Dispersal and Plant Arrangement Condition the Timing and Magnitude of Coffee Rust Infection

Abstract

One central issue in coffee-leaf rust (Hemileia vastatrix) epidemiology is to understand the role of rust dispersion on the intensity and the timing of yearly infections in coffee plantations. After reviewing the rust epidemic patterns of different sites, we present a spatially explicit and parameterized model where the host population is subdivided into discrete patches linked through spore dispersion. With this model, we study the role of the planting arrangement, the dispersion intensity and plant-level variables on the maximum average tree infection (MATI) and its timing. Our results suggest that the epidemic timeline can be divided into two phases: a time lag and a growth phase per se. The model shows that the combination of the dispersion intensity and the planting pattern modifies the MATI and the time to MATI, mainly by preventing some plants from reaching their maximum peak during the epidemic. It also affects the epidemic curves, which can have multiple peaks, or a rather smooth pattern in plots with otherwise similar conditions. The initial infection modulates the time lag and the leaf-fall rate drastically changes the MATI. These findings highlight the importance of explicitly considering the spatial aspects of coffee agroecosystems when measuring and managing rust infection.