Genetics of Resistance toUromyces phaseoliin aPhaseolus vulgarisLine Resistant to Most Races of the Pathogen

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Abstract
Tests of F1, F2 and F3 progeny from crosses of the rust-resistant bean (P. vulgaris) breeding line B-190 with the moderately susceptible snap bean cultivar Green Giant 447 to each of 8 races of U. phaseoli, applied simultaneously, indicated that the resistance to each race was controlled by a monogenic dominant gene. For 7 of these races, resistance (R) in B-190 was expressed as a limitation of uredinium size to < 0.3 mm in diameter. To the 8th race, B-190 had high resistance (HR), in which small necrotic spots, containing no urediniospores, were the only visible symptom; a single gene also governed the response of B-190 to this race. Two of the seven R genes apparently were allelic, but evidence was obtained that the rest of the R genes and HR gene were closely linked to one another. The tested monogenic R genes in B-190 were independent of the dominant single genes conditioning R or HR in the pinto cv. Olathe. The genes in ''Olathe'' that conditioned the HR reaction against 3 races were closely linked to one another and epistatic to the genes that conditioned R against the same races in B-190. B-190 and ''Olathe'' each had a single dominant gene for the R reaction to races to which one was resistant and the other susceptible. B-190 and its parent, Mexico 309, have many genes for rust resistance but probably only one for each of the races tested to which they were resistant or highly resistant. Implications of these results for breeding rust-resistant beans are discussed.