Studies on initiation, set and growth in grapes

Four-year-old grapevine (Vitis vinifera L.) cultivars Chasselas Doré, Chenin Blanc, Pinot Noir (two clones), and White Riesling growing in the experimental vineyard of Lincoln College were used to investigate the initiation of flower buds, fruit set, growth, colour development and other characteristics of grapes. 1. The number of flowers produced per cluster in the buds of Chasselas Doré, Pinot Noir and White Riesling were shown to be positively correlated with the temperature on the day when the subtending leaf had reached a size of 1.5 cm in diameter, i.e. when the subtending node was at position three nodes below the apex. The fruitfulness of buds on a cane is related to temperatures operating at this stage - thus basal and apical buds of grapevines in Canterbury had fewer flower primordia than those in the middle of the cane which were at their critical stage when temperatures were warmer. 2. Pinching and topping improved fruit set, with commensurate increase in cluster weight, only if done when flower caps were falling and berries were setting. The results suggest that pinching and topping increased set possibly by reducing competition between the developing leaves and ovaries for available assimilates. The study further revealed that the total soluble solids were increased and acidity was reduced on tipping. The increase in total soluble solids could be due to an increase in immediately-available assimilates to the cluster due to reduced competition. 3. Pre-bloom application of 7.5 ppm gibberellic acid effectively thinned the cluster, increased its length and that of the pedicels plus the size and length of the berries, and brought about a reduction in diseases. Gibberellic acid treatment caused little reduction in yield of fruit, but acidity was reduced and total soluble solids were increased. 4. Application of ethephon and/or girdling improved the colour development, total soluble solids, and reduced acidity in the berries of Pinot Noir grapes. Furthermore, these treatments did not alter the size of the berries and the weights of the cluster. The physiological implications of these results are discussed and their relevance to commercial grape-growing is considered