The exploration of rhizospheric microbial flora for crop yield enhancement is well established. Rhizospheric microbes influence the plant physiology by imparting several beneficial effects, namely, Nitrogen fixation, increased nutrient uptake, and secondary metabolites production on their host plants. The present study investigates the response of Bacillus megaterium ATCC No. 13525, Pseudomonas fluorescens ATCC No. 14581, and Trichoderma viride MTCC No. 167 in alone and combined treatments for their effect on growth and yield parameters in a commercially important Ocimum tenuiflorum L. cv. CIM-Ayu. The plant is therapeutically important for its essential oil constituents, namely, eugenol, β-caryophyllene, and various monoterpenes. The combination treatments, T7 (B. megaterium + P. fluorescens) and T8 (B. megaterium + P. fluorescens + T. viride), showed maximum enhancement (27.27%) of percentage essential oil as compared to untreated control. Nutrient uptake especially N2 content was significantly increased (43%) with the treatment T8 (B. megaterium + P. fluorescens + T. viride). Amongst major essential oil constituents, eugenol content was maximally increased by 58.5% as compared to 42.9% (control) indicating a cumulative role of microbial inoculants for crop yield boost-up. 1. Introduction The members of genus Ocimum (Gk. ozo = smell) from family Lamiaceae are medicinally important plants owing to their therapeutic potentials as antiseptics, antioxidants, antistressors, antipyretics, antimicrobials, and insecticidal [1]. Ocimum tenuiflorum is an imperative species from the genus, widely cultivated for its high essential oil yields (0.5 to 0.7%), rich in eugenol, methyl chavicol, and linalool content [2]. The commercial importance of essential oil depends on its constituents and hence methods are required to enhance these valuable phytomolecules. Rhizospheric microorganisms are recognized as an economic and sustainable input for increasing the productivity of several agricultural, horticultural, forestry, and medicinal crops [3–5]. Numerous microbes such as Pseudomonas, Azospirillum, Azotobacter, Klebsiella, Enterobacter, Alcaligenes, Arthrobacter, Burkholderia, Bacillus, and Serratia have been reported to enhance the plant growth [6, 7]. These microorganisms coexist in the rhizosphere, which is a thin soil layer immediately surrounding plant roots. Rhizospheric microbial wealth is widely acclaimed in agricultural practices for enhancement of crop yield attributes as they share their environment with the host plants and thus exhibit better adaptation
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