ABSTRACT
Sclerotial development of Grifola umbellata (Pers. : Fr.) Donk was investigated through microscopic examinations. The sclerotium of G. umbellata was bumpy and rugged, multi-branched, and dark-brown to black in color. The sclerotial development of G. umbellata was categorized into three stages such as sclerotial initial, development and maturation. Sclerotium development was initiated as the white fungal mass. The superficial part of white sclerotium changed into gray, light brown and then black as its development proceeded further. As a distinctive characteristic of this fungus, a large number of crystals were observed in the medulla layer of sclerotium during its maturation. For development of new sclerotium, G. umbellata formed a white sclerotial primordium on the matured sclerotium. Development of sclerotium in G. umbellata was intimately associated with rhizomorphs of Armillariella mellea and the developing sclerotia were often penetrated by rhizomorphs of A. mellea into medulla layer.