Response to selection for salt tolerance during germination in tomato seed derived from PI 174263

The effectiveness of directional phenotypic selection to improve tomato (Lycopersicon esculentum Mill.) seed germination under salt-stress was investigated. Seed of F₂ and F₃ progeny of F₁ hybrids between a salt- tolerant (PI 174263) and a salt-sensitive (UCT5) tomato cultivar were evaluated for germination response at three stress levels of 100 (low), 150 (intermediate), and 200 mM (high) synthetic sea salt (SSS). At each salt- stress level, the most tolerant individuals, as determined by the germination speed, were selected. Selected individuals (F₂s or F₃s) were grown to maturity and self-pollinated to produce F₃ and F₄ progeny families. The selected progeny from each experiment were evaluated for germination at four treatment levels of 0 (nonstress), 100, 150, and 200 mM SSS and were compared with unselected populations. The results indicated that selections were equally effective at all three salt-stress levels and in F₂ and F₃ generations and significantly improved seed germination of progeny under salt-stress and nonstress treatments. Estimates of realized heritability for rapid germination under the various salt-stress levels ranged from 0.67 to 0.76. Analysis of response and correlated response to selection indicated a genetic correspondence of up to 100% between germination at different salt- stress levels. Genotypic family correlations between germination at the low, intermediate, and high salt-stress levels ranged from 0.67 to 0.89, and those between nonstress and salt-stress conditions ranged from 0.25 (between 0 and 200 mM) to 0.71 (between 0 and 100 mM salt). The results indicated that similar or identical genes with additive genetic effects contributed to rapid germination response of tomato seeds at different salt-stress levels. Thus, selection at one stress level resulted in progeny with improved germination at diverse salt-stress levels. The results also indicated that to improve tomato seed germination, selection can be based on individual seed performance and early segregating generations.