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 nuclear architecture in durum wheat x tritordeum hybrids (2n = 5x = 35), where tritordeum is the fertile amphiploid (2n = 6x = 42) between Hordeum chilense and durum wheat. Using in situ hybridization, H. chilense total genomic DNA hybridized strongly to the H. chilense chromosomes and weakly to the wheat chromosomes, which showed some strongly labelled bands. pHcKB6, a cloned repetitive sequence isolated from H. chilense, enabled the unequivocal identification of each H. chilense chromosome at metaphase. Analysis of chromosome disposition in prophase nuclei, using the same probes, showed that the chromosomes of H. chilense origin were in individual domains with only limited intermixing with chromosomes 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 techniques gave complementary information, extending that available from phenotypic, chromosome morphology, or isozyme analysis, and perhaps are useful for following chromosomes or chromosome segments during further crossing of the lines in plant breeding programs.