MYCELIAL INCOMPATIBILITY OF SCLEROTINIA SCLEROTIORUM ISOLATES FROM A SINGLE RAPESEED FIELD IN SLOVAKIA

Sclerotinia sclerotiorum (Lib.) de Bary (1884) is economically important pathogen of rapeseeds damaging up to 20% of plants in Slovakia. There is a suggestion that S. sclerotiorum reproduces predominantly asexually, thus genetically identical clonal populations are dominating in fields. Genetically distinct isolates can be distinguished by mycelial compatibility-incompatibility grouping system. The aim of the study was to determine genetic variability of S. sclerotiorum based on mycelial interaction within a single oilseed rape field in Slovakia. S. sclerotiorum isolates were obtained from flower petals of commercial rapeseeds field in Hul, Slovakia (2018) by transferring a single hyphal tip to the plates with potato dextrose agar (PDA). Two sets of 20 isolates were paired in all possible combination and cultivated on PDA amended by bromophenol blue. Mycelial interactions were scored after 7 days. Each of the 20 isolates in 1st set was unique and belonged to the different mycelial compatibility groups (MCGs). In the 2nd set, 18 MCGs was determined with one isolate and only 1 MCGs consisted of 2 isolates. No prevalent MCG was found in this study, suggesting that S. sclerotiorum population affecting the target rapeseed field consisted of a very diverse group of isolates. The high level of incompatible reactions found in this first study from Slovakia may indicate that S. sclerotiorum undergoes frequent outcrossing in rapeseed stands.