The Screening And Identification Of Biocontrol Agents To Vegetable Root-knot Nematodes

One hundred and twenty Streptomyces spp. strains and fifty Bacillus spp. strains were used to screen biocontrol agents to J2 of root-knot nematodes. Six Streptomyces spp. strains were gotten in the first step, such as Z-L-2, Z-L-17, Z-L-19, Men-myco-93-19, Men-myco-93-38 and Men-myco-93-63. All of the 4-fold diluted ferment filtrates of the above six strains had more than 90% kill-down efficiency to J2.The six strains ferment filtrates were used to measure the death-rates of J2 of root-knot nematodes respectively in different concentration and treated time. The ferment filtrate showed strong nematicidal activity to J2. The 2-fold diluted ferment filtrates of Z-L-17 and Z-L-2 had 100% and 96% kill-down efficiency respectively, but 4-fold diluted ferment filtrate of Z-L-2 had trong nematicidal activity. At 8-fold, 16-fold and 32-fold, the ferment filtrate of isolate Z-L-2 expressed more effective to the J2 than others. When treated time reached to 4h, isolate Z-19 show strong nematicidal activity to J2, the kill-down rate reached to 85.6%. The 4-fold diluted ferment filtrate of isolate Z-L-2 had 87.4%, 94.6% and 95.2% respectively kill-down efficiency to the J2 when treated for 8 hours, 12 hours and 24 hours.The six strains ferment filtrate were all used to control cucumber root-knot nematodes disease, the control efficiency of Z-L-2 ferment filtrate reached to 75%. The fresh weight of plants above grand and under grand are increased in 89.4% and 66.7% compared with CK. The control result of avilamycin was 8.3%. Their fresh weight of above grand and under grand were 46.3% and 63.9% respectively.The ferment filtrate of Z-L-2 strain was used in greenhouse to control the pumpkin root-knot nematodes. The results showed that 1.8% Chongmankexing diluted 3000-fold increased production 49.9%, the Z-L-2 4-fold diluted ferment filtrate increased 51.3% production, the Z-L-2 10-fold diluted ferment filtrate increased 42.9% production compared with CK. The control effects of the three treatments on root-knot nematodes are not significantly difference, but are all significantly difference to control.The strain Z-L-2 DNA was extracted, and was amplificated with general primers of 16S rDNA. The amplification was detected, cloned and sequenced by Dalian Takara company. The sequence was compared with the known sequences in the database ofGenBank. The phylogenetic tree drew and analyzed according the sequence homology. BLAST analysis result suggests that Z-L-2 is 99.80% homology with S. roseoflavus , with only 3bp difference. There is only Ibp different compared with S'. roseoflavus and Men-myco-93-63 at the 120bp- Y regions of 16S rDNA. And the phylogenetic tree shows the genetic distance between Z-L-2 and Men-myco-93-63 is the shortest than any others. The strain Z-L-2 may be a mutation of Men-myco-93-63.