Influence of Cluster Exposure to Sun on Fruit Composition of ‘Norton’ Grapes (Vitis estivalis Michx) in Missouri

Abstract

The influence of cluster exposure to sunlight on fruit composition of ‘Norton’ grapes was studied. Three exposure levels, such as fully exposed, partly exposed, and fully shaded, were established by canopy management practices, such as shoot positioning, shoot thinning, and leaf removal. Row orientation significantly impacted fruit composition with east west orientation and resulted in high total soluble solids, anthocyanin, and tannin content. Titratable acidity, total phenol, and juice potassium was highest in vines planted in north south row orientation. Fully shaded clusters had the lowest total soluble solids, lower glucose and fructose content, and highest juice potassium and malic acid content. Fully exposed clusters displayed lowest titratable acidity. Fully exposed clusters on the west and south side of the canopy received photosynthetically active radiation of more than 1,100 μ mole m-2 sec-1, while partly exposed and fully shaded clusters received less than 10% of total photosynthetically active radiation at solar noon. Berries on fully exposed clusters exhibited a temperature that was about 10–15°F higher than air temperature, while fully shaded clusters were about 1–2°F higher than air temperature.