The effects of shoot positioning, leaf removal, cluster shading, and curtain orientation on fruit composition and primary bud cold hardiness were investigated in mature `Norton/Cynthiana' grapevines (Vitis aestivalis) trained to Geneva double curtain (GDC) trellis system. For four years (1995–1998) juice soluble solids content, total titratable acidity, and pH were not affected shoot positioning. Cluster shading, curtain orientation, and leaf removal affected fruit composition at harvest. Fruit from the south-facing curtain of the GDC trellis system had higher juice soluble solid content, pH, and skin pigmentation than fruit from the north-facing curtain. Cluster shading decreased skin pigmentation while cluster shading at the highest level only (95%) increased pH and decreased total titratable acidity. Leaf removal, which increases light exposure of the fruit, increased juice pH in the 1997 experiment only. Juice potassium level was decreased by shoot positioning, but not cluster shading or curtain orientation. Cold hardiness of primary buds was affected by these treatments early in the winter, but the differences in primary bud cold hardiness among the treatments diminished toward the end of the dormant season.
Identification of QTLs for berry acid and tannin in a Vitis aestivalis-derived 'Norton'-based population
