Genetics and Salt Stress Resistance Characteristics in Tomato Species

Several species of tomato are sources of salt resistance: S. pimpinellifolium, S. cheesmaniae, S. galapagense, S. pennellii and S. peruvianum (reviewed in Flowers 2004; Foolad 2004; Cuartero et al. 2006). As with drought, salt stress may have more than one definition, and resistance or tolerance to salt depends on the developmental stage of the plant (Foolad and Lin 1997). There are several possible physiological processes or components of salt tolerance and mapping of QTL for salt tolerance in tomato has been productive, particularly in interspecific crosses between cultivated tomato and S. pimpinellifolium (Foolad 1999; Foolad and Chen 1999; Foolad et al. 1997,1998, 2001). These analyses have focused on salt tolerance expressed during seed germination and vegetative growth. QTLs for salt tolerance have been mapped to chromosomes 3, 5 and 9. Markers for these loci are predicted to be useful in MAS breeding programs (Foolad 2004).

Salt stress tolerance during fruit development has been investigated primarily in crosses between cultivated tomato and S. pimpinellifolium or S. galapagense (Monforte et al. 1996,1997a, b, 1999). In these studies, total fruit weight and its components, fruit number, fruit weight and earliness were estimated and analyzed with molecular markers located throughout the genome. For the S. lycopersicum x S. pimpinellifolium analysis, a number of QTLs for salt tolerance were detected at loci known to be associated with fruit weight (Monforte et al. 1997a). In addition, there were differences depending on the specific S. pimpinellifolium accession and whether the plants were grown under saline or control conditions (Monforte et al. 1997a, b). When S. galapagense was the source of salt tolerance, results were confounded by a pleiotropic effect on earliness. F2 progeny were bimodal for fruit development with an early and late population. The salt tolerance phenotype of S. galapagense was not observed among the F2 in the early population, but could be detected in the late population (Monforte etal. 1999).

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