Abstract
Sclerotinia spp. are globally distributed, devastating plant pathogens with a broad host range, including lettuce, on which they cause lettuce drop disease. To investigate the geographical distribution of lettuce drop incidence and the population structure of Sclerotinia sclerotiorum and S. minor in Serbia, 27 commercial lettuce fields across 12 administrative districts were surveyed. Sclerotinia spp. were confirmed at 10 localities, with S. sclerotiorum occurring more frequently. Co-occurrence of both species within the same field was recorded at only one location. Clear phenotypic and physiological differences were found between Sclerotinia species, as well as among isolates within each species. The two species differed in colony appearance, sclerotia production, virulence, growth rate, oxalic acid production, and tolerance to elevated osmotic pressure. Haplotype analysis of S. minor revealed the existence of 9 haplotypes arranged in a star-shaped network. These findings highlight the importance of considering both inter- and intraspecific variability of Sclerotinia species when evaluating their impact on crops, improving our understanding of Sclerotinia populations in lettuce, and supporting the development of effective management strategies.