II. 10. Meiotic behavior of a barley-rye hybrid.
George Fedak, Ottawa Research Station, Central Experimental Farm, Ottawa, Ontario K1A 0C6, Canada. "R"
Many attempts have been made to hybridize rye with barley in many laboratories without much success. The failures are apparently due to incompatibility systems which prevent the formation of hybrid embryos. The post-pollination application of GA has apparently helped to overcome the incompatibility systems so that hybrid embryos are recovered. Several hundred hybrid seedlings have been produced in our laboratory to date but all have turned chlorotic and died at either the early seedling stage or late after producing only aborted spikes. In our most recent attempt 3363 florets of six different 2-rowed spring diploid cultivars were pollinated with Petkus rye.
Fifty-five hybrid seedlings were obtained, two with a chromosome number of 2n = 15 and the remainder with the expected numbers of 2n = 14. In somatic cells of the hybrid, the chromosomes of both species could be identified by differences in size with chromosomes of the rye genome being significantly larger. The nucleolar organizers (N.O.) of barley chromosome 6 and 7 were clearly visible (Figure 1) but the rye N.O. appeared to be suppressed. The same phenomenon was observed at diakinesis of meiotic cells where virtually all cells contained only one nucleolus and in 78% of these cells only two small chromosomes, presumably those of barley were associated with it (Figure 2). In the remaining cells only one chromosome was associated with the nucleolus. Since both parental species contain N.O. chromosomes, evidently in the hybrid the expression of one species (rye) was being suppressed by the other (barley).
Figure 1. Somatic chromosomes of barley-rye hybrid.
Figure 2. Fourteen univalent chromosomes at diakinesis
in the barley-rye hybrid.
A study of the meiotic behavior of chromosomes in the hybrid revealed a minimal amount of chromosome pairing. The majority of chromosomes in meiotic cells remained unpaired as univalents and only an average of .18 bivalents and .02 trivalents per cell was found to give an average chiasma frequency of .22. Heteromorphic bivalents would have revealed pairing between barley and rye chromosomes but none were observed. The lack of pairing between chromosomes of the two species indicates either a lack of homology between them or the existence of meiotic pairing control genes. The study of only one hybrid plant makes it difficult to choose between the two alternatives.
