Screening,identification,mutation And Optimization Of Fermentation Conditions Of Bacillus Amyloliguefaciens LXY-6-2 And Its Biocontrol Effects Against Fusarium Solani

The hot pepper root rot is caused by Phytophthora and Fusarium spp.in the fungi of the subphylum Eucalyptus,of which Fusarium solani and F.vasinfectum.and so on.Because of many years of continuous cropping and the long-lasting carrier and transmission of virus,the resting spores of M.sinica are extremely resistant,which makes the root rot of pepper more and more serious.Bacillus amyloliquefaciens can survive for at least 20 to 25 years in the soil and cannot be removed by cultivation measures or fungicides.The use of microorganisms to prevent root rot in pepper can alleviate a series of problems in the ecological environment caused by chemical control.It is an environmentally friendly,safe,effective,and sustainable means of controlling plant diseases.The strain LXY-6 with good broad-spectrum resistance was screened out as a pathogenic indicator strain of Pyricularia oryae Ca,Botrytis cinerea,and Fusarium vasinfectum.Morphological and molecular biology of the strain LXY-6 was identified by colony morphology,electron microscopy,and comparison with the"Bergeran&Gibbons Handbook"?Buchanan&Gibbons,1984?and the"Common Bacterial System Identification Handbook"?Dong Xiuzhu and Cai Miaoying,2001?Search was performed to determine that the strain LXY-6 was Bacillus.A phylogenetic tree constructed by further 16S rDNA identification and ITS sequence identification showed that the strain LXY-6 was Bacillus amyloliquefaciens.Bacillus amyloliquefaciens LXY-6 obtained by screening was induced into four strains of weakly hemolytic bacteria LXY-6-1-LXY-6-4 by UV,DES,and HNO₂ methods.The blood-agar plate medium was used to screen the weakly hemolytic mutant strains,and the antibacterial activity of the mutant weakly hemolytic strains was determined using a pathogen such as capsicum root rot.The hemolytic activity and antibacterial activity of B.amyloliquefaciens LXY-6-2 obtained by UV lamp power of 40W and 20 cm mutagenesis for5 min were the best,with the inhibition zone diameter of?24.0±1.76?mm and hemolytic ring diameter of?5.0±1.31?mm.The detection of hemolysis and resistance in the LXY-6-2generation demonstrated that LXY-6-2 has a stable weak hemolytic activity and antibacterial activity.For LXY-6-2,the single factor variable analysis method was used to optimize the fermentation conditions using the number of viable cells and the diameter of inhibition as criteria.It was determined that the optimum fermentation inoculation age of strain LXY-6-2was 20-23 h,the optimum carbon source for sucrose,and the best nitrogen source for yeast soaking,The appropriate pH and temperature are PH=7,28°C-32°C.The optimal amount of bacteria is 8%-10%of the volume of spore suspension and liquid medium,the best shaking speed is 220r/min.LXY-6-2 was cultured under optimized culture conditions.After 48 hours,the viable cell count was?8.9±1.13?×10 8 spores/mL,and the inhibition zone diameter was?29.53±1.32?mm.Compared with the basic medium,the number of viable cells and the antibacterial diameter increased,and the optimization effect was obvious.In this study,LXY-6-2 fermentation broth and 50%carbendazim WP,50%benomyl WP,thiophanate-methyl suspension efficacy of pepper root rot control efficacy.It was concluded that the control effect of LXY-6-2 fermentation broth was best reached 68.40%after 15d of the last application.The treatment of root rot inoculated with LXY-6-2 in the roots of the roots for 48 h was the best control effect after 7 d,14 d and 21 d.It was demonstrated that LXY-6-2 should be administered in advance when LXY-6-2 is used to prevent capsicum root rot.LXY-6-2 fermentation broth has good control effect on capsicum root rot,and it is safe and environment-friendly.It has high economic benefits and research application value.