Effect of cropping pattern on the incidence of Sorghum downy mildew disease in Uganda

Sorghum (Sorghum bicolor) is largely grown in Uganda as a subsistence food crop and it ranks as the third most important staple cereal food crop after maize and millet. Sorghum production is challenged by sorghum downy mildew (SDM) disease which is one of the most devastating diseases of sorghum. The disease is caused by an obligate soil-borne fungus Peronosclerospora sorghi which affects plants from seedling to flowering stage. Affected plants can result in 100 % yield loss when left uncontrolled. A survey was conducted on incidence and severity of downy mildew disease and the cropping pattern practiced in six districts across six agro-ecological zones in Uganda from September-December, 2015. Data on disease incidence and severity were collected and subjected to analysis of variance and the means were separated using Fisher’s protected least significant difference (P > 0.05). Correlation was done for cropping pattern, disease incidence and severity to establish any association. From the study, significant (P >0.05) differences were recorded for disease incidence and severity across the different districts reflecting the difference in environmental condition which affects the perpetuation and development of the disease. The mean downy mildew disease incidence varied significantly (P> 0.05) from 49.4 % for Pader to 63.4 % for Kabale. Disease severity also recorded significant difference (P >0.05) from a score of 2.3 (Pader) recorded as the lowest to 2.7 (Arua) recorded as the highest score. No significant (P>0.05) correlation was observed between disease incidence, severity and cropping pattern, however a weak positive correlation was observed between disease incidence and severity (r = 0.357) and disease incidence and cropping pattern recorded a strong non-significant correlation (r = 0.701). The observed variations in the incidence and severity of downy mildew disease makes it imperative to further screen sorghum genotypes to identify sources of resistance.