Fruitfulness in Grapevines: Effects of Changes in Temperature and Light Regimes

Abstract

Grapevines (Vitis vinifera L., c.v. Muscat Gordo Blanco, syn. Muscat of Alexandria) were grown in controlled-environment growth cabinets for 13 weeks after bud burst, and then buds which had developed on the shoot were examined for the presence of bunch primordia. Studies made were of effects due to (a) changing temperature and light intensity during the 13-week growth period, (b) length of daily period of exposure to inductive temperatures, and (c) night temperature. Fruitfulness of a bud was related to the temperature experienced over a period of approximately 3 weeks during which the node subtending it changed in location from the shoot apex to about 10 nodes below the apex. The effect of temperature was greatest wherr the subtending node just appeared below the shoot apex, and the effect fell proportionately to zero for a bud at a node about 10 below the apex. Fruitfulness must be decided at a very early stage of bud development. Fruitfulness was related to the maximum temperature experienced each day (rather than to temperature summation), so long as this maximum temperature was maintained for about 4 hr (1 hr was not long enough). Inductive temperature could be given during the day or night.