Plant growth promotion and nitrogen fixation in canola (Brassica napus) by an endophytic strain of Paenibacillus polymyxa and its GFP-tagged derivative in a long-term study

Paenibacillus polymyxa P2b-2R is an endophytic strain capable of fixing nitrogen (N) and promoting growth in a broad range of hosts. In this study, the ability of Paenibacillus polymyxa P2b-2R to fix N and promote the growth of canola (Brassica napus L.) was determined in a 3-month-long trial. We also compared growth promoting and N-fixing capability of wild-type P2b-2R and its GFP-tagged counterpart. Canola seedlings were inoculated with strain P2b-2Rgfp or P2b-2R. Non-inoculated seedlings were used as controls. Canola seedlings were grown for 3 months before evaluating plant growth promotion (length, biomass, and pod mass) and N fixation (using foliar N-15 dilution assay). P2b-2Rgfp inoculation significantly promoted canola growth by increasing seedling length by 2-fold, biomass by 2.5-fold, and fixing 35% of its foliar N, respectively. P2b-2R inoculation also increased seedling length by 70%, biomass by 2-fold, and fixed 27% of N. Seedling biomass and length, and the amount of N fixed by P2b-2Rgfp-treated seedlings was significantly greater than the P2b-2R-treated seedlings. P2b-2R or P2b-2Rgfp inoculation also lead to an increase of pod mass (more than 50%), indicating that these strains might play a role in enhancing the yield of canola by acting as biofertilizer.