Real time PCR detection targeting nifA gene of plant growth promoting bacteria Azospirillum brasilense strain FP2 in maize roots

The plant growth promoting bacteria (PGPB) Azospirillum brasilense has been recommended for use in commercial inoculants in Brazil. Effective methods are necessary to monitor PGPB strains in the rhizosphere. Our purpose was to develop a real time PCR method for detection of A. brasilense strain FP2 in maize seedlings targeting nifA. Primer pairs were designed and their specificity was verified using DNA from 12 different bacterial species. Standard curves were prepared for DNA quantification using serial dilution of A. brasilense DNA extracts. PCR efficiencies and correlation coefficient presented values within the acceptable range for qPCR, mean PCR efficiency was 95 % and correlation coefficient was 0.98, indicating that nifA gene was suitable for the quantitative analysis of the target bacterial genome. Inoculated maize seedlings were grown in vitro or in pots, bacterial DNA copy number per gram of fresh root was quantified 1, 4, 7 and 10 days after inoculation. The developed primers targeting nifA will be useful for monitoring Azospirillum brasilense strain FP2 in crops.