Studies on the ontogeny and ultrastructure of the sclerotium of Botrytis cinerea Pers. ex Nocca & Balbis

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Abstract
The ontogeny and ultrastructure of sclerotia of the fungus Botrytis cinerea Pers. ex Nocca & Balbis were studied by light, scanning, and transmission electron microscopy. Exudation droplets of various sizes and colour accumulated on sclerotial surfaces during development and eventually disappeared. A surface hyphal weft was present over sclerotia at maturity, forming a dense covering which often obscured the underlying rind. The rind consisted of highly vacuolated cells with thick, pigmented walls that remained intact even in old sclerotia. The cortex was poorly defined and usually consisted of only one layer of cells. The prosenchymatous medulla constituted the main volume of mature sclerotia. The ultrastructure of young sclerotial hyphae was similar to that of actively growing vegetative hyphae. Hyphae of mature sclerotia contained fewer nuclei and profiles of mitochondria and endoplasmic reticulum than young sclerotial hyphae. Electron-dense structures, tentatively identified as protein and polyphosphate bodies, were observed in hyphae of the cortex and medulla. Sclerotia of B. cinerea were structurally similar to those of Sclerotinia spp.