Increase in Epidermal Planar Cell Density Accompanies Decreased Russeting of ‘Golden Delicious’ Apples Treated with Gibberellin A4+7

Abstract

A 2-year study was conducted in a ‘Golden Delicious’ (Malus ×domestica Borkh.) orchard with a high incidence of physiological fruit russeting to examine the effect of gibberellin A4+7 (GA4+7) on apple epidermal cell size. Beginning at petal fall, four sequential applications of GA4+7 (0, 15, or 30 mg·L−1) were applied to whole trees every 7–10 days with an orchard air-blast sprayer at a volume of ≈1000 L·ha−1. Fruit epidermal tissue samples were taken approximately monthly beginning 1 week after the fourth application. Tissue was treated in the laboratory with an enzyme mixture to remove cellular debris in preparation for examination using either light or scanning electron microscopy (SEM). In 2007, because russeting was insignificant, treatment differences could not be established. Moreover, transillumination microscopy did not permit accurate measurement of ‘Golden Delicious’ fruit epidermal planar cell area beyond midseason because the isolated cuticle became thick and multilayered. In 2008, however, respective treatments of 15 and 30 mg·L−1 reduced calyx end russeting by 40% and 83% and increased epidermal planar cell density by 14% and 27% as measured using SEM.