A tomato line hyposensitive to simulated proximity shade shows altered auxin-related 1 gene expression and improved fruit yield under high-density field conditions

Plants detect the presence of nearby vegetation as a reduction in the ratio of red to far-red light (low R/FR). This proximity shade signal can be simulated in the lab by supplementing white light (W) with FR (W+FR). While shade avoidance strategies are considered undesirable in agricultural crops, FR supplementation enhances plant growth and fruit quality in tomato (Solanum lycopersicum). Here we compared the response of different tomato genotypes to W+FR in the lab and identified one S. pennellii introgression line (IL2-2) with a shade-tolerant phenotype at the seedling stage. Compared to the shade-avoider parental genotype M82, IL2-2 plants showed reduced elongation upon W+FR exposure and a disrupted expression of auxin-related genes both under W and W+FR. At harvest, W+FR treatment improved M82 fruit quality by increasing {degrees}Brix, ascorbic acid and carotenoids, and these quality traits remained virtually unchanged in IL2-2. Under high density (HD) conditions, fruit quality traits were hardly impacted by planting density or genotype, but IL2-2 showed improved fruit yield. Our findings suggest that IL2-2 could serve as a valuable genotype for high-density or intercropping agrosystems.