Light Quality and Quantity Effects on Fruit Ripening for Cabernet Sauvignon

Abstract

The light climate of potted fruiting Cabernet Sauvignon vines was modified by shading with one, two, or three layers of 44% transmission shade cloth. Control vines and three-layer shade cloth vines were exposed to red 660 nm light from a fluorescent tube to investigate phytochrome responses. Increasing shade markedly reduced ripening, causing reduced sugar, phenol, and anthocyanin concentrations. Levels of titratable acidity, malic and tartaric acids, and juice NH₄-N were increased by shade, but pH was similar despite large differences in acidity. Shade also caused major effects on mineral nutrition, especially for N metabolism. Shade caused increased concentrations of NO₃-N and NH₄-N in leaves, NO₃-N and total N in petioles, and NH₄-N and Mg in peduncles; peduncle K was decreased. Shade decreased photosynthesis, stomatal conductance, and leaf nitrate reductase activity. Red light supplementation caused increased nitrate reductase activity in leaves and earlier fruit coloration and harvest concentration of glucose and fructose, implicating phytochrome control over some aspects of fruit ripening.