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Ecology and Epidemiology

The Role of Airborne Conidia in Epiphytotics of Sclerospora sorghi on Sweet Corn. Yigal Cohen, Senior Lecturer, Department of Life Sciences, Bar-Ilan University, Ramat-Gan, Israel; Yehiel Sherman, M.S. Student, Department of Life Sciences, Bar-Ilan University, Ramat-Gan, Israel. Phytopathology 67:515-521. Accepted for publication 9 November 1976. Copyright 1977 The American Phytopathological Society, 3340 Pilot Knob Road, St. Paul, MN 55121. All rights reserved.. DOI: 10.1094/Phyto-67-515.

Sclerospora sorghi infected sweet corn (cultivar Jubilee) by soil-borne oospores and through leaves by airborne conidia. Oosporic inoculation resulted only in half-leaf systemic infection whereas conidial inoculation first produced local lesions on the lower leaves and systemic infection developed later. Local infection and the subsequent development of systemic infection was induced by conidia on 3-wk-old or younger plants. Older plants were resistant to conidial inoculum applied to leaves, but became infected systemically when conidia were injected into the stem. Conidial inoculum induced disease if inoculated plants were kept wet for only 2 hr, but 6-8 hr of leaf wetness were optimal. High infection percentages (88%) were obtained in darkness at 20-25 C; increasing conidium concentration resulted in higher incidence of local and systemic infections. The amount of infection from oospores in the filed increased from less than 1% in plants from seed sown in March and April to about 5% in plants from those sown in May through August. Conidia were dispersed from systemically infected plants from early June, and systemically infected plants were efficient foci for rapid spread to nearby younger plants. Under commercial field conditions, inoculum from systemically infected plants induced only local infection on plants of the same age. However, younger plants in close proximity to conidia-bearing plants, were heavily infected both locally and systemically. Local infections, as such, did not decrease yield, but 75% of the systemically infected plants produced only one ear or no ears at all. Plots with average systemic infection of 0, 13, and 57%, yielded 16,000, 14,500, and 8,400 kg of ears (fresh wt)/hectare, respectively.

Additional keywords: sorghum downy mildew, infection, oospores, epidemiology, crop losses, Zea mays.