VIEW ARTICLE

Ecology and Epidemiology

Host Specificity of Phytophthora megasperma from Douglas Fir, Soybean, and Alfalfa. P. B. Hamm, Graduate research assistant, Department of Botany and Plant Pathology, Oregon State University, Corvallis 97331; E. M. Hansen, assistant professor, Department of Botany and Plant Pathology, Oregon State University, Corvallis 97331. Phytopathology 71:65-68. Accepted for publication 15 May 1980. Copyright 1981 The American Phytopathological Society. DOI: 10.1094/Phyto-71-65.

A total of 28 isolates of Phytophthora megasperma from either Douglas fir, alfalfa, or soybean were tested for pathogenicity to Douglas fir, alfalfa, and soybean. Isolates from alfalfa and soybean were pathogenic only to their original hosts. One group of isolates from Douglas fir was strongly pathogenic to both Douglas fir and soybean; a second group was less pathogenic to Douglas fir and was not pathogenic to soybean. The first group from Douglas fir was virulent on seven soybean cultivars used to define races of P. megasperma f. sp. glycinea and on cultivar Tracy. Applicability of the formae speciales concept to P. megasperma is discussed.