Baseline Sensitivity and Resistance Mechanism of Isolates on Tea-Oil Trees of China to Tebuconazole.

fungi could cause anthracnose, a destructive disease in tea-oil trees. The sterol demethylation inhibitor (DMI) tebuconazole has been widely used in controlling plant diseases for many years. However, the baseline sensitivity of isolates on tea-oil trees to tebuconazole has not been determined. In this study, the sensitivity to tebuconazole of 117 isolates from tea-oil trees of seven provinces in southern China was tested. The mean effective concentration resulted in 50% mycelial growth inhibition (EC), 0.7625 μg/ml. The EC values of 100 isolates (83%) were lower than 1 μg/ml, and those of 20 isolates (17%) were higher than 1 μg/ml, which implied that resistance has already occurred in isolates on tea-oil trees. The EC values of the most resistant and sensitive isolates (named Ca-R and Cc-S1, respectively) were 1.8848 and 0.1561 μg/ml, respectively. The resistance mechanism was also investigated in this study. A gene replacement experiment indicated that the gene of resistant isolates Ca-R and Cf-R1 cannot confer Cc-S1 full resistance to DMI fungicides, although three single point mutants, Cc-S1-T306A and Cc-S1CYP51A-R478K, exhibited decreased sensitivity to DMI fungicides. This result suggested that resistance of isolates was partly caused by mutations in . Moreover, the expression level of was almost identical among Ca-R, Cf-R1, Cc-S1, and Cc-S1 point mutants, which indicated that the resistance was irrelevant to the expression level of , and other nontarget-based resistance mechanisms may exist. Our results could help to guide the application of DMI fungicides and be useful for investigating the mechanism of resistance.