Phosphate-solubilizing rhizobacteria enhance Zea mays growth in agricultural P-deficient soils

This work aimed to evaluate the ability of phosphate-solubilizing bacteria (PSB) to enhance Zea mays growth in an agricultural P-deficient soil. Five strains were screened for their ability to solubilize P and to produce plant growth promoting (PGP) substances. The best P-solubilizing strains Rhodococcus sp. EC35 (B1), Pseudomonas sp. EAV (B2) and Arthrobacter nicotinovorans EAPAA (B3) were inoculated in maize plants growing in P-deficient soils without P fertilization and amended with soluble (KH2PO4) and with tricalcium phosphate (TCP). The inoculated PSB were monitored in soil by DGGE. PSB enhanced maize biomass production in all P-treatments. In soils without P fertilization, bacterial inoculation increased P concentration in roots and shoots and plant dry biomass (ca. 20%). In soils amended with soluble P, strain B2 was the bacteria that better performed improving root and shoot biomass by 102% and 63%, respectively. In soils amended with TCP, plant biomass was also enhanced by bacterial inoculation as well as P accumulation in plant tissues (B3 and BM - mixed inoculation). Plant growth enhancement seems to be related not only to P solubilization but also to other PGP traits, like indol-3-acetic acid and ACC-deaminase activity. DGGE profiles allowed to confirm the presence of PSB in maize rhizosphere after 45 days. This work clearly indicates that inoculated PSB have great potential to be used as biofertilizers in P-deficient soils, especially strains Pseudomonas sp. EAV and A. nicotinovorans EAPAA since both highly increased P availability in soils and promoted maize growth, constituting an attractive alternative to the phosphatic fertilizers amendments.