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Title: A new Colletotrichum trifolii race identified in Ohio

Author
item Ariss, Jennifer
item RHODES, L - OHIO STATE UNIVERSITY

Submitted to: North American Alfalfa Improvement Conference
Publication Type: Proceedings
Publication Acceptance Date: 7/16/2006
Publication Date: 7/16/2006
Citation: Jennifer J. Ariss and Landon H. Rhodes. 2006. A new Colletotrichum trifolii race identified in Ohio. In Proceedings of the joint meeting of the 40th North American Alfalfa Improvement Conference and 19th Trifolium Conference. July 16-19, 2006, Bloomington, MN.

Interpretive Summary:

Technical Abstract: Anthracnose of alfalfa was identified as a potential economic problem on alfalfa in the US in the late 1960's. Colletotrichum trifolii, the causal agent of anthracnose of alfalfa, exists in the US as two distinct races, race 1 and race 2. Anthracnose disease management relies solely on the use of resistant cultivars with resistance being conferred by two separate genetic mechanisms. Two separate dominant genes, designated An1 and An2, are attributed to anthracnose resistance. Presence of the An1 gene confers resistance to race 1 while An2 confers resistance to races 1 and 2 but may mask the presence of the An1 gene. The purpose of the present study was to investigate an isolate of C. trifolii (isolate OH-WA-520) found in Columbus, Ohio, atypical of either race 1 or 2. Macroscopic and microscopic morphological characters were evaluated and compared to known race 1 and race 2 isolates. Experiments were undertaken to determine the race identity of C. trifolii isolate OH-WA-520 and relative levels of resistance in the standard check cultivars, Arc, Saranac AR, and Saranac to this isolate. Results of these studies revealed a reaction inconsistent with either C. trifolii race 1 or race 2. C. trifolii OH-WA-520 proved virulent on cultivars Saranac and Saranac AR but avirulent on Arc. These results are consistent with C. trifolii race 4 previously known only from Australia. To our knowledge, this is the first report in the US of an isolate consistent in reaction with Colletotrichum trifolii race 4 in the US.