First and third authors: Department of Crop and Soil Sciences; and second author: Department of Botany and Plant Pathology, Michigan State University, East Lansing 48824
Isolates of Colletotrichum lindemuthianum (138 total) from Argentina, Brazil, the Dominican Republic, Honduras, Mexico, and the United States were characterized into 41 races based on virulence to 12 differential cultivars of Phaseolus vulgaris. These 41 races were categorized into two groups: those found over a wide geographic area and those restricted to a single country. Races 7, 65, and 73 were widespread. Race 73 was the most common (28%). Race 7 was found once in Argentina and Mexico but at a higher frequency in the United States. Race 65 was found repeatedly in Brazil and the United States. Although 39% of the races were detected repeatedly and three races were widespread, no race was isolated from both P. vulgaris gene pools. Phenetic analyses showed no obvious patterns correlated with virulence clusters. No geographic pattern was evident. Molecular polymorphism generated by random amplified polymorphic DNA confirmed the extensive variability in virulence of C. lindemuthianum. Virulence phenotypes were grouped into 15 clusters. The two largest clusters contained isolates from all the geographic regions sampled. Molecular polymorphism was observed among isolates from races 65 and 73 within and among countries, except among Bra-zilian isolates of race 65. The genetic diversity of C. lindemuthianum was greatest in Mexico and Honduras. Our data suggest that C. lindemuthianum may not be highly structured to specific Phaseolus gene pools.