Mycelial Compatibility Groups and Pathogenicity of Sclerotinia sclerotiorum (Lib.) De Bary isolates, Causal Agent of Cabbage Head Rot in Urmia

In this study, 223 isolates of Sclerotinia sclerotiorum, the causal agent of cabbage head rot, were collected from different fields in Urmia. Identification of mycelial compatibility groups (MCGs) was done on Potato Dextrose Agar (PDA) culture medium amended with McCormick's red food coloring. A total of 36 MCGs were identified. 23 MCGs (63.88%) had one isolate and the others had more than one isolate. Aggressiveness of the isolates was done on detached cabbage leaves in laboratory conditions and lesion development was determined on treated leaves. All tested isolates were pathogenic on cabbage leaves and disease symptoms were developed, but the aggressiveness was varied greatly among isolates. There was not any correlation between aggressiveness of the isolates, MCGs and isolation location. Isolates obtained from one field were grouped in different MCGs, and there was a difference in aggressiveness, MCGs, and isolation location. The Obtained isolates from one field were grouped in different MCGs, and there was a difference in aggressiveness of isolates within and among MCGs. Results showed that there was a high level of mycelial incompatibility among the Sclerotinia sclerotiorum isolates which were obtained from cabbage fields in Urmia. The high level of mycelial incomtibility indicates the genetic heterogeneity in this fungus and should be considered in management strategies especially using resistant cultivars.