8228: Simulation of effect of leaf layer dynamics and vertical spore dispersal on competition between foliar pathogens

Vollmer, J.H. and Østergård, H. (2006) Simulation of effect of leaf layer dynamics and vertical spore dispersal on competition between foliar pathogens . Working Paper.

Summary

Diseases developing on a crop are not faced with a constant leaf area surface to develop over, but rather discrete areas in space and time, decided by development of single leaves and leaf layers of the plant. Density dependence is important to consider when evaluating foliar disease progress, due to the dependence on leaf area for development. Often, more than one disease develops in a field at the time. This has lead to research exploring potential antagonistic or synergistic effects between the two species. A logistic model for two simultaneously developing pathogen species, considering no antagonistic or synergistic effects but only density dependence has illustrated that in a two species situation, expected total disease level of the two pathogens is not a simple a sum of levels in the former. This is here expanded, to focus on the two pathogens and the effect of leaf layer development for observed final levels of the two diseases. A model is used to evaluate the effect of density dependence, leaf layer dynamics, differences in pathogen epidemic parameters and vertical spore dispersal, on simultaneous development of two foliar pathogens Rhynchosporium secalis and Drechslera teres. Epidemic parameters for the two species would indicate that R. secalis has a higher growth rate that D. teres, and would therefore be expected to be the dominant disease, if progress is simulated without consideration of canopy structure. The simulations showed that dispersal parameters vertically in the canopy influenced the dynamics, such that when leaf layer dynamics were considered, the dominating species was D. teres The model has illustrated, that the combination of density dependence and leaf layer dynamics influence the outcome of development of two diseases in a field, such that it is impossible simply from observations on disease levels to draw conclusions regarding interactions between pathogens, as expected levels in the two-species situation can not be described from the single-species observations.

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