Development And Application Of Biocontrol Agent For Root Rot Of Astragalus Membranaceus

Root rot is a common soil-borne disease in Astragalus cultivation.If not treated,the yield and quality of Astragalus will be seriously reduced.Compared with chemical agents,biocontrol agents have the advantages of no residue,no pollution,and longer duration of validity,which meets the development requirements of sustainable agriculture and is a practical and effective harmless alternative.In this paper,Fusarium oxysporum,the main pathogen of root rot of Astragalus.Wettable powders and microcapsules were prepared by using antagonistic J-1 and various materials,and the best formulation was explored.After screening the best dosage form and application amount of biocontrol agent,the biocontrol agent was verified by applying biocontrol agent to the Astragalus field in Hadapu Town.In order to improve the biocontrol effect,four stains of antagonistic bacteria,HQB-45,HQB-187,HQB-626 and HQB-641,were used to develop the compound biocontrol agent.The optimal dosage form and application conditions were preliminarily explored to provide reference for the development of biocontrol agents for Astragalus root rot.The main results are as follows:（1）The wettable powder of J-1 was composed of carrier,protective agent and dispersant.Diatomite was selected as the carrier and the mother powder was prepared according to the adsorption capacity of 1.464 L/kg.Sodium carboxymethyl cellulose was used as dispersant,and the dosage was 12%of the mother powder.Sodium alginate was selected as the protective agent,and the dosage was 8%of the mother powder,and the number of effective viable bacteria could reach the level of 2.16×10⁸ CFU/g.（2）The optimal formula for preparing microcapsules was sodium alginate solution of 3.0%mass fraction,injection needle of size 4.5-gauge,Ca Cl₂ solution of 0.15 mol/L concentration and skim milk of 5.0 m L volume.The number of effective viable bacteria in the microcapsules of J-1 reached the level of 1.34×10⁸ CFU/g.It was found that the microcapsules with smoother surface,more pores,less cracks and no crystal precipitation contained more effective viable bacteria,when observing the micromorphology of microcapsules,（3）The results of pot experiment showed that microcapsules were the optimal formulation of J-1 biocontrol agent.The optimal application rate is 15～20 g/bag（3～4 g/plant）.Reduced plant morbidity by 61.11%and plant lethality by 57.14%.（4）The results of the field experiment showed that the application of J-1 microcapsules could reduce the plant disease rate by 23.02%and the plant lethality by 3.05%,and increase2.53%per mu yield.The number of Fusarium oxysporum in the rhizosphere soil and roots of Astragalus was significantly decreased,and the AST I content and CAG content of Astragalus were significantly increased by 56.21%and 95.02%respectively.（5）In this study,the powders and microcapsules of compound microbial biocontrol agents were prepared by the optimum formulation and technology of J-1 microbial agent.Through pot experiment,the optimal dosage form of microcapsules were obtained.Under the same dose of treatment,the compound microbial agent increased the disease inhibition rate by50%and reduced the mortality rate by 60%compared with the single microbial agent.The optimal application rate was between 10～15 g/bag.Application time should be 7 days before inoculation of pathogens;The optimal addition ratio of the four antagonistic bacteria in the compound microbacterial agent is"1:1:1:1".