Water stress preconditioning to improve drought resistance in young apricot plants
Introduction
Apricot is one of the few temperate fruit trees not affected by overproduction. Most apricot trees are cultivated in Mediterranean countries, under where drought periods are increasingly common, a fact which makes irrigation water, the most limiting factor for apricot productivity, since it affects the viability of the young plantations.
Plants have developed physiological responses as well as ecological strategies to cope with water shortages, either by stress avoidance or stress tolerance. These responses allow them to survive and even to maintain some growth under adverse conditions. Plant response depends on the nature of the water shortage inducing physiological responses to short-term changes [1], acclimation to a certain level of water availability [2] and adaptation to drought [3], [4].
Knowledge of drought resistance mechanisms makes it easier to plan deficit irrigation strategies designed to save water while minimising the negative impacts on yield or crop revenue [5].
Previous studies have indicated that apricot drought resistance is mainly based on avoidance mechanisms, together with some degree of osmotic adjustment, when plants are submitted to short-term water stress periods [6]. However, drought imposition rates can have a large effect on the results of studies on drought resistance [7].
For these reasons, the aim of this study was to determine the ability of young apricot plants to drought hardening by the application of different water stress preconditioning treatments, as well as to improve our understanding of the physiological mechanisms involved in the response of apricot plants to water stress. Such information may be valuable in the nursery stage in order to improve the drought resistance of young apricot plantations.
Section snippets
Plant material and experimental conditions
The experiment was carried out on 1-year-old apricot trees (Prunus armeniaca L.), cv. Búlida, on Pollizo prune (P. domestica L.) rootstock, growing under field conditions in 35-l pots (40 cm diameter) containing a mixture of clay loam topsoil and peat, with 4% organic matter. Holed pots were buried in the soil in order to minimise the increases in soil temperature. Plants were drip irrigated daily using one emitter of 4 l h−1 per tree, maintaining the soil matric potential (Ψm) at about −20 kPa
Preconditioning period
During the preconditioning period (Table 1) a substantial depletion in soil water was observed in treatments T-3 (irrigated at 25% of control) and T-5 (irrigated every 6 days), with values of θv around 10.6%, and beyond the range of the tensiometer readings (<−80 kPa) (Table 1). Values of soil volumetric water content were slightly higher in pots from the T-2 treatment (irrigated at 50% of control) than those of the T-4 treatment (irrigated every 3 days). However, both promoted moderate plant
Conclusions
Young apricot plants exposed to slight-moderate water stress conditions developed avoidance mechanisms based on stomatal closure, accompanied by leaf epinasty, which can be considered as a complementary mechanism for regulating transpiration, and both have been recognised as important adaptive mechanisms to drought. Under more severe water stress conditions (Ψpd<−1.75 MPa) partial defoliation occurred and osmotic adjustment was triggered as a tolerance mechanism.
Water stress induced by daily
Acknowledgements
The authors are grateful to R. Galego, A. Jiménez, M. Garcı́a and J. Soto, for their collaboration. The study was supported by CICYT (HID1999-0951 and HID96-1342-CO4-03) grants to the authors.
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