The Development of Gloeocercospora sorghi in Sorghum

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Abstract
The development of G. sorghi in sorghum [Sorghum bicolor] 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 h after conidial germination. Lesions on these primary leaves 1st were observed 12-24 h 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 36-48 h 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.