Possible existence of Colletotrichum horii resistant to sterol demethylation inhibitor (DMI) fungicides on persimmon

Abstract

Persimmon (Diospyros kaki Thunb.) anthracnose is a serious plant disease caused by Colletotrichum horii B.S. Weir & P.R. Johnston and other closely related species. Sterol demethylation inhibitor (DMI) fungicides are effective against C. horii. Difenoconazole is a systemic fungicide that belongs to the DMI fungicides. In this study, we investigated the sensitivity of C. horii isolates collected from six commercial persimmon orchards in Wakayama Prefecture to difenoconazole. The sensitivity to difenoconazole was evaluated using both a medium test and a bioassay analysis. The medium test results revealed that the EC₅₀ values of difenoconazole ranged from 0.002 ppm to 54.54 ppm. The bioassay analysis indicated that C. horii isolates exhibiting EC₅₀ values of 1 ppm or higher in the medium test were resistant to difenoconazole. The results demonstrated the possibility of the presence of DMI-resistant C. horii on persimmons.