Mycelial compatibility groups and pathogenicity of Sclerotinia sclerotiorum (Lib.) De Bary causal agent of white mold disease of greenhouse grown cucumber in Antalya-Turkey

Population variability of Sclerotinia sclerotiorum, the causal organism of white mold disease of greenhouse grown cucumber plants in Kumluca, Finike and Demre districts of Antalya, was determined by mycelial compatibility grouping (MCG) and isolate aggressiveness comparisons. MCG, host specificity and aggressiveness of S. sclerotiorum isolates were assessed. Isolate pairs were designated compatible when no barrage zone formed at sites of contact. They were designated incompatible when a clear zone and red line formed in the region of hyphae interaction. Among the 119 isolates tested, 20 MCGs consisted of two isolates, 5 MCGs of three isolates and 2 MCGs of seven isolates, 1 MCG of four isolates, 1 MCG of five isolates and the remaining 41 MCGs of one isolate each. Each district of Antalya was a mosaic of MCGs, but MCGs frequencies between the three districts. Variation in isolate aggressiveness was determined using a limited-term, plug inoculation technique. Isolate aggressiveness varied (P=0.05) within and among MCGs. In each location (Demre, Kumluca and Finike), highly virulent and weakly virulent isolates were obtained. Even significant differences were determined in virulence of isolates within MCGs in the same location. Pathogen population structure and variability in isolate aggressiveness may be important considerations in disease management systems.