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Colletotrichum Species Composition and Fungicide Tolerance in Isolates Causing Bitter Rot of Apples in Pennsylvania

Phillip Martin: Penn State University

<div>Bitter rot of apples caused by a <em>Colletotrichum</em> spp. complex is an increasing problem in the mid-Atlantic and northeastern US. Several causes for this increase have been hypothesized, including increased tolerance of widely used fungicides and selection of species with increased fitness. <em>Colletotrichum </em>spp. were isolated from > 100 apples with bitter rot symptoms grown under both conventional and organic management practices from across Pennsylvania. Partial sequences of the beta-tubulin and GAPDH genes, and the ITS region of ribosomal DNA were amplified and sequenced to identify the fungi to species. Isolates were tested for tolerance to commonly used fungicides with differing modes of action using mycelial growth and conidial germination assays. <em>Colletotrichum fioriniae </em>was the dominant species identified and increased tolerance to FRAC (Fungicide Resistance Action Committee) group 11 fungicides was observed. Evaluations of FRAC Groups 1 and 7 are in progress. <em>C. fioriniae</em> is a widely distributed fungus that has been isolated from apple, forest trees, shrubs, and scale insects, and infects strawberries, lettuce, blueberries, peaches, apricots and peppers, among others. Findings from the current study will be discussed and are predicted to uncover aspects of understanding cross-infectivity between different crop hosts, elucidating inoculum sources, and for evaluating selection pressures from different mode of action fungicides.</div>