Screening Of Microbial Antagonistics Against Villosiclava Virens

The Villosiclava virens can specifically infect rice filaments at the booting stage,and form false smut balls,which caused a large number of adjacent florets not fructified,resulting in reduced rice yield.Meanwhile,rice false smut balls contain a lot of mycotoxins,which seriously affect the edible safety of rice.A large number of chlamydospores can be produced on the surface of rice false smut ball,and sometimes one to several sclerotia are also produced.Recent studies have shown that the sclerotia of the rice false smut can be safely overwintered and become the main source of primary infection in the next year.Therefore,sclerotia should be one of the important action targets for prevention and control of rice false smut.In this experiment,the germination process of sclerotia was carefully observed,and several biocontrol microorganisms with inhibition and degradation effects on V.virens and its sclerotia were screened.The mechanism of effect was also analyzed.The following main results were obtained.1.A bacterial isolate with potential biocontrol activity against V.virens was obtained.Blast results of the sequence of its 16s rDNA indicted that it belonged to Bacillus.Both dual culture and metabolites tests were carried out in this experiment.Results showed that both the Bacillus culture and its sterile filtrate could obviously inhibit the growth of V.virens hyphae.The inhibitory effects of the Bacillus sterile filtrate of increased along with the increase of its concentration,but the inhibitory effect decreased when time increased.A preliminary determination of its control effects on V.virens in field was carried out,but further verification was needed.2.The sclerotia could germinate under laboratory conditions and simulated field conditions,but the germination required a certain amount of illumination.When the germinated sclerotia were placed in the dark for a long time,the germinated hyphae were degradated.However,the sclerotia still germinated to produce fruiting bodies when the illumination was supplemented subsequently.The sclerotia could germinate multiple times under appropriate conditions.Therefore,as long as the sclerotia in fields have not been completely degraded,the overwintering ones can still germinate under appropriate conditions.3.Through the dual culture of V.virens with biocontrol bacteria and the liquid culture of V.virens,it was found that under the unfavorable conditions such as lack of nutrients and unfavorable growth environment,the V.virens formed a dormant state to resist the bad environment.4.Three strains of biocontrol fungi were screened,isolated and identified from paddy soil.Blast results of their sequences of rDNA-ITS indicted that they belonged to Epicoccum spp.,Trichoderma spp.and Fusarium spp.,respectively.Inoculation test to V.virens sclerotia showed that the isolated fungi could grow on the sclerotia.The sclerotia were fully covered by the biocontrol fungi after 5 days.After 16 days some sclerotia became soft under the action of biocontrol fungi,and could be broken by light touching.After about 30 days the sclerotia began to deform.After 60 days all the sclerotia nearly completely rotted and the original shapes could not be seen.The sclerotia could no longer germinate under suitable environmental conditions.The isolates of Epicoccum spp.and Trichoderma spp,were set to solid ferment.Preliminary tests of their controlling effects on V.virens in fields were carried out,but further verifications were needed.