The sls‐1 and sls‐2 Genes Confer Significant Resistance to Septoria Leaf Spot ( Septoria lycopersici L.) in Organic Field‐Grown Tomatoes ( Solanum lycopersicum )

Septoria leaf spot (SLS) is a major foliar disease affecting tomato production, causing significant yield losses. This study evaluates the effect of two novel SLS resistance genes, sls‐1 and sls‐2 , on SLS severity in open‐field tomatoes and their potential to be used in hybrid tomato varieties. Two F 2 populations segregating for sls‐1 and sls‐2 were grown in 2022 and 2023 using a randomized block design with six replicates per genotype. SLS severity was assessed biweekly, and the area under the disease progress curve (AUDPC) was calculated annually. sls ‐ 1 exhibited a dominance effect, with the resistant (R) genotype showing the lowest AUDPC score (296), followed by the heterozygous (H) genotype (311) and susceptible (S) genotype (794). The sls‐2 gene showed an additive effect, with the resistant genotype having the lowest SLS AUDPC (293), followed by the heterozygous (464) and susceptible genotypes (644). The R/R, R/H and H/R genotypes ( sls‐1/sls‐2 interaction genotypes) showed the lowest SLS scores in 2022. The incorporation of these genes into breeding programmes could offer a sustainable alternative to pesticide use, enhancing pest management and supporting more environmentally friendly tomato production systems.