VINE WATER-STRESS AND PEDUNCLE GIRDLING EFFECTS ON PRE-VERAISON AND POST-VERAISON GRAPE BERRY GROWTH AND DEFORMABILITY

To elucidate the effects of developmental xylem discontinuity in grape (Vitis vinifera L.) berries, greenhouse-grown Pinot noir vines bearin g pre- or post-veraison clusters were subjected to water stress or ped uncle girdling/detaching. Berry growth rate (change in diameter per da y) and deformability were measured as indicators of berry water status . Berry diameter increased slightly in pre-veraison clusters on well w atered vines; diameters of berries on unwatered vines decreased signif icantly. Pre-veraison berry deformability was four times greater in un watered versus watered vines on the final day of the experiment. Baggi ng pre-veraison clusters to slow transpiration had little effect on be rry growth rate or deformability. Post-veraison berry growth rate and deformability were not affected significantly by vine water stress. He at girdling cluster peduncles decreased pre-veraison berry growth rate s by 75%, but had a negligible effect on berry deformability. Diameter loss in post-veraison berries was increased by 40% after girdling; be rry deformability increased by 44%. The rate of berry diameter loss on a detached cluster was almost three times higher, and berry deformabi lity 26% higher, than the same measurements taken from a girdled clust er. A xylem discontinuity in the berry near veraison is consistent wit h these findings.