GENETIC-ANALYSIS OF LOW-TEMPERATURE TOLERANCE DURING GERMINATION IN TOMATO, LYCOPERSICON-ESCULENTUM MILL

The genetic basis of low-temperature tolerance during germination of t omato seed was investigated using two approaches. First, a cold-tolera nt (PI 120256) and a cold-sensitive tomato cultivar (UCT5) and their r eciprocal F-2, F-3 and BC1 progeny (total of 10 generations) were eval uated for germination at a low (11 +/- 0.5 degrees C) and a high (cont rol) temperature (20 +/- 0.5 degrees C). Weighted least-square regress ion analysis indicated that in the low-temperature treatment most of t he variation resulted from additive genetic effects, and dominance and epistatic interactions were nonsignificant. Partitioning of the total genetic variance into those attributable to the effects of embryo, en dosperm, testa and the cytoplasm indicated that additive effects of en dosperm and embryo could individually account for 80% and 77% of the t otal variance, respectively. In the control treatment, greater than 60 % of the variation could be explained by individual additive effects o f endosperm or embryo and approximate to 27% of the variation could be explained by embryo dominance effects. Across generations, there was a positive correlation (r = 0.78, P < 0.01) between germination in the control and low-temperature treatments and there were no significant genotype x temperature interactions. The results indicate the presence of similar or identical genes with predominantly additive effects on germination under both low and high temperatures. In the second approa ch, the effectiveness of directional phenotypic selection to improve t omato cold tolerance during germination was evaluated by selecting (in an F-2 population of the same cross) the fastest germinating seeds un der low temperature and comparing the germination of the selected F-3 progeny with germination of an unselected F-3 population. The results indicated that selection was highly effective and significantly improv ed germination performance of the progeny; a realized heritability of 0.74 was obtained for low-temperature tolerance during germination. It is concluded that in these tomato lines germination under low tempera ture is genetically controlled, with additivity being the major geneti c component, and thus the trait can be improved by phenotypic selectio n.