There is a wealth of genetic variability within modern and heirloom tomato cultivars, landraces, and wild species for improvement of fruit nutritive value. Progress in breeding for improved tomato nutritional value is largely influenced by availability of sufficient genetic diversity and knowledge of gene action. Breeding strategies for improved nutritional composition are similar to those for other traits in a cultivar development program. Based on knowledge gained through investigations of the character's heritability, the mode of inheritance, and existing genetic variability, appropriate breeding strategies based on phe-notypic selection of individuals or families have been implemented to realize improvements in crop nutritional quality. Development of gene-specific probes and identification of markers tightly linked to phy-tonutrient constituent loci enables implementation of MAS strategies for genotypic selection of well-studied traits. Recent studies demonstrate renewed interest in characterization of Solanum tomato germplasm collections for fruit phytonutrients and devising selection indices to maximize breeding efficiency (Hanson et al. 2004; Rousseaux et al. 2005; Willits et al. 2005). Recent applications of metabolic profiling to tomato ILs and wild species provide new opportunities to link QTL with specific phytonutrients (Overy et al. 2005; Schauer et al. 2005, 2006; Schauer and Fernie 2006) (see Sect. 1.16).
The evidence of accumulated studies indicates a positive link between fruit and vegetable consumption and improved health. By virtue of the volume of tomato products that are consumed, tomatoes make important contributions to the dietary intake of vitamin A (9.5%) and vitamin C (11.5%) (USDA 2002).
Lycopene imparts red fruit color and also acts as a dietary antioxidant. In addition to these well-known vitamins and antioxidants, other compounds in tomato fruit with antioxidant properties include chlorogenic acid, rutin, plastoquinones, tocopherol, and xantho-phylls (Beecher 1998; Leonardi etal. 2000). Tomatoes also contribute carbohydrates, fiber, flavor compounds, minerals, protein, fats and glycoalkaloids to the diet (Davies and Hobson 1981; Gundersen et al. 2001). Whereas nutrition studies have often focused on a single dietary phytonutrient, research clearly indicates that there are many bioactive compounds in food products and that it may be the combination of compounds that confer the beneficial health effects described (Laquatra et al. 2005).
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