EFFECT OF STRAWBERRY DENSITY ON DISPERSAL OF COLLETOTRICHUM-ACUTATUM BY SIMULATED RAIN

Studies were done with a rain simulator to evaluate the influence of plant density, inoculum source location, rain intensity, and their interactions on splash dispersal. Greenhouse-grown strawberry plants were mounted in support structures buried in soil to create artificial two-row canopies with 2-, 3-, 4-, and 8-cm intrarow spacings. Infected fruit placed either within or between the rows provided a source for spore dispersal by simulated rain, which was generated at constant intensities of 15 or 30 mm h(-1). Spore deposition, evaluated in sheltered petri plates exposed every 5 min over a period of 46 min, declined with increasing plant density when integrated over time at locations near the source. Deposition also declined with density when integrated over time and space for rows, area between rows, or the whole plot (P < 0.05). Within-row placement of inoculum and lower rain intensity reduced deposition compared to between-row placement and high rain intensity. Deposition gradients on plates between rows were described well by a negative exponential model. Slope parameters of spore deposition gradients between rows were not affected by any of the treatments, but the y-intercept was lowered by increased density, within-row placement of inoculum, and less intense rain (P < 0.05). Results suggest plant density affects both removal of spores from fruit and subsequent transport and may influence dispersal between sources and targets not within the canopy.