Abstract
Gray mold, caused by Botrytis cinerea, is one of the most destructive diseases of strawberry in China. For resistance monitoring, 198 B. cinerea isolates were collected from strawberry greenhouses at 10 locations in Hubei Province. The isolates were screened for resistance to fungicides procymidone and zoxamide. In mycelium growth assays for procymidone, the mean values of effective concentration at which mycelium growth is inhibited by 50% (EC50) for sensitive (ProS) and resistant (ProR) isolates were 0.25 μg/mL and 2.21 μg/mL, respectively. The frequency of ProR isolates was 14%, and the highest frequency (48%) was observed in Yichang. Positive cross-resistance was detected for ProR isolates to other dicarboximide fungicides, but not to phenylpyrroles. Comparative analysis of fitness parameters revealed increased osmotic sensitivity of ProR isolates compared to ProS ones. Sequence analysis of the dicarboximide target gene BcOs1 revealed that ProR isolates carried either a single point mutation at codon 365 (I365S) or a pair of point mutations (Q369P and N373S). The mean EC50 values for zoxamide sensitive (ZoxS) and resistant (ZoxR) isolates were 0.31 μg/mL and 7.76 μg/mL, respectively. Only six (3%) isolates from three locations were found to be resistant to zoxamide. All ZoxR isolates were found resistant to carbendazim. Fitness parameters did not show significant difference between ZoxR and ZoxS isolates. Sequence analysis of the beta-tubulin gene in resistant isolates revealed four previously reported point mutations (E198A, E198K, F200Y and T351I). The mutation T351I was detected only in the isolates possessing E198K point mutation. Mutation F200Y was detected in a highly resistant isolate. Results of this study will be helpful for the management of fungicide resistance in B. cinerea.
Highlights
Gray mold of strawberries, caused by Botrytis cinerea Pers. is considered one of the most destructive diseases threatening strawberry production, especially in greenhouses in Hubei Province and worldwide
Frequency of B. cinerea resistant isolates Monitoring of fungicide resistance among 198 isolates from strawberry in Hubei Province was conducted based on the determination of discriminatory doses of procymidone and zoxamide
Results showed that 14% (27 isolates) and 3% (6 isolates) of tested isolates were resistant to procymidone and zoxamide, respectively
Summary
Gray mold of strawberries, caused by Botrytis cinerea Pers. is considered one of the most destructive diseases threatening strawberry production, especially in greenhouses in Hubei Province and worldwide. Gray mold of strawberries, caused by Botrytis cinerea Pers. In the late 1970s, DCFs replaced MBCs for the management of B. cinerea (Elad et al 2004). Excessive use of DCFs to control B. cinerea has resulted in resistance selection and reduced their efficacy worldwide (Faretra and Pollastro 1991; Elad et al 1992; Moorman and Lease 1992; Pappas 1997; Leroux et al 1999). Various mutations in the Botrytis cinerea two-component histidine kinase gene (BcOs1) responsible for resistance to DCFs have been identified in B. cinerea populations from different countries. Mutation of glutanine to proline at codon 369 (Q369P) was always found to be paired with the mutation of asparagine to serine at codon 373 (N373S) (Liu et al 2016). Moderate resistant (MR) phenotypes were reported to be related to a combination of two mutations, e.g., Q369P and N373S, but mutations of isoleucine to asparagine/serine at condon 365 (I365N/S) were associated with low resistant (LR) phenotype (Grabke 2014)
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