Crop mixtures outperform rotations and landscape mosaics in regulation of wheat pathogens: a simulation study

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Abstract Context. Strategies of crop diversification such as crop rotations, within-field mixtures and landscape mosaics including susceptible and resistant crops can limit crop epidemics. Until now, the effects of these strategies have been studied separately, on single pathogen species, and with low environmental variability. Objectives. In this paper, we aim to compare the disease-limitation effect of these three crop diversification strategies on two highly damaging pathogens of wheat Puccinia recondita and Zymoseptoria tritici and under varying weather conditions.Methods. We built a dynamic mathematical model of epidemics at the field scale (based on classical Susceptible-Exposed-Infectious-Removed epidemiological models) embedded in a spatially explicit landscape grid framework. We use it to simulate an agricultural landscape in which diversification strategies translate into different proportions of wheat and resistant crops in the landscape.Results. In our simulations, for both pathogens and in all weather conditions, within-field crop mixtures had the greatest impact in limiting epidemics, crop rotations were second-best, while landscape mosaics were the least effective. We also found a threshold in the proportion of wheat in mixtures below which increase in the proportion of resistant plants does not lead to further disease limitation. However, a higher proportion of resistant crop was needed when the weather became favourable for the pathogens, suggesting that higher levels of diversification are needed to limit strong epidemics. Conclusions. Our findings imply that interactions between spatial the scale of crop diversification strategies, pathogen characteristics and weather conditions should be considered in order to maximize benefits from disease-regulation properties of diversified cropping systems under climate change.

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