A comparative study of Phialophora radicicola, an avirulent fungal root parasite of grasses and cereals

Abstract

SUMMARYThe biology and infection‐behaviour of a typical isolate of Phialophora radicicola Cain have been compared with those of a representative isolate of Ophiobolus graminis (Sacc.) Sacc. Both species can utilize a nitrate source of nitrogen and both require thiamine and biotin for growth on inorganic nitro‐gen; P. radicicola, but not O. graminis, was able to synthesize biotin when grown on asparagine as a nitrogen source. The pH range for good growth of P. radicicola in nutrient solution was narrower than that for O. graminis, and its growth rate on agar was only one‐third. P. radicicola was the more active decomposer of cellulose, and its cellulolysis adequacy index was I.66 as com‐pared with a value of 0.33 for 0. graminis. In agreement with prediction from Garrett's (I966) hypothesis on the cellulolysis adequacy index, saprophytic survival of P. radicicola in wheat straw was shortened by additional soil nitrogen, which prolongs survival of O. graminis.P. radicicola was found to spread ectotrophically over the roots of wheat, oats and barley by runner hyphae indistinguishable from those of O. graminis, but cortical infection caused no necrosis and no discernible check to growth of the infected cereals, nor any significant decrease in grain yield of inoculated wheat grown to maturity. Pre‐existing infection of wheat roots by P. radicicola retarded spread of infection by O. graminis; inoculation of several grass species with P. radicicola reduced the extent of infection by O. graminis of wheat following the grasses.