VIEW ARTICLE

Etiology

Aphanomyces euteiches f. sp. phaseoli, a Causal Agent of Bean Root and Hypocotyl Rot. W. F. Pfender, Research associate, Department of Plant Pathology, University of Wisconsin, Madison 53706; D. J. Hagedorn, professor, Department of Plant Pathology, University of Wisconsin, Madison 53706. Phytopathology 72:306-310. Accepted for publication 4 May 1981. Copyright 1982 The American Phytopathological Society. DOI: 10.1094/Phyto-72-306.

A previously unrecognized strain of Aphanomyces was found that caused severe root and hypocotyl rot of snap beans (Phaseolus vulgaris). It is proposed that two formae speciales of A. euteiches be recognized: A. euteiches f. sp. pisi, which infects peas and beans, and A. euteiches f. sp. phaseoli, which infects beans but not peas. A sample of isolates of the former had radial growth rates on cornmeal agar of ≥10 mm/day at 32 C, and a difference between oogonium and oospore diameters of ≤6 μm, whereas the latter grew 1–3 mm/day at 32 C, and the respective diameter differences were ≥8 μm. A. euteiches f. sp. phaseoli causes more severe damage to beans than does A. euteiches f. sp. pisi. Both formae speciales infect alfalfa. Although all bean cultivars and breeding lines tested were susceptible to infection by A. euteiches f. sp. phaseoli, Wis. (RRR) 46 showed little damage, whereas all commercial cultivars tested were severely damaged by the pathogen.