Halotolerant Bacillus Species as Plant Growth Promoting Rhizobacteria from Hyper - Arid Area of Algeria

The aim of this study was to determine the diversity of aerobic halotolerant Bacillus plant growth promoting rhizobacteria (PGPR), their production of hydrolytic exo-enzymes and their inoculation effect on two cowpea plants. The soil dilution plate technique was performed on tryptic soy agar complemented with thermal pretreatment to select Bacillus strains associated with the Phoenix dactylifera rhizosphere growing in hypersaline and arid soil in Algeria (In Salah, Tamanrasset). The inoculation effect of these strains on cowpea plant growth was assessed based on biometric and physiological parameters. As a result, thirteen halophilic, halotolerant and non-halophilic Bacillus strains were isolated. Upon screening, all strains were capable of producing at least two hydrolytic enzymes under saline conditions and most of the strains (n=10/13) showed at least two plant growth promoting (PGP) traits. Strains were identified as members of Bacillus genera based on their phenotypic and biochemical characteristics. The inoculation of these strains in cowpeas significantly improved biometrics and physiological growth parameters of the inoculated plants. Based on their PGP effects, five strains were identified: RP 7 (B. coagulans), RP 8 (B. circulans), RP 10 (Paenibacillus polymyxa), RP 12 (B. circulans) and RP 13 (B. cereus). The isolation and characterization of halophilic and halotolerant Bacillus strains increased knowledge about the microflora in the rhizosphere associated with date palms in saline and arid soils. Bacillus-PGPR strains proved to be highly effective to improve cowpea plant growth and development.