Stimulation of nitrogen fixation and induction of flavonoid-like compoundsby rhizobacteria

Bacteria belonging to fluorescent Pseudomonas and to the spore-forming Baci llus groups, predominantly found in the rhizosphere and rhizoplane of healt hy chickpea plants, were studied in order to determine their effect on effe ctive strains of Rhizobium sp. 'Cicer' (Ca181 and Ca313) and their plant gr owth-promoting ability under aseptic and soil conditions. Go-inoculation of the rhizobacteria with effective Rhizobium strains of chickpea resulted in a significant increase in nodule weight, root and shoot biomass and total plant nitrogen when grown either in sterilized chillum jars or under pot cu lture conditions. The Rhizobium stimulatory Pseudomonas sp. 'CRP55b' showed maximum increase in all the symbiotic parameters. On co-inoculation with ' Ca181' and 'Ca313', Pseudomonas sp.'CRP55b' and 'CRS68' resulted in signifi cant increases in nodule weight, root and shoot biomass and total plant nit rogen. The nodule stimulating rhizobacteria enhanced levels of flavonoid-li ke compounds in roots on seed bacterization. Also, ethyl acetate extracts o f culture supernatant fluids when applied to seeds resulted in enhancement of flavonoids in roots, suggesting that the rhizobacteria have a direct inf luence on root flavonoids which might be an additional factor in nodule pro motion by these bacteria. These rhizobacteria also produced fluorescent com pounds with absorption maxima at 252 nm, similar to those of plant flavonoi ds but having a different Rf value. Whether such fluorescent compounds act as signal molecules for induction of plant flavonoids in plant roots requir es further study.