Co inoculated treatment with native and reference Bradyrhizobium: alternative to enhance peanut yields

VICARIO J.C., PRIMO E.D., GIORDANO W.F., AND DARDANELLI M.S.

La Falda

Workshop; II Workshop latinoamericano sobre rizobacterias promotoras del desarrollo vegetal; 2014

Introduction Inoculation of peanuts has yielded controversial results and is a discussed agricultural practice. The application of the appropriate strain of rhizobia, can produce a higher yield of fruits with high protein content. This refers to the relative ability of particular strains to occupy nodules on host plants in the presence of other symbionts. The soils of the groundnut area are characterized by a native population of rhizobia able to nodulate peanut, which is not always sufficiently effective. The optimization in the process of nitrogen fixation should be achieved with the use of a strain according to the host which is accomplished with studies related to its ability to colonize, competition, efficiency in fixing, among other features. Bacteria of the family Rhizobiaceae interact with leguminous plants in a host-specific manner and form N2-fixing root nodules. On the other hand, bacteria of the genus Azospirillum are free-living, surface colonizing, sometimes endophytic diazotroph and plant growth promoting rhizobacteria (PGPR). They are capable of increasing the yield of important crops growing in various soils and climatic regions. Objective The aim of this research was to study the effect of co-inoculation of recommended and indigenous bradyrhizobia and a PGPR (Azospirillum brasilense Az39) on nodulation and symbiotic performance of peanut. Materials and methods Treatments tested in the in vitro assays were: simple inoculations with Bradyrhizobium strains (C145, SEMIA6144, USDA4438, 15A, PC34), Azospirillum brasilense Az39 and co-inoculated Bradyrhizobium-Azospirillum brasilense Az39. They were inoculated at the time of transferring the pregerminated seeds with A. brasilense Az39 at 1x106 CFU/ml and rhizobial strains 1x109 CFU/ml. Six parameters were determined in each trial: length and dry weight of stem and root, number of nodules/plant and dry weight estimated inmg/plant root nodules. The field trial was performed according to the described by Boginoet al. (2006). The treatments tested were: co-inoculated Bradyrhizobium (C145, 15A and Pc34)-A. brasilense Az39. Results The maximum values of stem and root length were observed in the co-inoculated treatments. A similarbehavior was observed in the dry weightsof roots and stems. The number and dry weight of nodules was increased whenco-inoculate withAz39; obtaining maximum values the native strains 15A, Pc34 and the reference strain USDA4438. The behavior of the native strains in the field proved to be variable, the 15A strain showed the best performance in all measured variables: stem dry weight, number of boxes, number and dry weight of nodules, beating C145 strain recommended by INTA (Instituto Nacional de Tecnología Agropecuaria). Conclusion A general positive effect was observed in the presence of Azospirillum. Co-inoculation with native bradyrhizobia (15A and Pc34) and A. brasilense Az39 caused a significant increase in the overall number and dry weight of nodules per plant being equals or mayors to those obtained by the reference strains. In assessing the behaviour of native strains in the field in contrast to C145, 15A scored the best test results, demonstrating that the selection of native strainsadapted to groundnut soils can be a strategy for the development of new products to obtain better yields of peanut.