhathy, 1950). Konzak et al. (1951) did however observe anther dehiscence in one VBB hybi7id-with up to 23% stainable pollen. It was surprising therefore to find that of the VB+B+ hybrids examined, 14 had dehiscent anthers, 41 indehiscent and 14 had both dehiscent and indehiscent anthers on the same spike. Meiosis in 20-25 pollen mother cells (PMCs) of the 64 VBcBc hybrids analyzed so far, correspond to results already published (loc.cit.) with trivalents at MI ranging from 0.35 to 2.44 per cell (Table 1). An anther from one anomalous VBB derived from Golden Promise x Cb 2929/l/Colch contained two distinct types of PMCs. One of these had the expected chromosome configurations of a VBB (4.95 1, 4.90 11, 1.70 111) whereas in the other type of PMC seven divalents were regularly observed. From these preliminary data it appears that VBcBc hybrids with Cb 2920/4/Colch as pollinator are more vigorous, stable and fertile and tend to form a greater number of trivalents at MI than Cb 2929/l/Colch as male parent, although the differences were not significant. Hybrids derived from crosses using Golden Promise as female parent possessed significantly more trivalents than hybrids from Emir (P=0.05).
Potential pollen germinability was assessed by means of the FCR test (Heslop-Harrison et al. 1984) and results are presented in Table 2. It appears that even hybrids with mainly indehiscent anthers possess germinable pollen. These data were supported by results from crosses using the various VBB hybrids (Table 3). VBcBc and VB+B+ hybrids with fully dehiscent anthers both gave similar proportions of seed sets when used as pollinator. When it was possible to collect small amounts of pollen from VB+B+ hybrids with mixed anther dehiscence and the pollen used on H. vulgare spikes, seed sets were markedly reduced. Occasional seeds were obtained by selfing the VBcBc plants, but so far not from any VB+B+ hybrids.
Endosperm of developing seeds from these crosses were solid or watery. Plants were either regenerated directly from embryos on B5 medium (without 2,4-D) or via a callus phase on B5 + 2 mg/1 2,4-D prior to subculture on B5 without hormones. VBB hybrids involving Emir and especially Golden Promise, should be more useful for regenerating plants from calli as these cultivars are known to respond well in tissue culture experiments using both diploid (Luhrs and Lorz 1987) and haploid embryos (Pickering and Morgan, 1984, 1985).
Somatic chromosome counts on progeny from barley × VBcBc were mostly 7 and 14 or ca. 21 chromosomes. Those from selfed sVBcBc ranged from 14-35 chromosomes. Several of the fertile 14 chromosome progeny resembling H. vulgare have been assessed in the field but so far without any sign of gene transfer from H. bulbosum. One interesting plant from H. vulgare. × VBcBc resembled that described by Finch (1983) both morphologically and cytologically. Most of the tip cells analyzed contained 13 chromosomes and a telocentric chromosome (possibly 6S). 50 PMCs from one spike regularly formed 6 ring bivalents with 1 heteromorphic rod. In PMCs from three other spikes, a ring quadrivalent was frequently observed with either 4 ring bivalents and the heteromorphic rod or 5 ring bivalents. The plant crossed fairly readily with barley and has also set over 50 seeds which are being screened.
It is hoped that the VBB hybrids may be more useful for the transfer of disease resistance from H. bulbosum to H. vulgare than the fertile VVBB hybrids, from which very few recombinants between H. vulgare and H. bulbosum have been identified. Trivalents in VBB hybrids have been shown to be formed from the pairing of BBV chromosomes (Xu and Snape, 1988) and as there is only one barley genome in the VBB hybrids, chromosome pairing between the two species may well be greater than in the VVBB hybrids in which intragenomic chromosome pairing is likely to be favored. Future work will be concentrated on crossing VBcBc as female to avoid possible certation effects when these hybrids are used as pollinators.
Acknowledgement: I am very grateful to Professor E. A. Hockett, Montana State University, Bozeman, U.S.A. for supplying me with seed of the two male sterile stocks, and Mr. W. Rennie for technical assistance.
References:
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Finch, R. A. 1983. Deficiency of 6L in diploid barley. Barley Genetics Newsletter 13:2-3.
Heslop-Harrison, J., Y. Heslop-Harrison and K. R. Shivanna. 1984. The evaluation of pollen quality, and a further appraisal of the fluorochromatic (FCR) test procedure. Theor. Appl. Genet. 167:367-375.
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