Screening Of Biocontrol Bacteria In Chrysanthemum Continuous Cropping Obstacles Soil And The Study On Its Biocontrol Effect

With the trend of a positive correlation between the large demand for flowers and the people’s rising living standards,the seriousness of chrysanthemum continuous cropping obstacles caused by the large-scale production of chrysanthemums and the cumulative accumulation is growing within years.Among them,Fusarium oxysporum f.sp.chrysanthemi is the causal agent of fusarium wilt,which is one of the serious problem caused by continuous cropping.Continuous cropping obstacles have an important impact on the normal growth and quality assurance of chrysanthemums,and will also cause certain damage to the local soil environment.Regarding the impact of continuous cropping obstacles,and the growing demand for chrysanthemums,there is a urgent demand to find a greener and more effective method for chrysanthemum fusarium wilt controlling.Biological control is currently recognized as a healthy and sustainable method for controlling plant diseases.In this study,two biocontrol bacteria were screened out by the confrontation experiment,and the biocontrol effects of these two stains on fusarium wilt controlling of chrysanthemum and plant growth promotion were carried out.The main results are as follows:1.A large number of bacterial strains were isolated and analyzed from the rhizosphere soil of healthy chrysanthemums in the fusarium wilt affected feild.In the confrontation experiments between the isolates and the pathogenic Fusarium oxysporum,we obtained two strains through continuous screening experiments:CFD-1 and CFD-2,both strains showed high antagonistic to Fusarium oxysporum f sp.chrysanthemi tested by the confrontation experiment.Among them,the bacterial inhibition rate of CFD-1 and CFD-2 against Fusarium oxysporum f.sp.chrysanthemi was 74.4%and 87.8%,respectively.The CFD-1 and CFD-2 were identified as Bacillus velezensis and Pseudomonas aeruginosa by traditional culture,morphologicalobservation,physiological,biochemical analysis and molecular identification.2.The growth characteristics of strains CFD-1 and CFD-2 indicated that the logarithmic growth stages of CFD-1 and CFD-2 in LB medium at 37℃ were 6-12h and 12-24h,respectively.The optimal growth temperature was 37℃.Both CFD-1 and CFD-2 are able to use a variety of carbon and nitrogen sources,and fructose are their most suitable carbon sources.Among them,potassium nitrate is the most suitable nitrogen source for CFD-1.Ammonium sulfate cannot be used efficiently,and peptone and glycine are used as its sole source of nitrogen.CFD-2 uses beef extract as its most suitable nitrogen source,and it grows the worst in cultures using urea as the nitrogen source.The biological function of antagonistic CFD-1 and CFD-2 showed that both strains have the ability to produce IAA and activate the insoluble phosphorus in the soil,so they have the potential to promote plant development.In addition,strain CFD-1 has stronger ability to produce IAA than CFD-2.At the same time,CFD-1 also has the ability to produce ammonia.3.The pot experiment explored the effects of the strains CFD-1 and CFD-2 on the prevention and control of Fusarium oxysporum ’Jinba’ fusarium wilt and the promotion of chrysanthemum plants.The results showed that both CFD-1 and CFD-2 could reduce the quantity of Fusarium oxysporum in rhizosphere soil of chrysanthemum to different extents,thereby reducing the incidence of fusarium wilt.FB and FP represent the treatments inoculated chrysanthemum with antagonistic strain CFD-1 and CFD-2.respectively,FBP represent the treatment inoculated chrysanthemum with both stains.Compared with the treatment F,the incidence of fusarium wilt was reduced by 31.82%,40.90%and 45.46%.FBP show the best control effect offusarium wilt of chrysanthemum.Strain CFD-1 and CFD2 also have growth promoting effects on chrysanthemum plants.With the addition of biocontrol bacteria,the index of plant height,stem thickness,leaf length,flower diameter,branch number,leaf width,and plant fresh weight show increased when compared with control.Among them,the treatment group BP,which added two kinds of antagonistic bacteria at the same time,had the most obvious accelerating effect.These results indicated that the strains CFD-1 and CFD-2 had additive effects in controlling plant diseases and promoting plant growth.In summary,it is believed that the strains CFD-1 and CFD-2 are effective in preventing and controlling of chrysanthemum fusarium wilt and promoting chrysanthemum growth,and which can be used as biocontrol bacteria for subsequent research.