Seasonal variability in essential oil composition and biological activity of Rosmarinus officinalis L. accessions in the western Himalaya

Rosmarinus officinalis L. is an imperative herb used in pharmaceutical yet knowledge on chemical and activity profile of essential oil (EO) to harvest seasons and accessions from the Himalayan region is limited. Thus, accessions were evaluated to determine the EO content, compositional, antimicrobial, and cytotoxic potential of rosemary in different harvest seasons during 2018‒2019. EO content was 30.5% higher in IHBT/RMAc-1 compared with IHBT/RMAc-2 accession while 27.9% and 41.6% higher in the autumn as compared with summer and rainy season, respectively. Major EO compound was 1,8-cineole; ranged from 32.50‒51.79% during harvest seasons and 38.70‒42.20% in accessions. EO was active against both the tested Gram-positive bacteria (Micrococcus luteus MTCC 2470 and Staphylococcus aureus MTCC 96). EOs showed inhibition of Gram-negative bacteria (Salmonella typhi MTCC 733), while Klebsiella pneumoniae MTCC 109 was found to be resistant. The rosemary EO of T1 (Rainy season IHBT/RMAc-1) was most effective against S. aureus MTCC 96 with the minimum inhibitory concentration (MIC) of 4% (v/v). In vitro cytotoxicity evaluation showed no potential anti-proliferative activity of EO. The rosemary EO profile in the western Himalayan region was influenced by harvesting seasons and genetic variability within the accessions; furthermore, a promising antibacterial agent in pharmaceutical and flavour industries.