EFFECTS OF PACLOBUTRAZOL AND REDUCED HUMIDITY ON STOMATAL CONDUCTANCE OF MICROPROPAGATED GRAPEVINES

A new method has been proposed to produce hardier micropropagated plants by modification of Stage III procedures and thus avoid acclimatization. It consists of protection of roots by cellulose plugs, addition of a growth retardant (paclobutrazol) to the liquid culture medium and the use of culture vessels with reduced humidity (94% RH). Trials were carried out on Vitis vinifera 'Nebbiolo', previously grown in vitro and then placed in cellulose plugs with or without 1 mg 1^-1 PBZ. After 3 weeks of culture, conductance measurements were performed for a 24 h period. Plantlets grown in vessels with reduced RH and/or with PBZ showed a rapid initial reduction in leaf conductance, followed by a more gradual reduction. With plantlets grown at 100% RH and no PBZ, the final values reached were lower than with plantlets grown at 100% RH with PBZ, and plantlets grown on reduced humidity with or without PBZ.