Azospirillum is a genus of free-living bacteria that live in soils of varied ecological situations and are frequently connected with plant rhizospheres and endorhizospheres. Because of their ability to fix atmospheric nitrogen (N2) and release phytohormones including auxins, cytokinins, and gibberellins, these bacteria can benefit host plants in a variety of ways. They can also breakdown soil contaminants and decrease populations of phytopathogenic bacteria in the soil. The goal of this study was to see if topinambur (Helianthus tuberosus) and yacón (Smallanthus sonchifolius) plants grown in the Central Valley of Catamarca Province have natural mutualistic symbiosis with endorhizospheric bacteria of the genus Azospirillum and/or other genera of native atmospheric nitrogen-free fixing bacteria. Döbereiner et al.  suggested a technique for isolating the N2-free binding endorhizospheric bacteria, Azospirillum sp., from the roots of each species. The endorhizosphere of topinambur and yacón did not yield any native rhizobacteria of the species Azospirillum. The isolates were visually and physiologically assessed, and three distinct morphotypes of each plant species were chosen for genetic identification. There were eleven nitrogen-fixing autochthonous bacteria found in the endorhizosphere of the research cultures, six in topinambur and five in yacón. Pseudomonas isolates are all members of the genus Pseudomonas. Pseudomonas sihuiensis in topinambur and Pseudomonas resinovorans and Pseudomonas sihuiensis in the yacón of Pseudomonas alcaligenes. The presence of autochthonous rhizobacteria of the genus Azospirillum in the endorhizosphere of topinambur (H. tuberosus) and yacón (S. sonchifolius) cultures could not be confirmed. It is the first time that autochthonous atmospheric nitrogen-free fixing bacteria of P. sihuiensis, P. alcaligenes, and P. resinovorans have been isolated in the endorhizosphere of topinambur and yacón, cultivated in soils of the Province of Catamarca’s Central Valley.
María Gabriela Di Barbaro
Faculty of Agricultural Sciences, National University of Catamarca, Avda, Belgrano and Maestro Quiroga (4700), Catamarca, Argentina
Eleodoro Del Valle
Faculty of Agricultural Sciences, National University of the Litoral, Kreder 2805. (3080) Esperanza, Santa Fe, Argentina and National Council for Scientific and Technical Research, Argentina.
Celia Brandán de Weht
Faculty of Agronomy and Zootechnics, National University of Tucumán, Argentina
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