Los datos del trabajo

Genetic and phenotypic characterization of phosphate-solubilizing bacteria and their effects on growth and symbiotic properties of alfalfa plants

Lorena B. GUIÑAZÚ¹, Javier A. ANDRÉS^1,2, Nicolás A. PASTOR¹, Marisa ROVERA¹ and Susana B. ROSAS^1
 1Laboratorio de Interacción Microorganismo - Planta, Facultad de Ciencias Exactas, Físico-Químicas y Naturales, Universidad Nacional de Río Cuarto. Campus Universitario. X5804BYA, Río Cuarto, Córdoba, Argentina.
²Microbiología Agrícola, Facultad de Agronomía y Veterinaria, Universidad Nacional de Río Cuarto. Campus Universitario. X5804BYA, Río Cuarto, Córdoba, Argentina.
Correspondence to: Javier A. ANDRÉS, e-mail: jandres@ayv.unrc.edu.ar,  jandresjov@yahoo.com.ar

 ABSTRACT

Alfalfa is the most important forage legume in the semiarid Argentinean Pampas because of the quality nutrients that it provides. Furthermore, the effect that this plant has on soil fertility is very important, as well as the contribution of its root system to the improvement and conservation of the soil structure. The alfalfa productivity could be increased if it is inoculated by to high efficiency rhizobia strains as well as other plant growth-promoting rhizobacteria (PGPR). The use of phosphate-solubilizing bacteria as inoculants increases phosphorous uptake and yield of crops. The objectives of this work were to phenotypically and genetically characterize alfalfa rhizosphere bacteria and to evaluate the effect of single or mixed inoculation upon nodulation and biological nitrogen fixation (BNF) efficiency. More than forty isolated rhizobacteria showed tricalcium phosphate solubilization in vitro assays and four of them caused greater solubilization than the control strain Pseudomonas putida SP22. The comparison of the 16S rDNA sequences indicated that the strains were phylogenetically related to Bacillus spp. and Pseudomonas spp.  A beneficial effect of these isolates on the alfalfa growth was observed in the coinoculation assays. The inoculation of Sinorhizobium meliloti B399 and Pseudomonas sp. F10 caused a significant increase in fresh and dry biomass of plant organs (roots and shoots), length and surface area of roots and symbiotic properties of alfalfa plants. The plants co-inoculated with S. meliloti B399 and Bacillus sp. M7 showed a significant increase in the measured parameters. The coinoculation of Pseudomonas sp. U14 and Bacillus sp. B11 with S. meliloti B399 also showed increases in some of the physiological parameters studied. A single or mixed inoculant containing these strains could be developed in order to be used in agricultural practices.