Resistance to Boscalid in Botrytis cinerea From Greenhouse-Grown Tomato

Gray mold, caused by the fungus Pers ex Fr., is one of the most destructive spoilage diseases, severely affecting tomato production in Henan Province, China. Spraying fungicides from the flowering to the harvest stage is a necessary measure to reduce losses associated with infection. However, has developed resistance to fungicides in many countries. Boscalid is a succinate dehydrogenase inhibitor (SDHI) fungicide and was registered for the control of gray mold. In this study, a total of 269 isolates were collected from tomato in commercial greenhouses in different locations of Henan Province in 2014 and 2015. The sensitivity and resistance of field isolates were determined based on mycelial growth. The effective concentration 50 ranged from 0.11 to 15.92 µg/ml and 0.16 to 8.54 µg/ml, in 2014 and 2015, respectively. The frequency of low resistance to boscalid was 12.6 and 7.6%, and moderate resistance was 2.7 and 1.3% in 2014 and 2015, respectively. No highly resistant isolates were found in Henan Province, China. Mycelial growth, mycelial dry weight, spore production, and pathogenicity were not significantly different between resistant and sensitive phenotypes of the isolates. The results of cross-resistance testing showed no correlation between boscalid and carbendazim, procymidone, pyrimethanil, fluazinam, or fluopyram. In this study, the succinate dehydrogenase genes ( ), ( ), and ( ) were analyzed and compared in sensitive and low-resistance and moderately resistant isolates to boscalid. Results showed that point mutations occurred simultaneously at amino acid positions 85 (G85A), 93 (I93V), 158 (M158V), and 168 (V168I) in 4 out of 10 sensitive isolates and 23 of 26 low-resistance and 5 of 5 moderately resistant isolates to boscalid. No point mutations were found in the and genes of all isolates. Furthermore, no point mutations were found in , , and genes in 3 of 26 low-resistance isolates to boscalid. Therefore, we speculate that the simultaneous point mutations in the gene may not be related to the resistance of to boscalid. These results suggested that there might be a substitution mechanism for the resistance of to the SDHI fungicide boscalid.