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The Development of Gloeocercospora sorghi in Sorghum. D. F. Myers, Department of Plant Pathology, Cornell University, Ithaca, NY 14853, Present address of senior author: Department of Plant Pathology, Montana State University, Bozeman, MT 59717; W. E. Fry, Department of Plant Pathology, Cornell University, Ithaca, NY 14853. Phytopathology 68:1147-1155. Accepted for publication 27 February 1978. Copyright 1978 The American Phytopathological Society, 3340 Pilot Knob Road, St. Paul, MN 55121. All rights reserved.. DOI: 10.1094/Phyto-68-1147.

The development of Gloeocercospora sorghi in sorghum seedlings and mature plants was investigated by light microscopy to provide a background for studying the involvement of hydrogen cyanide (HCN) in zonate leafspot. On primary leaves of 1-wk-old seedlings, penetration was initiated over nonspecialized epidermal cells from appressoria or appressorium aggregations within 8 hr after conidial germination. Lesions on these primary leaves first were observed 12 to 24 hr after inoculation as water-soaked, chlorotic areas surrounding sites of penetration. Generally, pathogen development was restricted to subcuticular hyphae or stroma in the primary leaf epidermis until 36 to 48 hr after inoculation when advanced intercellular colonization became prevalent. In contrast, ingress into 3- or 5-wk-old leaves of 6- or 10-wk-old plants, respectively, occurred most frequently through leaf trichomes. After penetration, pathogen development and lesion appearance in these older leaves of older plants was similar to that in seedlings. However, lesions appeared more slowly and did not coalesce as rapidly on older leaves of older plants.