Fruitfulness in Grapevines: Effects of Light Intensity and Temperature

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 dissected and examined for the presence of bunch primordia. Environmental variables examined were light intensity and temperature. Fruitfulness (number of bunch primordia per bud) increased with increasing light intensity over the range 900 ft-c-1,800 ft-c-3,600 ft-c (16-hr days at 25 C or 30 C). At 20 C buds were barren at 13 weeks, and fruitfulness was achieved above this temperature and increasingly so to a maximum between 30 C and 35 C. Temperature appeared to exert an effect on both rate of bud development and on actual number of bunch primordia differentiated. A temperature which promoted stem dry-weight accumulation (20 C) retarded differentiation and development of bunch primordia. There is evidence that light intensity affected fruitfulness via effects on carbohydrate level, but th...