Sensitivity stability and fitness of Botrytis cinerea isolates to captan

The present study investigated the sensitivity and stability of Botrytis cinerea isolates collected from vineyards to captan. To determine the stability of sensitivity to captan, B. cinerea isolates on fungicide-free potato dextrose agar (PDA) was evaluated after 15 culture cycles. In some isolates with reduced sensitivity to captan, EC50 value of the isolates did not change compared to that of isolates that were initially sensitive to captan; suggesting that the decrease/increase in the sensitivity to fungicide may be stable. Isolates sensitive to captan adapted to increasing doses of captan by decreasing their sensitivity, and this adaptation remained stable in the fungicide-free medium. The fitness components included mycelial growth rate, sporulation, and virulence of the isolates. There were significant differences between isolates sensitive to captan and those with decreased sensitivity to captan, in terms of mycelial growth rate, sporulation, and virulence. The growth rate of isolates with decreasing sensitivity to captan was as high as the growth rate of those sensitive to captan. However, isolates with decreased sensitivity to captan showed higher virulence than those sensitive to captan, and the difference between these isolates was significant. Sporulation was dependent on the performance of the individual isolates. Key words: Gray mould, sensitivity, captan, fungicide, virulence.