Conflicting Effects of Climate and Vector Behavior on the Spread of a Plant Pathogen

Abstract

Local climatic conditions are important determinants of disease dynamics through effects on vector population performance or distribution. Yet, climate may also be epidemiologically significant due to effects on host−pathogen infection dynamics. We developed a model to explore interactive effects between climate-mediated acceleration in disease phenology (i.e., faster incubation or symptom onset) and vector preference based on host symptom status. Higher incubation rates favored pathogen outbreaks, but more rapid symptom onset may constrain spread if vectors avoid symptomatic hosts. Next, we tested whether warmer conditions favored greater spread of the plant pathogen, Xylella fastidiosa, by its leafhopper vector, Graphocephala atropunctata. Inoculated and healthy plants were reared in two temperature-controlled greenhouses. At six times postinoculation, a healthy and inoculated plant were exposed to noninfective vectors, after which pathogen spread was evaluated. Incubation rate and symptom onset in infected hosts was significantly accelerated at higher temperature. Although there was a tendency for greater pathogen spread at higher temperature, the effect depended on time since inoculation. In later introductions, after disease symptoms manifest, vectors were more likely to be found on healthy hosts. Vector avoidance of symptoms, particularly for hosts reared at higher temperature, constrained pathogen spread at later introductions. These results indicate that climate and vector behavior may mediate interactively pathogen spread. Further consideration of such epidemiological complexities is needed to predict adequately the consequences of climate change for disease dynamics.

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