THE EFFECTS OF PRE-VERAISON AND POST-VERAISON WATER-STRESS ON GROWTH AND PHYSIOLOGY OF POTTED PINOT-NOIR GRAPEVINES AT VARYING CROP LEVELS

The interactions of water stress timing and crop level on growth, gas exchange, water relations and ripening of potted Pinot Noir grapevines were examined. Pre-veraison water stress induced a greater reduction of shoot and berry growth and a more rapid limitation of net photosynt hesis (Pn) and stomatal conductance (g(s)) as compared to post-veraiso n stress. At the end of stress, when mid-day and pre-dawn leaf water p otential were below -1.1 and -0.6 MPa, the reduction in Pn of stressed vines was more marked in the 2- and 4-cluster plants versus 1-cluster plant. Crop level had almost no significant effects on gas-exchange, growth and ripening and but few interactions with timing of water stre ss. These responses seem to reflect the high leaf area-to-fruit ratios at each crop level which probably buffered the effects of reduced lea f function induced by water stress.