EFFECT OF RAIN DISTRIBUTION ALTERATION ON SPLASH DISPERSAL OF COLLETOTRICHUM-ACUTATUM

Splash dispersal of Colletotrichum acutatum conidia from infected stra wberry fruit was assessed using a rain simulator to determine the prop erties of rain (e.g., intensity [millimeters/hour] or drop size distri bution) most related to dissemination. Dispersal with a simulated rain corresponding to a natural rain of about 11 mm/h was compared with di spersal of three other simulated rains that had larger and smaller dro p sizes, on average, than idealized natural rains. Splash droplets wer e collected in sheltered petri plates with a selective medium for Coll erotrichum, and colonies formed from conidia entrained in the droplets were counted and used as the measure of dispersal. Colonies were most ly confined to a 27-cm radius from the source, and density of colonies decreased exponentially with the distance squared, as indicated by th e fit of a diffusion-type model to the data. Splash dispersal was more affected by drop size distribution than rain intensity or other prope rties of the generated rains. That is, there was a direct positive rel ationship between total colonies over 61 min of rain for a circular ar ea with a 72-cm radius (Sigma) and the mass (volume) median diameter o f impacting drops (D-0') for four rain-simulation treatments. In a sep arate study, strawberry fruit were exposed to the same four simulated rains at two distances from a point source and for two rain durations. Although the proportion of infected fruit (y) increased with time and decreased with distance, rain treatment did not significantly affect y, as predicted based on past work with a wide range of intensities of simulated rains.