Effect of High Temperatures during the Bloom-Set Period on Fruit-Set, Ovule Fertility, and Berry Growth of Several Grape Cultivars

Abstract

To test the effects of high daytime temperatures (35 or 40°C from 11 AM to 7 PM) from two to eight days before bloom until 12 to 18 days after bloom (bloom-set period) on fruit-set, ovule fertility, and berry growth of several <i>Vitis vinifera</i> L. cultivars, three and four years old potted vines were grown in phytotron rooms. Control vines were maintained at day/night temperatures of 25/20°C during the bloom-set period. After bloom-set, vines in all treatments were held at 25/20°C during the remaining period of berry development and ripening. The percentage of berries set was significantly greater (P&lt;0.05) at 25° than at 35 or 40°C for both Pinot noir and Carignane. Ovule fertility and berry weight were also significantly greater at 25 than at 35 or 40°C in Carignane vines. With Pinot noir, however, only vines held at 40°C during bloomset had significantly fewer ovules fertilized per cluster than occurred at 25°C. During bloom-set, shoot growth was fastest at 25°C (Carignane) or 35°C (Pinot noir), but no significant correlation existed between rate of shoot growth and fruit-set or ovule fertility. Temperatures of 32.5 to 40°C from 7 AM to 7 PM during bloom-set gave a significantly (P&lt;0.05) lower weight and size of Cabernet Sauvignon and Tokay berries during most stages of berry development and ripening than did 25°C. Cabernet Sauvignon berries grown at 32.5 and 35°C during bloom-set had a significantly greater (P&lt;0.05) berry weight and size during ripening and at fruit maturity than when grown at 37.5 or 40°C. Tokay berries at 32.5 to 40°C, however, did not differ significantly in weight and size. Anatomical data indicated that the Tokay berries were larger at 25°C than at 40°C due to greater numbers of cells in the pericarp tissue rather than to larger cell size.