Evidence of gene flow between pea and bean pathotypes of Aphanomyces euteiches.

Abstract

Aphanomyces euteiches is a phenotypically diverse pathogen, but the origins of this diversity are not known. To determine if cross-fertilization occurred between pea and bean pathotypes of A. euteiches, a technique to outcross isolates of A. euteiches was developed. Random amplified polymorphic DNA (RAPD) markers and several phenotypic traits were used to identify F, hybrids. Following 16 matings among isolates of different pathotypes, 4 of 82 germinated oospore isolates were inter-pathotype F, hybrids. Two of the four hybrids were infertile, but two were fertile and used to analyze the inheritance of virulence phenotype, host specificity (pathotype), hyphal growth rate, size of the aplerotic zone, and RAPD markers. As compared with parental pea and bean pathotype isolates, F, hybrids exhibited a pea pathotype and intermediate phenotypes in hyphal growth rate and size of the aplerotic zone. Subsequent self-fertilization of F1 hybrids yielded an F2 population that demonstrated segregation of virulence phenotypes, host specificity, hyphal growth rate, and RAPD markers. The results suggest that this diploid homothallic oomycete is capable of outcrossing and that sexual reproduction may play an important role in the generation of phenotypic variation.