Multicellular appressoria and terminal sclerotia formed by Botrytis cinerea in infection process.

In the presence of inosine solution containing glucose, the sclerotial formation of Botrytis cinerea was observed on glass slides 5 days after the onset of incubation. By light microscopy, the sclerotial initials arose from the hyphal tips by dichotomous branching, followed by cross-wall formation in the same way as the formation of multicellular appressoria by the fungus. The sclerotia were formed by repetition of dichotomous branching and septation, followed by deposition of pigment in the surface hyphae of spherical masses. The purine-related compounds tested (cyclic AMP, adenosine, inosine and adenine) stimulated the formation of Sclerotia. Among these compounds, inosine showed highest effect alike to that in the formation of appressoria. On rice leaves, the sclerotial formation on non-spreading lesions (necrotic lesion) was observed in the presence of inosine. On the epidermal cells around multicellular appressoria, the spherical masses of hyphae or sclerotia were formed. Necrotic reaction of the epidermal cells was found, but infection hyphae could not be observed in the cells. On cucumber leaves, invasion from the multicellular appressoria and formation of spreading lesions were observed, but the sclerotial formation was not. The present study suggested that the sclerotial formation in B. cinerea might closely be related with success or failure of infection by the multicellular appressoria.