Laboratory study on influence of plant growth promoting rhizobacteria (PGPR) on growth response and tolerance of Zea mays to petroleum hydrocarbon

The influence of rhizobacteria on the growth and tolerance of Zea mays (maize) in a petroleum hydrocarbon (crude oil) impacted medium was investigated. This study evaluated the effect of inoculating maize seeds with plant growth promoting rhizobacterial strains in a crude oil impacted medium. The rhizobacterial strains used in this study were tested for plant growth promoting traits [indole-3-acetic acid production, siderophore production, phosphate solubilisation and 1- aminocyclopropane-1-carboxylate (ACC) deaminase activity] following standard methods and plant root and shoot elongation activity of these strains were assayed using modified root elongation assay. The isolates were identified as Bacillus circulans, Enterobacter intermedius and Staphylococcus carnosus, by analytical profile index (API). The results showed that seeds inoculated with plant growth promoting rhizobacteria (PGPR) exhibited significant vegetative growth at various petroleum crude oil concentrations (1, 2 and 4 ml) compared with uninoculated seeds. The root and shoot length of inoculated seeds were 10.2 and 4.3 cm (B. circulans), 7.2 and 1.7 cm (E. intermedius), 5.2 and 3.8 cm (S. carnosus) and 0.9 and 1.5 cm (uninoculated), all at 1 ml concentration of petroleum crude oil. Tolerance Index (TI) for PGPR inoculated maize seeds in the crude oil impacted medium was highest with B. circulans (2.08 to 1.92), S. carnosus (0.69 to 0.59) and E. intermedius (0.79 to 0.71). Thus, this study suggests that B. circulans could be employed as a crude oil tolerant rhizobacterium (PGPR) for mitigating the toxic effects of crude oil on plants and subsequently enhancing the plant growth in a crude oil-impacted soil.Keywords: Plant growth-promoting rhizobacteria, tolerance index, crude-oil, impacted medium, growth parameter