Sorghum downy mildew (Peronosclerospora sorghi) infecting sorghum and maize, and pearl millet downy mildew (Sclerospora graminicola) infecting pearl millet can cause considerable yield loss in Africa. The last 15 years have witnessed an increase in knowledge of the biology, epidemiology and control of these two pathogens. Much information has been obtained on the effect of environmental factors on disease epidemiology, spore production and dispersal. Molecular techniques applied to study pathogenic variability have aided in defining relationships among these pathogens, although scope of the work is limited. Knowledge of the genetics and inheritance of resistance, and of resistance mechanisms, has also increased. This review presents the current state of knowledge of both downy mildew pathogens, with focus on their status on sorghum and pearl millet in Africa. Despite the advances in knowledge over the last 15 years, these downy mildews remain important constraints to sustainable crop production in the semi‐arid regions of Africa. In some cases information obtained in Asia and the Americas can be extrapolated to Africa but care must be taken in ensuring its applicability. Priorities for future research relevant for Africa are proposed and discussed.

Cardinal temperatures for mycelial growth of Phytophthora porri on corn-meal agar were <5 (minimum), 15-20 (optimum) and just above 25 ~ (maximum). The number of infections after zoospore inoculation of young leaf plants was relatively low at supra-optimal temperatures, but was not affected by sub-optimal temperatures. Even at 0 ~ plants were infected. The incubation periods needed for symptom formation were 36-57 d at 0 ~ 13-18 d at 5 ~ and 4-11 d at > 11 ~ and were fitted to temperature between 0 and 24 ~ with a hyperbolical model (1/p = 0.00812"T + 0.0243). Oospore germination, reported for the first time for P. porri, was strongly reduced after 5 h at 45 ~ and totally absent after 5 h at 55 ~ Soil solarization for six weeks during an exceptionally warm period in

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The constraints upon pearl millet (Pennisetum glaucum (L.) R. Br.) cultivation were investigated in four regions in southwest Niger. Drought and low soil fertility constitute the principal problems according to farmers. Pearl millet downy mildew (Sclerospora graminicola (Sacc.) Schroet.) is one of the possible biotic constraints. Its occurrence and epidemiology were studied in two regions in southwest Niger with different mean annual rainfalls. Disease incidence ranged from 7× 6% to 42× 0% in the area with highest rainfall and from 0% to 16× 4% in the drier region. Disease severity ranged from 4× 3% to 24× 8% and from 0% to 8× 5%, respectively, in the two regions, which gave a good indication of estimated crop loss. Oospore density in the soil was highly correlated with disease incidence at 90 days after sowing (r = 0× 83, 18df) indicating the important role of oospores in disease epidemiology. Soil organic C content, pH(H2O) and loam fraction showed significant correlations with disease incidence (r = 0× 70, 0× 47 and 0× 46 respectively, 18df), but fractions of sand and clay were not significantly correlated with disease incidence (r = 0× 39 and 0× 13 respectively, 18df).