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

Passito wine (wine made with dehydrated grapes) is very wide-spread in Italy. The quality of the grapes to be withered is strongly influenced by qualitative parameters and morpho-anatomical characteristics of the berry, which can again be affected by vineyard management and by the microclimatic factors. In Trebbiano toscano and Rossetto vines grown in the Latium region, the epicuticular wax content of berries from bunches developed in intra-canopy and extra-canopy position was analyzed from pre-veraison to pre-harvest period, during the two growing seasons 2007 and 2008. At harvest the characteristics of cuticle and epidermis of each sample were examined by light and electron microscopy and subsequently the berries were subjected to a dehydration process at 20\ub0C and 45% moisture content, with the aim of evaluating differences both in water loss rate and the mechanical characteristics of the skin. Results showed that 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 extra-canopy berries. The number of cell layers and the thickness of the berry skin were significantly different between cultivars and position in the canopy, whereas the thickness of the cuticle was not affected by the compared factors. Shaded berries of both vines dehydrated slower, particularly in vigorous Trebbiano toscano vines, in which intra-canopy berries reached 40% of weight loss later than did the extra-canopy berries. During the dehydration process the berry skin color (hue angle) decreased and berries of both varieties increased the skin resistance to puncturing without significant differences whatever the position of the berry in the canopy