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Cytology and Histology

Pathological Anatomy of Dactylis glomerata Infected by Stagonospora arenaria. R. T. Sherwood, Research plant pathologist, U.S. Regional Pasture Research Laboratory, Agricultural Research, Science and Education Administration, U.S. Department of Agriculture, University Park, PA 16802; Phytopathology 72:146-150. Accepted for publication 18 May 1981. This article is in the public domain and not copyrightable. It may be freely reprinted with customary crediting of the source. The American Phytopathological Society, 1982. DOI: 10.1094/Phyto-72-146.

Stagonospora arenaria penetrated guard cells, subsidiary cells, and long cells of orchardgrass leaves via penetration pegs from appressoria and via hyphal wedges between cells. Most penetration attempts at guard and subsidiary cells were successful. A few penetrations occurred through stomatal openings. Penetration attempts at long cells were usually unsuccessful. Resistance to penetration was associated with papilla formation. Papillae were more frequently formed in long cells than in guard or subsidiary cells. Penetrated epidermal cells were colonized, and then the pathogen ramified intercellularly, but sparsely, in the mesophyll. Host responses began outside the margin of hyphal growth. As the typical purple leaf spot lesions developed, epidermal nuclei migrated toward the infection center, leucoplasts of mesophyll cells enlarged and became amber, and a dark amber gel formed between mesophyll cells. Some leaf tips, leaves, or plants formed large tan lesions. Tan lesions were characterized by development of diffuse light-brown pigment, collapse of mesophyll cells, and early disintegration of plastids, chloroplasts, and nuclei. In tan lesions, hyphae emerged from stomata, grew across the surface, and entered other stomata. Hyphae rarely emerged from purple lesions.