Electron microscope observation on infection process of Beauveria bassiana to Sitona callosus
The infection process of Beauveria bassiana strain B1 on the body wall of adult Sitona callosus were observed using SEM and TEM to elucidate the pathogenic mechanism.Following inoculation,B.bassiana conidia adhered to the rough areas and concave regions of S.callosus.Germination occurred between two ommatidium depressions 12 hours post-inoculation,initiating invasion into the body wall through mechanical pressure and enzymatic action.Infiltration of B.bassiana was observed in the digitus 48 hours after inoculation,establishing a parasitic relationship with the host organism.At 72 hours post-inoculation,the epidermal layer undergoes deformation,while the endothelium layer initiates separation.The adipose tissue and muscular fibers undergo destruction.Mycelium spread throughout elytron and penetrated setal alveolus.By 96 hours post-inoculation,mycelial growth continued to invade other tissues until complete colonization occurred along with spore formation resulting in host mortality.At 120 hours,mycelium emerged from the host's body enveloping its corpse while the apoptosis of mycelium was observed at 144 h in vitro.The attachment of B.bassiana was influenced by the physical structure of S.callosus.The conidia parasitize S.callosus 96 hours post-inoculation,leading to the onset of disease and subsequent mortality in the host,demonstrating a high degree of pathogenicity.
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