Selection of a Suitable Medium to Determine Sensitivity of Monilinia fructicola Mycelium to SDHI Fungicides

Succinate dehydrogenase inhibitor (SDHI) fungicides are important tools to control preharvest and postharvest brown rot of stone fruits. In this study we determined the mycelial growth rate of Monilinia fructicola isolates on various media and picked the three that allowed the fastest growth to assess the sensitivity of mycelium to SDHI fungicides boscalid, fluopyram, and penthiopyrad. Minimal medium (MM) supported mycelial growth the best and yielded lowest EC50 values for three SDHI fungicides. EC50 values corresponded with disease incidence data obtained from detached fruit assays. Penthiopyrad had significantly greater intrinsic activity in vitro compared to fluopyram at the α = 0.05 level and compared to boscalid at the α = 0.1 level. However, detached fruit assays revealed that this ‘advantage’ did not carry over in vivo. In conclusion, MM appears to be the best medium currently available to assess the sensitivity of M. fructicola mycelium in vitro.