Boron foliar application enhances oleuropein level and modulates volatile compound composition in olive leaves

•1-year old olive plantlets were sprayed with boron (B+) against untreated control.•After 90 days B+ old leaves had higher oleuropein and total phenol concentration.•Young leaves had notably higher secoiridoid concentrations after B+ treatment.•B+ leaves infusion had higher concentration of certain terpenes and norisoprenoids.•These results may give a new perspective in biochemical farming practice.