Improved control of water loss of micropropagated plants of Vitis vinifera cv. Nebbiolo

Micropropagated plantlets are generally susceptible to rapid desiccation when exposed to reduced relative humidity, and require a costly acclimatization procedure. Detached leaves of micropropagated Vitis vinifera cv. Nebbiolo plantlets were examined, in order to evaluate the relative contribution of leaf cuticle and stomata to water loss. Water loss occurred mainly from the abaxial surface of detached leaves; moreover, a large majority of stomata was still open 3 h after exposure to 63 % RH. An indirect estimation of epicuticular wax suggested a lower wax deposition for micropropagated plantlets compared to acclimatized and field-grown plants of the same clone. A previously developed method to produce hardier 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 micropropagation. Under our experimental conditions, rRH was more effective in improving stomatal efficiency to reduce transpiration than PBZ; a combination of both treatments improved plant survival during acclimatization.