This study was carried out to verify the occurrence and genetic diversity of diazotrophic bacteria associated to the native graminaceus plants Elyonurus muticus (Carona grass) and Axonopus purpusii (Mimoso grass) and the exotic Brachiaria humidicola (Brachiaria) that form the pastures in the Nhecolândia region of the Pantanal in the state of Mato Grosso do Sul, Brazil. The plants were harvested in the dry and rainy seasons and the diazotrophic bacteria populations in the soil and on roots and leaves of the three grasses were determined. Strains belonging to the species Azospirillum brasilense, A. lipoferum, A. amazonense; Herbaspirillum spp., and Burkholderia spp. were isolated. The number of diazotrophic bacteria associated to the three forage grass species during the rainy season was smaller than in the dry season. Genetic diversity in the isolated bacteria was studied by amplified rDNA restriction analysis (ARDRA) using the amplified 16S rDNA region. The isolates were divided into five different genotype groups. A. brasilense and A. lipoferum presented 50 % similarity while A. amazonense was included in another group with 25 % similarity to other species of the genus. The bacteria of genus Herbaspirillum formed a separate group with only 25 % similarity to genus Azospirillum. The fifth group consisted of only one isolate with 25 % similarity to the other groups.
Biological Nitrogen Fixation; Azospirillum; ARDRA
