Phenomena of Antagonism in Cultivated Soil

Abstract Experience shows that yields ate normal if crop rotation is practised sufficiently. The case of Ophiobolus graminis Sacc. is studied in particular and it appears that after 2 or more years of the successive cultivation of winter wheat this fungus has accumulated to such an extent that the crop decreases to 50, 30 or even 10% depending on the weather conditions at that time. With sufficient crop rotation, the parasite is eliminated, within a certain time, by the antagonistic soil microflora. Methods of evaluating the impact of different species or groups on O. graminis are discussed and also the so‐called “decline” effect, according to which the accumulation of the pathogenic fungus responsible for losses in a continuous cultivation of the same crop is followed, after several years, by a depletion of the pathogen.