Screening And Application Of Functional Bacteria For Clubroot Disease Control

Cruciferous clubroot disease is a worldwide soil-borne fungal disease caused by Plasmodiophora brassicao.This disease occurs in a wide range of the world and causes serious loss.At present,the method to control clubroot disease mainly relys on the chemical fungicides.Biological control is favored due to its environmental protection and safety.Focused on biocontrol of the cabbage clubroot disease,this study was performed to screen those bacteria with functions of antifungal activity,promting plant growth,and plant-induced resistance.The mechanisms of promting growth and induce resistance of candidate bacteria were characterized,and their disease control efficiencies were evaluated under greenhouse and field conditions.The main results obtained were concluded as the follow.1.Totally,12 strains promoting cabbage growth were screened out from the bacteria isolated from cabbage rhizosphere soils according to their potential to increase biomass.These strains could increase the fresh weight,plant height,and leaf length of cabbage.Based on the 16 S rRNA gene sequences,the 12 strains were identified as Bacillus siamensis AN.01,Alcaligenesfaecalis subsp.phenolicus AN.02,B.methylotrophicus AN.09,B.endophyticu AN.11,B.licheniformis AN.10 and B.amyloliquefaciens AN.03?AN.0?AN.05?AN.06?N.07?AN.08?AN.12.Of them,strains AN.04,AN.05 and AN.12 showed the abilities of iron carrier-producing,phosphate-solubilizing and nitrogen-fixing.Strains AN.09,AN.11 could produce plant hormone IAA,and only the strain AN.02 could produce ACC deaminase.2.Four strains showing induce resistence were screened out by detected the plant defense enzymes of POD,PPO and PAL.These strains included A.faecalis subsp.phenolicus AN.02,B.licheniformis AN.10,B.amyloliquefaciens AN.05,and B.amyloliquefaciens AN.08.RT-PCR method was used to analyze the expression of the genes(TGA,PR1,PR2,AOS,PDF1.2,ETR,and CTR1)involved in signaling pathways of salicylic acid,jasmonate,and ethylene.Results indicated that all the 4 strains couldinduce expression of the key genes in these signal pathways.A.faecalis subsp.phenolicus AN.02 induced cabbage resistance mainly through the JA/ET pathway,while the other three by SA and JA/ET pathways.3.The antifungal activity of growth promoting strains(AN.01-AN.12)were determined using Oxford cup method by targeted phytopathogens Pestalotiopsis sp.and Fusarium oxysporum.Results showed that all the strains could inhibit mycelial growth of the pathogens with inhibited rates of 25%-68%.Of the strains,A.faecalis subsp.phenolicus AN.02,B.amyloliquefaciens AN.07,B.amyloliquefaciens AN.08,B.methylotrophicu AN.09 and B.licheniformis AN.10 could strongly inhibit the germination of P.brassicao rest spores.4.Five bacteria with functions of growth promotion,induce resistance and anti-fungi were selected to evaluate their efficiencies to control cabbage clubroot disease by greenhouse and field experiments.B.amyloliquefaciens AN.05,B.amyloliquefaciens AN.08 and A.faecalis subsp.phenolicus AN.02 showed the best capacities to protect the cabbage.The control efficiencies of the three strains respectively were 63.64%,67.24% and 69.67% under greenhouse condition,and56.74%,60.02% and 63.96% in field trial.All the tested strains could increase fresh weight of cabbage,and the yield was increased by 85.72% when applied the B.amyloliquefaciens AN.05.