Acclimation to low temperatures and water deficit improve freezing avoidance in olive trees

Abstract

Olive is an evergreen tree that has been cultivated all over the world. In the last years olive crops expands their limits to higher latitudes and we observed new crops in south areas like Patagonian steppe. This is a challenge for farmers and scientists because they have to improve olive oil quality of plants that grown in dry and cold zones. The aim of this work was to determine how Olea europaea L. cope with drought and cold temperatures in Patagonian steppe and its consequences on fruit quality. We determined leaf water relations, ice nucleation temperature (INT), temperature at which 50% of ions release of the plasmatic membrane occurs (LT50) and oil fatty acid composition during summer and winter under different water treatments in 5 olive cultivars growing in pots in Patagonian steppe, Argentine. INT and LT50 varied seasonally in all cultivars and treatments. LT50 ranged between -6.51°C and -10.83°C in summer and -10.13 to -13.5 ° C in winter. LT50 was negatively correlated with osmotically solutes content, cell wall elasticity (ε) and apoplastic water fraction (AWF) across cultivars, treatments and seasons. There was a significant treatment effect in INT and LT50 during summer. Manzanilla that was the cultivar that exhibited less supercooling capacity increased in 3.5°C its resistance to frost when water soil content decreased. During winter we found strong correlations between INT and Ψmin, ε and AWF. Olive oil was of an excellent quality and exhibited oleic acid values ​​of 76.8%. The results suggest that the maintenance of water in an unfrozen state under cold temperature was the consequence of acclimation process which involved changes in water relations traits. In a similar way applying moderate water deficit decrease stem water content and modified water relations improving supercooling capacity . These study demonstrate that Patagonian steppe is a possible new area for developing commercially olive cultivars.