Enhancement of Rice Growth and Production of Growth-Promoting Phytohormones by Inoculation with Rhizobium and Other Rhizobacteria

4 Abstract: Excessive use of chemical fertilizers & repetition of same crops not only causes pollution but also a source of depletion of soil nutrients, ultimately reducing rice yield in the world. Co-Inoculation of various strain of bacteria are usually applied to overcome this problem. In present study, PGPR were isolated from washed-surface sterilized roots of rice (Oryza sativa L.) field near Gujranwala city in Pakistan. The isolates were identified on the basis of their morphological and biochemical characteristics. Two of the PGPR isolates were found belonging to Enterobacter spp. while the other two isolates were Azosprillium spp. The two rice cultivars Basmati and Super Basmati were inoculated with bacterial isolates alone and in combination with Rhizobium and Azosprillium respectively and their growth responses were examined. Our results confirmed the beneficial effects of co-inoculation with sufficient increase in root length, shoot length and fresh and dry weight of plants, when compared to single inoculation or uninoculation. All the Isolated strains were found capable of producing phytohormones i.e. indole-3-acetic acid (IAA) and gibberellic acid (GA). The dual inoculation of rice with Rhizobium and Azosprillium produced higher IAA & GA as compared to single inoculation. Furthermore IAA production by the Rhizobium and PGPR cultures with tryptophan was more prominent than single inoculation.