Evaluation of Adult-Stage Salt Tolerance Identifies Promising Tomato Accessions Under Saline and Non-Saline Conditions

Soil salinization is a major abiotic constraint on tomato production worldwide. To evaluate adult-stage tomato performance under contrasting saline and non-saline conditions, 23 tomato accessions (13 large-fruited and 10 cherry types) were evaluated at two solar-greenhouse locations in Hebei Province, China: a non-saline site in Shijiazhuang and a saline–alkali site in Huanghua, Cangzhou. Eleven growth, biomass, yield, and quality traits were assessed, and salt tolerance coefficients (STCs) were calculated to characterize relative trait performance between the two sites. Accessions were also genotyped using a PARMS marker linked to SlHAK20. Biomass accumulation was generally lower at the saline site, with above-ground and root dry weights showing the largest relative differences between the two sites, whereas plant height differed comparatively little. Total soluble solids (TSS) were higher at the saline site in most accessions, with the largest relative difference (91.7%) observed in large-fruited accession 305. Correlation analysis revealed strong positive associations between fresh and dry weights of both shoot and root tissues (p < 0.0001). Large-fruited accession 305 and cherry accession 436 showed comparatively favorable biomass retention and relatively small morphological differences between the two sites and therefore represent candidate accessions for further evaluation. The observed SlHAK20-linked marker genotypes were not consistently aligned with phenotypic performance among accessions, indicating that the predictive value of this marker requires further validation. These findings should be interpreted cautiously because salinity was confounded with location, the experiment was conducted during a single growing season, and the marker analysis was not validated in an independent population. This study provides a preliminary comparative evaluation approach and candidate accessions for further investigation and breeding of tomatoes adapted to saline environments.