Physiological, chemical and gene expression analyses under salt stress for several tomato genotypes

Water salinity greatly affects growth and production of agricultural crops. Thus, yield enhancement under salinity conditions is a major goal of plant breeders. Six advanced tomato lines along with their original populations and two salinity tolerant lines were used to evaluate their response to salt stress and select starting material for salinity tolerance breeding program. Proline accumulation, water use efficiency (WUE), leaf Na+, Cl-, Ca2+ and K+ concentrations were measured. The expression of salt responsive genes were measured for all genotypes under salt stress using real-time PCR, where action levels were used to normalize the data. There was a great decrease in WUE as salinity level increased. High salinity levels increased leaf proline contents, Na+ and Cl- concentrations. In addition, it lowered Ca++ and K+ concentrations. The maximum proline content was found in BL 1239, BL 1076, L56 and L26 genotypes, respectively. However, the minimum value was found in L46 and Shohba genotypes. The improved line L56 had the highest value for WUE while BL1239 had the lowest value. Significant differences among genotypes were found in all traits, suggesting they could be taken into account when selecting for salt tolerance. The classification of the genotypes for salt tolerance would vary according to a specific trait. Based on ion concentration and proline accumulation as affected by salinity, the selected salinity tolerant tomato genotypes were BL 1076 and L56. However, L46 was selected as salinity susceptible. The expression level of NAM, GRX1, TAS14 and JERF3 as an indicator for salinity tolerance varied from improved line to another. JERF3 expression showed more than 100-fold increase in L12 compared to the parent cultivar, while TAS14 expression increased 10- to 90-fold for all improved lines as comapred to their original parents. Expression was prominent for three genes (NAM, GRX1, TAS14 and JERF3) in L12 and L56 lines as compared to the salt tolerant lines (BL 1076 and BL 1239).