CONICET | Buscador de Institutos y Recursos Humanos

Previous studies about the effect of saprophytic strains of actinomycetes native from Patagonia, on the actinorhizal symbiosis Ochetophila trinervis - Frankia showed growth promotion and a higher nodulation in co-inoculated plants. According to these results, preliminary studies were conducted to determine if similar effects could be found in legumes. Alfalfa and soybean seedlings co-inoculated with rhizobia and saprophytic actinomycetes had an increased nodulation and plant biomass than plants inoculated only with rhizobia. Based on the promotion effects by rhizospheric actinomycetes (named as ?rhizoactinomycetes?), we proposed to study the effect of these actinomycetes on the legume Lotus tenuis (syn. L. glaber), and to isolate and characterize new native strains from forage soils. L. tenuis seedlings were inoculated either with the single symbiotic N2-fixing strain Mesorhizobium loti, or with each saprophytic strain (Streptomyces MM40, Actinoplanes ME3, Micromonospora MM18), and with a combination of one, two o three saprophytic strains together with the symbiotic strain. The plants were grown in growth chamber in pots and in pouches. After 11 weeks of post-inoculation the following plant growth parameters were measured: shoot and root length, dry weight of shoot, root and root nodules, nodules number and nodulation kinetics. Isolations of the saprophytic actinomycetes were performed from soils of Pampa Deprimida of Lotus tenuis rhizosphere by applying differents methods. Isolates were characterized with a preliminary taxonomic standing by describing the colonial morphology, and different physiological properties such as IAA production, degradation of cell materials as cellulose and hemicelluloses, phosphorus solubilization, nitrogen fixation, siderophores production and ACC-deaminase activity. L. tenuis seedlings co-inoculated with the symbiotic strain M. loti and with saprophytic actinomycetes showed an increased plant growth. Moreover, a flowering promoting effect was also produced. A total of 33 isolates of actinomycetes were obtained and the majority belonging to the genus Streptomyces (91%), and fewer Actinoplanes (6%) and Actinomadura (3%). In conclusion, the promoting effect of actinomycetes on rhizobial symbioses under laboratory conditions is a first step to show the broad spectrum action of these microorganisms in plant-microbe interactions. The positive effect on N-fixing plants open a wide range of applications in agriculture as a potential tool for enhacement of forage in Pampa zone and in other lands. Also, the characterization reavead that the actinomycetes are new strains, many which are diazotrophs that need to be profoundly studied regarding their potential agronomic applications. These results show the presence of actinomycetes in forage soils such as L. tenuis in Pampa Deprimida, with potential PGPR traits, and open a new line of research on native actinomycetes which could be useful for the forage inoculants industry.