Induced Expression of CYP51 Associated with Difenoconazole Resistance in the Pathogenic Alternaria Sect. on Potato in China

Background: Early blight caused by Alternaria spp. is amongst the most important diseases in potato. Demethylation inhibitor (DMI) fungicides are widely used to control the disease but long-term use may decrease its control efficacy due to fungicide resistance. This study investigated the occurrence of difenoconazole resistance in Alternaria spp. and molecular resistant mechanisms.

Results: EC values of 160 isolates to difenoconazole ranged from 0.026 μg mL to 15.506 μg mL and the frequency of difenoconazole sensitivity formed a non-normal distribution curve with a major and a minor peak. Isolates with EC values of 4.121 and 5.461 μg mL were not controlled effectively at fungicide doses of 50 and 100 μg mL . Cross-resistance was observed between DMI fungicides difenoconazole and propiconazole, but not between difenoconazole and other fungicide groups, including boscalid, iprodione, or carbendazim. The CYP51gene was 1673 bp encoding 525 amino acids in length and contained two introns. All sensitive and resistant isolates had the identical amino acid sequence of CYP51, with the exception of one resistant isolate carrying a mutation of R511W. A 6 bp insertion in the upstream region was observed in half of the resistant isolates. In the absence of propiconazole, the relative expression of CYP51 was not significantly different in sensitive and resistant isolates. In the presence of difenoconazole, expression of CYP51 gene was induced significantly in the DMI-resistant isolates but not in the sensitive ones.

Conclusion: Induced expression of CYP51 in resistant isolates exposed to difenoconazole is an important determinant for DMI resistance in potato pathogens Alternaria sect. © 2019 Society of Chemical Industry.