1999 Volume 16 Issue 1 Pages 55-64
Quantitative genetic analysis of tomato response to salt or cold stress during seed germination and vegetative growth indicated that both salt and cold tolerance were complex traits, controlled by more than one gene and highly influenced by environmental variation. Molecular marker analyses indicated that at each stage of plant development salt tolerance or cold tolerance was generally controlled by the effects of a few major QTLs (quantitative trait loci) which acted in concert with a number of smaller-effect QTLs. At the seed germination stage, two types of QTLs were identified: those which affected germination under both stress and nonstress conditions, and thus were called stress-nonspecific QTLs, and those which contributed to rapid seed germination only under specific stress conditions, and thus were called stress-specific QTLs. Generally, the stress-nonspecific QTLs exhibited larger effects than the stress-specific QTLs. Consistent with this observation, selection for either salt or cold tolerance during germination resulted in progeny with improved germination under salt and cold stress as well as nonstress conditions. Comparison of salt tolerance during germination and vegetative growth indicated that mostly different QTLs contributed to tolerance at these two developmental stages; furthermore, selection for salt tolerance during germination did not affect progeny salt tolerance during vegetative growth. Similar results were obtained when cold tolerance during germination and vegetative growth were compared. The overall results indicate that, in tomato, stress tolerance during germination is independent of stress tolerance during vegetative growth. However, simultaneous improvement of plants for stress tolerance at multiple stages of plant development should be feasible through marker-assisted selection and breeding.