LAUSR

Previous studies in Botrytis cinerea showed that the resistance to methyl benzimidazole carbamates (MBCs) was mainly related to E198A/V/K and F200Y mutations of the β-tubulin gene, and the E198V was the dominant mutation in the resistant sub-population in Hubei Province of China, indicating that resistant mutation might influence the fitness. However, little is known on the effect of each E198A/V/K mutation on fitness. In this study, the fitness and competitive ability of isolates with E198A/V/K mutations were investigated. Results showed that E198A/V/K isolates and the wild-type isolates shared similar fitness components at virulence, sporulation, conidial germination, oxidative sensitivity, sclerotial production and viability. However, slower mycelial growth at 4°C, higher sensitivity to 4% NaCl, and increased sclerotial production percentage at 4°C were observed in the isolates with E198V, E198K, and E198A mutation, respectively. Competitive analysis showed that the wild-type sub-population became dominant after three disease cycles in the absence of fungicide selection pressure, whereas the resistant sub-population seized the space of sensitive sub-population upon MBC application. Unexpectedly, the frequency of E198V isolates decreased dramatically since the first disease cycle with or without fungicide selection pressure. These results suggest that MBC resistant isolates suffer little fitness penalty, but possess competitive disadvantages in the absence of fungicide selection pressure. Under fungicide selection pressure, E198V isolates could not compete with E198A/K isolates. According to the current results, there was a great possibility that the E198V mutation would lose the dominance in the future in China.