Potted 'Cabernet Sauvignon) and 'Pinot noir' grapevines (Vitis vinifera L.) grown in a sunlit phytotron were used to study the influence of cluster light exposure during various stages of fruit development on berry growth and composition, Clusters grown without light during berry development stages I and II, stage III, or stages I, II, and III, were compared to clusters exposed to light throughout fruit development (control). The temperature of light-exposed and nonexposed fruit was similar, The weights and diameters of berries grown without light during stages I and II, or stages I, II, and III, were similar and significantly lower than those of the control. Fruit softening in both cultivars, as well as the initiation of berry coloration, was delayed when berries were grown without light during stages I and II, Following fruit softening, berries grown without light during stages I, II, and III were lower in sugar than the control, On the final sample date, 'Cabernet Sauvignon' berries grown without light during stages I, II, and III were higher in malate compared to the control. 'Pinot noir' berries grown without light during stages I and II, or stages I, II, and III, were lower in malate before fruit softening, and higher in malate following fruit softening, than the control. Control berries had greater skin anthocyanins and phenolics compared to the remaining treatments, Berries grown without light during stages I and II, or stage III, were greater in anthocyanins and phenolics than fruit grown without light during stages I, II, and III, Light had no effect on fruit tartrate concentration or juice pH. Light had its greatest impact on fruit development during the initial stages of berry growth. Berry growth was reduced and ripening delayed when fruit were grown without light during stages I and II. Normal fruit development was not fully restored when these fruit were exposed to light during stage III.
