Interactions between Erysiphe graminis and Septoria nodorum on wheat

Abstract

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/dt = 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 5. nodorum, and which are important factors for disease progress in the field.

Interactions between foliar diseases: concepts and epidemiological approaches

“…M. graminicola acted as a hypostatic parasite. Weber et al (1994) observed that, in greenhouse, S. nodorum reduced the severity of mildew. On the other hand, under field conditions, E. graminis increased the final intensity of S. nodorum.…”

“…However, even for wheat, the crop that receives the most attention regarding interactions among diseases, there are little multi-disease studies concerning management or epidemiological approaches. Moreover, the observed effects of reported interactions (for instance synergism, antagonism or additive effect) are highly dependent on inoculum concentration, disease levels (Jörg, 1987;Weber et al, 1994), pre-infection by one of the interacting pathogens (Donchev et al, 1980), and climatic conditions (Weber et al, 1994). Cox et al (2004) have demonstrated the potential of cultivar mixtures for the simultaneous management of tan spot (Pyrenophora tritici-repentis) and leaf rust of wheat (Puccinia triticina).…”

“…The apparent contradiction was explained as a result of different climatic conditions, which allowed secondary infections of S. nodorum in the field. Based on the studies of Brokenshire (1974), Geuting (1984) and Jörg (1987), Weber et al (1994) concluded that these pathogens couldn't strictly be described as competitors sensu Odum (1953). The relation between E. graminis and S. nodorum is better described, sensu Powell (1979), as "predisposition with dominance of the secondary pathogen", with E. graminis as primary, and S. nodorum as secondary pathogen (Jörg, 1987;Weber et al, 1994).…”

“…The interactions may alter the occurrence and speed of epidemics. Weber et al (1994), for instance, concluded for the two wheat pathogens Septoria nodorum and Erysiphe graminis that wherever the two pathogens occur together, neither their dynamics, nor the influence of external factors could be understood, if interspecific interactions are neglected. Interactions may have significant implications for assessing crop losses, diagnosing the causes of these losses and for selecting appropriate management strategies, as well as for forecasting, modelling and simulations of epidemics (Waller & Bridge, 1984;Bassanezi et al, 1998).…”

“…The examples of interactions presented in literature are mainly dealing with their effects on yield. Epidemiological aspects of these interactions in terms of changes in the component analysis have rarely been studied (Zadoks & Schein, 1979;Weber et al, 1994). Here some aspects related to the dynamics and to crop losses of the interactions between diseases caused by aerial pathogens are discussed.…”