Physiology of salt tolerance introgressions from in the domesticated tomato.

INTRODUCTION

Wild trait introgression is a valuable breeding tool for increasing tomato salinity tolerance. However, this process often results in deleterious linkage drag. Understanding the physiological and molecular mechanisms underlying salinity response can aid in developing salt-tolerant cultivars while minimizing undesirable traits. This study investigates the salinity response of the tomato cultivar OH8245, accession LA1141, and two derived introgression lines (ILs SG18_197 and SG18_247) that were previously screened for salt tolerance traits.

METHODS

The physiological and molecular responses of OH8245, LA1141, and the two ILs were analyzed under salinity stress. Key salinity tolerance traits were evaluated, including root characteristics, water status, ion homeostasis, stomatal density, photosynthetic rate, and relative growth rate. Differential gene expression analysis was conducted to identify genes associated with salinity tolerance, comparing the number and uniqueness of differentially expressed genes (DEGs) across genotypes.

RESULTS

LA1141 exhibited multiple salinity tolerance traits, such as higher specific root length, increased root hydraulic conductivity, and improved plant water status. It also maintained better ion homeostasis and had lower stomatal density compared to OH8245. In contrast, OH8245 demonstrated traits supporting greater biomass accumulation, including a higher photosynthetic rate and relative growth rate. Differential gene expression analysis revealed that LA1141 had the fewest DEGs (706), whereas OH8245 had one of the highest (2524), suggesting a constitutive set of genes contributing to salinity or abiotic stress tolerance. Additionally, 40 DEGs were uniquely found in LA1141 under salinity, with nine and 16 of these transferred to ILs SG18_197 and SG18_247, respectively.

DISCUSSION

Salinity tolerance is a complex trait that imposes an energy cost on the plant. However, key beneficial traits, including improved plant water potential, higher photosynthetic rate, and a lower sodium/potassium ratio, were successfully transferred from LA1141 to at least one of the ILs. These findings provide valuable insights for tomato breeding programs aimed at enhancing salinity tolerance while balancing growth and stress resistance traits.