Formae Speciales Differentiation ofPhytophthora megaspermaIsolates From Soybean and Alfalfa

Abstract

Colony morphology of 30 isolates of P. megasperma from various sources varied with isolates and growth media. There were no distinct differences in oospore morphology and the diameters of oogonia ranged from 30 to 58 .mu.m and apparently were of a single continuously varying population. Isolates from alfalfa and soybean were pathogenic only to the hosts from which they were isolated. Special forms were proposed to subdivide the alfalfa and soybean isolates of P. megasperma into P. megasperma f. sp. medicaginis for isolates that attack alfalfa and P. megasperma f. sp. glycinea for isolates that infect soybean.