Control Effect Of Rhizosphere Growth Promoting Bacteria With High Yield Of Siderophore On Tomato Bacterial Wilt

Although iron is abundant in Earth’s crust,the bioavailability of iron is generally low for the influence of soil pH and other factors.In response to iron shortage,microorganisms secrete siderophores to scavenge iron from environment to meet their own growth and development needs.The survival of rhizosphere microorganisms is closely related to plant health.Nutrients availability determines the colonization of rhizosphere microorganisms as well as their functions.The strong affinity of siderophore for ferric iron makes it a secret weapon for the survival of rhizosphere microorganisms.Siderophore production and its mediated ironacquisition play important roles in the disease suppression and growth promotion of PGPR strains.In this paper,firstly,two high-yield and disease-suppression strains were screened out based on four paramaters:siderophore production,siderophore mediated pathogen inhibition rate,biocontrol efficiency of bacterial wilt and growth ability.Then,the biomass production and growth promoting effect of the two strains were studied.Finally,the culture conditions of high-yield strains were optimized.The main results are as follows:1.Iron is an important limiting factor for microbial growth.95%of bacteria that were isolated from rhizosphere grew better under iron rich condition than under iron limited condition.To cope with the iron deficiency,most rhizosphere bacteria produced siderophores to obtain iron under the iron limitation condition.Most of the isolated rhizosphere bacteria can suppress the disease incidence of bacteria wilt,the biocontrol efficiency of strains No.2,No.5,No.7 and No.12 were 42.31%,53.85%,42.31%and 34.62%,respectively.The inhibition effects of rhizosphere bacteria on bacterial wilt can be well explained by the production of siderophore and siderophore mediated inhibition on the growth of Ralstonia solanacearum.Taking four results of siderophore production,siderophore mediated pathogen inhibition rate,biocontrol efficiency of bacterial wilt and growth ability in consideration,two high-yield siderophore and disease-suppression strain No.5 and No.7were selected.2.Further species identification of two high-yield and disease-suppression strains,and physiological characteristics and promotion of plant growth were determined.The results showed that Strain No.5 was identified as Chrysobacterium cucumeris based on 16S rDNA sequence analysis,It’s named C5,which could produced IAA and ammonia,but lacked the ability of phosphate solubilization.A total of 15 kinds of carbon sources of tomato root exudates can be used by Strain C5.It also significantly increased the chlorophyll content,dry weight of aboveground part,dry weight of underground part,fresh weight of underground part and seedling index.Strain No.7 was identified as Enterobacter sichuanensis,It’s named E7,which produce IAA and ammonia,and had the ability of phosphate solubilization.It could use 29kinds of carbon sources of tomato root exudates,and significantly improved the chlorophyll content,shoot dry weight and seedling index of tomato.3.Finally,the methods of culturing high-yield strains C5 and E7 were optimized for the siderophore production.Firstly,glycerol and casein amino acids were selected as the optimal carbon and nitrogen sources for the siderophore production.Then the effects of culture time,inoculation amount,temperature,pH,carbon and nitrogen source addition and other factors on the production of siderophore were determined.For C5,three factors(nitrogen source,aluminum ion and temperature)that significantly affected siderophore production were selected to get the optimal culture conditions,and the optimal culture condition was temperature nitrogen source:23.82 g/L,aluminum ion:88.91 μmol/L,temperature:29.02℃.Under the optimum conditions,the relative siderophore production was 11.58.For E7,three factors(temperature,nitrogen source and carbon source)that significantly affected siderophore production were selected to get the optimal culture conditions,The optimal culture conditions for E7 were as follows:temperature:32.48℃,nitrogen source:74 g/L and carbon source:5.51 g/L.Under the optimal conditions,the relative siderophore production was 10.65.In conclusion,the high-yield siderophore strains C5 and E7 played the important roles in growth promotion and disease suppression of tomato plants.The relative siderophore prodution of high-yield siderophore strains C5 and E7 were 11.58 and 10.65 under the optimal conditions.