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Plant growth promotion and nitrogen fixation by Paenibacillus polymyxa in corn and canola Puri, Akshit


Availability of nitrogen is the most yield-limiting mineral factor in crop production. Several Paenibacillus bacterial strains that were able to fix nitrogen from atmosphere were isolated from extracts of surface-sterilized lodgepole pine seedling and tree tissues. One strain, Paenibacillus polymyxa P2b-2R, was found to derive high amounts of nitrogen from the atmosphere when introduced into gymnosperm species, namely lodgepole pine and western red cedar. I wanted to determine if Paenibacillus polymyxa P2b-2R could colonize, fix nitrogen and promote the growth of important agricultural crops such as corn and canola. For this I inoculated corn and canola seeds with P. polymyxa P2b-2R and grew them for 30 and 60 days, respectively. Corn seedlings were harvested 10, 20 and 30 days after inoculation and canola seedlings were harvested 20, 40 and 60 days after inoculation for evaluation of rhizospheric and internal tissue (endophytic) colonization (cfu). Seedlings were also evaluated for biological nitrogen fixation (¹⁵N dilution) and growth promotion (length and biomass) at these harvest intervals. The entire experiment was repeated to confirm the treatment effects. P2b-2R successfully colonized the corn rhizosphere with 5.52 x 10⁶ cfu/g dry root and the canola rhizosphere with 1.08 x 10⁸ cfu/g dry root. P2b-2R also colonized internal tissues of corn and canola root with population densities of 4.54 x 10⁵ cfu/g fresh weight and 2.36 x 10³ cfu/g fresh weight, respectively. Corn seedling growth was promoted significantly by inoculation with P2b-2R with an increase of 35% in length and 31% in biomass, 30 days after inoculation. Similarly, canola seedling length was promoted by 25% and biomass by 30%, 60 days after inoculation. Corn seedlings inoculated with P2b-2R were able to derive about 17% of foliar nitrogen from the atmosphere, 30 days after inoculation. Similarly canola seedlings derived nearly 20% of foliar nitrogen from atmosphere, 60 days after inoculation. These results clearly suggest that Paenibacillus polymyxa P2b-2R might have a broad range host capability and is able to fix nitrogen and promote the growth of at least certain important agricultural crops – corn and canola.

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