In Vitro Study of Fitness Parameters in Fungicide-Resistant and -Sensitive Venturia inaequalis Isolates

The developing resistance of Venturia inaequalis to toxicants commonly used in systemic fungicides against apple scab has reduced their effectiveness, causing substantial fruit loss in orchards. To improve the situation and manage the resistance, a thorough analysis of the fitness potential among different pathogen biotypes, particularly those resistant to fungicides, is needed. In this study, the mycelial growth of V. inaequalis isolates with baseline sensitivity and resistance to one or more fungicides was assessed in vitro at four temperatures (6, 18, 27, and 30°C) and three agar concentrations in the nutrient medium (2, 4, and 6% m/V). Except for the mycelial growth at 27°C, the indicators of fitness predicted in vitro did not differ significantly between the V. inaequalis isolates with multiple resistance to fungicides and the biotypes with baseline sensitivity.