CHARACTERIZATION OF APHANOMYCES-EUTEICHES STRAINS BASED ON PATHOGENICITY TESTS AND RANDOM AMPLIFIED POLYMORPHIC DNA ANALYSES

Genotypic variation among 62 strains of Aphanomyces euteiches, four of A. cochlioides, and a Saprolegnia sp. was investigated using RAPD ana lysis. Pathogenicity assays on pea, bean, alfalfa, red clover, and sug arbeet were used to determine host preference among the strains of A. euteiches and A. cochlioides. Pathogenicity tests revealed six pathoty pes of A. euteiches with host preferences for bean, alfalfa, pea, pea and alfalfa, red clover and alfalfa, and bean and alfalfa. Another gro up of strains was non-pathogenic on the five plant species. The host o f origin tended to be the host on which each strain incited the highes t disease severity. A. euteiches did not incite root rot symptoms on s ugarbeet, and A. cochlioides was pathogenic only to sugarbeet. RAPD an alyses provided a measure of genetic diversity in Aphanomyces. Fifty r andom decanucleotide primers were screened with five test strains from four hosts representing different pathotypes, and 32 primers amplifie d DNA fragments from all five strains. Eight primers were chosen for m ost of this study based on number and polymorphic nature of the bands generated. RAPD assays of 62 strains of A. euteiches with the eight pr imers yielded 159 polymorphic and no monomorphic, strongly amplified b ands. Cluster analyses of RAPD data revealed genotypic differences amo ng three groups of A. euteiches which corresponded to their host of or igin and host preference for bean, alfalfa, and red clover/alfalfa. St rains nonpathogenic on all plants tested formed another genotypic grou p, corroborating results from the pathogenicity assays that indicated this is a discrete group. The bean and non-pathogenic groups were the most distinct. The A. cochlioides and Saprolegnia strains were genotyp ically distinct from the pathogenic, but not the non-pathogenic strain s of A. euteiches. Reproducibility of RAPD assays was confirmed by rep licated amplifications and DNA hybridization analysis. Results indicat ed that A. euteiches is composed of distinct subspecific groups based on genotype and host preference.