Evidence of drought-sensitive periods from flowering to maturity on highbush blueberry

The effects of water deficit on highbush blueberry (Varcinium corymbosum L.) have been little studied. This study, conducted on container-planted shrubs, aimed at determining the influence of water stress on growth, water relations and fruit production of the plant during two consecutive years. Drought periods of approximately 3 weeks, as monitored from the transpiration of control plants, were applied at various phenological stages of plant development, from blossoming to harvest, so as to evaluate their direct effects. Highbush blueberry reacted very quickly to drought by reducing transpiration and stopping stem diameter growth and shoot elongation. Its ability to recover depended on the stress level and the drought implementation dynamics. Under moderate stress (35% less transpiration than a well-watered shrub) the recovery potential was almost complete. In all cases water stress during fruit growth and ripening strongly influenced yield by reducing the mean fruit weight and size. Drought after-effects, as assessed from one season to the other, were small, except when stress occurred during flower induction. In that c:ase the number of Rowers was reduced in the following year as well as the number of fruits, although fruit size was greater resulting in only a slight reduction in yield. In all cases, photosynthetic performance during the following year appeared not to alter, but water stress imposed to obtain large fruit cannot replace pruning without jeopardising the shrub architecture. (C) 2001 Elsevier Science B.V. All rights reserved.