Inheritance of resistance to Hawaiian bean rust (Uromyces appendiculatus (Pers. ex Pers.) Unger var. appendiculatus) in common beans (Phaseolus vulgaris L.)

Abstract

Bean rust, as caused by Uromyces appendiculatus (pers. ex Pers.) Unger var. appendiculatus, is a major fungal disease affecting common beans (Phaseolus vulgaris L.) in many tropical and sub-tropical regions of the world. One major characteristic of the fungal pathogen is its high degree of pathogenic variability with over a hundred races identified worldwide. In this study, four different races of bean rust were identified from isolates collected from several locations based on the reactions of a set of nineteen differential bean cultivars. The inheritance of resistance to the bean rust pathogen was studied using eight of the differentials that showed resistance to one, two, or all of the four rust races, four of the differentials that were susceptible to all four races, two Hawaiian cultivars, and five 'slow rusting' cultivars. Disease inoculation was done with a standardized spore inoculum, and evaluations were made in a greenhouse. Pustules were rated 15 days later on a scale of 1 to 6 based on size. Individual plants were classified on the predominance of pustules of different sizes. Dominant genes were identified that caused a hypersensitive reaction (but accompanied by pustules also) to two races (called HR1andHR2) and that caused a resistant reaction (small pustules only) to all four races (called R1, R2, R3, and R4). There were at least two different R1 genes, at least three different R2 genes, at least two different R3 genes, and at least three different R4 genes. The HR genes were epistatic to the R genes. Actopan x Sanilac37 had HR genes for races H1 and H2. Ecuador 299, NEP-2, and Mexico 235 had an HR gene for race H1 only. These parents and Mexico 309 and Compuesto Negro Chimaltenango had R genes for all the races for which they did not have an HR gene. CSW643 had R genes for races H2 and H4. Kentucky Wonder 765 and Royal Red had R genes for race H2 only. All 12 genes identified in all the resistant parents seemed linked into one gene complex, although crossing over (usually < 10%) was observed between genes for resistance to different races as well as between different genes for resistance to the same race.