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Poster: Biology & Disease Mgmt: Chemical Control


Characterization of resistance to DMI fungicides in Colletotrichum spp. isolates from peach
S. CHEN (1), C. Luo (1), M. Hu (2), G. Schnabel (2) (1) Huazhong Agricultural University, China; (2) Clemson Universitiy, U.S.A.

Isolates of the Colletotrichum acutatum species complex were collected from South Carolina and Georgia peach orchards. Phylogenetic analysis of the combined ITS, glyceraldehyde-3-phosphate dehydrogenase, and beta-tubulin gene sequences separated the isolates into two species, Colletotrichum nymphaeae and Colletotrichum fioriniae subgroups 1 and 2. The sensitivity of these and three other Colletotrichum species from peach (Colletotrichum fructicola, Colletotrichum siamense, and Colletotrichum truncatum) to demethylation inhibitor (DMI) fungicides difenconazole, propiconazole, tebuconazole, metconazole, flutriafol, and fenbuconazole were determined. C. truncatum was resistant to tebuconazole, metconazole, flutriafol, and fenbuconazole. C. nymphaeae was resistant to flutriafol and fenbuconazole. C. fructicola and C. siamense were sensitive to all DMI fungicides, and C. fioriniae subgroup 2 was reduced-sensitive to DMI fungicides compared with C. fioriniae subgroup1. Difenconazole and propiconazole provided the best control efficacy in vitro to all five species. Tebuconazole and metconazole were effective against all Colletotrichum species, except for C. truncatum. The 14-α sterol demethylase genes CYP51A and CYP51B from resistant isolates revealed point mutations associated with resistance to DMI fungicides. The strong in vitro activity of some DMI fungicides against Colletotrichum species may be exploited for improved anthracnose disease management of peach.