Novel isolates of phosphate-solubilizing bacteria for the development of biofertilizers for soybean cultivation

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

Taller; III Taller Latinoamericano de PGPR; 2016

Phosphorus (P) requirements of cultivated crops are usuallymet by chemical fertilization. However, a high proportion of the P supplied bythese means precipitates into insoluble forms that cannot be assimilated byplants. In this context, biofertilizers based on microorganisms able tosolubilize soil P represent a low-cost and environmental-friendly alternative.The limited number of bacterial species currently usedfor commercial formulations may not always adapt to a wide range of crops andsoil conditions, an issue that restricts their efficiency. The highly diversecommunities of rhizospheric microorganisms is a potential source of strains forthe development of improved biofertilizers based on bacteria well-adapted to thetarget environment and also able to solubilize various phosphate sources.Our goal is to contribute to the development of high-qualitybiofertilizers for soybean cultivation, through the isolation andcharacterization of P-solubilizing bacteria (PSB) able to promote plant growth.Seven hundred isolates of PSB were obtained from  soybean fields in Buenos Aires and Santa Fe provinces,among which we selected those  that maintainedthe ability to solubilize organic (sodium phytate) and inorganic P (tricalciumphosphate) after repeated subcultures. Non-redundantstrains were identified by REP-PCR and weretaxonomically identified by PCR amplification and sequencing of the 16S rRNAgene. Gram-negative bacteria prevailed among the isolates thus identified. Isolatesof different bacterial taxa were tested for their ability to promote growth ofsoybean plants. Bacteria related to the genera Enterobacter, Pantoea, Pseudomonas and Rhanella were the mostefficient growth-promoters under conditions of soluble phosphate limitation.The most efficient isolates were also verified not to be pathogenic on soybeanplants. Our results demonstrate that the rhizosphere ofsoybean plants harbors a variety of PSB bacteria whose potential for theformulation of novel biofertilizers is worth to be explored.