Screening And Identification Of Biocontrol Bacteria And Their Biocontrol Effects On Meloidogyne Incognita

Meloidogyne incognita is a kind of plant parasitic nematode that threatens the growth of crops.It forms a large number of root knots in the roots of the crop,hinders the absorption of nutrients of plants,and even damages the plant root system.It is reported that worldwide losses from nematodes are more than $125 billion a year,most of which is due to root-knot nematodes.As the chemical pesticides do harm to the environment and human health,its use was strictly limited nowadays.The use of biological pesticides combined with other methods to control agricultural diseases,including root-knot nematode disease,is a very meaningful way.Finding microbial resources to develop into bio-pesticides has a far future.(1)Screening nematocidal strains.The strains against root-knot nematode were screened by two methods,fermentation solution treatment and volatile gas suppression.Two strains of E5 and E9 were screened from 23 strains of bacteria and 22 strains of actinomycetes by fermentation experiments.After incubation with LB medium at 37? for 48 h,the lethal rates of nematode larvae J2 caused by the fermentation solution of the two test strain were all above 90% after 12 h of treatment.The strain E17 was screened from 23 strains of bacteria and 22 strains of actinomycetes by the volatile gas inhibition experiment.The volatilization of the second instar larvae of Meloidogyne incognita was carried out by the design of the volatile gas experiment device,and the inhibition rate of the J2 larvae was more than 75%.(2)Effects of three biocontrol bacteria on nematode infection.The results showed that the nematodes in the treatments of E5 and E9 fermentation broth could not infect the roots of tomato seedlings,and the rate of infection inhibiting reached 100%.In the treatment of E17 bacteria,nematodes J2 lost the ability of infection,and the infection inhibition rate was as high as 98.28%.(3)Effects of three biocontrol bacteria on embryonic development of nematodes.After three days of treatment,it was observed that serious damage to the nematode eggs occurred,and the fermentation broth of the three strains could lead to severe necrosis of the embryo,causing the internal structure of the egg to shrink or vacuate.These might be related to the multiple mechanisms of the biocontrol strains.(4)The activity of fermentation supernatants of three strains of bacteria.The larvae of nematode larvae were treated with the fermentation supernatant of three strains respectively.It was found that the lethal rate of the three supernatants of the three strains reached the maximum for the nematode larvae after 36 h incubation with LB medium at 37?.The lethal rate of three strains to nematode larvae was E5>E9>E17,and the lethal rate of three strains of nematode larvae was higher than that of treatment for 12 h under the same condition,(5)Pot experiments of the three biocontrol strains on the nematodes.Two types of experiments were conducted,namely,pouring of the fermentation broth to root system(treatment 1),and the addition of the fermentation broth of the three test strains to the soil with nematodes(treatment 2).Each experiment was repeated twice.In the treatment 1,the average biocontrol efficacy against nematodes of the two repetitions reached over 80%,strain E9 reached 75%,strain E17 65%,compared wit the positive control avermectin 100%.However,in the second batche of pot experiments,the control efficacy of E5 was 73% and 67%,the control effect of E9 was 67% and 60%,the control effect of E17 was 60% and 53%,while the positive control avermectin was 80% at 20 d.The control efficacy of E5 was 64% and 60%,the control effect of E9 was 60% and 56%,the control effect of E17 was 52%,and the positive control avermectin was 76%,respectively at 45 d.(6)Identification for three biocontrol strains.The morphological observation,physiological and biochemical tests and molecular biology identification of three strains were all carried out.Strain E5,Strain E9 and strain E17 were identified as Bacillus.spp.Through the study of these three kinds of bacteria on plant parasitic nematode,we can develop new biocontrol agents against plant parasitic nematodes.