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 following 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 vines had greater leaf area, shoot length and leaf numbers per vine, but one-shoot vines had longer shoots, larger leaves, and greater leaf area and leaf number per shoot. Crop load effects on canopy morphology were relatively small. Berry number per cluster, berry weight and fruit soluble solids were not different among treatments, but 4/2, 4/3, and 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 dry weight was never different among treatments, but there was a positive linear relationship between berry number and vine dry weight at harvest. This suggests that carbohydrate sink strength must be in balance with sources to maximize dry matter production. Partitioning of dry matter to fruit at the expense of vegetative tissues accounted for fruit dry weight at low crop loads. Increased dry matter production per unit leaf area was necessary to mature fruit at high crop loads. Since fruit is approximately 75% H2O by weight at harvest, small increases in dry weight result in large increases in yield. These data indicate that: (a) vegetative sinks have a greater impact than fruit on canopy morphology; and (b) carbohydrates used in fruit production are primarily derived from greater partitioning to fruit at the expense of vegetative tissues and greater dry matter production between veraison and harvest in vines with increasing fruiting sink strength.