INFLUENCE OF SHOOT NUMBER AND CROP LOAD ON POTTED CHAMBOURCIN GRAPEVINES .1. MORPHOLOGY AND DRY-MATTER PARTITIONING

Two-year-old Chambourcin grapevines were grown in 19-L pots with the f ollowing treatments: one or four shoots and no clusters (1/0 and 4/0, respectively); one shoot and one cluster (1/1), and; four-shoots with one (4/1), two (4/2), three (4/3) or four (4/4) clusters. Four-shoot v ines had greater leaf area, shoot length and leaf numbers per vine, bu t one-shoot vines had longer shoots, larger leaves, and greater leaf a rea and leaf number per shoot. Crop load effects on canopy morphology were relatively small. Berry number per cluster, berry weight and frui t soluble solids were not different among treatments, but 4/2, 4/3, an d 4/4 vines had two to three times greater fruit fresh weight than did 1/1 and 4/1 vines due to greater berry numbers per vine. Whole vine d ry weight was never different among treatments, but there was a positi ve linear relationship between berry number and vine dry weight at har vest. This suggests that carbohydrate sink strength must be in balance with sources to maximize dry matter production. Partitioning of dry m atter to fruit at the expense of vegetative tissues accounted for frui t dry weight at low crop loads. Increased dry matter production per un it leaf area was necessary to mature fruit at high crop loads. Since f ruit is approximately 75% H2O by weight at harvest, small increases in dry weight result in large increases in yield. These data indicate th at: (a) vegetative sinks have a greater impact than fruit on canopy mo rphology; and (b) carbohydrates used in fruit production are primarily derived from greater partitioning to fruit at the expense of vegetati ve tissues and greater dry matter production between veraison and harv est in vines with increasing fruiting sink strength.