Screening And Application Of Bacterial Antagonist Against Root-knot Nematodes

In this study, Meloidogyne populations were collected and purified from various plants inJiangsu province, all of which were identified as Meloidogyne incognita with morphology andmolecular biology method.Rhziobacterial strains were isolated and then screened by using protease and cellulose ac-tivities from various plants that not infected by root-knot nematodes in root-knot disease field.Twenty-five strains that have strong hydrolase activities of both were tested to access their sup-pressive abilities against Meloidogyne incognita in Petri dish test. Results indicated that strainJdm1and Jdm2culture supernatant could significantly inhibit the second-stage juveniles’ activ-ity and the egg hatching. The strain Jdm1and strain Jdm2, both isolated from Chinese medicinalherb Trichosanthes kirilowii, were identified as Bacillus cereus and Bacillus subtilis, respectively,by morphological, physiological and molecular biology methods.The pot test showed that strain Jdm1and strain Jdm2could not only significantly decreasethe galls indices of tomato roots, but also promote plants growth by efficiently colonizing on therhizosphere soil. In field test, the control efficacies of Jdm2, Avermectins and J+A treatmentswere all more than69%at30d post-inoculation and then decreased after that. However, theM. incognita suppression of strain Jdm2can last longer than that of Avermectins. Moreover,interestingly, when the strain Jdm1were inoculated together with/without Avermectins for themanagement of M. incognita the yield of tomatoes was significantly increased on similar level,increasing tomato yield by31%and34%, respectively. However, Avermectins treatment has nothat much satisfying effect, the yield increase was only13%.The effect of strain Jdm2on the bacterial community in the tomato rhizosphere soil wasalso monitored using polymerase chain reaction denaturing gradient gel electrophoresis in fieldtest. In order to determine the shifts of tomato rhizobacterial community composition and diver-sity as a consequence of inoculation with Jdm2or Avermectins, the DGGE fingerprinting wasanalyzed over time. The results of clustering and statistical analyses suggested that the influenceof Jdm2treatments on bacterial community in tomato rhizosphere decreased over time. At15dpost-inoculation, the bacterial community composition of Jdm2-amended soils was dramaticallydifferent (d-value>100) from those for control. At30d, the difference between samples Jdm2-amended and the non-treated control was less (d-value=24.4). While at60d, only minor dif-ference(d-value=0.9) was observed between treatment of Jdm2-amended and control. However,the differences between bacterial composition of Avermectins-amended and control rhizospheresoil are more or less as same as each time.The clustering and principal component analysis of over-time DGGE banding patterns showed that the application of the strain Jdm2was not able to imperil, though exerted tran-sient impact at first, the rhizobacterial community which can spontaneously recover soon. On thecontrary, the plant growth stage is the main factor that influenced the bacterial community in thetomato rhizosphere soil.The results of combined use of Jdm2and various botanical nematicides to control root-knotnematodes on cucumber showed that when only one single application was applied during the cu-cumber growth period, the control efficacy reached to42%,48%,48%and30%, respectively, forstrain Jdm2, matrine, azadirachtin and veratridine, resulting in improved fruit weight over controlby14%,18%,25%and10%, respectively. However, interestingly, when the strain Jdm2were in-oculated together with the three botanical nematicides, the control efficacies were increased andreached56%,54%and44%. Moreover, the fruit weights were also increased to31%,27%and18%, respectively. The results also indicated that the cucumber fruit weight was closely relatedto the disease severity of root-knot nematode.