VIEW ARTICLE

Cytology and Histology

Cytology and Morphological Development of Basidia, Dikaryons, and Infective Structures of Urocystis agropyri from Wheat. Berlin D. Nelson, Jr., Former graduate research assistant, Department of Plant Pathology, Washington State University, Pullman 99164-6430, Present address: Department of Plant Pathology, North Dakota State University, Fargo 58105; Rubén Durán, professor, Department of Plant Pathology, Washington State University, Pullman 99164-6430. Phytopathology 74:299-304. Accepted for publication 22 September 1983. Copyright 1984 The American Phytopathological Society. DOI: 10.1094/Phyto-74-299.

The morphology and cytology of basidia, dikaryons, and infective structures of Urocystis agropyri from wheat were studied in vitro and in vivo. The blastogenous basidiospores developed synchronously, but remained adnate to the promycelial apex, despite attempts to remove them by micromanipulation. Meiosis, which apparently occurred in the teliospores, was followed by mitoses; thereafter, haploid nuclei migrated to the basidiospores. Nuclear migration was correlated with the completion of basidiospore elongation. Generally, one nucleus migrated to each basidiospore, although occasionally two migrated into some of them. Plasmogamy occurred in situ between mononucleate basidiospores during which the nucleus of one basidiospore migrated into the protoplast of the other. In most of these cases, fusions occurred between two hyphal pegs, one at the base of each basidiospore, although apical fusions also were seen. Some dikaryons also formed following fusions between promycelia and basidiospores, or by the ingress of two nuclei into single basidiospores, or from the promycelium itself when teliospores germinated directly. On wheat coleoptiles, the apical cells of dikaryotic infection hyphae formed appressoria with penetration pegs which directly penetrated the epidermis and emptied their contents into a system of intracellular hyphae.