Improved control of water loss from micropropagated grapevines (Vitis vinifera cv. Nebbiolo)

Micropropagated plantlets are generally susceptible to rapid desiccation wh en exposed to reduced relative humidity and require a costly acclimatizatio n procedure. Detached leaves of micropropagated Vitis vinifera, cv. Nebbiol o, plantlets were used to evaluate the relative contribution of leaf cuticl e and stomata to water loss. Water loss occurred mainly from the abaxial su rface of detached leaves; moreover, a large majority of stomata was still o pen 3 h after exposure to 63 % RH. An indirect estimation of epicuticular w ax suggested a lower wax deposition for micropropagated plantlets compared to acclimatized and field-grown plants of the same clone. A previously deve loped method to produce hardened micropropagated plants was adopted: 1 mg(. )l(-1) paclobutrazol (PBZ) was added to the medium and culture vessels with reduced relative humidity (rRH) were used during the last stage of micropr opagation. Under our experimental conditions, rRH was more effective to red uce transpiration than PBZ; a combination of both treatments improved plant survival during acclimatization.