STUDIES ON FUSARIUM CULMORUM BLIGHT OF CRESTED WHEAT AND BROME GRASS SEEDLINGS

Abstract

A number of pathogenic fungi were isolated from blighted brome grass and crested wheat grass seedlings grown in Saskatchewan and Ontario soils. The parasitism of one of the widely distributed and commonly occurring of these, Fusarium culmorum (W. G. Sm.) Sacc, was studied in more detail.One per cent of F. culmorum sand–cornmeal inoculum caused more blight of brome grass seedlings in sterilized soil than did 6% in unsterilized soil. The development of F. culmorum in sterilized soil was optimum at 25 °C. and declined rapidly with rising and more slowly with falling temperatures. Seedling blight was severe in sterilized soil at all temperatures from 10° to 35 °C., but was significantly more severe near the optimum for the fungus provided the soil was not infested too heavily. In unsterilized soil, however, both the development of F. culmorum and the incidence of seedling blight were much greater at 10 to 20 °C. than at 25 °C. and higher, whereas other soil fungi and bacteria were more numerous at 25° C. and above than at the lower temperatures.An infusion of unsterilized soil, a suspension of miscellaneous soil bacteria, and a mixture of 75 soil fungi suppressed the development of F. culmorum in sterilized soil, and also caused reductions in seedling blight. Of 136 soil fungi tested, only three reduced fusarial blight in sterilized soil. These antagonistic fungi included isolates of Acremonium, Gliocladium fimbnatum Gilman and Abbott, and Phialophora. Their ability to reduce disease incidence was not consistently correlated with the production of toxic filtrates, or the inhibition of F. culmorum in culture or in the soil but it was related to the effect they had on the development of F. culmorum in the environment in the immediate vicinity of the germinating seeds. This zone within which the germinating seed induces a characteristic change in the microbiological balance is designated as the 'spermatosphere'.Disease incidence varied among different unsterilized field soils uniformly infested with F. culmorum and in these experiments was more severe in clay than in the soils of lighter texture. There was no consistent correlation between the suppression of blight and the numbers of fungi, bacteria, or actmomycetes in the different soils, but there was a correlation with the numbers of bacteria in the spermatosphere.