Fine-mapping of sm6.1, a novel locus conferring resistance to gray leaf spot from Solanum habrochaites accession LA1777.

The single recessive locus, sm6.1, conferring high resistance to gray leaf spot and was fine-mapped to a 78.4 kb region on chromosome 6 of tomato through a genetic mapping strategy. Gray leaf spot (GLS), caused by the necrotrophic fungal pathogen of the genus Stemphylium, is one of the most prevalent and destructive foliar diseases affecting tomato production worldwide. In this study, we identified a novel resistance locus, designated sm6.1, derived from the wild tomato species Solanum habrochaites accession LA1777, which confers high resistance to Stemphylium solani. Genetic analysis revealed that resistance conferred by the sm6.1 locus follows a recessive inheritance pattern. Through genetic mapping strategy, we fine-mapped the sm6.1 locus to a 78.4 kb region on chromosome 6, containing nine annotated genes based on the tomato reference genome Heinz 1706 (SL4.0, ITAG4.0). By integrating synteny analysis, sequence variation screening, and expression analysis, we identified Solyc06g053340 and Solyc06g053350 as the critical candidate genes underlying sm6.1. To facilitate marker-assisted breeding, we developed InDel markers that are tightly linked to the sm6.1 locus. The identification and fine-mapping of sm6.1 not only provide a novel genetic resource for breeding GLS-resistant tomato cultivars but also establish a foundation for elucidating the molecular mechanisms underlying GLS resistance in tomato.