W. Mark Kliewer

Effect of root temperature, rootstock and fertilization on bud-break, shoot growth and composition of ‘Cabernet Sauvignon’ grapevines

Abstract Two-year-old ‘Cabernet Sauvignon’ grapevines on own-roots or on A×R No. 1 (Ganzin 1) rootstock were grown at low (12°C) or high (25°C) root temperatures in combination with 2 fertilizer treatments (0 and 2.4, 1.2 and 1.2 grams of N,P,K, respectively, per 20-liter pot) in a greenhouse for a period of 15 weeks. The dormant vines were pruned to two 10-node canes just prior to initiation of temperature and fertilizer treatments. Air temperatures ranged between 15°C at night and 30°C during the day, and were the same for all treatments. The time of bud-break was earlier at high root temperature than at low temperature, with fertilization than without fertilization, and with own-rooted vines than with vines on A × R stock. The number of buds that broke and total shoot growth were significantly higher at 25°C than at 12°C. Fertilized vines also had significantly greater bud-break and shoot growth than unfertilized vines at both 12 and 25°C root temperatures. More buds broke and developed on A × R vines than on own-rooted vines at 12°C; whereas, at 25°C they did not differ significantly. Shoot growth of own-rooted vines, on the other hand, was significantly greater than vines on A × R stock at both low and high root temperatures. The levels of arginine, NO 3 and total N in roots was greater at low root temperature than at high root temperature. High root temperature, however, increased the concentration of total N in leaf blades and NO 3 in blades and petioles of own-rooted vines compared to low root temperature. Fertilization increased the concentration of nitrogenous substances in leaves and roots of all vines. The levels of K, Ca and Mg in leaf blades, petioles and roots were generally higher at 25 than at 12°C root temperature. The level of K was higher in leaves and roots of vines on own-roots than vines on A × R; however, the Ca and Mg content of these tissues did not show any consistent trends between A × R and own-rooted vines.

Influence of temperature and ethephon concentration on growth and composition of Cabernet Sauvignon grapevines

Potted Cabernet Sauvignon grapevines were acclimated to two different temperature regimes (25°C/15°C and 35°C/25°C day/night temperatures, respectively) until 100% bloom, when the vines were treated with either 0, 250, 500, or 750 ppm ethephon (Ethrel®). Three days after ethephon application all vines were combined and held at 25°C/15°C in a phytotron room for 15 weeks. Growth was suppressed by a greater range of ethephon concentrations at the cool temperature, but effects were shorter-lived than at the high temperature. Generally, the 500 ppm treatment reduced vigor most effectively. The degree to which ethephon influences vine growth is mediated by temperature. Ethephon and temperature treatments caused significant differences in the concentrations of potassium, calcium, and magnesium in leaves.