Evaluation of Lettuce (Lactuca sativa L.) Genotypes for Resistance to Lettuce Drop Caused by Sclerotinia minor Jagger

Lettuce drop caused by Sclerotinia minor Jagger is among the most economically important diseases affecting lettuce production worldwide. The present study aimed to evaluate the response of 51 lettuce genotypes originating from the gene banks of the Institute of Plant Genetic Resources, Sadovo, Bulgaria, and the Centre for Genetic Resources (CGN), Wageningen, the Netherlands, to artificial infection with S. minor. Field experiments were conducted during 2025 and 2026 under open-field conditions. Plants were inoculated with isolate 35A of S. minor, and survival rates were assessed 30 days after inoculation. Significant differences among genotypes were observed regarding their response to pathogen infection. No immune genotypes were identified. The highest survival rates were recorded for the genotypes Lollo Rossa, Bianka, Belokriska-16260 and Therna Gyumurdjaska-13312, which were classified as slightly susceptible. These accessions may serve as valuable sources of partial resistance in future breeding programs. The results confirm the scarcity of highly resistant lettuce germplasm and emphasize the necessity of integrating genetic resistance with other disease management strategies.