Influence of Bunch Position in the Canopy on Berry Epicuticular Wax during Ripening and on Weight Loss during Postharvest Dehydration

Passito wine, made with dehydrated grapes, is widespread in Italy. The quality of the grapes to be withered is strongly influenced by qualitative factors and the anatomy and morphology of the berry, which in turn, are affected by vineyard management and microclimate. In Trebbiano toscano and Rossetto vines grown in the Latium region, the epicuticular wax of berries from bunches developed in intracanopy and extracanopy positions was analyzed from preveraison to preharvest during the 2007 and 2008 growing seasons. At harvest, the characteristics of cuticle and epidermis of each sample were examined using light and electron microscopy. The berries were then dehydrated at 20°C to 45% moisture to evaluate differences in water loss rate and the mechanical characteristics of the skin. The amount of epicuticular wax decreased during berry development. SEM observations of the berry skin at harvest showed differences in the structure of the epicuticular wax layers, with a wider berry surface covered with plate-like wax in extracanopy berries. The number of cell layers and the thickness of the berry skin were significantly different between cultivars and canopy positions, but these factors did not affect cuticle thickness. Shaded berries of both varieties dehydrated more slowly, particularly in vigorous Trebbiano toscano vines, in which intracanopy berries reached 40% weight loss later than the extracanopy berries. During dehydration, the berry skin color (hue angle) decreased and berries of both varieties increased skin resistance to puncturing; this was not affected by the position of the berry in the canopy.