Groundnut (Arachis hypogaea L.) growth and yield enhancement by consortium of diazotrophic and non-rhizobial root nodule endophytic bacteria

Modern agriculture rely heavily on costly and environmentally pernicious chemical fertilizers. To investigate possible alternatives to chemical fertilization in A. hypogaea cultivation, consortium of three plant growth promoting bacteria (PGPB): P. aeruginosa, A. chrococcum and A. faecalis were isolated from rhizosphere and root nodules of A. hypogaea using spread plate dilution method on Azotobacter chroococcum agar, and yeast extract manitol agar growth media. Isolates identified using cultural, morphological, biochemical and molecular characterization. Isolates were scaled-up, inoculated into 4000.0g of soil in pots at rate of 4.5 x 10 ⁶ cfu/ml ( A. chrococcum ), 2.0 x 10 ⁹ cfu/ml ( P. aeruginosa ), 1.5 x 10 ⁹ cfu/ml ( A. faecalis ) in the following treatments: Uninoculated (control); NPK; Pseudomonas-Azotobacter; Pseudomonas-Alcaligenes; Pseudomonas-Alcaligenes-Azotobacter in triplicates. Seeds of A. hypogaea belonging to two varieties (SAMNUT 25 and 26) were propagated in treated soils in two separate sets. Growth enhancement parameters: germination time, percentage germination, shoot, root lengths growth, fresh plant and pods weights, pods and nodule numbers, and chemical properties of soils determined after 120 days. Results showed soils inoculated with PGPB enhanced all growth parameters over uninoculated (control) and NPK treated soils which were statistically significant for germination time, shoot, root lengths, fresh plant and pods weights, pods and nodule numbers (p < 0.5). Soil chemical properties: pH, P, N, CEC and SOM contents were maintained and enhanced. P. aeruginosa, A. chrococcum and A. faecalis soil inoculation offered effective alternative to chemical NPK fertilization.