OCCURRENCE AND DISTRIBUTION OF PERONOSCLEROSPORA-SORGHI [WESTON AND UPPAL (SHAW)] IN SELECTED COUNTRIES OF WEST AND SOUTHERN AFRICA

Surveys of sorghum and maize crops were undertaken in Nigeria, Zimbabw e, Zambia, Mozambique and Rwanda during 1991 and 1992. The occurrence and prevalence of sorghum downy mildew (SDM) caused by Peronosclerospo ra sorghi [(Weston and Uppal) Shaw] was assessed in regions of each co untry. In Nigeria only maize was systemically infected in the southern humid zone, where rainfall was 1200-1800 mm and the altitude 300-1000 m. This epidemic zone appeared to be geographically isolated from oth er areas of Nigeria where SDM was observed. Within the southern epidem ic zone, yield loss was estimated to be 11.7%. Individual fields had u p to 95% incidence of systemically infected plants. In the arid north of Nigeria (rainfall < 1300 mm, altitude 600-1200 m) both maize and so rghum were infected, and disease incidence was invariably low (<5%). S ystemic SDM incidence on maize was negatively correlated with growth s tage (r = -0.7746, P = 0.01). In Zimbabwe, Zambia, Mozambique and Rwan da sorghum and maize were infected with SDM in areas with an annual ra infall of 600-1200 mm and an altitude range of <300-1800m. Incidence o f infection within crops was generally low, and sites with infected cr ops were scattered in these countries. SDM local lesion infection was observed only on sorghum. Yield loss due to SDM in Zambia, Zimbabwe an d Rwanda at the time of the survey was negligible. However, SDM is wid espread in Africa and occurs in many different agricultural areas, and thus remains a threat to sorghum and maize production. Management of the disease using resistant varieties, cultural and chemical control s hould reduce the risk of future epidemics. Crown Copyright (C) 1998 Pu blished by Elsevier Science Ltd. All rights reserved.