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Title: Reaction of common bean cultivars to the Asian soybean rust pathogen, Phakopsora pachyrhizi, under field conditions in South Africa and Brazil.

Author
item Pastor Corrales, Marcial - Talo
item LIEBENBERG, M - ARC-SOUTH AFRICA
item SARTORATO, ALOISIO - EMBRAPA-BRAZIL
item ARRAES-PEREIRA, P - EMBRAPA-LABEX,OIP,USDA

Submitted to: Bean Improvement Cooperative Proceedings
Publication Type: Trade Journal
Publication Acceptance Date: 12/30/2007
Publication Date: 12/30/2007
Citation: Pastor Corrales, M.A., Liebenberg, M.M., Sartorato, A., Arraes-Pereira, P.A. 2007. Reaction of common bean cultivars to the Asian soybean rust pathogen, Phakopsora pachyrhizi, under field conditions in South Africa and Brazil. . Bean Improvement Cooperative Proceedings. 50:123-124.

Interpretive Summary: The Asian soybean rust (ASR) disease is very severe in Brazil and South Africa. Although ASR also affects common beans, there are no reports indicating whether ASR can cause major yield losses on dry beans. We planted a group of selected dry beans next to soybeans under field conditions in South Africa and Brazil. While in Brazil, the soybeans developed severe ASR symptoms, several common bean cultivars had no visible ASR symptoms while the other dry beans had very mild symptoms. In South Africa, soybeans had also severe ASR symptoms about 70 days after planting while the common bean cultivars only had mild symptoms. Near the end of the growing season, the soybeans were completely defoliated prematurely by the ASR pathogen but only a low infection was observed on the dry beans. The mild ASR symptoms observed on dry beans contrasted with the severe symptoms on soybeans in Brazil and South Africa and suggest that under field conditions dry beans are much less susceptible to ASR than soybeans. More research needs to be done to confirm these initial results. This is the first report of the reaction of common bean cultivars to the ASR pathogen under field conditions in any country. Scientists, particularly plant pathologists from universities, experiment stations and private industry will benefit from this knowledge.

Technical Abstract: Phakopsora pachyrhizi, the Asian soybean rust (ASR) pathogen, infects soybeans (Glycine max) and some 95 other leguminous species, including dry and snap beans (Phaseolus vulgaris). This pathogen has been reported infecting dry beans under field conditions in South Africa and the United States in 2005 and 2006, respectively. However, there are no reports indicating whether P. pachyrhizi occurs in most common bean cultivars under field conditions and whether the ASR pathogen can cause major yield losses on dry beans. We evaluated the reaction of selected common bean cultivars to the ASR pathogen under field conditions in Brazil and South Africa. In Brazil, the trials were planted in Goiania and Rio Verde in the state of Goias. In South Africa, the trial was planted at the Cedara Agricultural Research Station in KwaZulu-Natal. In Brazil, soybeans developed severe ASR symptoms; 70 % average severity in Goiania and 60 % in Rio Verde. In both locations, the common bean cultivars Aurora, CNC, and PI 181996 had no visible ASR symptoms, while the other cultivars had very mild symptoms. In South Africa, soybeans had also severe ASR symptoms about 70 days after planting while most common bean cultivars had isolated pustules on the foliage. By April, the soybeans were completely defoliated prematurely while only low infection was observed on the lower leaves of most common beans planted adjacent to the heavily infected soybeans. The mild ASR symptoms on common beans in South Africa and Brazil compared to the severe symptoms on soybeans suggest that common beans are much less susceptible to ASR than soybeans. More research needs to be done to confirm these initial results.