Diversity in Morphological Traits, Cultural Characteristics, and Virulence of Sclerotinia sclerotiorum Isolates in Oilseed rape in Germany

Sclerotinia sclerotiorum causes white mold or stem rot in numerous important crops, including oilseed rape. Evaluating morphological traits, cultural characteristics, and virulence among various pathogen isolates is essential for an efficient management strategy. Thus, this study aimed to collect and characterize S. sclerotiorum isolates from diverse regions across Germany. The occurrence of Sclerotinia stem rot in oilseed rape fields in Germany varied from 2020 to 2022, with a total of 62 infested fields identified across 12 federal states. The disease incidence varied notably within these fields, ranging from 2 to 42%. In total, 62 isolates were collected, revealing differences in colony colour, number of produced sclerotia, weight of them, sclerotia formation patterns, mycelium growth index, and mycelial compatibility grouping. Furthermore, the virulence of the isolates were evaluated through their inoculation into five oilseed rape cultivars at the cotyledon stage. The outcomes of the one and two-way ANOVA analysis revealed significant effects for both S. sclerotiorum isolate and oilseed rape cultivar, as well as their interaction (P ≤ 0.05). Out of the evaluated isolates, 16 had low virulence (lesion area below 10%), 39 displayed moderate virulence (lesion area between 10 and 30%), and seven showed high virulence (lesion area above 30%). The evidence presented in this study contributes to a comprehensive understanding of the morphological and reproductive behaviours within German S. sclerotiorum populations, along with insights into pathogen virulence. Such systematic assessments can significantly improve the development of effective management strategies to reduce Sclerotinia stem rot disease.