Synergistic Bio-stimulant Efficacy of a Co-cultured Methylobacterium Consortium on the Vegetative Growth of Cicer arietinum under Complete Macronutrient Deprivation

Abstract

This study evaluated the biostimulant efficacy of a co-cultured Methylobacterium symbioticum and Methylobacterium extorquens consortium on the vegetative growth and biomass yield of Cicer arietinum under complete macronutrient (NPK) deprivation. In vitro microbial functional characterisation was followed by a controlled in vivo greenhouse pot trial using a randomised block design at Arihant Bioscience (India) Pvt. Ltd. between March 2026 and June 2026. Native methylotrophic strains were isolated on selective Ammonium Mineral Salts agar supplemented with 0.5% methanol. The isolates were assessed for phosphorus solubilisation, potassium mobilisation and nitrogen-fixation potential, and phenotypic compatibility was examined using a cross-streak assay. Cicer arietinum seeds were inoculated with the standardised consortium (10⁸ CFU/mL) and sown in a fractionally sterilised NPK-free sand-perlite matrix irrigated only with a macronutrient-deficient Hoagland solution. In vitro assays indicated preliminary diazotrophic potential in M. symbioticum, while M. extorquens showed tricalcium phosphate solubilisation and potassium mobilisation. The cross-streak assay showed a 0 mm inhibition zone, indicating phenotypic compatibility. In the pot trial, uninoculated plants exhibited severe stunting under macronutrient starvation, whereas consortium-treated plants showed higher shoot length, root length and total dry biomass than the uninoculated control. These findings suggest that the compatible methylotrophic consortium may support early vegetative growth of C. arietinum under controlled nutrient-deprived conditions, although field validation and molecular confirmation are required.