Rain Splash Dispersal ofColletotrichum acutatumfrom Infected Strawberry Fruit

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Abstract
A rain simulator was used to investigate the influence of rain intensity (15 and 30 mm/hr), rain duration (15-60 min), and ground cover on splash dispersal of Colletotrichum acutatum from infected strawberry [Fragaria .times. ananassa] fruit. Potted strawberry plants were held in two concentric circles (30- and 60-cm radii) by a wood frame which was levelly exposed to a uniform zone of generated rain. Infected fruits with sporulating lesions were placed in the center of the circles. Studies were conducted with three ground covers: soil, soil covered with fresh straw (6-8 cm deep), and plastic. With plastic cover, 100% disease incidence was obtained at both distances and all times. With soil and straw, disease incidence was generally less in the outer compared with the inner circle, but increased in both circles over time only with soil. With 60 min of rain at 30 cm from the source, mean disease incidence was .gtoreq. 90%. Rain intensity, however, did not have a consistent effect on dispersal. Influence of number (source strength) and distribution of infected fruit on resultant dispersal was evaluated, with one, five, or nine infected fruits clustered in the center of the circles, or five or nine fruits uniformly scattered over the frame. Neither source fruit number nor its spatial distribution, however, was found to significantly affect disease incidence. A simple wind tunnel also was incorporated into the study to evaluate the effect of horizontal air flow. With a flow of .apprxeq. 2.3 m/sec, differences in disease incidence between up- and downwind locations were significant at 60 cm from the source but not at 30 cm. At 60 cm, disease incidence downwind (.apprxeq. 60%) was triple the incidence upwind (.apprxeq. 18%).