Tomato under Salinity Stress: Correlation between Growth and Yield Components and Responsive Genes

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 vegetative and yield traits response to salt stress using five salinity levels of NaCl (0.5 control treatment, 2.4, 4.8, 7.2 and 9.6 dS m(-1)). At 50% flowering, random samples of plants were chosen for measuring plant growth traits; plant height, stem diameter, leaf area, leaf fresh and dry weight. The dried leaf samples were ground and used to determine leaf concentrations of Na+, Cl-, Ca2+ and K+. Total yield, average fruit weight, number of fruit per plant and water use efficiency were also measured. Random representative samples of five fruits were taken from each experimental unit to determine fruit quality traits (fruit flesh thickness, total soluble solids, Vitamin C and pH). For expression analysis, total RNA was isolated from leaves using an isolation dedicated kit. Fragmented aRNA was hybridized into Affymetrix tomato genome microarray. The top 50 genes were selected based on the fold increase in expression when comparing salinity stressed plants to those grown under control conditions. The phenotypic correlation coefficients (r) were calculated for all possible pairs of the studied traits, over all the five salinity levels and the fourteen genotypes over two seasons The results showed significant and desirable positive correlation between total yield and nine traits; plant height (0.83(star star)), stem diameter (0.76(star star)), leaf area (0.67(star star)), average fruit weight (0.84(star star)), average fruit number (0.95(star star)), Ca2+ content (0.45(star)), K+ content (0.80(star)), fruit flesh thickness (0.88(star star)) and WUE (0.99(star star)). On the other hand, significant negative correlations were detected between total yield trait and both Na+ content (-0.53(star)) and total soluble solids (-0.82). These results indicated the importance of these traits in yield improvement and in selection program. Based on the performance of the tomato genotypes at different salinity levels, four genotypes were selected to represent salt susceptible, moderately salt tolerant, salt tolerant, and reference salt tolerant. The phenotypic correlation coefficients values between the total yield trait and 50 responsive genes for the selected tomato genotypes under high salinity level were determined. The results showed significant and desirable positive correlation between total yield trait and eight potential genes; JAZ8 (0.97(star)), Polcalcin jun (0.99(star star)), Polcalcin jun (0.98(star)), ER5 (0.96(star)), ATPase 3 (0.96(star)), XTH (0.97(star)), WRKY (0.95(star)), and TSW12 (0.95(star)). Therefore, these genes can be considered as salinity responsive genes that can be further utilized in breeding programs.