ARTIFICIAL INFESTATION OF SOIL WITH GAEUMANNOMYCES-GRAMINIS VAR. TRITICI TO STUDY THE RELATIONSHIP BETWEEN TAKE-ALL AND WHEAT YIELDS IN FIELD EXPERIMENTS

Abstract. The relationship between take‐all and grain yield was investigated in a first spring wheat crop grown in a field experiment on artificially infested soil. Different incidences and severities of disease were obtained by using different cultivations to incorporate equal amounts of inoculum (killed oat grains colonized by the fungal pathogen) at different depths. The intention of incorporating inoculum at different stages in the same sequence of cultivations to achieve identical soil conditions with inoculum at different depths was not entirely successful because of weather conditions. For most sampling dates and different assessments of disease, there was a strong relationship between yield and disease: regression coefficients were negative and significant (P= 0.01). The linear regression model using logit transformations of disease data from infestations achieved using similar sequences of cultivations accounted for > 70% of the variance at all sampling dates, but with untransformed data (percentage plants and percentage roots infected) percentages of variance accounted for were much less at sampling times before anthesis. The plot area affected by premature ripening (whiteheads) also correlated well with yield where similar sequences of cultivations were used, but less well where rotovating to different depths created different soil conditions. The results are discussed in relation to published results from (1) farm surveys, (2) field experiments with natural infection and (3) experiments using different amounts of artificially‐produced inoculum. The wider application of artificially‐produced inoculum in field experiments on take‐all is also considered. Copyright © 1990, Wiley Blackwell. All rights reserved