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Genetics

Genetics of Resistance to Uromyces phaseoli in a Phaseolus vulgaris Line Resistant to Most Races of the Pathogen. J. R. Stavely, Research plant pathologist, Plant Pathology Laboratory, Plant Protection Institute, Agricultural Research Service, U.S. Department of Agriculture, Beltsville, MD 20705; Phytopathology 74:339-344. Accepted for publication 11 October 1983. This article is in the public domain and not copyrightable. It may be freely reprinted with customary crediting of the source. The American Phytopathological Society, 1984. DOI: 10.1094/Phyto-74-339.

Tests of F₁, F₂, and F₃ progeny from crosses of the rust-resistant bean (Phaseolus vulgaris) breeding line B-190 with the moderately susceptible snap bean cultivar Green Giant 447 to each of eight races of Uromyces phaseoli, applied simultaneously, indicated that the resistance to each race was controlled by a monogenic dominant gene. For seven of these races, resistance (R) in B-190 was expressed as a limitation of uredinium size to less than 0.3 mm in diameter. To the eighth 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 appeared to be allelic, but evidence was obtained that the rest of the R genes and the 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 cultivar Olathe. The genes in Olathe that conditioned the HR reaction against three 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.