Effect of Shoot Number on Potted Grapevines: I. Canopy Development and Morphology

Abstract

Potted, one-year old Chambourcin grapevines grafted to 5C rootstock were grown with one-, three-, or six-shoots in the absence of fruit to determine the effect of competition among vegetative sinks on canopy morphology and development. As shoot number increased, leaf area per shoot, shoot length, leaf size, and flower cluster length decreased for individual organs. On a whole-vine basis, total leaf area, shoot length, and flower cluster length increased with increasing shoot number. Leaf area of three- and six-shoot vines was 38% greater than that of one-shoot vines at harvest. Vine dry weight at harvest, however, was 22% and 20% greater for three- and six-shoot vines, respectively. Whole-vine photosynthesis (Pn) measurements showed no differences among treatments at bloom, but Pn had a positive, linear relationship to shoot number both at 5mm-berry size and at veraison. These data indicate that: (1) smaller flower clusters and less leaf area per shoot are responsible in part for the reduction in shoot fruitfulness observed in vines with many shoots; (2) many shoots allow a vine to develop greater leaf area relative to vines with few shoots earlier in the growing season and produce more vegetative sinks for carbohydrates. (3) The presence of relatively large shoot numbers causes important morphological changes in canopy vegetative structure. These include shorter shoots and smaller leaves and flower clusters but greater shoot length, leaf area and flower cluster length per vine.