INTERACTIONS BETWEEN ERYSIPHE-GRAMINIS AND SEPTORIA-NODORUM ON WHEAT

Interactions between Erysiphe graminis f.sp. tritici and Septoria nodo rum on wheat were studied in the greenhouse and in a 2-year field expe riment using artificial inoculation. The integrated form of the logist ic growth model dy/dt = ry (1-y/K), with infection rate r and final ac cumulated disease K, was fitted to the disease progress data. Septoria nodorum substantially reduced the disease severities of E. graminis, and caused significant reductions of at least 60% in final accumulated disease K of E. graminis. In the field trials, E. graminis increased the final accumulated disease K of S. nodorum. Owing to the extremely low severity of E. graminis, the increase of S. nodorum severity was s mall, and significance was given in one of the two years only, with an increase in K of roughly 30%. In the pot experiment, final accumulate d disease K of S. nodorum remained unchanged, but there was a signific ant 30% increase in the infection rate r of S. nodorum. The difference between field and pot trials was explained by the climatic conditions in the greenhouse which excluded secondary infections of S. nodorum, and which are important factors for disease progress in the field.