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Water stress limits for vegetative and reproductive growth of Barlett pears

Marsal, J., Mata, M., Arbones, A., Rufat, J., Girona, J.
Acta horticulturae 2002 no.596 pp. 659-663
containers, drought, gas exchange, irrigation, leaves, pears, shrinkage, spring, summer, tree growth, trees, water potential, water stress
To assess the response of pear trees subjected to severe drought during short periods of about 1 month and to evaluate the impact on tree growth and stress recovery, sixteen two-year-old pear trees ('Barlett'/'Mantecosa Hardy'/'Quince BA-29') grown in 120-liter containers were chosen for the experiment and four irrigation treatments were applied. Control treatment was watered to non-stress conditions. SU and SP treatment received a summer and spring water stress cycle, respectively, by progressively reducing the water applied (from 100% to 20% of control dose). The Sp&Su treatment received two drought stress cycles, one in spring and the other in summer, as in SU and SP. Pressure chamber parameters were determined as water stress indicators, and the increase of trunk diameter and fruit size were used as crop parameters. The change in fruit size was linearly related to midday stem water potential (stem). Fruit growth both in spring and summer occurred at (stem) values higher than -2.7 MPa, while lower values led to fruit shrinkage. Secondary trunk growth, evaluated as increase in trunk diameter, was active during spring for a (stem) value higher than -1.9 MPa, whereas during summer this level was slightly more negative (-2.2 MPa). A minimum of two week period was necessary to recover leaf gas exchange when (stem) exceeded -3.5 MPa, whereas leaf necrotic mottling due to tissue dehydration appeared at (stem) values of -3.9 MPa. In general, the occurrence of leaf tugor loss (at -3 MPa in (stem)) defined the boundary between fruit growth impairment and limitations in plant recovery to water stress.