Colletotrichum Causing Anthracnose of Citrus in Thailand Including C. kokhaense sp. nov. and a New Host Record for C. gigasporum

Colletotrichum species are important fungal plant pathogens associated with citrus pre- or postharvest disease globally. Seventy-three Colletotrichum isolates were collected from diseased leaves, fruits, and twigs of lime, tangerine, and pomelo in the provinces of Chiang Mai, Nakhon Pathom, and Lampang in Thailand. Colletotrichum siamense, C. gloeosporioides, C. fructicola, C. gigasporum, C. kokhaense sp. nov., C. plurivorum, and C. tropicicola were identified using morphological characters and multigene phylogenetic analysis (combinations of internal transcribed spacer, glyceraldehyde-3-phosphate dehydrogenase, Apn2–Mat1–2 intergenic spacer and partial mating type, glutamine synthetase, β-tubulin, actin, and histone depending on the species complex). C. siamense was the most prevalent species in Thailand, C. gigasporum was reported for the first time as a pathogen of citrus globally, and the new species C. kokhaense in the magnum species complex was described. Pathogenicity tests confirmed that C. siamense, C. gloeosporioides, C. gigasporum, C. kokhaense sp. nov., and C. plurivorum were pathogenic to citrus fruits, seedlings, and in planta shoots, with C. gigasporum being the most aggressive species. The non–wound inoculation technique provided good discrimination between high and low aggressive species compared with wound inoculation, where most species appeared to be very aggressive. Knowledge of Colletotrichum species causing citrus disease and their pathogenic ability will assist the development of effective disease management strategies.