Genotypic characterization of two fast-growing peanut rhizobia isolated from Cordoba soils, Argentina

TAURIAN, T., IBAÑEZ, F., AGUILAR, O.M., FABRA, A.

Mérdia, México

Congreso; XII International Congress on Molecular Plant-Microbe Interactions; 2005

Abstract Arachis hypogaea L. (peanut) is an important crop all over the world that provides food for direct human subsistence and other several food products. Argentina is one of the major peanut producers in the world, and 94% of its production takes place in the province of Cordoba. Previous phenotypic studies of native peanut rhizobia isolated from this region revealed the presence of two populations which group within the slow and fast growing rhizobia. Considering these results and that there are no previous reports describing peanut fast-growing rhizobia, the aim of this study was further characterize this group. Methods: Peanut isolates: NET30 and NCHA22. 16S rDNA amplification (Weisburg et al., 1991). nodC amplification (Laguerre et al., 2001).  16S rRNA gene and partial nodC gene analysis (BLAST, ClustalX 1.64b). Plasmid profiles (Eckhardt, 1978, Wheatcroft et al., 1990). Results: 16S rDNA sequence of isolates NET30 and NCHA22 showed 99% identity with those of Rhizobium giardinii H152 and Rhizobium tropici type IIB, respectively. On the other hand, the phylogenetic analysis of nodC gene showed similarity between the isolates and Rhizobium tropici. Profile of indigenous plasmids showed the presence of one plasmid of similar size in both rhizobial isolates and an additional plasmid in NCHA22. Conclusion: Our results demonstrated that peanut rhizobial isolates having 16S rRNA alleles similar to species R. giardinii and R. tropici were found among the diverse rhizobial population able to nodulate peanut. These observations invite to speculate that some of the lineages found to form nodules in the peanut centre of cropping in Cordoba, may have evolved from more than one Rhizobium background which gained the ability to nodulate peanut by lateral gene transfer of nod genes.