Development and Cytology of Plectosphaerella Cucumerina

Abstract

Development of the ascoma of Plectosphaerella cucumerina begins with the formation of a coiled ascogonium that becomes surrounded by branches from the parent hypha or from neighboring hyphae or both. Paraphyses develop as rows of cells with the lower ones laterally expanded to form an apparent pseudoparenchyma. Apical meristematic cells of the ascoma grow upward parallel to each other and form the neck and neck canal. Neck hyphae are septate, may be branched, and remain unpigmented until late in development of the ascoma. A cavity within the ascoma is present only near the entrance to the ostiole until late in development. Centrum development is the Sordaria-type. The ascogonium branches in a horizontal layer among the bases of the paraphyses and produces short ascogenous hyphae which give rise to asci by crozier formation. Meiosis followed by a mitotic division gives rise to eight nuclei, each of which becomes enclosed within an ascospore. Mitosis and septum formation produce bicellular ascospores with two uninucleate cells. The apical apparatus of the ascus is inamyloid and annellascous but is often obscure. The haploid chromosome number is four.