Abstract
Gray mold caused by Botrytis cinerea leads to serious losses in various crops. Fluxapyroxad, a succinate dehydrogenase inhibitor (SDHI) fungicide, has been used to control gray mold for several years in China. In this study, we identified six fluxapyroxad-resistant (FluR) isolates from 96 isolates of B. cinerea collected in fields. Phenotypic assays showed that the FluR isolates exhibited defects in mycelial growth, conidiation, sclerotium formation, stress tolerance and virulence. Analysis of nucleotide sequences of succinate dehydrogenase subunit-coding genes revealed that various point mutations, including P225F, N230I, K283N and H272R in BcSdhB, G37S and P80H in BcSdhC, and V9A in BcSdhD, were associated with the resistance to fluxapyroxad in B. cinerea. Sensitivity assays showed that the FluR isolates also exhibited resistance to another SDHI boscalid, but there was no cross-resistance between fluxapyroxad and other fungicides with different modes of action. These results indicate that the resistance of B. cinerea to fluxapyroxad has occurred in fields, and further monitoring and management of the resistance to fluxapyroxad in B. cinerea should be carried out.
Highlights
Gray mold caused by Botrytis cinerea is an important plant disease that seriously threatens the yield and quality of economically important crops, including vegetables, fruits and ornamental plants (Williamson et al 2007)
The six FluR isolates exhibited resistance to boscalid, whereas the FluR isolates and FluS isolates showed similar sensitivity to tebuconazole, fluazinam and fludioxonil (Table 2), indicating that positive cross-resistance occurred between fluxapyroxad and boscalid but not between fluxapyroxad and tebuconazole, fluazinam or fludioxonil
FluR isolates have increased sensitivity to multiple stresses and decreased virulence on host plants To determine if the stress tolerance of FluR isolates is changed compared with FluS isolates, the stress tolerance assay was performed on Potato dextrose agar (PDA) medium supplemented with Congo red, KCl, NaCl or H2O2, and the results showed that the mycelial growth inhibition rate of FluR isolates was significantly higher than that of FluS isolates under all these stress conditions (Fig. 3)
Summary
Gray mold caused by Botrytis cinerea is an important plant disease that seriously threatens the yield and quality of economically important crops, including vegetables, fruits and ornamental plants (Williamson et al 2007). Fluxapyroxad is an SDHI fungicide produced by the BASF Corporation. It binds to the succinate dehydrogenase complex (Sdh, complex II) of the respiratory chain and disrupts cellular respiration (Lin et al 2021). Different amino acid mutations in SdhC were identified in field isolates of B. cinerea; these mutations are responsible for the decreased sensitivity of B. cinerea to SDHIs (Shao et al 2020). Compared with sensitive isolates, boscalid-resistant isolates containing single amino-acid mutations (H272L/R/Y, P225F or N230) in SdhB have decreased virulence on host plants (Veloukas et al 2013). Yin et al (2018) reported that boscalid-resistant isolates containing the H272R mutation in SdhB did not exhibit significant differences in mycelial growth, osmotic sensitivity and virulence compared with boscalid-sensitive isolates. Various SDHIs have been registered to control gray mold in fields, and investigation into the development of resistance of B. cinerea to SDHIs is essential for the management of gray mold
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