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

This study focused on water relations of Asian pear to provide informa tion for optimising irrigation management. Water stress was imposed on plants, in 25-1 containers, at early and at late stages of the growin g season by partial replacement of evapotranspiration losses. Water po tential and osmotic potential of leaves and fruit were measured before dawn and at midday. The difference in water potential between pre-daw n and noon was greater for leaves than for fruit. Fruit water potentia l was higher than leaf water potential before dawn and at midday. Midd ay turgor potential of leaves, but not fruit, became progressively low er 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 plant s 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, resu lting in a leaf water potential of less than -2.5 MPa, should be avoid ed in Asian pear as it was shown to have negative effects on water rel ations, photosynthesis, and fruit growth.