Biological Control Mechanism Of Streptomyces Aureoverticillatus HN6 Against Banana Fusarium Wilt

Banana is one of the largest tropical fruits in China.Because of its relatively stable planting profits and high economic benefits,Hainan Province takes banana cultivation as the leading industry to give priority to development in the adjustment of economic structure.Banana Fusarium wilt is caused by Fusarium oxysporum f.sp.Cubeme FOC.It is a destructive fungal disease that causes necrosis of banana vascular bundles.It is pointed out that the root cause of banana Fusarium wilt is the disorder of plant rhizosphere microbial community and the accumulation of a large numbers of pathogens in the rhizosphere.The introduction of colonizable antagonistic bacteria into the site of the disease can not only reduce the severity of the disease.And in most cases,it will promote plant growth.This study started with the effect of Streptomyces sp.HN6on the rhizosphere microecology of susceptible banana seedlings,and analyzed the mechanism of constructing healthy banana orchard rhizosphere microflora.1.The colony number of Streptomyces sp.HN6 in soil was counted by antibiotic labeling and dilution coating,and its colonization ability in soil was determined.Streptomyces sp.HN6 could colonize effectively in both aseptic soil and non-aseptic soil.2.Five in vitro growth promoting indexes were used to evaluate the growth promoting ability of Streptomyces sp.HN6 in vitro.according to the results,Streptomyces sp.HN6 could produce IAA,iron carrier,cellulase and lipase activity,and the potassium hydrolysis rate was 13.43%.3.The antimicrobial activity of volatile organic compounds of Streptomyces sp.HN6 was determined by separation plate method.The volatile gases in the culture process of Streptomyces sp.HN6 were collected by HS-SPME,and the components of volatile gases were analyzed by GC-MS.A total of 33 volatile components were detected,of which 9-methylacridine had a certain inhibitory effect on the mycelial growth of the target strain Foc·TR4,and the EC₅₀ was 109.824μg·m L^-1.4.A pot experiment was carried out to evaluate the ability of Streptomyces sp.HN6to prevent disease and promote growth in vivo.The ability of Streptomyces sp.HN6 to prevent and control Foc·TR4-GFP infection was evaluated by laser confocal microscopy.The results showed that at the initial stage of infection,the banana seedlings treated with Streptomyces sp.HN6 had less invaded green hyphae in the vascular bundles and root corms,the lowest disease index and the most survived banana seedlings.Compared with the control,the physiological indexes of aboveground banana seedlings were significantly improved in Streptomyces sp.HN6 treatment,in which plant height and stem diameter increased by 23.23%and 24.31%respectively,leaf area and leaf thickness increased by 12.71%and 14.29%respectively,fresh weight and dry weight increased by 12.23%and 22.03%respectively,and chlorophyll content increased by 21.98%.5.The effect of Streptomyces sp.HN6 on the rhizosphere microenvironment of susceptible banana seedlings was evaluated,and the physical and chemical properties of rhizosphere soil samples were determined.The results showed that Streptomyces sp.HN6 had the ability to regulate the balance of micronutrient elements in rhizosphere soil,in which the contents of nitrogen,phosphorus,potassium and organic matter,and reduced the content of mycotoxin fusaric acid in rhizosphere and the degree of toxicity to banana seedlings.6.Through isolation,pure culture and molecular biological identification of culturable microorganisms in rhizosphere soil samples,the species and number of culturable microorganisms in different treatment groups were counted.The results showed that most of the culturable fungi isolated from different treatment were Fusarium,and Streptomyces sp.HN6 treatment had lower Fusarium abundance and lower culturable fungal diversity,and Streptomyces sp.HN6 treatment had higher abundance of Bacillus and Pseudomonas,and the overall diversity of culturable bacteria was higher.In the HN6 treatment,the Streptomyces sp.N6FXJ01was isolated.Phylogenetic tree analysis showed that it was 99.80%similar with Streptomyces sp.HN6.The results showed that Streptomyces sp.HN6 was successfully colonized in the whole pot experiment.7.The microbial diversity in the rhizosphere was analyzed by high-throughput sequencing and Real-time PCR.Based on the results of absolute quantitative analysis,the amount of Foc·TR4 in rhizosphere soil was reduced by Streptomyces sp.HN6treatment.Among the high-throughput sequencing results,the soil samples treated with Streptomyces sp.HN6 had the highest abundance of Bacillus,Pseudomonas and Acinetobacter,indicating that Streptomyces sp.HN6 induced the change and reorganization of the microbial community dominated by Fusarium in the rhizosphere of banana seedlings,and evolved into a community dominated by some probiotics,which was not conducive to the occurrence of diseases,reduced the relative abundance of pathogens and increased fungal diversity.At the same time,the relative abundance of beneficial bacteria in the rhizosphere was increased.