Effects of zinc and boron foliar application on soluble carbohydrate and oil contents of three olive cultivars during fruit ripening

• In warm locations, percentage of olive oil decreases during fruit ripening.
• Foliar application of zinc and boron leads to an increase of the percentage of the olive oil.
• Boric acid treatment in the warm climates improves the quality of olive oil e.g. decreasing saturated fatty acid while increasing unsaturated fatty acid.

Fertility management for olive (Olea europea L.) production depends on the growing conditions and type of cultivar. The present study was conducted to investigate the influence of zinc and boron foliar spray on fruit quality of three olive cultivars of Keylet, Coronaiki and Mission. Zinc sulphate (0.25%), boric acid (0.25%), and zinc sulphate (0.25%) + boric acid (0.25%) were sprayed on selected trees twice; at full bloom and 15 days after blooming. Results indicated that during fruit ripening, oil content increased from 11.7 to 19.4%, whereas soluble carbohydrate tended to decrease from 5.9 to 4.9%. The zinc and boron treatments enhanced the ratio of unsaturated/saturated fatty acids compared to untreated plants. The highest level of oleic acid (57.2%) and the lowest level of palmitic acid (15.19%) were recorded in cv. Coronaiki fruits treated with combination of zinc sulphate + boric acid.