Canopy Light Effects in Multiple Training Systems on Yield, Soluble Solids, Acidity, Phenol and Flavonoid Concentration of ‘Frontenac’ Grapes

Abstract

Phenolic compounds contribute greatly to the sensory attributes of wine and have a wide range of human health benefits as well. In this study, four trellis/training systems were evaluated for effects on fruit-zone light environment, fruit chemical composition (including phenol and flavonoid concentrations), and yield of ‘Frontenac’ grapes (Vitis sp. MN 1047) grown in southeastern Nebraska over two growing seasons. Photosynthetically active radiation (PAR) was measured above the canopy and within the fruiting zone at berry set, veraison, and harvest. Point quadrat canopy analysis was performed at veraison. Both bound and free (unbound) flavonoid and total phenolic contents were determined for the skins and seeds of fruit samples in 2008. At all sampling dates in 2008, vines grown on Geneva double curtain (GDC) and high cordon (HC) had higher midday percentage PAR transmittances than vines grown on Smart-Dyson (SD) and vertical shoot positioned (VSP) training systems. In 2009, transmittance relationships between trellises were not consistent throughout the season. In both years, leaf layer number (LLN) was lower for GDC and HC than for SD and VSP. Flavonoid and total phenol concentrations of the bound seed and bound skin extracts did not differ among trellises. Within the free extracts, VSP had higher total phenol concentration than SD (GDC and HC were intermediate) and there were no differences in flavonoid concentration. In 2008, GDC had higher pH than other trellises and higher soluble solids than SD and VSP; titratable acidity (TA) was lower in GDC and HC than in SD and VSP. In 2009, SD and VSP had the highest soluble solids concentrations; HC had lower pH than SD and VSP and there were no differences in TA. Results were inconclusive regarding light environment effects on fruit chemical composition.