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

Aphanomyces enteiches is a phenotypically diverse pathogen, but the origins of this diversity are not known. To determine if cross-fertilization occur red between pea and bean pathotypes of A. euteiches, a technique to outcros s isolates of A. euteiches was developed. Random amplified polymorphic DNA (RAPD) markers and several phenotypic traits were used to identify F-1 hybr ids. Following 16 matings among isolates of different pathotypes, 4 of 82 g erminated oospore isolates were inter-pathotype F-1 hybrids. Two of the fou r hybrids were infertile, but two were fertile and used to analyze the inhe ritance of virulence phenotype, host specificity (pathotype), hyphal growth rate, size of the aplerotic zone, and RAPD markers. As compared with paren tal pea and bean pathotype isolates, F-1 hybrids exhibited a pea pathotype and intermediate phenotypes in hyphal growth rate and size of the aplerotic zone. Subsequent self-fertilization of F-1 hybrids yielded an F-2 populati on that demonstrated segregation of virulence phenotypes, host specificity, hyphal growth rate, and RAPD markers. The results suggest that this diploi d homothallic oomycete is capable of outcrossing and that sexual reproducti on may play an important role in the generation of phenotypic variation.