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Abstract
Nitrogen (N) is an essential element for the growth and yield of rice. Some endophytic bacteria can fix N2 from the air and convert to nitrogen compounds that can be utilized by plants. In this study, endophytic bacteria were isolated from one-month-old seedlings of five rice (Oryza sativa L.) varieties (Muey Nong 24, Muey Nong 25, Pathum Thani 1, Suphan Buri 1 and Chai Nat 1) growing without nitrogen fertilizer in the farmers’ field. One hundred and twenty-three isolates of endophytic bacteria were obtained from the roots, stems and leaves of these rice varieties. Nitrogenase activity of the bacteria in N-free culture medium was determined by acetylene reduction assay. Seven isolates of the bacteria with highest nitrogenase activity were identified by phylogenetic analysis of the 16S rRNA genes, and found to belong to Burkholderia cepacia (CS5), Citrobacter sp. (CR9), Citrobacter sp. (SS5), Citrobacter sp. (SS6), Bacillus amyloliquefaciens (25R14), B. amyloliquefaciens (SR1) and B. thuringiensis (25R2). Inoculation of Bu. cepacia (CS5) and Citrobacter sp. (CR9) to the seedlings of local rice variety (Muey Nong 24) significantly increased nitrogen concentration in the roots of rice.
Highlights
Rice is the most important crop in Asia as the main staple food and to those who depend on rice farming for their livelihoods
Endophytic bacteria were isolated from one-month-old seedlings of five rice (Oryza sativa L.) varieties (Muey Nong 24, Muey Nong 25, Pathum Thani 1, Suphan Buri 1 and Chai Nat 1) growing without nitrogen fertilizer in the farmers’ field
Seven isolates of the bacteria with highest nitrogenase activity were identified by phylogenetic analysis of the 16S rRNA genes, and found to belong to Burkholderia cepacia (CS5), Citrobacter sp. (CR9), Citrobacter sp. (SS5), Citrobacter sp. (SS6), Bacillus amyloliquefaciens (25R14), B. amyloliquefaciens (SR1) and B. thuringiensis (25R2)
Summary
Rice is the most important crop in Asia as the main staple food and to those who depend on rice farming for their livelihoods. Nitrogen is the most important nutrient in rice production It is the primary input in modern rice farming (Craswell et al, 1981; Yoshida, 1981). Economic crops, including rice, maize, wheat, sorghum and sugarcane have been reported to harbor endophytic bacteria that can convert N2 from the atmosphere into combined N that can be utilized by plants while having no pathogenic effect on them (James et al, 1997; Bhattacharjee et al, 2008; Lima et al, 1987). Nitrogen fixing endophytic bacteria inoculation of rice seedlings has been shown to significantly increase biomass and grain yield of rice included Gluconacetobacter diazotrophicus, Serratia marcescens, Burkholderia sp. There is a possibility that endophytic N2-fixing bacteria might play an important role in maintaining the yield of wetland rice in the mountains of northern Thailand without fertilizer input. This study was set out to (1) isolate endophytic N2 fixing bacteria from rice plants grown without N fertilizer, (2) identify the bacteria selected on the basis of their N2-fixing capacity and (3) evaluate the effect of selected bacteria on the growth of rice seedlings
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