Studies On The Biocontrol Effects And Mechanism Of Lipopolypeptide Producing Strain QHZ-3 On Black Scurf Disease Of Potato

Black scurf disease?stem canker?caused by Rhizoctonia solani is a soil-borne fungus disease,which has become the most serious disease in potato production,seriously affecting the tuber yield,appearance quality and commodity of potatoes,especially the planting efficiency of seed potato enterprises.Therefore,it is urgent to explore safe and effective biological control measures for this disease.Therefore,in this study,by comparing the five strains of biocontrol bacillus?QHZ-1,QHZ-2,QHZ-3,QHZ-4,QHZ-5?screened by the research group on the ability to produce biomass and synthesis of lipopeptide antibiotic Enzyme gene detection,select the strain with the best biocontrol potential.Research on its biocontrol mechanism and its effect,and optimize the fermentation conditions to make bio-organic fertilizer,through pot experiments to verify its biocontrol effect,the main results are as follows:1.The test antibacterial can produce a lot of plant growth promoting substance:?1?The five biocontrol bacteria can secrete iron carrier,but the secretion of strain QHZ-3 is the largest,which is significantly higher than other strains.Quantitative analysis results show that the expression of iron carrier of QHZ-3 in the fermentation broth reaches 40.59%,Which is 14.58%higher than QHZ-1 with the smallest secretion;?2?5 biocontrol strains all had the ability to solubilize Ca3?PO4?2.Among the 5biocontrol strains,QHZ-2,QHZ-3 and QHZ-4 had the strongest ability to solubilize Ca₃?PO₄?₂,with 9.89,10.53 and 10.19?g/mL of available phosphorus in the broth,respectively;?3?All five strains of biocontrol bacteria can produce indoleacetic acid IAA,and the yields of QHZ-3 and QHZ-5 are significantly higher than other strains,which are17.20 mg/ml and 16.18 mg/ml,respectively.2.Using molecular biology methods to detect the antibiotic synthesis genes of 5strains,it was found that QHZ-1 and QHZ-2 have Fengycin and Iturin synthetase genes;QHZ-4 has only Fengycin Synthetase gene;QHZ-3 and QHZ-5 strains have three lipopeptide antibiotic synthetase genes including Surfactin,Iturin and Fengycin.Comprehensive analysis of the potential growth and antagonism of the five strains of biocontrol bacteria,and finally select the most developmental potential QHZ-3 for further optimization of fermentation conditions and the development of bio-organic fertilizer and its biocontrol effect test.3.Using LC-MS technology to characterize the type of lipopeptide antibiotics produced by strain QHZ-3,it was found that QHZ-3 can produce secreted lipopeptide antibiotics of Surfactin,Iturin and Fengycin,indicating that QHZ-3 is a lipopeptide antibiotic Strains.4.The optimization results of the liquid and solid fermentation conditions of strain QHZ-3 are as follows:?1?The single factor test results show that the best conditions for QHZ-3 liquid fermentation are 60/250ml Erlenmeyer flask,6%inoculation volume,shaker speed180 r?min^-1,fermentation time 48 h.?2?Orthogonal test results show that the combination of 40/250 ml Erlenmeyer flask,shaker speed 170 r·min^-1,inoculation volume 6%,fermentation time 48h,the growth state of QHZ-3 is the best,The number of viable bacteria can reach 1.31×10¹⁰cfu·ml^-1;?3?QHZ-3 lipopeptide bio-organic fertilizer was prepared by inoculating QHZ-3into decomposed cattle manure,and the optimal inoculation amount was 10%.The number of living bacteria could reach 1.02×10⁹ cfu·ml^-1.5.Three treatments were set for the QHZ-3 lipopeptide strain bio-organic fertilizer pot biocontrol effect test:control group?CK?,QHZ-3 bacterial suspension?QHZ-3?and lipopeptide-produce strain biological organic fertilizer?BOF?,The shoot and root growth of potato,and the amount of Rhizoctonia solani in the soil were measured during the formation of potato tuber,the results showed that:?1?The plant height,stem thickness and biomass of QHZ-3 and BOF treated plants were higher than those of CK control group.Among them,the effect of BOF treatment is significantly better than that of QHZ-3,especially the most significant effect on the growth of potato underground.The dry weight of underground is increased by 1.81 times than that of QHZ-3;?2?QHZ-3 and BOF treatment also improved the morphology of the potato plant leaves,increased the thickness of the leaves,and increased the leaf chlorophyll content?SPAD value?and photosynthetically active radiation,especially the BOF treatment SPAD value increased by 40.3%compared with CK It is 15.91%higher than QHZ-3.?3?BOF significantly changed the root morphology of the potato.Root parameters such as root surface area,number of root tips and root volume were significantly higher than QHZ-3 and CK,especially the number of root tips of BOF reached4.11and 1.82 times than CK and QHZ-3 treatment respectively,creating conditions for promoting the absorption of potato roots.?4?The BOF treatment significantly reduced the absolute amount of Rhizoctonia solani in the potato rhizosphere.The quantitative results on the 60th day after planting showed that BOF treated by potato root rhizosphere was 1.34×10⁵ copies/g,The CK group remained at 1.02×10⁶ copies/g.In summary,QHZ-3 not only has a significant growth promoting effect,but also promotes the establishment and growth of root systems by activating soil nutrients;QHZ-3 inhibits the growth of the pathogenic Rhizoctonia solani by producing a variety of lipopeptide antibiotics,is a highly effective strain with biocontrol potential;the bio-organic fertilizer made from this strain has better effect than bacterial suspension treatment,indicating that the secondary solid fermentation of antagonistic antibacterial significantly enhances the growth promotion and antagonistic ability of antagonistic antibacterial.