INFLUENCE OF LIGHT ON GRAPE BERRY GROWTH AND COMPOSITION VARIES DURING FRUIT-DEVELOPMENT

Potted 'Cabernet Sauvignon) and 'Pinot noir' grapevines (Vitis vinifer a L.) grown in a sunlit phytotron were used to study the influence of cluster light exposure during various stages of fruit development on b erry growth and composition, Clusters grown without light during berry development stages I and II, stage III, or stages I, II, and III, wer e compared to clusters exposed to light throughout fruit development ( control). The temperature of light-exposed and nonexposed fruit was si milar, The weights and diameters of berries grown without light during stages I and II, or stages I, II, and III, were similar and significa ntly lower than those of the control. Fruit softening in both cultivar s, as well as the initiation of berry coloration, was delayed when ber ries were grown without light during stages I and II, Following fruit softening, berries grown without light during stages I, II, and III we re lower in sugar than the control, On the final sample date, 'Caberne t Sauvignon' berries grown without light during stages I, II, and III were higher in malate compared to the control. 'Pinot noir' berries gr own without light during stages I and II, or stages I, II, and III, we re lower in malate before fruit softening, and higher in malate follow ing fruit softening, than the control. Control berries had greater ski n anthocyanins and phenolics compared to the remaining treatments, Ber ries grown without light during stages I and II, or stage III, were gr eater in anthocyanins and phenolics than fruit grown without light dur ing stages I, II, and III, Light had no effect on fruit tartrate conce ntration or juice pH. Light had its greatest impact on fruit developme nt during the initial stages of berry growth. Berry growth was reduced and ripening delayed when fruit were grown without light during stage s I and II. Normal fruit development was not fully restored when these fruit were exposed to light during stage III.