Submitted to: HortScience
Publication Type: Peer reviewed journal
Publication Acceptance Date: 12/25/2011
Publication Date: 2/1/2012
Citation: Curry, E.A. 2012. Increase in epidermal planar cell density accompanies decreased russeting of “Golden Delicious” apples treated with gibberellin A4+7. HortScience. 47(2):1-6. Interpretive Summary: Development of russet on the peel of 'Golden Delicious' apples has long been a concern to producers and marketers of fresh fruit throughout the world because it detracts from the smooth, uniform finish and often results in economic loss due to grade reduction. One of the better ways to reduce russeting is by applying naturally occurring gibberellins (GA4+7) to the tree during early fruit development. This study was conducted to better understand how gibberellins improve apple peel finish. In 2007 and 2008, whole, mature trees growing in a commercial “Golden Delicious” orchard with a 70-80% historical incidence of russeting were treated with four applications of GA4+7 (ProVide®) at 0, 15 or 30 ppm. Apple peel tissue was sampled after the fourth application and enzymatically treated so that the epidermal cell imprints in the cuticle could be examined and measured using either light or electron microscopy. In 2007, little russeting in the orchard was observed. In 2008, however, treatments of 15 and 30 mg'L-1 GA4+7 1) reduced fruit russeting by 40 and 83% and 2) increased epidermal planar cell density by 14 and 27%, respectively, over controls. It is postulated that a greater number of epidermal cells with a smaller superficial surface area are better able to withstand desiccation stress.
Technical Abstract: A two-year study was conducted in a “Golden Delicious” (Malus Xdomestica Borkh.) orchard having a high historical 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 about 1000 L'hectare-1. Fruit epidermal tissue samples were taken approximately monthly beginning a week after the fourth Treatment application. Tissue was treated in the laboratory with an enzyme mixture to remove cellular debris in preparation for evaluation using either light or scanning electron microscopy. In 2007, because russeting was insignificant, treatment differences could not be established. In 2008, however, respective treatments of 15 and 30 mg'L-1 reduced fruit russeting by 40 and 83%, and increased epidermal planar cell density by 14 and 27%. Implications of increased epidermal cell division and associated reduction in cell planar surface area are discussed.