Foliar application of potassium to improve the freezing tolerance of olive leaves by increasing some osmolite compounds and antioxidant activity

Abstract

Freezing damage is an important factor that limits olive production. The main aim of the present research was to investigate the possible impacts of the foliar application of potassium sulphate (K; K2SO4; 0.0, 0.5, 1.0, and 2.0 %) fertilization on the freezing tolerance (FT). Further, this research evaluated some physiological and biochemical changes of ‘Rashid’ olive (Olea europaea L.) at six sampling dates; these included November, December, January, February, April, and July. For this purpose, K was sprayed three times at 1-week intervals starting on 22 August 2016, on 16-year-old olives that had been located in a research orchard at Isfahan University of Technology (Iran), based on randomized complete block design. The results revealed that the effect of K sprays on the olives FT was significant at six stages of sampling. This was such that the highest (LT50 = −11.17 °C) and lowest FT (LT50 = −6.98 °C) was recorded in 2.0 % K-treated and control untreated olives during January, respectively. In addition, K application, particularly at 2.0 %, led to high increases of carbohydrate, proline, protein and total phenol concentration, antioxidant enzyme activity and DPPH (1, 1-diphenyl-2-picrylhydrazyl) scavenging capacity, as well as the ratio between unsaturated fatty acids and saturated fatty acids (UFA/SFA). It could be concluded that the foliar application of K could contribute to enhancing the olives FT by changing UFA/SFA ratio, in addition to the changes in other metabolites, like the accumulation of soluble carbohydrate, proline, protein, total phenol content and activation of the antioxidant system.