MOLECULAR CYTOGENETIC ANALYSIS OF DURUM-WHEAT X TRITORDEUM HYBRIDS

Southern and in situ hybridization were used to examine the chromosome constitution, genomic relationships, repetitive DNA sequences, and nu clear architecture in durum wheat x tritordeum hybrids (2n = 5x = 35), where tritordeum is the fertile amphiploid (2n = 6x = 42) between Hor deum chilense and durum wheal. Using in situ hybridization, H. chilens e total genomic DNA hybridized strongly to the H. chilense chromosomes and weakly to the wheat chromosomes, which showed some strongly label led bands. pHcKB6, a cloned repetitive sequence isolated from H. chile nse, enabled the unequivocal identification of each H. chilense chromo some at metaphase. Analysis of chromosome disposition in prophase nucl ei. using the same probes. showed that the chromosomes of H. chilense origin were in individual domains with only limited intermixing with c hromosomes of wheat origin. Six major sites of 18S-26S rDNA genes were detected on the chromosomes of the hybrids. Hybridization to Southern transfers of restriction enzyme digests using genomic DNA showed some variants of tandem repeats, perhaps owing to methylation. Both techni ques gave complementary information, extending that available from phe notypic, chromosome morphology, or isozyme analysis, and perhaps are u seful for following chromosomes or chromosome segments during further crossing of the lines in plant breeding programs.