| Wheat is a major grain crop in our country,but in recent years,the incidence of wheat sharp eyespot and wheat take-all has increased,leading to a decrease in wheat production.Therefore,the prevention and control of soil-borne diseases in wheat has become the key to wheat production.Currently,chemical pesticides are still the main method for controlling wheat sharp eyespot and wheat take-all,but their use can cause environmental pollution and harm to human health if not used properly.Additionally,the long-term use of chemical pesticides can lead to pathogen resistance.Therefore,biological control has become the main way to prevent and control wheat sharp eyespot and wheat take-all.In this study,medicinal chrysanthemum endophytic bacteria were isolated and screened for their antagonistic effects against wheat sharp eyespot and wheat take-all.Two endophytic bacterial strains with plate antagonistic effects were obtained and identified and tested for in vitro prevention and control effects.Finally,the biological control mechanism of the strains was explored and the fermentation of the antagonistic bacteria was optimized.Through plate confrontation experiments,two strains of biocontrol bacteria,HB-10 and JS-59,were obtained with antagonistic effects against wheat sharp eyespot and wheat take-all.The inhibition rates of the fermentation liquid of HB-10 and JS-59 against wheat sharp eyespot were 75.14%and 80.94%,respectively,and the inhibition rates against wheat take-all were 91.71%and 89.50%,respectively.The physiological and biochemical identification,morphological identification,and molecular determination of the two biocontrol bacteria revealed that HB-10 is Pseudomonas aeruginosa and JS-59 is Burkholderia gladioli.The fermentation optimization results of the biocontrol bacteria revealed that HB-10grows best in a culture medium containing 1.0%glucose,2.0%yeast powder,and 1.0%KCl,under the conditions of 4%inoculation at p H 7.3 and cultivation at 35℃and 221r/min.JS-59 grows best in a culture medium containing 1.0%sorbitol,1.0%yeast powder,and 0.05%Fe SO4,under the conditions of 4%inoculation at p H 6.5 and cultivation at 34℃and 220 r/min.The antibacterial spectrum test results showed that HB-10 and JS-59 have good inhibitory effects against 14 pathogens,including Botrytis cinerea,Fusarium oxysporium,Valsa mali,Physalospora piricola,Fusarium moniliforme,Curvularia lunata,Curvularia clavata,Cochliobolus heterostrophus,Sclerotinia sclerotiorum,Magnaporthe oryzae,Alternaria alternata,Rhizoctonia solani,and Phytophthora parasitica.The best control effects were observed against Physalospora piricola,Phytophthora parasitica,and Rhizoctonia solani,with inhibition rates of around 90%.The colonization results of the biocontrol bacteria HB-10 and JS-59 with resistance to rifampicin(300μg/m L)showed that colonies appeared on the resistant plate when the soil sample was diluted 10~5 times,indicating that HB-10 and JS-59 can colonize the wheat rhizosphere.In pot experiments with wheat seedlings treated with the fermentation liquid of HB-10 and JS-59,the control effects against wheat sharp eyespot were 69.42%and63.75%,respectively,and the relative control effects against wheat take-all were 72.14%and 71.09%,respectively,with no harm to the wheat.Through exploration of the antibacterial active substances of biocontrol bacteria HB-10and JS-59,the results showed that the volatile substances of HB-10 have almost the same inhibition rate against wheat sharp eyespot pathogen as in the plate confrontation experiment,suggesting that the inhibitory effect of HB-10 on wheat sharp eyespot is due to its volatile substances.Additionally,it was found that the chloroform extract of JS-59 can effectively inhibit the pathogen of wheat take-all,and the antibacterial substance of JS-59and the pathogen of wheat take-all can dissolve in chloroform.The crude peptide and protein extracts of HB-10 and JS-59 had relatively small inhibitory effects on the pathogen,indicating that the main antibacterial substances of HB-10 and JS-59 are non-peptide and non-protein substances.The research results on the taxonomic identification,antagonistic effect verification,fermentation condition optimization,antibacterial spectrum detection,colonization detection,and antibacterial mechanism of biocontrol bacteria HB-10 and JS-59 provide theoretical basis for the field comprehensive control of wheat sharp eyespot and wheat take-all and the preparation of antagonistic agents. |
