Study On Screening Biocontrol Agents From Prokaryotic Organisms For Control Of Myloidogyne.spp

The root knot nematode (Meloidogynidae spp.) is an important kind of plant parasitic nematodes, which harm agriculture badly every year. The prokaryotic Organisms (bacteria and actinomycete) have multiply mechanisms to control the root-knot nematodes, the effects are significant, the period long. In addition, the biocontrol agents are safety to human, mammal and beneficial insects, and adapt to the development of green agriculture. Nowadays, the research of bacteria and actinomycete control the root knot nematodes have became a hot field.In laboratory, we get a large number of target nematodes (Bursaphelenchus xylophilus), which are cultured with the Borytis cinerea. When the nematodes are cultured 5 days in 28℃, the density is about 1400 individual/cm2. In water, the nematodes can live 7-12 days (the density is about 1 individual /ul), their mortalities are below 5% in 12 hours. With the method of drops, treat the nematodes with Abamectin 30-45 minutes, the knockdown rate of nematodes is between 57.7% and 76.9%. In green house, through the examination in the pots, the 418# strain was selected as CK.We collected 32 samples of the plant parasitic nematodes disease soil and natural soil from china diluted solution method, 346 strains of bacteria and 960 strains of actinomycete were isolated from all soil samples. Through the bioassay in laboratory and greenhouse, six strains were selected, which can kill the nematodes and decrease the root knots significantly. Among them, the strain B24-14 and the strain G21-31 are the excellent. In laboratory, their knockdown rates to the nematodes are 95.4%, 84.5%. In greenhouse, the effects of control nematodes are 75.0% and 67.6%. They can promote plant growth .The strains B24-14 and G21-31 are better than the 418# strain and Abamectin.Combined the classical, chemical and 16SrDNA sequence methods, the five selected strains were identified. The strain G10-16 is Streptomyces Fradiae)；the strain G21-31 is Streptomyces Gyaneus；the strain G21-33 is Streptomyces Flavus；Both of the strains B22-3 and B24-14 are Bacillus thuringiensis.With the methods of the ethanol sediment and ultraviolet ray scan, the β-exotoxin was extracted and identified from the fermentation broth of the strain B24-14, it can kill the nematodes 93.6% at 8 hours. The resolvable protein was get from the crystal protein solution, the solution (1.6mg/ml) can kill the nematodes 66.4% at 16 hours. Through the test of AgNO3, the B24-14strain can produce the NH3 and resolvable raw, which show the strong activity to the nematodes in laboratory and greenhouse, and can kill the nematodes 100% in 30-45 min. In addition, with the method of solution culture, showed that the B24-14 strain produce some substance, which promote plant growth in diluted solution and restrain in concentrated solution.