EVALUATION OF THE GROWTH AND RESPONSES OF IN VITRO CULTURES OF SEVERAL PEAR ROOTSTOCKS EXPOSED TO SIMULATED DROUGHT STRESS USING POLYETHYLENE GLYCOL TREATMENTS

Pear rootstocks affect the environmental adaptability as well as the nutritional status of the scion. In this research, we investigated the response of pear rootstocks to drought stress using polyethylene glycol (PEG) treatment to pear cultivars in vitro. Materials were obtained from the cultivars ‘Chuhwangbae’, ‘Hwangkeumbae’ (Pyrus pyrifolia Nakai), a Pyrus betulaefolia × Pyrus calleryana hybrid (PBPC), and open pollinated Oregon Pear Rootstock 195 (P. calleryana) (OPR195 OP) by shoot tip culture on MS medium supplemented with BA 1.0 mg/L and subjected to several concentrations of polyethylene glycol (PEG). In this experiment, PEG (0, 10, 15, 20, 25%, MW 6,000) inhibited shoot fresh weight and the total chlorophyll content of PBPC to the greatest extent at PEG 20% concentrations. Proline contents of PBPC and OPR195 OP were increased from 2.9 to 6.1 mg g^-1 FW and from 6.2 to 10.8 mg g-1 FW, respectively, as PEG concentration increased. However, ‘Chuhwangbae’ and ‘Hwangkeumbae’ exhibited no increase in concentrations above 10 and 5%, respectively.