Principal component analysis-assisted screening and selection of salt-tolerant tomato genotypes

Tomato ( Solanum lycopersicum L.) has been classified as a moderately salinity tolerant vegetable crop. Screening germplasm for salinity-tolerant is one of the critical steps in tomato breeding programs. In the present study, levels of salt tolerance for eleven tomato genotypes (TG1 to TG11) were assessed at the seedling stage under laboratory conditions and the vegetative stage under field conditions. Salt stress was imposed by watering with 150 mM NaCl. Twenty morphological and physio-biochemical traits were measured and analyzed using multivariate analysis [Pearson’s correlation analysis and Principal component analysis (PCA)] to discern salt sensitivity from tolerant genotypes. The PCA-I was applied for nineteen variables and the PCA-II was performed only with fourteen variables. The effects of salt exposure on morpho-physiological parameters (dry weight, relative water content and chlorophyll stability index) are the main contributors to differential salt tolerance in tomato genotypes. The first and second axes of the PCA analyses classified the genotypes TG7 & TG8 as salt tolerant and TG9 & TG10 as salt sensitive under laboratory (at the seedling stage) and field conditions (at the vegetative stage). Our data additionally demonstrates that the salt tolerance identified at the seedling stage was also discerned as such when grown and analyzed at the vegetative stage. The two groups of genotypes identified as having a contrasting levels of salt tolerance may be used as parents in future tomato breeding programs. This study furthermore authenticates the practical application of PCA analysis to distinguish the variability in tomato genotypes and its possible application to other crops for screening salt tolerance.