Characterization of tebuconazole resistance in Botrytis cinerea from tomato plants in China

Abstract

AbstractFungal pathogen Botrytis cinerea, the casual agent of gray mold of vegetables and fruits, has a high risk of developing resistance to fungicide. Tebuconazole, one kind of demethylation inhibitor (DMI) fungicides, has been increasingly applied for the control of tomato gray mold in China. However, very limited information is available on the resistance profile of B. cinerea to tebuconazole. In this study, the baseline sensitivity of B. cinerea to tebuconazole was determined based on 138 isolates from field sites having no history of DMI usage, with a mean EC50 value of 0.29 μg/mL. Another 159 B. cinerea isolates collected in the greenhouse and field from 2011 to 2016 were demonstrated to have a shifted sensitivity to tebuconazole, with a mean EC50 value of 0.66 μg/mL. EC50 values of 10 B. cinerea isolates with reduced sensitivity to tebuconazole were greater than 1.56 μg/mL, and these reduced-sensitive isolates had a fitness penalty in sporulation and conidial germination, but showed similar mycelial growth rate and pathogenicity with those of the sensitive isolates. Positive cross-resistance was observed only between tebuconazole and the other two DMIs difenoconazole and prochloraz, but not between tebuconazole and the non-DMIs iprodione, procymidone, or fludioxonil. In reduced-sensitive isolates, no amino acid variation was found in the BcCYP51 protein. When exposed to tebuconazole, the expression level of BcCYP51 increased in these reduced-sensitive B. cinerea isolates as compared to sensitive ones, thus contributing to the reduced sensitivity of the pathogen to tebuconazole. Additionally, the nucleotide mutation observed in the 1200 bp upstream region of BcCYP51 had no correlation with the development of fungicide resistance in B. cinerea isolates. These findings will be helpful for the understanding of DMI resistance mechnism in B. cinerea.