First Detection of Sclerotinia nivalis on Carrot (Daucus carota subsp. sativus) in Russia and Comparative Pathogenicity of Sclerotinia Isolates on Carrot

White mold of carrot is mainly caused by <i>Sclerotinia sclerotiorum</i>, while <i>Sclerotinia nivalis</i> is rarely reported. This study provides the first molecular confirmation of <i>S. nivalis</i> on carrot in Russia, expanding knowledge of its global distribution. <i>rDNA-ITS</i> sequencing (100% identity with reference strains) and phylogenetic analyses confirmed the isolate as <i>S. nivalis</i>. The growth, sclerotia formation, temperature response, pathogenicity, and fungicide sensitivity of four <i>Sclerotinia</i> strains (<i>S. sclerotiorum</i> from carrot, rapeseed, and soybean, and <i>S. nivalis</i> from carrot) were compared. <i>S. nivalis</i> showed slower growth, smaller but more numerous sclerotia (2-5 mm), and an optimal temperature of 15 °C, lower than <i>S. sclerotiorum</i> (25 °C). The soybean strain <i>S. sclerotiorum</i> SC382 was the most aggressive, causing 62% necrosis of carrot leaves and complete root decay within 9 days, while <i>S. nivalis</i> and the carrot isolates showed moderate aggressiveness. The <i>S. nivalis</i> SM8 strain was four times less sensitive to fluazinam (EC₅₀ = 0.0107 µg/mL) than <i>S. sclerotiorum</i>, whereas sensitivity to boscalid and pyraclostrobin varied. These findings confirm <i>S. nivalis</i> as a new causal agent of carrot white mold in Russia and demonstrate the potential of <i>Sclerotinia</i> strains from soybean and rapeseed to infect carrot, emphasizing the need for species-level monitoring and adapted control strategies.