THE INFLUENCE OF WATER-DEFICIT ON WATER RELATIONS, PHOTOSYNTHESIS AND FRUIT-GROWTH IN ASIAN PEAR (PYRUS-SEROTINA REHD)

This study focused on water relations of Asian pear to provide information for optimising irrigation management. Water stress was imposed on plants, in 25-1 containers, at early and at late stages of the growing season by partial replacement of evapotranspiration losses. Water potential and osmotic potential of leaves and fruit were measured before dawn and at midday. The difference in water potential between pre-dawn and noon was greater for leaves than for fruit. Fruit water potential was higher than leaf water potential before dawn and at midday. Midday turgor potential of leaves, but not fruit, became progressively lower with continuation of early-season water stress. There was evidence of osmotic adjustment in fruit, but not in leaves. The photosynthetic rate was higher in fully irrigated plants than in water stressed plants except for cloudy days. Fruit diameter was significantly smaller in plants during water stress applied early in the season, compared with that in control plants, but it recovered upon re-watering. Late season stress did not affect fruit diameter. Early season water stress, resulting in a leaf water potential of less than -2.5 MPa, should be avoided in Asian pear as it was shown to have negative effects on water relations, photosynthesis, and fruit growth.