Effects of Controlled Temperature and Light Intensity on Growth and Carbohydrate Levels of ‘Thompson Seedless’ Grapevines1

Nonfruiting ‘Thompson Seedless’ grapevine rootings were grown for 30-day periods in phytotron rooms at variable day temp (6:00 AM to 6:00 PM) from 20 to 40°C, in combination with high light (HL,>2,000 ft-c) and low light (LL, <400 ft-c). Night temp in all treatments was 15°C. Maximum total vine growth and net assimilation rate occurred at 30°C under HL and at 20°C under LL. Gain in dry matter per vine was 3- to 18-fold greater under HL than under LL. The level of total carbohydrates (sugars plus starch) in roots of plants grown under HL was also maximal at 30°C. The concn of total carbohydrates in trunk tissues however, varied little with temp from 20 to 35°C, but was significantly (P<0.01) reduced at 40°C. Low light intensity markedly reduced (P<0.01) the levels of sugars and starch in root and trunk tissues compared to the levels in vines grown at HL, regardless of temp.