Screening Of Biocontrol Bacteria Against Smut Of Broomcorn Millet And Field Control Effect

Panicum miliaceum L.is cultivated in a large area in arid and semi-arid areas and has the same effect as medicine and food.The smut of broomcorn millet is a soil borne disease,which is caused by the fungus Sporisorium destruens.The incidence rate reaches 40%when the disease is serious,it can lead to plant dwarfing and deformities,and inhibit plant reproductive growth by reversing inflorescence development,greatly reduces the yield and quality of broomcorn millet.The smut of broomcorn millet is a systemic infection disease.After the chlamydospore matures,it is scattered in the soil or attached to the seeds for overwintering.The first hyphae will be produced by germination in the second year.With the elongation and growth of the first hyphae,the basidiospores will be produced.Then the basidiospores of different sex lines will combine to form the hyphae to infect the broomcorn millet and colonize it,and black powdery bracts grow at maturation stage.After the black powdery bracts mature,the chlamydospores disperse,causing cyclic infection of the broomcorn millet.At the present stage,the main way to control broomcorn millet smut is seed dressing with chemicals,but the use of chemicals will bring about issues like environmental pollution,changes in soil properties,and increased resistance of pathogens.Compared with chemical control,biological control has been paid more and more attention because of its huge potential and ecological friendliness,and has become the current research hotspot.Therefore,it is of great significance to prevent and control broomcorn millet smut by means of biological control to ensure the formation of yield and quality and promote the green production of broomcorn millet.The strain of Streptomycin v-3 with strong biocontrol effect has been isolated from the rhizosphere soil of broomcorn millet with basidiospores as the object of the study,and identified based on morphological,physiological and biochemical characteristics and molecular biology.The optimal conditions of liquid and solid fermentation preparations have been investigated,and the field control effect has been verified.The results provide theoretical basis and practical guidance for field control of broomcorn millet smut.The main research results are as follows:（1）A total of 21 strains of fungi,33 strains of bacteria and 31 strains of actinomycetes with different morphological characteristics have been isolated from 18samples of broomcorn millet rhizosphere soil.The actinomycete strain v-3 with strong inhibitory activity against the basidiospores of the smut pathogen was screened out by the in-dish antagonistic test and the method of toxic plate medium.The biocontrol strain v-3 was identified as Streptomyces toxytricini by combining morphological observation,physiological and biochemical reactions and 16S r DNA sequence analysis.（2）In order to improve the biocontrol activity of strain v-3,the fermentation conditions were optimized.The optimization of fermentation conditions showed that the combination of glucose as a carbon source and soybean powder as a nitrogen source is beneficial for the liquid fermentation of strain v-3;The best fermentation medium components are soybean powder 15 g/L,glucose 5 g/L,Na Cl 2 g/L,K₂HPO₄1 g/L,Ca CO₃1.5 g/L;The optimum fermentation conditions were 28℃,p H 7.0,5%inoculum,100 m L liquid in shaking flask,and 160 rpm rotating speed of shaking table for 6 days.The antibacterial effect of the optimized strain v-3 on broomcorn millet smut is 51%higher than that before optimization.The stability test of liquid fermentation liquid shows that the fermentation liquid still has certain antibacterial activity when it was irradiated by UV for 12 hours,treated at 100℃for 30 minutes at p H 4.0 and 10.0,and stored at-20℃for 30 days.The solid fermentation test finds that when wheat bran and earthworm dung with a mass ratio of 1:1 were used as solid fermentation substrate could promote the solid fermentation of strain v-3.The fermentation can reach the fermentation end point on the fifth day and the growth amount could reach 10¹⁰CFU·g^-1.（3）In order to verify the biocontrol effect of strain v-3 fermentation preparation on smut disease of broomcorn millet,field experiments were conducted.The results showed that the fermentation preparation of strain v-3 had a promoting effect on the growth of broomcorn millet,promoting the growth of aboveground plant height and underground roots.The test results of antioxidant enzymes show that it could improve and activate the resistance to broomcorn millet smut.The statistical results of incidence rate showed that the use of the preparation could significantly reduce the incidence rate of the broomcorn millet smut,and the field control effect could reach70%.The above research results laid a theoretical foundation for the application of biological bacteria control in the prevention and control of broomcorn millet smut,which is of great significance for promoting the green production of broomcorn millet.