THE EPIDEMIOLOGY, VARIABILITY AND CONTROL OF THE DOWNY MILDEWS OF PEARL-MILLET AND SORGHUM, WITH PARTICULAR REFERENCE TO AFRICA

Sorghum downy mildew (Peronosclerospora sorghi) infecting sorghum and maize, and pearl miller downy mildew (Sclerospora graminicola) infecti ng pearl miller can cause considerable yield loss in Africa. The last 15 years have witnessed an increase in knowledge of the biology, epide miology and control of these two pathogens. Much information has been obtained on the effect of environmental factors on disease epidemiolog y, spore production and dispersal. Molecular techniques applied to stu dy pathogenic variability have aided in defining relationships among t hese pathogens, although scope of the work is limited. Knowledge of th e genetics and inheritance of resistance, and of resistance mechanisms , has also increased. This review presents the current state of knowle dge of both downy mildew pathogens, with focus on their status on sorg hum and pearl miller in Africa. Despite the advances in knowledge over the last 15 years, these downy mildews remain important constraints t o sustainable crop production in the semi-arid regions of Africa. In s ome cases information obtained in Asia and the Americas can be extrapo lated to Africa but care must be taken in ensuring its applicability. Priorities for future research relevant for Africa are proposed and di scussed.