Author
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Stavely, J |
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Submitted to: Bean Improvement Cooperative Annual Report
Publication Type: Peer Reviewed Journal Publication Acceptance Date: 5/7/1999 Publication Date: N/A Citation: N/A Interpretive Summary: Epidemics in crops of edible snap and dry beans, caused by the bean rust fungus, result in serious losses in production, losses to farmers, synthetic fungicide usage, market instability, and consumer price increases in many bean production areas, including central Africa. Effective rust resistance is the most economically and environmentally preferable control for bean rust, but the great variability of the rust pathogen makes resistance that will remain effective over distance and time hard to achieve. Considerable acreages of snap beans are produced in central Africa for fresh shipment to Europe from areas where rust is a major problem. In late 1997 and early 1998, rusted snap bean leaves from the central African production areas of Kenya, Zambia, and Zimbabwe were sent to Beltsville for determination of pathogenic race composition. Seven pathogenic races of the rust fungus were identified from these collections. .These seven included four previously identified races and three not previously found in rust collections from anywhere. Several of these races, especially two, races 110 and 111, produced susceptible rust reactions on many of the differential cultivars used for race identification. However, the rust resistant plant introductions and Mexico 309 were resistant to all seven races. Identification of additional pathogenic races of the rust fungus and resistances effective against them will facilitate development of stable resistant cultivars for central Africa, the United States and elsewhere by breeders to reduce losses, and fungicide use by farmers and stabilize food supply for consumers. Technical Abstract: Seven collections of rusted leaves from snap bean plants having viable urediniospores of the bean rust fungal pathogen, Uromyces appendiculatus, were received at Beltsville from Kenya, Zambia, and Zimbabwe during the winter of 1997-98. Following urediniospore increases, each of the collections was inoculated onto each of the 19 bean cultivars used for differentiation of pathogenic races of this fungus and five of the rust resistant plant introductions used in developing rust resistant germplasm. Seven pathogenic races of U. appendiculatus were purified and identified from these collections. One collection from Zimbabwe contained a mixture of three races, but the others had little or no such mixture. The identified races included four previously identified and three new races. Several of the seven races had a wide host range of susceptibility on the differential cultivars, but the five resistant plant introductions, Mexico 309, and a few other cultivars were resistant to all seven races. Race 90, originally identified earlier from Egypt, was the sole race in two of the evaluted collections. |
