Dispersal of Colletotrichum acutatum Sensu Lato Conidia from Infected Citrus and Strawberry Under Simulated Rainfall and Different Laminar and Turbulent Wind Speeds

Abstract

Species of the Colletotrichum acutatum complex cause postbloom fruit drop of citrus and anthracnose fruit rot of strawberries. C. acutatum produces acervuli in diseased citrus flowers and strawberry fruit, surviving asymptomatically on vegetative tissues. Previous studies have suggested that dispersal mechanisms other than windblown rain may be involved in the dispersal of conidia of C. acutatum sensu lato. Our hypothesis is that wind alone may play a role in dispersal, especially for inocula surviving on vegetative tissue. Our objectives were to study the dispersal pattern of C. acutatum sensu lato from strawberry fruit and leaves and citrus flowers and leaves by placing semiselective media at known distances away from inoculum sources in laminar flow and turbulent wind tunnels. The number of C. acutatum sensu lato colony-forming units on each plate was correlated with the distance from the inoculum sources. Conidia were dispersed up to 15 m in wind speeds greater than 10 m/s, but observed dispersal patterns were not described by the models we tested. A negative exponential model adequately described the dispersal gradient of the inoculum downwind, particularly for the dispersal gradient in turbulent wind. Dispersal in rain splash and wind was limited to short distances. Our data describe how conidia spread from inoculum sources and for the first time describe how the dispersal of C. acutatum sensu lato secondary conidia occurs from citrus and strawberry leaves. Knowledge of the dispersal of conidia of C. acutatum sensu lato can provide valuable information on epidemic development and, thus, approaches for disease management.

Keywords: diseases in natural plant populations; ecology; epidemiology; fungal pathogens; modeling.