INCIDENCE AND DISTRIBUTION OF DOWNY MILDEW DISEASE (PERONOSCLEROSPORA SORGHI) OF SORGHUM IN UGANDA

Sorghum (Sorghum bicolor) ranks as the third most important staple cereal food crop in Uganda after maize and millet. The crop is hampered by several biotic stresses of which Sorghum Downy Mildew disease is one of the most devastating diseases. The disease is caused by a soil-borne fungus Peronosclerospora sorghi but it is also air-borne through conidia. Incidence and severity of downy mildew were conducted between March-June, 2016 and September-December 2016 growing seasons in 13 sorghum-growing districts across ten agro-ecological zones. Data collected were subjected to analyses of variance, correlation and linear regression. Significant (P < 0.001) differences were recorded for disease incidence and severity across the different agro-ecologies. The mean downy mildew disease incidence varied significantly (P< 0.001) from 49.4 % for Pader to 78.9 % for Namutumba. Disease severity varied significantly (P <0.001) from 2.3 for Pader to 3.5 for Pallisa. Chi-square test for independent association between cropping season and downy mildew disease incidence showed a high significant test statistic values (χ2 = 140.89, d.f = 3, and P < 0.001). A significant (P<0.001) positive correlation was observed between disease incidence and severity (r = 0.498) while a significant negative correlation was observed between disease incidence and rainfall (r = -0.675) due largely to temperature and relative humidity. Multiple linear regression analysis revealed that temperature, relative humidity, rainfall and altitude explained 49 % of the total variation associated to disease incidence. Variations in the incidence and severity of downy mildew disease prompt the need to screen for resistant/tolerant sorghum varieties.