PHIALOPHORA RADICICOLA CAIN, A CORN ROOTROT PATHOGEN

Abstract

During the summer of 1950, Phialophora radicicola, was found on corn roots in soil near Chatham, Ridgetown, and Harrow, Ont. Owing to its color and parasite-host relations, it may have been mistaken previously for Rhizoctonia solani or a Rhizophagus species. It can be isolated only when a piece of apparently healthy corn root tissue with the adhering mycelium is removed from an infected root and placed on agar media. After two or three months of culture on nutrient and on potato dextrose agar, P. radicicola lost its ability to sporulate, but this ability was revived when it was cultured on moist corn roots. No sexual stage of the organism has been found. The fungus may attack corn roots at any time throughout the season and its brown runner-hyphae or macrohyphae grow parallel to the roots. The finer infection hyphae or microhyphae penetrate the outer root tissue and their infection threads are surrounded by "wall tubules". The fungus is quite aggressive, but not very pathogenic, and apparently it is followed by numerous secondary organisms. The similarity of this organism to Ophiobolus graminis is very noticeable.