Screening And Application Of Biocontrol Bacterial In Clubroot Of Crucifers

Cruciferous vegetable clubroot,caused by Plasmodiophora brassicae Woronin,is one of the worldwide soil-borne diseases.This disease has various characteristics,including extensive routes of transmission,strong ability of infection as well as long survival time in soil,which result the widely spread of clubroot in our country,finally,threaten the sustainable development of cruciferous Vegetable industry.While,biological control has intensively been researched by researchers due to its wide range of sources,safety to humans and animals,and high efficiency and environmental protection.The purpose of this study was to obtain stable biocontrol bacteria for the prevention and treatment of clubroot,and to provide a theoretical basis for the biological control of clubroot.The main results are as follows:(1)Four strains of biocontrol bacteria with stable control effect on cruciferous vegetable clubroot were obtained.A total number of 1198 strains of biocontrol bacteria were isolated from 128 soil samples.115 strains of biocontrol bacteria with antibacterial effect were screened using the dual culture with pathogen indicator bacteria method.Through pot experiment,4 strains of biocontrol bacteria with stable control effect on clubroot were obtained,and the bio-control efficiencies of ZF129,ZF72,ZF480 and ZF481 strains were78.26%,74.58%,72.82%,and 71.23% respectively.(2)The taxonomic status of biocontrol bacteria of cruciferous vegetable clubroot was determined.Based on morphology,cultural character,physiological and biochemical properties,Biolog automatic identification system and molecular biological identification,the strain of ZF480 was identified as Bacillus paralicheniformis,and strain of ZF481 and ZF72 were Bacillus velezensis,and strain of ZF129 is Paenibacillus polymyxa.(3)The mode of action of biocontrol bacteria on cruciferous vegetable clubroot was preliminarily determined.Strains of ZF129,ZF480 and ZF72 could significantly promote the rotting of the root,by stimulation of the germination of the dormant spores,making the early germinated spores die before finding the new host.The fatality rates of dormant spores of Strains of ZF481,ZF72 and ZF129 were 47.63%,39.23% and 44.67%,respectively,which promote the inactivation of dormant spores,and therefore result in the suppressed occurrence of clubroot.(4)The fermentation conditions of cruciferous vegetable clubroot were optimized,anda good control efficiency was obtained in the field experiment.The optimal fermentation medium composition of strain ZF480 was determined as follows: sorbitol 0.2%,tryptone 1%,calcium chloride 0.7% and magnesium chloride hexahydrate 0.7%;the optimum fermentation conditions were: p H8,temperature 30℃,loading volume 100 m L/250 m L,inoculation amount 3% and rotation speed 180 r/min.The optimum fermentation medium composition of strain ZF481 was: sorbitol 0.5%,bran 1.5%,calcium chloride 0.1% and magnesium sulfate0.5%.The optimum fermentation condition was: p H6,temperature 30℃,loading volume 50 m L/250 m L,inoculation amount 4%,and rotation speed 180 r/min.The optimum fermentation medium composition of strain ZF72 was: sorbitol 0.3%,bran 0.8%,calcium chloride 0.1% and magnesium chloride hexahydrate 0.3%;the optimum fermentation conditions were: p H6,temperature 28℃,loading volume 50 m L/250 m L,inoculation amount1%,and rotating speed 180 r/min.The optimal fermentation medium of strain ZF129 were:1.63 g of corn flour,1.43 g of cottonseed cake powder and 1.07 g of dipotassium hydrogen phosphate;the optimum fermentation conditions were: p H8,temperature 28℃,liquid loading40 m L/ 250 m L,inoculation amount 5% and rotation speed 160 r/min.The bio-control efficiencies of strains ZF480,ZF481,ZF72 and ZF129 were 64.08%、60.61%、63.82%和64.49%,respectively,in the control effect test of clubroot of cruciferae.Through the excavation of biocontrol resources for clubroot prevention,4 strains of biocontrol bacteria with high efficacy and stability against cruciferous vegetables clubroot were obtained,providing a theoretical basis for the biological control of clubroot and the further implementation of the guideline of fertilizers as well as pesticides reduction.