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1

A landscape-scale population model of rust transmission between soybean and kudzu

Presenter: Anna M. Fabiszewski

Other authors and affiliations: James Umbanhowar, Charles E. Mitchell. The University of North Carolina at Chapel Hill, Department of Biology, Chapel Hill, NC 27599, U.S.A.

Many pathogens infect more than one host species. Phakopsora pachyrhizi, the soybean rust fungus, infects many legumes, including nonnative kudzu (Pueraria montana). Pathogen spillover between wild hosts such as kudzu and crops such as soybeans can make pathogens with multiple hosts particularly difficult to eradicate or manage. Crops are often maintained at high density over the landscape, decoupling them from negative impacts of disease and increasing transmission. Wild host populations can also serve as pathogen reservoirs and cause landscape-scale spillover to domestic populations. To investigate the dynamics of such systems, we developed a two-host compartment model of disease with mechanistic, landscape-level transmission by airborne spores. We explore the model’s general dynamics, and consider its implications for a broad range of host-pathogen systems. We parameterized our model for P. pachyrhizi, kudzu, and soybean in the southeastern United States. Our model shows that because of the low landscape abundance of the wild host, transmission dynamics are driven by the agricultural host. The wild host acts as a primary inoculum source rather than driving within-season transmission. Wild plants growing in uncultivated patches can act as temporal reservoirs, sustaining pathogen populations between agricultural growing seasons. Our model predicts that epidemic spread in the crop is highly sensitive to very low overwintering survivorship in the wild host. These results suggest that only small amounts of wild host tissue, located in patches distant from crop fields, are sufficient to initiate epidemics. Therefore, prevention of epidemics by removal of wild host tissue may not be feasible.

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