Some aspects of epidemiology of sorghum downy mildew (Peronosclerospora sorghi) in Uganda

Studies on Peronosclerospora sorghi (weston and uppal) C. G.Shaw the causal agent of sorghum downy mildew (SDM), were conducted in response to the increased occurrence of the disease in Uganda. The geographic distribution of SDM on maize, sorghum and johnson grass was investigated by undertaking five consecutive surveys between 1994-1995 (chapter three). The relative susceptibility of six maize genotype to P. sorghi and the effect of time of planting on the development of SDM were also studied in two different locations of the country, Nazaretti and Ikulwe (chapter four). The third study (chapter five) compared the development of SDM on maize, sorghum and johnson grass, investigated sporulation of P. sorghi on these hosts and, the cross general inoculation using ospores (soil-borne inoculum) and conidia from the three hosts. The results of the survey revealed that SDM is now prevalent in 11 of the 39 districts (covering approximately 28.2%of the country) as opposed to only 4 districts (approximately 10.3% of the country) in the early 1970s. The disease was most prevalent in the districts of Iganga and Mbale, but of relatively minor significance in the districts of Mubende and Arua. While the incidence of SDM was generally low, the ability of this pathogen to produce large quantities of both asexual and sexual inoculum indicates that the disease is a potential threat to both sorghum and maize production in the country. More fields of maize had SDM than sorghum was generally more diseased than maize.