EFFECT OF SHOOT NUMBER ON POTTED GRAPEVINES .1. CANOPY DEVELOPMENT AND MORPHOLOGY

Potted, one-year old Chambourcin grapevines grafted to 5C rootstock we re grown with one-, three-, or six-shoots in the absence of fruit to d etermine the effect of competition among vegetative sinks on canopy mo rphology and development. As shoot number increased, leaf area per sho ot, shoot length, leaf size, and flower cluster length decreased for i ndividual organs. On a whole-vine basis, total leaf area, shoot length , and flower cluster length increased with increasing shoot number. Le af 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-vi ne photosynthesis (Pn) measurements showed no differences among treatm ents at bloom, but Pn had a positive, linear relationship to shoot num ber both at 5mm-berry size and at veraison. These data indicate that: (1) smaller flower clusters and less leaf area per shoot are responsib le in part for the reduction in shoot fruitfulness observed in vines w ith many shoots; (2) many shoots allow a vine to develop greater leaf area relative to vines with few shoots earlier in the growing season a nd produce more vegetative sinks for carbohydrates. (3) The presence o f relatively large shoot numbers causes important morphological change s in canopy vegetative structure. These include shorter shoots and sma ller leaves and flower clusters but greater shoot length, leaf area an d flower cluster length per vine.