Soil environment influences plant growth-promotion traits of isolated rhizobacteria

Abstract

Plant growth-promoting rhizobacteria (PGPR) occur naturally in the rhizosphere, but our understanding of the soil and climatic variables that influence the occurrence of beneficial bacteria is poor. Here, we examined the effects of environmental factors on the occurrence of PGPR in the chickpea rhizosphere soils. A total of 743 rhizobacteria were isolated from the chickpea rhizosphere collected from 74 sampling sites across Australia. Results revealed that the ability of isolates to produce indole acetic acid (IAA) and 1-aminocyclopropane-1- carboxylate (ACC) deaminase were positively correlated with the potential of rhizobacteria to promote root growth. The amount of IAA production was positively correlated with soil copper, manganese and zinc con- centrations, electric conductivity and the aridity index, but negatively correlated with soil carbon (C), nitrogen (N) and phosphorus (P) in the soils from which the PGPR were isolated. Additionally, the ability of PGPR to tolerate metal ion toxicity and water stress was related to their ability to produce IAA. The potential of isolates to solubilise P was negatively correlated with the C/N ratio, N, P, C and magnesium content of the soils but none of the soil environmental factors was correlated with the ACC deaminase activity of the isolates. In a principal component analysis, these environmental variables explained 53 % of the variation in the ability of the rhizo- bacteria to produce IAA and ACC deaminase and/or to solubilise P. These findings could be applied to the design of an efficient PGPR development strategy that incorporates ecological traits and plant growth-promoting mechanisms to increase chickpea production.