Root pruning reduces photosynthesis, transpiration, growth, and fruiting of container-grown French-American hybrid grapevines

'Seyval blanc' and 'Vidal blanc' grapevines (Vitis sp.) grown in large cont ainers were root-pruned at different severities and/or stages of developmen t and the effects on growth of both cultivars and fruiting of 'Seyval blanc ' were determined. As the severity of root pruning increased, stomatal cond uctance (g(s)) and transpiration (E) decreased and the number of wilted lea ves increased in both cultivars, In both cultivars, root pruning reduced ne t photosynthesis (Pn) and E for as long as 18 to 20 days, as well as total leaf area and dry weight of leaves and petioles plus tendrils. The reductio ns were proportional to the degree of root pruning. A similar pattern exist ed for cane and root tissue of 'Vidal blanc', As the severity of root pruni ng increased, berry and cluster weight, and titratable acidity (TA) of 'Sep val blanc' decreased. There was no effect of root pruning on berries per cl uster, soluble solids content (SSC), or pH of the juice, No interaction was significant for any factor between time of root pruning and fruiting measu red on 'Seyval blanc' vines. Root pruning at bloom reduced leaf area, numbe r of leaves, and dry weight of petioles, trunks, and canes. Root pruning at veraison had no effect on any vegetative or fruit parameters. Fruiting 'Se yval blanc' vines had less leaf area and smaller petiole and cane dry weigh ts than did nonfruiting vines.