Perithecial development by Gibberella zeae:: a light microscopy study

Gibberella zeae (anamorph Fusarium graminearum) is the causal agent of head blight, and foot and crown rots of wheat, corn, oats and barley. The developmental sequence of perithecia from homothallic Group II isolates of G. zeae was traced by light microscopy. Cultures induced to form perithecia produced wide hyphae with two or more nuclei per cell that gave rise to perithecial initials composed of undifferentiated, uninucleate cells. Neither ascogonia nor antheridia were observed. The ascogenous system arose from cells ill the inner wall of the young perithecium and as the perithecium matured, formed a hymenium at the base of the centrum. Apical paraphyses, differentiated fr om cells in the upper periderm, grew downward and became attached to the hymenium. In the central axis of the perithecium, the ostiole for med from small, darkly-staining, uninucleate cells that differentiated into the periphyses. Once the apical paraphyses were completely developed, typical croziers formed in the hymenium. As the asci elongated, the apical paraphyses collapsed, although their walls remained intact between the asci. Mature asci contained eight, four-celled ascospores in a biseriate arrangement. The ascus walls were simple with a slight thickening at the tip.