WATER RELATIONS AND GROWTH OF ROSE PLANTS CULTURED INVITRO UNDER VARIOUS RELATIVE HUMIDITIES

Stomatal malfunctioning is one of the main reasons why plants desiccate when transferred from in vitro to greenhouse conditions. In order to overcome this problem in Rosa hybrida cv. Madame G. Delbard (R) Deladel, two techniques, bottom cooling and water vapour permeable lid, were used. Both methods aimed to increase the vapour pressure gradient between leaf and atmosphere and consequently to improve plant transpiration. The results showed that these techniques increased leaf resistance to dehydration and improved stomatal regulation. Water relations of treated plantlets were similar to those generally observed in hardened plants: lower leaf water and osmotic potentials, and lower leaf water content than in the control ones. Osmotic adjustment occurred in treated plantlets maintaining turgor pressure. Each technique also induced some effects on growth during the rooting phase: with bottom cooling, roots were shorter, with permeable lids, apices were necrosed. These results are discussed in terms of physiological causes and in terms of effect during the following acclimatization.