Sensitivity analysis of Colletotrichum spp. from wolfberry to four sterol demethylation inhibitors in Gansu Province

The objective of this work is to evaluate the sensitivity of Colletotrichum spp. isolated from wolfberry in Gansu Province to sterol demethylation inhibitors (DMIs). The petri plate was adopted to test the sensitivities of 102 isolates of Colletotrichum spp. from wolfberry at three different regions in Jingyuan and three different regions in Jingtai in Gansu province to 4 DMIs fungicides including difenoconazole, tebuconazole, propiconazole and flusilazole. The sensitivity differentiation of C. gloeosporioides species complex and C. acutatum species complex collected indifferent years and from different regions to four fungicides was analyzed respectively. The results indicated that the overall sensitivities of 46 C. gloeosporioides species complex to difenoconazole, tebuconazole, propiconazole and flusilazole were high. EC₅₀ value ranged from 0.28 to1.20 μg/mL, 0.11 to 2.98 μg/mL, 0.32 to 2.84 μg/mL and 0.35 to 3.85 μg/mL, respectively. However, the sensitivities of 56 tested C. acutatum species complex isolates to four DMIs fungicides were different and some strains were suspected to have decreased sensitivity. The average EC₅₀ values of the least sensitive strains to difenoconazole, tebuconazole, propiconazole and flusilazole are 1.63, 3.8, 6.21 and 4.74 μg/mL, respectively. The sensitivities of C. gloeosporioides species complex and C. acutatum species complex collected in different years to those 4 DMIs fungicides showed significant difference and the collected strains in 2017 showed relatively lower sensitivities. The average EC₅₀ values of C. gloeosporioides species complex to four DMIs fungicides respectively were (0.84 ± 0.03), (1.23 ± 0.13), (1.19 ± 0.09) and (1.69 ± 0.17) μg/mL, respectively. The average EC₅₀ values of C. acutatum species complex to four DMIs fungicides respectively were (1.06 ± 0.03), (2.25 ± 0.15), (2.43 ± 0.20) and (2.85 ± 0.19)μg/mL, respectively. The sensitivities of Colletotrichum spp. isolates collected from different areas to those 4 fungicides were different. The strains of C. gloeosporioides species complex collected from Wuhe Jingyuan county had the lowest sensitivity. The average EC₅₀ values were (0.79 ± 0.12), (1.28 ± 0.87), (1.39 ± 1.05) and (1.74 ± 1.04) μg/mL, respectively. The strains with the highest sensitivity to difenoconazole and propiconazole were collected from Caowotan Jingtai county, and the average EC₅₀ values were (0.28 ± 0.10) and (0.46 ± 0.10) μg/mL, respectively. The strains with the highest sensitivity to tebuconazole and flusilazole were collected from Sitan Jingtai county, and the average EC₅₀ values were (0.42 ± 0.16) and (0.65 ± 0.09) μg/mL, respectively. There was no significant difference among the sensitivities of C. acutatum species complex from different areas to those 4 fungicides. The results provided the theoretical basis for the rational use of fungicides to control wolfberry anthracnose in Gansu Province and delaying resistance development.