Relationship between cold tolerance during seed germination and vegetative growth in tomato: Analysis of response and correlated response to selection

The genetic relationship between cold tolerance (CT) during seed germination and vegetative growth in tomato (Lycopersicon esculentum Mill.) was determined. An F₂ population of a cross between accession PI120256 (cold tolerant during both seed germination and vegetative growth) and UCT5 (cold sensitive during both stages) was evaluated for germination under cold stress and the most cold tolerant progeny (the first 5% germinated) were selected. Selected progeny were grown to maturity and self-fertilized to produce F₃ families (referred to as the selected F₃ population). The selected F₃ population was evaluated for CT separately during seed germination and vegetative growth and its performance was compared with that of a nonselected F₃ population of the same cross. Results indicated that selection for CT during seed germination significantly improved CT of the progeny during germination; a realized heritability of 0.75 was obtained for CT during seed germination. However, selection for CT during germination did not affect plant CT during vegetative growth; there was no significant difference between the selected and nonselected F₃ populations in either absolute CT [defined as shoot fresh weight (FW) under cold stress] or relative CT (defined as shoot FW under cold as a percentage of control). Results indicated that, in PI120256, CT during seed germination was genetically independent of CT during vegetative growth. Thus, to develop tomato cultivars with improved CT during different developmental stages, selection protocols that include all critical stages are necessary.