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Dispersal of Colletotrichum acutatum conidia from citrus and strawberry under controlled conditions

Andre Bueno Gama: University of Florida - Gulf Coast Research and Education Center

<div><em>Colletotrichum acutatum</em> <em>sensu latu</em> causes postbloom fruit drop of citrus and anthracnose of strawberries. These diseases are usually widespread within infected fields, although primary conidia (PC) are water dispersed to short distances. <em>C. acutatum</em> produces quiescent infections on citrus and strawberry leaves, which eventually produce secondary conidia (SC) that are not in mucilage. Dispersal potential for SC is not known, and we hypothesized that they might be wind dispersed. Strawberry and citrus leaves were inoculated with 5x10<sup>5</sup> and 1x10<sup>6</sup><sup>-1</sup>, respectively. Secondary conidiation was stimulated in a moist chamber with 1% sucrose. After 48 h, inoculated leaves were placed in a wind tunnel, with <em>C. acutatum </em>selective media plates placed at 15 to 300 cm from inoculum source. Winds of 2.5 m.s<sup>-1</sup> were applied for 2 h over inoculated leaves combined or not with sprays of water or sucrose solution. The experiments were also conducted with symptomatic strawberry fruit, and <em>C. acutatum </em>colonies on Potato Dextrose Agar, sources of PC. <em>C. acutatum </em>colony forming units (CFU) were counted after one week. The exponential model was fitted to data of CFU over distances (<em>p</em>=0.05). SC were not dispersed when exposed to wind alone. Most of water or sucrose-dispersed SC was limited to short distances, less than 60 cm from strawberry or citrus leaves, whereas PC water dispersal went further, with abundant conidia found at 3 m from sources.</div>