The genetic diversity of dinitrogen-fixing bacteria associated with rice (Oryza sativa) was assessed by a polymerase chain reaction–restriction fragment length polymorphism (PCR–RFLP) approach on the nifH gene amplified directly from DNA extracted from washed rice roots and rhizospheric soil. Restriction digestion with the enzymes MnlI and HaeIII was performed to characterize 54 cloned nifH PCR products. RFLP profiles were clustered and analysed with the UPGMA program. Eight pairs of similar RFLP patterns (similarity>50%) and two pairs of homologous RFLP patterns (100% identity) were found from the washed roots and the rhizospheric soil, respectively. Three specific diazotrophic patterns were found from rhizospheric soil and rice roots. The analyses have revealed the presence of different nifH types, which appear to be significant components of the diazotrophic community in paddy fields, indicating that some of the diazotrophs may colonize the inside and the surface of the rice roots.
