CONICET | Buscador de Institutos y Recursos Humanos

Introduction In general it is known, that actinomycetes have a high capacity to synthesize an array of biodegradative enzymes, antibiotics, phytohormones, and antifungal metabolites, and can promote plant growth by producing promoters such as indole-3-acetic acid (IAA), and siderophores. However, yet there is less information in relation to saprophytic bacteria non-Azospirillum, such as actinomycetes in the rhizosphere of Lotus tenuis plants. Previous studies on the actinorhizal symbiosis Ochetophila trinervis - Frankia showed a growth promotion by co-inoculation with actinomycetes isolated from the rhizosphere of this plant, and they produced phytohormones and produced cellulose and hemicellulose degradation. The aims of the present work were to isolate and characterize rhizospheric actinomycetes of Lotus tenuis forage soils, with potential characteristics as plant growth promoting rhizoactinomycetes. Materials and methods Saprophytic and rhizosphere actinomycetes of Lotus tenuis were isolated applying differents methods. The determination of their preliminary taxonomic standing was based mainly on the morphological characterization, and different physiological characteristic such as IAA production, degradation of cellulose and hemicelluloses, phosphorus solubilization, ability to fix nitrogen, siderophores production, and ACC-deaminase activity were studied. Results A total of 32 isolates of actinomycetes were obtained and the majority belonging to the genus Streptomyces (91%), and fewer Actinoplanes (6%) and Actinomadura (3%). All strains were positive for IAA production, and twelve strains showed positive reactions for cellulose and hemicellulose degradation, and seven isolations were positive for phosphate solubilization. Eight strains were selected, and which were performed other physiological tests, typical of the PGPR such as: N-fixation, ACC-deaminase activity and siderophores production. Conclusion These results show the presence of actinomycetes in forage soils such as L. tenuis fields, with potential PGP traits, and as potential Plant Growth Promoting Rhizoactinomycetes. These results confirm that these rhizoactinomycetes are new in terms of soil microorganisms with potential agronomic applications.

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