The Role of Sporangia in the Epidemiology of Pearl Millet Downy Mildew

Exposure of field plants to sporangial inoculum provided by earlier planted "infector rows" resulted in considerably more downy mildew on all Pennisetum americanum cvs. tested than was obtained by exposure of the cvs. to oospores of Sclerospora graminicola. In large, isolated field plots of susceptible hybrids, downy mildew incidence and severity were considerably greater in plots with a central source of sporangia (potted plants with sporulating infected leaves) present from crop emergence than in plots with no such initial sporangial source. Sporangia remained infective for up to 340 m downwind from a sporangial source during the rainy season, but during the dry, post-rainy season no infection occurred at >80 m from a sporangial source. The significance of these results in epidemiology and their application for large scale field screening for resistance are discussed