Biocontrol Mechanism And Application Of Biocontrol Bacteria X-20 Against Root-knot Nematodes

With the prohibition of chemical nematicide, biological control has become a safe, fast and friendly way of prevention for root-knot nematode. Antagonistic strains that has good control effect to root knot nematodes were screened and identified. Antagonistic mechanism of metabolites of X-20 on root-knot nematode was studied. Solid-liquid two-phase fermentation was conducted by combining strain X-20 with organic manure, and biocontrol organic fertilizer was developed which could inhibit or kill root-knot nematode and be applied in controlling root-knot nematode in field. The results are as follows:1.27 strains were screened from soil that infected root-knot nematode heavily by serial dilution. And nematicidal rate of strains was detected by their fermentation broth. The results showed correcting mortality rate of X-2, X-6, X-1 1, X-20 were 50.54%,51.67%,58.96%,100.00%, respectively. Correcting mortality rate of X-20 was the highest, and the fermentation broth of X-20 could kill root-knot nematode at 24h completely. With the increasing of dilution ratio, nematicidal rate was decreasing. With the longer of the treatment time, the mortality rate of root-knot nematode showed a slight upward trend.2. By evaluating on morphology, measuring the physiological and biochemical features, analyzing of 16s rDNA sequences, X-20 were characterized as Pseudomonas fluorescens.3. In order to understand the nematicidal mechanis of X-20 strain against root-knot nematode, the changes of physiological indexes of root-knot nematode, including locomotory behavior, Growth, eath symptoms, fluid leakage, total sugar, glycerin and soluble protein content, were detected after treatment with metabolites of X-20 strain. The results show that metabolites of X-20 strain significantly interfered the body fluctuation frequency, head thrashes, body bending frequency, reduced the length of the root-knot nematode worms, increase the length of the stylet and the transparent tail length, increased the osmotic pressure of root-knot nematode body, interfered the sugar, glycerol and protein metabolism of root-knot nematode.4. The optimal culture conditions was determined. The results showed that the fermentation time was 24h, inoculation density was 3%, loading volume was 110mL, the PH of culture was 6 and revolving speed was 80r/min. Sucrose was the most optimal carbon source and peptone was the most nitrogen source.5. The aim of the study is to test the effect of bio-organic fertilizer (BOF) to the growth of zucchini and the inhibitory efficacy of BOF in control of zucchini disease caused by root-knot nematode (RKN) in field. The indexes were determined by applying the BOF fermented by different strains in the fields of healthy zucchini and diseased seriously by RKN, respectively. Compared with the control.The results show that, firstly, the plant stem diameter, chlorophyll content, shoot weight and root weight were obviously increased after application of the BOF; Secondly, the population of the second-stage juveniles RKN, gall index, number of eggs per plant and the incidence of RKN in field were significantly reduced with the maximum control efficiency of 63.00%; Thirdly, the number of freedom nematodes in soil were tremendously increased. Therefore, the application of the BOF promoted the zucchini growth and effectively prevented the damage caused by RKN in field.