Phytohormone biosynthetic potential of different Rhizobium species

Abstract

Plants may not have optimum growth hormone production potential under suboptimal growth and environmental conditions. The exogenous application of microbes is a potential and economical source of plant hormones. A laboratory trial was performed to evaluate the hormone biosynthesis potential of several soil microbes. Rhizobium sp. (Rhizobium trifolii, Rhizobium etli, Rhizobium meliloti, Rhizobium ciceri, Azorhizobium caulinodans, Bradyrhizobium japonicum, Rhizobium vulgaris, and Rhizobium phaseoli) were isolated from root nodules of various legumes and were biochemically characterized. Absorption spectroscopy (535, 254 and 665 nm λ) was used to quantify indole acetic acid (IAA), gibberellin and cytokinin production of different Rhizobium species. B3 isolate of Rhizobium trifolii had yielded (14.54 and 21.37 µg mL-1) IAA equivalents without and with L-tryptophan (L-TRP) supplement, that was statistically at par with same species while significantly greater than other Rhizobium isolates. Gibberellin production was found statistically non-significant in all isolates. Rhizobium phaseoli (Vp1) yielded 1.68 µg mL-1 cytokinin that was at par with the same species isolates and with Rhizobium trifolii but was critically greater in amount than other species. It was concluded that Rhizobium plays a vital role in plant growth and development can produce auxin and gibberellins, but some could produce cytokinin. Keywords: Phytohormone, Biosynthesis, IAA, PGPR, Auxin, Gibberellins, Cytokinin