Divergent Gene Expression Responses to Salinity Stress in 16 Geographically Diverse Spinach Genotypes

Salinity stands as a critical abiotic stress factor, posing significant challenges to global agricultural productivity. However, there is no comprehensive study that simultaneously investigates multiple spinach genotypes; integrates assessments of various parameters like biomass yield, ion uptake, and partitioning; and conducts genetic characterization of salinity tolerance mechanisms. To address this gap, we conducted a greenhouse experiment with 16 spinach genotypes, from diverse geographical regions, irrigated with saline waters of 1.87 and 23.3 dS m–1. The salt tolerance index for shoot biomass exhibited significant variability among the genotypes, with 'Dikenli', 'Victoria', and 'Cornell ID #148' being the top performers and 'Cornell ID #87', 'Gazelle', and 'Polag Benaresi' being the bottom performers. Under high salinity, on average, plants accumulated 25-fold higher Na and 8.5-fold higher Cl in leaves compared to the control. Leaves accumulated 2.4-fold more Na and Cl than roots under salinity compared to the control. Expression analyses of specific genes in roots and leaves provided insights into Na+/Cl–efflux, vacuolar sequestration, root-to-shoot movement, ion homeostasis, and scavenging of reactive oxygen species. Our results demonstrate the importance of screening geographically diverse genotypes and considering multiple traits when selecting genotypes for salt tolerance.