Abstract
Free living heterotrophic bacteria were isolated from the rhizosphere of 10 local and cultivated varieties of rice grown in Karimganj district of South Assam. Among the 25 isolates, 11 isolates withplant growth promoting activity were identified based on phenotypic and 16S rDNA sequence analysis. The strains were identified as Shingomonasa zotifigens, Pseudomonas putida, Stenotrophomonas maltophila, Acinetobacter radioresistance, Alkaligenes faecalis, Enterobacter cloaceae subsp. dissolvens, Pantoea agglomerans, Klebsiella pneumoneae, Achromobacter xyloxidans, Herbispirillum rubrisubalbicans and Herbispirillum sp. The efficient strains are isolated from the local varieties of rice plant. The isolate KR-23 (Sphingomonas azotifigens) was a novel bacteria reported for the first time as nitrogen fixing bacteria from India. The nitrogen fixing ability along with IAA production, ACC deaminase activity and P-solubilisation by the bacteria has shown their potential for plant-growth-promoting rhizobacteria. KR-6 (Stenotrophomon asmaltophila) and KR-7(Herbispirillum rubrisubalbicans) have been reported earlier as plant pathogens but they have shown a high potential for nitrogen fixing and auxin producing activity in the present study.
Highlights
Free living nitrogen fixing bacteria have been considered as an alternative for inorganic nitrogen fertiliser for promoting plant growth (Ladha and Reddy, 2000; Park et al, 2004)
Inspite of the fact that a variety of nitrogen fixing bacteria have been isolated from the rhizosphere of various crops, interest in isolating more beneficial plant growth promoting bacteria has increased recently due to their potential use as bio fertiliser (Vessey, 2003)
The IAA production and ACC deaminase activity of the microbes help in the stimulation of growth and pathogenesis of the plants
Summary
Free living nitrogen fixing bacteria have been considered as an alternative for inorganic nitrogen fertiliser for promoting plant growth (Ladha and Reddy, 2000; Park et al, 2004). Inspite of the fact that a variety of nitrogen fixing bacteria have been isolated from the rhizosphere of various crops, interest in isolating more beneficial plant growth promoting bacteria has increased recently due to their potential use as bio fertiliser (Vessey, 2003). Cultivated rice (Oryzasativa) originated from species of wild rice and was domesticated several thousand years ago (Hoshikawa,1989; Oka,1988; Kennedy et al, 2001). Wild rice species are likely to harbour unique populations of nitrogen-fixing bacteria that differ from those in extensively bred modern varieties of cultivated rice (Hurek et al, 2000). The use of bio-fertilisers may be an alternative to the chemical fertiliser for achieving sustainable rice farming while improving productivity in rice-agro ecosystem
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