Functional Roles of Two ß-Tubulin Isotypes in Regulation of Sensitivity of Colletotrichum fructicola to Carbendazim.

Colletotrichum fructicola is the major pathogen of anthracnose in tea-oil trees in China. Control of anthracnose in tea-oil trees mainly depends on the application of chemical fungicides such as carbendazim. However, the current sensitivity of C. fructicola isolates in tea-oil trees to carbendazim has not been reported. Here, we tested the sensitivity of 121 C. fructicola isolates collected from Guangdong, Guangxi, Guizhou, Hainan, Hunan, Jiangsu, and Jiangxi provinces in China to carbendazim. One hundred and ten isolates were sensitive to carbendazim, and 11 isolates were highly resistant to carbendazim. The growth rates, morphology, and pathogenicity of three resistant isolates were identical to those of three sensitive isolates, which indicates that these resistant isolates could form a resistant population under carbendazim application. These results suggest that carbendazim should not be the sole fungicide in control of anthracnose in tea-oil trees; other fungicides with different mechanisms of action or mixtures of fungicides could be considered. In addition, bioinformatics analysis identified two ß-tubulin isotypes in C. fructicola: Cfß1tub and Cfß2tub. E198A mutation was discovered in the Cfß2tub of three carbendazim-resistant isolates. We also investigated the functional roles of two ß-tubulin isotypes. CfΔß1tub exhibited slightly increased sensitivity to carbendazim and normal phenotypes. Surprisingly, CfΔß2tub was highly resistant to carbendazim and showed a seriously decreased growth rate, conidial production, pathogenicity, and abnormal hyphae morphology. Promoter replacement mutant CfΔß2-2×ß1 showed partly restored phenotypes, but it was still highly resistant to carbendazim, which suggests that Cfß1tub and Cfß2tub are functionally interchangeable to a certain degree.