CYTOLOGICAL AND MOLECULAR CHARACTERIZATION OF A TRITICUM-AESTIVUM X LOPHOPYRUM-PONTICUM BACKCROSS DERIVATIVE RESISTANT TO BARLEY YELLOW DWARF

Barley yellow dwarf is the most damaging virus-caused disease in bread wheat (Triticum aestivum L.). A resistant line, SW(3)35.1.2-13-11-1-5 (2n = 47), derived from a cross of T. aestivum X Lophopyrum ponticum was characterized by meiotic chromosome pairing, by in situ DNA hybrid ization and by expression of molecular markers to determine its chromo some constitution. All progeny of this line had three pairs of L. pont icum chromosomes from homoeologous chromosome groups 3, 5, and 6 and t he 2n = 47 progeny had an additional L. ponticum monosome. The pairs f rom groups 3 and 6 were in the added state, while the group 5 pair was substituted for wheat chromosome 5D. Several wheat-wheat translocatio ns with respect to the parental wheat genotype occurred in this line, presumably owing to the promotion of homoeologous chromosome pairing b y L. ponticum chromosomes. It was hypothesized that homoeologous recom bination results in homoeologous duplication-deletions in wheat chromo somes. An aberrant 3:1 disjunction creates the potential at each meios is for replacement of these wheat chromosomes by homoeologous L. ponti cum chromosomes. Wheat chromosomes 3A and 6A appeared to be in interme diate stages of this substitution process.