Influence of Light Intensity and Growth Regulators on Fruit-Set and Ovule Fertilization in Grape Cultivars under Low Temperature Conditions

The percentages of berries set and ovules fertilized per cluster, and berry development, were studied in five Vitis vinifera L. cultivars grown in a phytotron room under day/night temperatures of 15/10°C and average light intensities of 2680, 750, and 480 ft-c. Benzyladenine (BA) and 2-(chloroethyl) trimethylammonium chloride (CCC) were applied to vines grown at the two lower light levels. There was no fruit-set at 480 ft-c in any cultivar, but at 750 ft-c some set occurred in Carignane. All cultivars set berries at 2680 ft-c, ranging from 13% (White Riesling) to 31% (Pinot noir). The percentage ovules fertilized per cluster ranged from 0% (French Colombard) to 5.1% (Pinot noir). Percentage fruit-set and ovule fertilization at 2680 ft-c were about 3- and 8-fold greater, respectively, than at 750 ft-c. Neither BA nor CCC significantly improved fruit-set at 750 or 480 ft-c compared to nonhormone-treated vines; however, both reduced the number of fertilized ovules. Berry weight of seedless Carignane fruits treated with BA was about 6-fold greater than that of control fruits (no hormone), whereas CCC had no effect on berry weight.