Influence of Temperature, Solar Radiation and Nitrogen on Coloration and Composition of Emperor Grapes

Abstract

Fruit coloration was investigated in Emperor vines grown in pots in sunlit phytotron, lathhouse, and field conditions under various temperature and light regimes in combination with different levels of nitrogen. At day/night temperatures of 37/32°C no anthocyanins were formed in fruits under either high light (HL; 66.5% sunlight) or low light (LL; 9.5% sunlight), whereas at field temperatures (FT; mean daily temperature 20.3°C), considerable anthocyanins formed under HL (100% sun) or LL (8.9% sun). At 37/32°C, soluble solids in fruits did not increase above 12.9° Brix, whereas at FT, 21° Brix was obtained under HL. The inhibition of anthocyanin formation and sugar accumulation in berries at 37/32°C and HL could not be reversed by transferring vines to temperature favorable for anthocyanin synthesis (FT), whereas when vines at 37/32°C and LL were transferred to FT at HL there was rapid accumulation of sugars but only slight formation of anthocyanin. Anthocyanin in berries decreased 59% in 20 days when the vines were transferred from FT-HL to 37/32°C-HL. Anthocyanin and soluble solids were significantly greater (P<0.01) in fruits ripened under FT-HL than under FT-LL. Anthocyanin and soluble solids were significantly less (P<0.05) in berries that received 15% sunlight than 54 or 100% sunlight. Anthocyanin formation did not occur in the complete absence of light, whereas °Brix did not differ significantly between 15%, 3%, and 0% sunlight. Fruit color and soluble solids were significantly less (P<0.05) and arginine and total free amino acids greater with high levels of nitrogen fertilization than with low levels. The reduced fruit coloration at high nitrogen fertility conditions was attributed mainly to reduction in carbohydrate accumulation and an increase in nitrogenous substances stored in fruits.