Some Factors Affecting Cuticle and Wax Accumulation on Grape Berries

Abstract

Various factors were investigated to determine their effects on the accumulation of cuticle and epicuticular wax on grape berries (Vitis vinifera L.). Factors investigated included variety, sun exposure, irrigation rate, and contact with other berries within the cluster. Cabernet Sauvignon berries had more than twice as much cuticle per unit surface area as Grenache, Zinfandel, Carignane, and Pinot noir. The size, density, and visual appearance of the wax platelets that make up the epicuticular wax layer also varied among cultivars. Cabernet Sauvignon is considered relatively resistant to infection by Botrytis cinerea, while the other varieties examined are considered severely to moderately affected. These results support the suggestion that the thickness and structure of the epicuticular wax layer may contribute to the susceptibility of grape berries to Botrytis. Grape berries from clusters that developed in the canopy shade had less cuticle per unit surface area than berries from clusters developing in sun-exposed positions on the same vine. Irrigation rates of 0.5, 1.0, or 1.5 times the evapotranspiration rate estimated by a standard evaporation pan had no significant effect on the accumulation of cuticle and wax, however. Tissue disks isolated from the flattened areas of berry contact in tight clusters had significantly less cuticle and less wax than disks isolated from non-contact areas of the same berries (p < 0.05). Previous work demonstrated that the areas of berry contact are more susceptible to infection by Botrytis cinerea than non-contact areas under conditions of identical humidity and temperature.