Polyethylene Glycol Induced Water Stress Effects on Apple Seedlings. I. Methodology, Water Consumption, and Dry Matter Production1

Apple seedlings ( Malus domestica Borkh.) were grown in the greenhouse under a range of polyethylene glycol (PEG)-induced osmotic potential stresses up to −7.5 bars. Water use by seedlings (ml water consumed/dm 2 leaf area) responded to ambient temperature fluctuations after 4 days in the solution. During the first 4 days after initiation of the stress, no response was obtained indicating that the seedlings were undergoing an “adaptation period.” Plants receiving higher osmotic stresses were less able to respond to ambient temperature fluctuations as measured by transpiration. Transpiration rate decreased as osmotic stress was increased. PEG-induced osmotic water stress and water stress in soil were compared, the latter by letting the soil mass dry out. Comparable transpiration rates from the 2 methods, when plotted, showed that PEG-induced osmotic stresses of −0.5 and −4.0 bar were equivalent to greenhouse potting soil at 75% of field capacity and approaching the wilting point, respectively. It was concluded that the PEG-induced water stress was similar to water stress in soil, thus PEG-induced stress can be used in experiments with apples to study various effects of water stress. Use of a freezing point depression osmometer in determining solution osmotic potentials of PEG-modified solutions is described.