DOMINANT RESISTANCE TO BARLEY POWDERY MILDEW RACE-D1, ISOLATED AFTER MUTAGEN TREATMENTS IN 4 HIGHBRED BARLEY VARIETIES

After treatments with ionizing radiations and chemicals in the commercial barley varieties 'Bonus', 'Mari', 'Pallas', and 'Kristina', 43 lines with dominant resistance to the mildew race D1 were isolated, 34 in infection tests on M3 seedlings from M2 spikes, and 9 as resistant M2 seedlings from M1 spikes. Genetical analyses of these dominant resistant lines included crosses to susceptible material, crosses to the ml-o variety 'Refoma', crosses among the lines, crosses to sources of known dominant resistance genes, and tests to a panel of 30 different races of barley powdery mildew. In the panel tests, 27 among the lines showed resistance spectra similar or identical to Ml-a7, Ml-a9, Ml-a12, Ml-a13, Ml-a3 + Tu2 in Sv 57/510-44, Ml-g, and Ml-(La), whereas the remaining 16 lines formed 12 groups showing new spectra of resistance. The genetical analyses of F2 and F3 data from crosses indicate that the majority of the 43 lines are due to a restricted chromosomal segment in or close to the Ml-a region. There is ample evidence that the vast majority of the isolated dominant lines represent genuine mutations. Mutation breeding is suggested to offer a convenient way to introduce into the genome a tightly linked new dominant resistance gene, and so to create complex building-stones for further use in conventional combination breeding.