Sensitivities of poplar anthracnose fungi isolates to carbendazim and three C-14α-demethylation inhibitors

Sensitivities of 59 Colletotrichum gloeosporioides isolates and four C. aenigma isolates causing poplar anthracnose to four fungicides (carbendazim, difenoconazole, tebuconazole and triadimefon) were determined by measuring the mycelium growth. The mean and the range of EC50 values of 59 C. gloeosporioides isolates were (0.066 4±0.013 1) and 0.037 1-0.130 1 μg/mL for carbendazim, (0.374 1±0.254 8) and 0.102 5-1.680 μg/mL for difenoconazole, (0.681 2±0.442 1) and 0.069 1-1.917 μg/mL for tebuconazole, and (19.82±6.200) and 3.053-38.59 μg/mL for triadimefon. The frequency distribution of EC50 values of C. gloeosporioides for carbendazim was described by continuous, unimodal curve, indicating the absence of carbendazim-resistant subpopulation among these isolates. The frequency distribution of EC50 values of C. gloeosporioides for difenoconazole and tebuconazole was bimodal curves, implying the appearance of resistant subpopulation. The highest EC50 values were 1.33-, 13.19-, 13.66-, and 2.14-times greater than the lowest values for carbendazim, difenoconazole, tebuconazole and triadimefon in the case of four C. aenigma isolates. The EC50 values of C. aenigma isolate Ca-4 to difenoconazole and tebuconazole were higher than 4 μg/mL. There was no significantly difference among the sensitivities of C. gloeosporioides isolates from different poplar hosts (P>0.05). Spearman's rank correlation analysis showed that there was positive correlation between sensitivities of C. gloeosporioides isolates for difenoconazole and tebuconazole (ρ=0.665 5, PC. gloeosporioides isolates for tebuconazole and triadimefon (ρ=0.489 6, P<0.000 1). However, no correlation between other fungicides was observed. The results will be an important reference for chemical control of poplar anthracnose.