FROST TOLERANCE IN YOUNG PLANTS OF OLEA EUROPAEA L. 'ARBEQUINA' AND 'BARNEA': ROLE OF TISSUE WATER STATUS

Low freezing temperatures during winter is one the most limiting environmental constraints for olive productivity in Argentina and other new olive growing areas. Freezing temperatures damage most organs and tissues during periods of active vegetative growth, but the same temperatures may have little or no impact during winter recess or dormancy. When days get shorter and temperature falls, a cold-hardening process begins, involving a decrease of water content, improving tolerance to low winter temperatures. The aim of this study was to assess if plant water status modifies cold tolerance in two different frost-tolerant olive cultivars, when young plants were submitted to a water stress induced by deficit irrigation and salt concentration in water solution. One-year old ‘Arbequina’ and ‘Barnea’ olive plants were placed in pots. Treatments were applied from March to September (autumn-winter) and consisted of mild water stress (T2; Ψ_pre-dawn between -1 to -1.5 MPa) and moderate water stress (T3; Ψ_pre-dawn near -2.5 MPa), two salt concentrations (T4, 4 dS/m; T5, 8 dS/m) and a control of 2 dS/m solution and no water deficit (T1). A moderate water stress increased freezing tolerance in -1.18°C in ‘Arbequina’ and -1.91°C in ‘Barnea’ in comparison to non-stress treatments. The LT₅₀ in plants exposed to mild water stress or salt stress did not show any differences over the control. A high correlation was found between plant water status with tolerance to low temperatures (LT₅₀) in ‘Arbequina’ (R²=0.8) and ‘Barnea’ (R²=0.74) when only water stress treatments were considered. The increase in frost-resistance could be explained by the decrease of RWC. Exposing the plants to a higher level of water stress led to less tissue damage at freezing temperatures.