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 dispersal of conidia of C. acutatum sensu lato. Our hypothesis is that wind alone may play a role in dispersal, especially for inoculum 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 semi-selective 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 (CFU) on each plate was correlated to the distance from inoculum sources. Conidia were dispersed up to 15 meters in wind speeds greater than 10 meters per second but observed dispersal patterns were not described by the models we tested. A negative exponential model adequately described the dispersal gradient of inoculum downwind, particularly for the dispersal gradient in turbulent wind. Dispersal in rain splash and wind was limited to short distances. Our data describes how conidia spread from inoculum sources, and for the first time describes how 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.