AUTHOR: EZEMA, LYNDA NGOZI
DEPARTMENT: APPLIED MICROBIOLOGY AND BREWING
AFFILIATION: NNAMDI AZIKIWE UNIVERSITY, AWKA
Chemical fertilizers are expensive and cause environmental pollution. The need has therefore arisen to develop cheaper and more sustainable methods of fertilizing the soil for agriculture. In this study, Phosphate solubilizing bacteria (PSB) isolated from the roots of some perennial grasses ( spear grass and giant blue stem) were evaluated for their potentials as inocula in Phosphate-biofertilizer production. PSB were isolated using Pikovskaya (PVK) agar medium containing the insoluble phosphate P, Ca3(P04)2. Colonies of isolates which solubilized the insoluble phosphate showed halozones, were purified and further screened for the ability to solubilize P in liquid PVK medium. Isolates showing good potentials were further screened for plant growth promoting properties such as production of Indole acetic acid (IAA), Ammonia (NH3) and Hydrogen cyanide (HCN). The ability of the isolates to compete with other soil microflora and survive agrochemicals was estimated by tests for resistance to various antibiotics and agrochemicals. Isolates selected on the basis of the above tests were evaluated in the plate bioassay and the pot experiment. A total of six bacterial isolates were selected and screened. Isolates PLB, PM6, PM11, RP1, PC and PLC solubilized Ca3(P04)2 on the PVK agar with solubilization indices of 1.57, 4.5, 3, 1.43, 3.4 and 2.75 respectively. In the liquid PVK medium, the isolates yielded P in the amounts of; 41mg/l, 37mg/l, 36mg/l, 33mg/l, 24mg/l and 26mg/l respectively. IAA production by the isolates were; 205uM, 30uM, 50uM, 85uM, 35uM and 40um respectively. PM6, PM11, RP1 produced both NH3 and HCN while PLB produced only NH3. Isolates PLC, PM6 and PM11 were resistant to the antibiotics; amoxicillin, ciprofloxacin, streptomycin, septrin, erythromycin, pefloxacin, gentamycin, ampiclox and zinacef, but susceptible to Rocephin. At 1% concentration of the agrochemicals (glyphosate, 2,3-dichlorovinyl dimethyl phosphate DDVP and NPK fertilizer), all the isolates were susceptible to glyphosate and DDVP while RP1, PLB, PLC and PM11 were resistant to NPK fertilizer. In the plate bioassay, PM6 gave a 100% germination rate but the root and shoot lengths, 4.5 and 6.5 respectively, were shorter than the control. PLB, PM11, RP1, PC and PLC gave germination rates of 40%, 90%, 70%, 40% and 70% respectively. In the pot experiments, the isolates PLB, PM11 and PM6 promoted mean percentage increase in plant height, root and shoot weight with respect to the control plant. The combined properties of PLB, PM6 and PM11 indicate their potential for use in biofertilizer production. Isolates PM11 and PM6 were identified as Pseudomonas aeruginosa and Burkholderia species respectively, using the 16S rDNA sequence analysis.
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