Physiology of salt tolerance introgressions from Solanum galapagense in the domesticated tomato

Soil salinity is one of the major abiotic stresses limiting tomato yield and no tolerant cultivar is available yet. This study utilized two introgression lines (ILs) and their parents (a cultivated tomato and Solanum galapagense) previously screened for salt tolerance traits, including higher plant water potential and photosynthetic rate, to understand the physiological and molecular mechanisms from wild relative introgressions. We performed an extensive physiological characterization of all genotypes, including the mechanistic responses to salinity such as leaf gas exchange, plant water relations, biomass, leaf and root morphology, root hydraulic conductivity, and leaf nutrient content. After a three-week exposure to salt stress, we analyzed gene expression in the root tips through RNA-seq and the transcriptome SNPs among genotypes to understand the molecular mechanisms in the roots that allow for better plant water and nutrient status under salinity stress. Not a single trait could markedly improve salinity tolerance although the tomato wild relative LA1141 showed a set of salt tolerance traits, such as ion homeostasis, low stomatal density and high plant water status. Some of these traits were successfully transferred to the ILs and improved their performance under salinity. This study provides information to effectively support tomato breeding for salinity tolerance.