Characterization of rhizosphere Pseudomonas chlororaphis IRHB3 in the reduction of Fusarium root rot and promotion of soybean growth

•Rizhosphere bacterium IRHB3 was identified as Pseudomonas chlororaphis by MLSA.•IRHB3 could prevent pathogen invasion by degrading fungal cell wall.•IRHB3 could dissolve phosphorus, release siderophores and produce IAA.•IRHB3 antagonized five Fusarium of root rot and seven other pathogens in vitro.•IRHB3 had strong tolerance to nutrition, salt and pH stress.•IRHB3 promoted soybean growth and effectively controlled Fusarium root rot. Rhizosphere beneficial bacteria play an important role in plant health and disease control, and have been widely explored as biocontrol resources and agents for the ecological and sustainable management of soil-borne diseases. In our previous study, a bacterium strain IRHB3 was isolated from soybean rhizosphere under maize-soybean relay strip intercropping. To clarify the characterization of IRHB3 and its biocontrol effects of soybean root rot, we systemically investigated the taxonomy, biological characteristics, bacteriostatic activity, environmental stress tolerance of IRHB3, and also analyzed its effects on the control of root rot as well as growth promotion. Our results showed that IRHB3 as a Gram-negative bacterium was identified as Pseudomonas chlororaphis by multi-locus sequence analysis of 16S rRNA, gyrB, rpoD and gapA. The colony was characterized by yellowish circular and rugby-shaped with rough surface and gullies under scanning electron microscropy.. IRHB3 not only activated kinds of hydrolase such as protease, caseinase, and cellulase, but was also capable of dissolving phosphorus, releasing siderophores and producing IAA. IRHB3 suspension treatment with proper concentration significantly promoted seed germination and seedling growth. Antagonistic assay showed that IRHB3 displayed good inhibition effects on various pathogenic fungi, especially aggressive Fusarium species causing root rot, with the average inhibition rate as high as 69.89%. And meanwhile, introducing IRHB3 into soil effectively alleviated the damage of F. oxysporum to soybean root. Moreover, IRHB3 had strong environmental adaptability of wide pH, low nutrition and salt stress. In conclusion, these results indicate that Pseudomonas chlororaphis IRHB3 from intercropped soybean rhizosphere is one kind of typically plant growth-promoting rhizobacteria (PGPR) and has immense potential and strong environmental adapatability on the control of soil-borne fungal disease.