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