REPRODUCTIVE AND VEGETATIVE RESPONSE OF MATURE GRAPEVINES SUBJECTED TO DIFFERENTIAL CROPPING STRESSES

Mature grapevines were divided into two groups based on the amounts of mature one-year-old canes removed at pruning at the beginning of the study. Small vines produced between 0.80 kg and 1.0 kg and large vines 1.4 to 2.4 kg cane prunings per vine, respectively. Each group was ei ther balance-pruned, or pruned to 90 or 120 buds to give a 2 X 3 facto rial experiment in a completely randomized design. Growth and yield fl uctuated for all vines over the course of the study. Vines with 90 and 120 buds produced greater fruit yields, but at the expense of vegetat ive production. Vegetative production was inversely proportional to bu d number with the relationship being strongest in small vines. Reprodu ctive yields were directly proportional to bud number in large vines, but this was true in small vines only for the first two years of the s tudy. Crop load increased rapidly in small vines until after four year s, 120-bud vines had either died or were unable to produce 120 mature buds. Crop load in large vines increased steadily, but not as rapidly as in small vines. Crop load was directly proportional to bud number i n both small and large vines. Fruit quality was inversely proportional to bud number in both groups. Large vines have a greater capacity tha n small vines to buffer the stress associated with high reproductive y ields. However, under growing conditions in the Great Lakes region of North America, both groups weaken under continuous high reproductive s tress, leading to an overall decrease in the mean vine size as well as fruit quantity and quality.