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. The present study investigated the effect of boron (B) foliar application on the dynamic changes in the concentration of phenols, especially oleuropein, and volatile compounds of olive leaves during a 90-day period. The trial was conducted in a greenhouse on one year old olive plantlets, sprayed with B at 41.62 mM against a water treated control. It was revealed that total phenols and oleuropein concentration in old and in young olive leaves increased in B treated leaves 90 days after application. Furthermore, B enhanced the concentration of particular terpene and norisoprenoid volatiles in olive leaf infusion. The obtained results may give a new perspective in biochemical farming practice, with a possibility to increase the amounts of phenols and terpenes in olive leaves intended for medical uses, and to enhance olive plant resistance to pathogens and insects.