Interactions between <em>Erysiphe graminis</em> and <em>Septoria nodorum</em> on wheat.

Interactions between Erysiphe graminis f.sp. tritici and Septoria nodorum on wheat were studied in the greenhouse and in a 2-year field experiment using artificial inoculation. The integrated form of the logistic growth model dy/dr = ry (1 -y/K) with infection rate r and final accumulated 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 small, and significance was given in one of the two years only, with an increase in K of roughly 30%. In the pot experiment, final accumulated disease K of S. nodorum remained unchanged, but there was a significant 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. [ABSTRACT FROM AUTHOR]