Arbuscular mycorrhiza augments essential oil composition and antioxidant properties of Ocimum tenuiflorum L. - A popular green tea additive

The increasing interest and demand of Ocimum tenuiflorum L. and its products in different industrial sectors necessitate appropriate cultural practices for cultivation of the plant with increased herbage and essential oil yield. Studies on O. tenuiflorum in relation to arbuscular mycorrhiza are restricted to evaluation of diversity of the mycorrhizal fungi in its rhizosphere or assessment of the ability of different species to colonize its roots. Hence, the present study aimed to assess the effect of arbuscular mycorrhizal fungus (Rhizophagus intraradices) inoculation on the pharmaceutically desired parameters of two high yielding genotypes of O. tenuiflorum. Colonization by R. intraradices fungus resulted in significant increase in the leaf biomass and concentration of essential oil in both the genotypes. Formation of arbuscular mycorrhiza resulted in up to 59.01 % and 86.95 % increase in essential oil concentration in mycorrhizal genotype A and B plants, respectively, in comparison with control. The characterization of essential oils by Gas Chromatography-Mass Spectrometry showed significant effect of arbuscular mycorrhiza on their chemical profile. A total of 23 and 37 compounds were identified in essential oils of control genotype A and B, respectively, while 21 and 34 compounds were detected in essential oils of their respective mycorrhizal counterparts. Concentration of eugenol (a valued phenylpropanoid), and other medicinally important terpenoids (beta-elemene, beta-caryophyllene, germacrene A, and germacrene D) increased in essential oils of mycorrhizal plants. While genotype and mycorrhizal interaction significantly influenced biomass and essential oil concentration in leaves, the effect of R. intraradices on concentration of eugenol, beta-elemene, and beta-caryophyllene did not vary between the two genotypes. Additionally, principal component analysis also highlighted that the volatiles common in the essential oil of the four treatments contributed significantly to the variation in the essential oil composition. Phenol, flavonoid, and polyphenol contents in the leaves were also enhanced on formation of arbuscular mycorrhiza. The study also aimed to evaluate the ability of leaves (fresh and processed) to scavenge reactive oxygen and nitrogen species. Arbuscular mycorrhiza augmented the antioxidant capacity of fresh and processed leaves of both the genotypes. Thus, findings of the study demonstrate that R. intraradices inoculation enhances productivity of O. tenuiflorum and also improves the quality of the products.