Phosphate-solubilising bacteria promote horticultural plant growth through phosphate solubilisation and phytohormone regulation

Microorganisms in the plant's rhizosphere are capable of solubilising insoluble soil phosphates and can promote plant growth. In this study, a total of 30 bacteria were isolated from soils in Changji city, and one highly efficient strain (B5) was identified as a member of Pseudomonadaceae. B5 exhibited phosphorus (P) solubilisation of 519.66 mg/L in a culture medium containing tricalcium phosphate (Ca3 (PO4)2). Results showed that strain B5 had a high P utilisation rate in a medium containing glucose (monosaccharide), ammonium sulphate and tricalcium phosphate. B5 treatment significantly promoted plant growth and increased the dry weight, the chlorophyll content as well as P content of tomato, marigold and cucumber. Moreover, B5 produced plant growth-promoting hormones, including indole-3-acetic acid (IAA) (4.18 g/L) and gibberellin (GA) (19.8 mg/L). In addition, organic acids including oxalic acid, succinic acid, gluconic acid, arabic-hexanoic acid and glutraic acid were produced by B5 under different phosphorus sources. Our results indicated that B5 is a potential candidate for development as a bioinoculant for horticultural application.