Vine Water Stress and Peduncle Girdling Effects on Pre- 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 bearing pre- or post-veraison clusters were subjected to water stress or peduncle girdling/ detaching. Berry growth rate (change in diameter per day) and deformability were measured as indicators of berry water status. Berry diameter increased slightly in pre-veraison clusters on well watered vines; diameters of berries on unwatered vines decreased significantly. Pre-veraison berry deformability was four times greater in unwatered versus watered vines on the final day of the experiment. Bagging pre-veraison clusters to slow transpiration had little effect on berry growth rate or deformability. Post-veraison berry growth rate and deformability were not affected significantly by vine water stress. Heat girdling cluster peduncles decreased pre-veraison berry growth rates by 75%, but had a negligible effect on berry deformability. Diameter loss in post-veraison berries was increased by 40% after girdling; berry deformability increased by 44%. The rate of berry diameter loss on a detached cluster was almost three times higher, and berry deformability 26% higher, than the same measurements taken from a girdled cluster. A xylem discontinuity in the berry near veraison is consistent with these findings.