Isolation,identification of a salt-tolerant,phosphate-solubilizing and crop-growth promoting Aspergillus japonicus

Abstract:

[Objective] To isolate high effective phosphate-solubilizing microbial strains from growing sunflower in saline-alkali soils for bio-fertilizer production. [Methods] Phosphate-solubilizing fungus M1 was isolated by petri-dish methods and identified using ITS rDNA sequence homology analysis. The phosphate-solubilizing capacity of M1 was measured by broth medium and soil pot experiment. The effect of isolate M1 on plant growth promotion was studied in field experiment. Organic acids and phytohormone produced by isolate M1 were analyzed by means of LC-MS. [Results] Isolate M1 was identified as Aspergillus japonicus and had a strong ability to dissolve insoluble phosphates. The rate of Ca₃(PO₄)₂ dissolved by M1 was 63.30% and the concentration of available phosphorus was 1020.89 mg/L at 6 d shaking incubation. Soluble phosphorus in AlPO₄ liquid culture by M1was lower than in Ca₃(PO₄)₂ added medium, the content concentration of available phosphorus was 995.69 mg/L and the solubilized rate of AlPO₄was 48.59%.The greatest concentration of available phosphorus dissolved by isolate M1 from Jinning rock phosphate was 363.64 mg/L after 6 d shaking incubation. Isolate M1 combining salt resistance properties as well, the greatest content of NaCl was 10%. In greenhouse pot experiment, isolate M1 had a significant growth-promoting effect on corn in four kinds of soils (paddy soil, viscous fluvo-aquic soil, salinized fluvo-aquic soil and calcareous fluvo-aqui soil) under three kinds of insoluble phosphates treatment such as Ca₃(PO₄)₂, AlPO₄ and Kaiyang rock phosphate with 4 replicates per treatment. Compared with control (CK), inoculation with M1 increased the fresh weight of corn biomass by 2.14%-90.91% and dry weight of corn biomass by 22.15%-268.28%, and soil available phosphorus content increased 21.81-24.24 mg/kg. The adaptability of isolate M1 with four kinds of soils is greater than strain DSM 821. Field experiment showed that isolate M1 had a greater effect on enhancement of peanut yield, the yield was average 4.46 t/hm² and increased 22.19% being greater over control. 7 organic acids and 2 phytohormones were analyzed in liquid culture of Ca₃(PO₄)₂, AlPO₄ and Kaiyang rock phosphate. Out of seven acids, significant increases in the concentration of oxalic acid (616.16 mg/L) and citric acid (413.69 mg/L) were recorded in 3 liquid cultures by isolate M1, respectively. The concentration of indole acetic acid (IAA) was 15.45-77.58 mg/L, zeatin was 0.06-0.11 mg/L. [Conclusion] One new phosphate- solubilizing isolate M1 was obtained and identified as Aspergillus japonicus. Isolate M1 could solubilize insoluble phosphates in petri dishes, broth medium as well as pot experiments and increased soil available phosphate and corn biomass significantly in pot condition. So Aspergillus japonicus M1 strain have a better potential for bio-fertilizer production in the future.