Crosses between barley and Hordeum bulbosum have been carried out by many research groups, first, to obtain doubled haploids for breeding purposes and genetical analysis (e.g. Simpson and Snape, 1981; Snape and Simpson, 1981), and secondly, to attempt to introduce 'useful' variation from H. bulbosum into the cultivated species (e.g., Lange and Jochemsen, 1975; Pickering, 1980). To date this latter approach has been largely unsuccessful. In a further attempt to introgress H. bulbosum variation into barley we have commenced a programme of hybridization between barley and diploid clones of H. bulbosum previously identified as producing a high frequency of hybrid progeny (Simpson et. al., 1980), and tetraploid clones identified as having a high crossability with wheat (Sitch and Snape, 1986).
In initial studies four barley varieties were used as female parents; Su Pie, a chinese cultivar, and the European spring barleys Marion, Triumph and Sabarlis. As male parents we used the diploid clones PB1 (J. Jensen clone 51-44), PB8 (W. Lange clone HB2032), PB11 (W. Lange clone HB2082), and tetraploid clones PB168 and PB179 (Sitch and Snape, 1986). Previous experiments have shown that PB8 and PB11 produce about 50% hybrid and 50% haploid progenies in crosses with barley. The crossing procedures and embryo culture techniques of Simpson and Snape (1981) were used with the exception that two sprays of gibberellic acid (75 ppm) were applied at 24 hr amd 48 hr after pollination. Approximately 200 florets were pollinated per cross combination.
The crossabilities of the four barley varieties with the five H. bulbosum genotypes are shown in Table 1, together with the frequencies of grains obtained and the frequencies of grains that contained embryos.
Although there were barley variety × H. bulbosum clone interactions some clear patterns emerge from these data. First, as has been found in previous studies both barley varieties and H. bulbosum genotypes possess variation for gene controlling crossability in this interspecific cross. In these studies Sabarlis was the superior barley genotype for seed set with all clones but the differences between the other varieties and clones depended on the particular combination. Amongst the H. bulbosum genotypes PB1 was
Overall there was no significant difference between the mean crossabilities of the diploid and tetraploid clones although there were ploidy x variety interactions. Thus these data do not suggest that an increase in ploidy per se increases crossability in this interspecific cross but rather, it depends on an interaction between the genotypes of the two species regardless of ploidy. However, it does appear that there is an increase in the frequency of embryo development with ploidy. Since these progenies have not yet been examined cytologically it is not clear if this is associated with differences in the frequencies of hybrid and haploid progenies. Nevertheless, clone PB179 gave the highest overall frequency of culturable embryos and it was noticeable that grains from crosses with 4x genotypes often had normally developed embryos and contained a little residual endosperm whilst grains from crosses with 2x genotypes had smaller embryos and no endosperm.
There was no correlation between the frequencies of grains set and the frequencies of grains that contained embryos (r=-0.09) although both characters showed genotypic variation. This suggests that they appear to be under independent genetic control.
Acknowledgements:
The senior author is grateful to the British Council for a Technical Cooperation Training Award.
References:
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