EFFECTS OF RELATIVE HUMIDITY IN THE CULTURE VESSEL ON THE TRANSPIRATION AND NET PHOTOSYNTHETIC RATES OF POTATO PLANTLETS IN VITRO

Single node leafy cuttings excised from subcultured potato (Solanum tuberosum L. cv. Benimaru) plantlets were cultured for 25 days in four different relative humidity conditions to investigate the transpiration and net photosynthetic rates in vitro and in situ. Different relative humidity levels were obtained using distilled water or salt-saturated solutions. Transpiration rate per unit leaf area of the plantlets in vitro on day 20 showed no marked differences among the treatments although on day 10 the differences were observed. Reduced relative humidity in the vessel was associated with higher abaxial leaf resistance to transpiration. On both days 10 and 20, the highest and lowest net photosynthetic rates per unit leaf area were observed in RH100 and RH75, respectively. Net photosynthetic rate per unit leaf area on day 21 indicated that the net photosynthetic rate for CO₂ concentrations between 100 and 2000 μmol mol^-1 increased with increasing relative humidity. There were no significant differences in plantlet dry weight among the treatments on day 22.