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Title: EVIDENCE FOR THE INDEPENDENCE OF THE UR-4 (UP-2) AND UR-6 RUST RESISTANCE GENES

Author
item Stavely, J
item KELLY, J - MI STA UNIV E LANSING MI

Submitted to: Bean Improvement Cooperative Annual Report
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 8/15/1996
Publication Date: N/A
Citation: N/A

Interpretive Summary: The bean rust fungus causes disease epidemics that seriously reduce snap and dry bean production, resulting in losses to farmers, destabilizing markets, and increasing food costs to consumers. A few synthetic fungicides control rust, but control by plant resistance is more economical and environmentally favorable. The rust fungus has many pathogenic races (strains), differentiated by whether or not they cause disease on specific bean cultivars (varieties) that may or may not have genes for resistance to specific races. To determine relationships of two theoretically different genes for resistance, reactions were recorded from inoculations of certain races onto each of 187 second generation plants from crosses between plants having one of the resistance genes, Ur-4, but not a second gene, Ur-6, with plants having Ur-6, but not Ur-4. These 187 plants segregated, with many having Ur-4 and Ur-6; some with Ur-4, but without Ur-6; some with Ur-6, but without Ur-4; and a few with neither. The numbers of plants in each group have an excellent statistical fit to a 9:3:3:1 ratio, indicating independence of Ur-4 from Ur-6. Independence of these and other resistance genes will facilitate introducing combinations of them into cultivars by breeders to provide multiple gene resistance that will better protect against new races, improve production efficiency, and reduce losses for farmers, and provide more dependable and cheaper food for consumers.

Technical Abstract: Among genes tentatively or well defined that provide resistance to multiple races of the bean rust fungus, evidence for independence of Ur-4 from Ur-6 has been lacking. Among 83 races of the bean rust fungus, Uromyces appendiculatis, that have been identified and are maintained in storage at the Beltsville Agricultural Research Center, the Ur-4 gene is effective against 30, Ur-6 is effective against about 24, and both are effective against nine of this total of 54. An F2 population of 187 plants from crosses between plants containing either one or the other, but not both of theses genes, were inoculated with each of several specififc races of U. appendiculatus to detect each gene. The F2 plants segregated into a 9:3:3:1 ratio with a probability of 0.58. These results indicate independence of Ur-4 from Ur-6. When combined with other defined genes effective against many or all races, Ur-4 and Ur-6 will be useful in providing multiple gene rust resistance in bean.