Screening Of Bacillus Strains Against Cereai Cyst Nematode In Wheat And Research Of The Biocontroi Mechanisms

The cereal cyst nematode (CCN),Heterodera avenae,,has caused economically significant damage to the wheat in China. So far, there is no effective way to prevent for this disease. This research is based on biological control theory to screen the beneficial bacteria to control the cereal cyst nematode and study the mechanism. These effective bacteria strains will be provided to the biofungicide.In this study,293Bacillus strains were isolated from wheat root and rhizosphere soil samples collected from middle plain region of China. Their antagonistic abilities to the second stage juvenile(J2) of Heterodera avenae, were tested. The ferment suspension of these8strains showed strong nematicidal activity to J2. The strain B202, BMT8, BMT19, BMT20,YLT24had100%mortality to J2in vitro test after48hours treatment. Through the potted experiments of wheat in greenhouse, the better strains were selected. The results of control test showed that5strains could suppress the formation of the galls. The control efficiency of strain B202was59.1%after60days. The strain B202also was proved best control efficacy in field by three years field experiments. The strain B202selected for biocontrol effectiveness against Heterodera avenae was identified as Bacillus. pumilus using the Biolog microbial identification system., which was further confirmed by16S rDNA sequence analysis. So the strain B202was name as Bacillus. Pumilus B202.The biocontrol mechanisms of strain B202controlling the cereal cyst nematode were studied. The ability of colonization in wheat root was determined in pot experiment by labeled antibiotic mutant. The ability of colonization of the biocontrol bacteria B202could maintain about107CFU/g in rhizosphere of wheat above65days, suggesting the potential to be developed as biocontrol agents. The strain B202could change trophic group structure of oil free-living nematode, and improve the texture ratio of bacterivores nematodes and fungivores nematodes. The strain B202could degrade the population number of omniovores nematodes and herbivores nematodes. PCR-DGGE molecular techniques was used to study the effect of strain B202on the wheat rhizosphere bacteria and fungi community. The results showed that the strain B202could improve the main bacterial populations in soil, including Chloroflexi, Gemmatimonadetes, Bacteroidetes, and Proteobacteria. Also the stain B202could improve the main fungi populations of Mastigomycota and Ascomycota, and degrade the population of Zygomycota. The nematicidal material named1-16and3-11in the fermentation supernatant of strain was isolated and purified by the technology of column chromatography and HPLC. The structure of1-16and3-11were identified as dibutyl phthalate and4,4’-diphenylmethane-bis carbamates by HPLC-MS and NMR. The two compounds were first found in the bacteria of Bacillus. pumilus.