Effects of Controlled Day and Night Temperatures and Nitrogen on Fruit-Set, Ovule Fertility, and Fruit Composition of Several Wine Grape Cultivars

Abstract

Four-year-old vines of Cabernet Sauvignon, Sylvaner, and Zinfandel were grown in phytotron rooms at three different day/night temperature regimes (25°/10°, 25°/20°, and 15°/10°C) during the period from about one week before bloom until véraison. Half of the vines at each temperature treatment received 1.69 g of N (HN) per 20-liter pot, and the other half received no N (ON). The rate of temperature increase or decrease between the daytime maximum and nighttime minimum for each temperature regime was programmed to approximate field conditions in the Soledad and Fresno areas of California during bloomtime.

Ovule fertility and number of seeds per berry in vines grown at 25°/10° and 25°/20° were approximately double that of vines held at 15°/10°C, whereas fruit-set did not differ significantly between temperature regimes. Fruit-set, ovule fertility, and number of seeds per berry were significantly less in Cabernet Sauvignon than in the other two cultivars. When data for temperature treatments and cultivars were combined for unfertilized and N-fertilized vines, the HN vines had significantly greater (P<0.01) fruit-set, ovule fertility, seeds/ berry, berry weight, total shoot length, internode length, rate of shoot growth, petiole nitrate level, fruit acidity, and anthocyanin level in berry skins than did ON vines. Fruit maturity and the pH of berry juice did not differ significantly between nitrogen treatments. The level of NO₃-N in petiole at bloomtime ranged from 170 to 330 ppm in ON vines and from 1510 to 6880 ppm in HN vines. The level of petiole nitrate in HN vines of each cultivar was usually significantly greater (P<0.05) at 25°/ 10° and 25°/20°C than at 15°/10°C. Chemical and physiological data supported the conclusion that ON vines were nitrogen-deficient. However, the high fruit-set, ovule fertility, and level of soluble solids in fruits of HN vines did not indicate that excess nitrogen existed, even though bloomtime petiole NO₃-N levels averaged 3651 ppm, which is generally considered in the excess range for maximum vine yields.