INTERACTION OF NITROGEN AVAILABILITY DURING BLOOM AND LIGHT-INTENSITYDURING VERAISON - II - EFFECTS ON ANTHOCYANIN AND PHENOLIC DEVELOPMENT DURING GRAPE RIPENING

Grape ripening is affected by a number of environmental factors, and o f these light and nitrogen (N) are of particular importance. Using pot -grown Cabernet Sauvignon (Vitis vinifera L.) vines, we studied the ef fects of N availability at bloom (0.34, 1.7, or 3.4 g N per plant as N H4NO3) and light intensity at veraison (3 weeks at 100%, 20%, or 2% su nlight, using shade cloth) on the accumulation of total phenols, antho cyanins and flavonols in ripening grapes. Total soluble solids in the pulp were closely correlated with total phenols (r(2) = 0.91**), tota l anthocyanins (r(2) = 0.90**) and total flavonols (r(2) = 0.52***) i n the skin in all treatments. High rates of N supply delayed the accum ulation of phenolic compounds, particularly flavonols, in the grape sk in at veraison, However, the differences between N treatments generall y decreased towards fruit maturity. Low light intensity at veraison re stricted phenolics accumulation even more than did heavy N supply and the effects of low light were most severe in vines with high N status. However, ripening was not stopped entirely by light intensities as lo w as the light compensation point of photosynthesis. Moreover, removal of the shade cloth partly restored the rate of phenolics accumulation in the berry skin. All five anthocyanins started accumulating concurr ently at the inception of ripening. However, while peonidin-, malvidin -, and cyanidin-3-glucosides were the major pigments at veraison, malv idin- and delphinidin-3-glucosides became most abundant towards maturi ty. The accumulation of cyanidin-3-glucoside was most strongly influen ced by prevailing environmental conditions, while malvidin-3glucoside was the least affected. Thus, the proportions of individual anthocyani ns were most equal at low N status and high light intensity, whereas t he percentage of malvidin-3-glucoside increased with high rates of N f ertilization and became predominant under low light intensity. This is important for red winemaking, because the grape skins' anthocyanin pr ofile determines the color potential of the resulting wine. Excessive N fertilization can decrease wine quality, particularly when light con ditions during grape ripening are poor.