Resistance of Botrytis cinerea to thiophanate-methyl, diethofencarb, and procymidone in postharvest cherry

The pathogenic fungi of postharvest grey mold on cherry fruits from Hanyuan, Sichuan Province, and Yantai, Shandong Province were collected and identified by single-spored method. The sensitivity of the tested strains to thiophanate-methyl, diethofencarb, and procymidone was determined by differential dose method. The alignments of the DNA sequences of β-tubulin gene and BcOS1 gene were carried out to analyze the molecular mechanism of resistant strains. The results showed that the 54 isolates collected from postharvest cherry were Botrytis cinerea, and the total resistance frequency to thiophanate-methyl was 79.6%. Among them, the resistance frequency of thiophanate-methyl-resistant and diethofencarb-sensitive strains (BEN R1) was 25.9%. The resistance frequency of strains resistant to both thiophanate-methyl and diethofencarb (BEN R2) was 53.7%. Nine procymidone-resistant strains (DCF R) were detected, and the resistance frequency was 16.7%. There were two types of mutation in β-tubulin gene of benzimidazole-resistant strains. In BEN R1, the codon at position 198 was mutated from GAG to GCG, resulting in the amino acid encoded by Glutamate-Glu (E) being changed to Alanine-Ala (A). In BEN R2, the codon at position 198 was mutated from GAG to GTG, resulting in the change of the encoded amino acid from Glu (E) to valine-Val (V). The codon at position 365 in BcOS1 gene of DCF R was mutated from ATC to AAC or AGC, resulting in the change of the encoded amino acid from isoleucine-Ile (I) to asparagine-Asn (N) or serine-Ser (S). The results indicated that B. cinerea on cherry had different degrees of resistance to thiophanate-methyl and procymidone. It is necessary to alternate with other types of fungicides while strengthening resistance monitoring to delay the development of resistance.