NOVEL ISOLATES OF PHOSPHATE-SOLUBILIZING BACTERIA FOR THE DEVELOPMENT OF BIOFERTILIZERS FOR SOYBEAN CULTIVATION

SANNAZZARO AI; DOFFO MJ; CASTAGNO LN; RODRÍGUEZ J; PIECKENSTAIN FL; ESTRELLA MJ

Taller; III Taller Latinoamericano de PGPR; 2016

Phosphorus (P) requirements of cultivated crops are usually met by chemical fertilization. However, a high proportion of the P supplied by these means precipitates into insoluble forms that cannot be assimilated by plants. In this context, biofertilizers based on microorganisms able to solubilize soil P represent a low-cost and environmental-friendly alternative. The limited number of bacterial species currently used for commercial formulations may not always adapt to a wide range of crops and soil conditions, an issue that restricts their efficiency. The highly diverse communities of rhizospheric microorganisms is a potential source of strains for the development of improved biofertilizers based on bacteria well-adapted to the target environment and also able to solubilize various phosphate sources. Our goal is to contribute to the development of high-quality biofertilizers for soybean cultivation, through the isolation and characterization of P-solubilizing and plant growth promoting bacteria. Seven hundred P-solubilizing isolates were obtained from soybean fields in Buenos Aires and Santa Fe provinces, among which those that maintained the ability to solubilize organic (sodium phytate) and inorganic (tricalcium phosphate) P after repeated subcultures were selected. Non-redundant strains were identified by REP-PCR and taxonomically characterized by PCR amplification and sequencing of the 16S rRNA gene. Gram-negative bacteria prevailed among the isolates. Strains from different bacterial taxa were chosen for testing their ability to promote growth of soybean plants. Bacteria related to the genera Enterobacter, Pantoea, Pseudomonas and Rhanella were the most efficient growth-promoters under limited soluble phosphate conditions. All tested isolates were also verified not to be pathogenic on soybean plants. Our results demonstrate that the rhizosphere of soybean plants harbors a variety of P-solubilizing bacteria whose potential for the formulation of novel biofertilizers is worth to be explored.