Role of leaf removal on grape quality of Sauvignon and Grechetto cultivars in Umbria

The shading of the productive belt produces clusters with minor sugar contents and higher acidity. Further it creates optimal conditions for the establishment of Botrytis cinerea. The present work aims to analyze the effects of leaf removal on Sauvignon blanc and Grechetto with three different ways of defoliation (leaf removal to east, west and total) in addition to the control test (non defoliation). The study was carried out in the vineyard "Arnaldo Caprai, Montefalco" (PG) and consisted in collecting data during the period from 2007 to 2010 (for Grechetto only 2007, 2009 and 2010). In the vineyards which are located on a plain, a spurred cordon system was applied, the rows were north-south orientated and cover cropping was made on soil. For each year the main vegetative-productive and analytic parameters, as well as the polyphenolic content of grapes, have been observed; for each thesis of 2010 the curves of technological and polyphenolical ripening were identified, with the aim to better understand the course of those components, because they may cause oxidation in wines, above all in the white ones, leading to browing and aroma losses. From the years' average resulted that Grechetto the not-defoliated vines had the highest average cluster weight with a medium sugar content, a good level of acidity and lowest pH. It could be further seen that in 2010 in Grechetto the not-defoliated vines recorded the highest quantity of malic acid together with the west-defoliated ones; from a polyphenolical point of view, west defoliated maintains a constant percentage of polyphenols in skins during the three years of observation, even if sometimes the quantities are low. Sauvignon with east defoliation shows a good sugar and acidity level, maintaining a medium-low pH; in addition east defoliation leads to a reduced percentage of polyphenols in skins in 2008 and 2010, whereas the control test presents in every medium-low levels of all the analytical parameters