Effect of Immature Green Tomato Fruit Color on Yellow Shoulder Incidence and Soluble Solids Content of Ripe Fruit

Tomato (Solanum lycopersicum) breeders have observed that plants with uniform green-shouldered fruit are less prone to yellow shoulder (YS) than are plants with (dark) green-shouldered tomatoes and thus have selected for tomato cultivars with uniform green-shouldered fruit. However, a recent publication reported that a cultivar with green-shouldered fruit had significantly higher soluble solids content (SSC) than an isogenic cultivar with uniform green-shouldered fruit and postulated that selection of uniform green shoulder has negatively affected tomato flavor and processing quality. Lines with dark green (u(+)), uniform green (u), uniform gray-green (ug), apple green (u(Ag)), medium green, and pale green (u(Pg)) immature fruit colors were crossed in all combinations to produce F-1 plants that were self-pollinated to produce F-2 seed. Parents, F-1, and F(2)s were planted in the field in completely randomized block designs over two seasons. Plants were visually phenotyped for immature fruit color, and fruit from each plant were selected to measure shoulder and base color with a colorimeter. Ripening fruit were harvested to measure the incidence of YS, and SSC was measured on ripe fruit from each plant with a refractometer. In the spring season, fruit from F-2 plants with green-shouldered fruit had significantly higher YS incidence than all phenotypes with uniform fruit colors. In the fall, phenotypes with medium-green shoulders were also tested, and these had greater YS than all other phenotypes except green shoulder. YS incidence for green shoulder was not significantly greater than that in the other phenotypes. Fla. 7956, the apple green parent, had 0% YS and appeared to be resistant. Higher SSC was observed in the spring season than in the fall season. However, in both seasons, when comparisons were made between phenotypes that segregated in the F(2)s, the SSC of green-shouldered phenotypes was not significantly higher than that of other phenotypes. Plants with apple green fruit tended to be higher in SSC in the fall, but this may relate to the dark green foliage of apple green plants and not just the fruit color. A hypothesis that stress may relate to reported SSC increases because of u(+) is discussed.