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Hierarchical Analysis of Diversity, Selfing, and Genetic Differentiation in Populations of the Oomycete Aphanomyces euteiches

First author: Horticultural Crops Research Laboratory, U.S. Department of Agriculture-Agricultural Research Service and Department of Botany and Plant Pathology, Oregon State University, 3420 NW Orchard Ave., Corvallis 97330; and second author: Irrigated Agriculture Research and Extension Center, Washington State University, 24106 North Bunn Rd., Prosser 99350

Relatively little is known about the population biology of the legume pathogen Aphanomyces euteiches. A. euteiches is a soilborne pathogen causing Aphanomyces root rot of several legumes, including alfalfa, bean, lentil, and pea. Our objectives were to assess the degree of diversity, selfing, and population differentiation in A. euteiches. We contrasted populations within and among two geographically separated fields with a history of pea production. Molecular genotyping relied on amplified fragment length polymorphism analysis. Samples of A. euteiches recovered from two fields in northeast Oregon and western Washington confirmed previous reports of moderately high genetic diversity in populations of A. euteiches at the regional scale, but revealed higher-than-expected genotypic diversity within individual soil samples. Populations of A. euteiches were significantly differentiated at the soil sample, field, and regional level. The population structure appears to be patterned by regular selfing via oospores, a mixed reproductive system including both asexual and sexual reproduction, with occasional migration of novel genotypes or outcrossing.

Additional keyword: recombination.