Identification of plant growth hormones produced by bacterial isolates from rice, wheat and kallar grass

Abstract

Identification and quantification of the plant growth hormones indoleacetic acid and gibberellic acid, produced by plant growth-promoting rhizobacteria (PGPR), was carried out by using high-pressure liquid chromatography (HPLC). The PGPR strains were isolated from roots of rice, wheat and kallar grass and belonged to the genera Azoarcus, Azospirillum, Enterobacter, Pseudomonas and Zoogloea. For these studies, bacteria were grown in liquid nitrogen free malate (NFM) or combined carbon medium (CCM) containing tryptophan and combined nitrogen. Some Azospirillum strains produced both indoleacetic acid and gibberellic acid, while none of the Enterobacter spp. tested produced these growth hormones. Azoarcus strain K-1 produced higher amounts of gibberellic acid and Azospirillum strain ER-2 produced higher amounts of indoleacetic acid. Indoleacetic acid production increased with the age of bacterial cultures while a decrease in the production of gibberellic acid was noted at later growth stages. Pure indoleacetic acid and gibberellic acid in the concentration range 1–2 µg/ml increased root area and plant biomass of rice and wheat. Among PGPR strains tested, Pseudomonas 96–51 and its extract containing growth hormones increased root area, root length and plant biomass of rice and wheat.