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Rain Dispersal of Colletotrichum gloeosporioides in Simulated Rice Field Conditions. X. B. Yang, Department of Plant Pathology, University of Arkansas, Fayetteville 72701; D. O. TeBeest, Department of Plant Pathology, University of Arkansas, Fayetteville 72701 Phytopathology 82:1219-1222. Accepted for publication 26 May 1992. Copyright 1992 The American Phytopathological Society. DOI: 10.1094/Phyto-82-1219.

Rain splash dispersal of Colletotrichum gloeosporioides f. sp. aeschynomene, a pathogen used as a commercial mycoherbicide (a type of herbicide having fungal spores as the active ingredient) to control northern jointvetch in rice, was examined in a wind tunnel (2.3 m/sec) with simulated rain (40 mm/h). The effects of different surface conditions including water, soil, and concrete and rice density were examined. Dispersal of the pathogen was significantly reduced when weeds were present within a rice canopy. The high rice density not only reduced the steepness of the dispersal gradient but also reduced the intercept of the dispersal curve. The half-distances of the disease dispersal curves (values of distance when lesions per plant decrease by half) varied from 42 cm for weeds on a concrete surface to 99 cm for weeds on a water surface. The half-distances are much greater than the spore dispersal curves reported previously for pathogen of Colletotrichum. Total lesions determined by integrating power law model in the range 30180 cm from the inoculum source were 24.7 and 38.2 for high and low rice densities and 47.1 and 67.1 for soil and water surfaces, respectively. Vertical distributions of disease lesions on plant stems were also studied. The average height of lesions on stems was significantly higher for concrete than for soil and water surfaces. The vertical distribution of lesions on plants suggested that the energy reflection of water droplets from the surface determined the height and distance of dispersal. The relationship between pathogen dispersal and disease epidemic of this pathosystem is discussed.

Additional keywords: biological control, epidemiology.