Study On The Diversity And Biocontrol Potential Of Chemotactic Nematicidal Bacteria

Disease caused by root-knot nematodes is a soil-borne disease that seriously damage crops worldwide.Although chemical nemacides are still the main means to control rootknot nematodes,it is easy to cause environmental pollution and nematode resistance.Thus,biological control has been widely concerned.Bacteria are important resources for biological control of nematodes,but the rhizosphere colonization of bacteria is seriously affected by soil bacteriostasis,resulting in low and unstable control efficiency of bacterial agents.Chemotaxis is an important characteristic of both root-knot nematodes and bacteria.Biocontrol bacteria take advantage of chemotaxis to locate host and move to the root system,which is beneficial for improving their efficiency of rhizosphere colonization.However,few reports on the exploitation and application of the chemotactic nematcidal bacteria are available.This paper focuses on the resource screening of chemotactic nematicidal bacteria,rhizosphere colonization detection and their biocontrol potential.The following main results were obtained:1.Totally,1471 bacterial strains from endophytes of Panax notoginseng,Nicotiana tabacum and animal feces were used for screening of nematicidal bacteria,and 99 strains were obtained which showed nematicidal mortality ≥30% against J2 of Meloidogyne incongnita.Of the 99 strains,58 strains of chemotactic nematicidal bacteria with chemotactic index(CI)>0 were screened by method of chemotactic plate,including 11 strains with CI>0.2,20 with 0.1<CI≤0.2,and 27 with 0<CI≤0.1.The 58 strains belonged to Actinobacteria,Bacteroidetes,Firmicutes and Proteobacteria.Among them,30 strains were included into Firmicutes which included 16 strains of 6 species in the dominant genus Bacillus.2.By method of CheA molecular diagnosis,15 strains of biocontrol bacteria with CheA gene were initially screened out from the 58 chemotactic nematicidal bacteria.Further,2 strains of chemotactic nematicidal bacteria(Pseudomonas corrugate YMF3.02205,P.rhodesiae YMF3.02254)were screened out by swarm plate method and drop assay with trans-Cinnamic acid and Ferulic acid as chemotactic substrates.3.P.corrugate YMF3.02205 and P.rhodesiae YMF3.02254 were labelled with GFP and used in pot experiments.In the treatment of YMF3.02205 plus 40 μM Ferulic acid,the rhizosphere colonization of YMF3.02205 was 19.85% higher than that of the control without addition Ferulic acid,and the number of root knots was decreased by35.85%.In the treatment of YMF3.02254 plus 60 μM trans-Cinnamic acid,the rhizosphere colonization of YMF3.02254 was 114.88% higher than that of the control without addition trans-Cinnamic acid,and the number of root knots was decreased by18.52%.