Prevalence of Sorghum (Sorghum bicolor L Prevalence of Sorghum (Sorghum bicolor L.) Diseases in Tanzania and Uganda Samuel M. C. Njoroge1, John Peter Takan2, Elias A. Letayo3, Patrick S. Okoth4, Daniel O. Ajaku4, Henry Ojulong4, and Eric Manyasa4. ABSTRACT: A survey was conducted in 2014 to determine the prevalence of sorghum diseases across different agroecologies of major sorghum production areas in Tanzania and Uganda. In Tanzania, 40 sorghum fields were sampled in Dodoma and Singida Provinces representing the central drier areas, and in Simiyu, Shinyanga, Mwanza, and Mara Provinces representing the humid Lake-zone region. In Uganda, 143 fields were sampled across 4 agroecologies of Teso, Western, Northern, and West Nile. Farmers were purposefully selected, at least 30 plants per field along two diagonal transects were visually assessed for disease, and samples were taken to the laboratory to confirm the diseases observed. In Tanzania, 16 diseases were identified and the most prevalent (% of fields) were leaf blight caused by Exserohilium turcicum, at 76%, anthracnose caused by Colletotrichum sublineolum, at 56%, and rust caused by Puccinia purpurea, at 43%. In Uganda, 15 diseases were identified and the most prevalent were leaf blight at 55%, anthracnose at 43% and ladder leaf spot caused by Cercospora fusimaculans, at 20%. Disease prevalence differed significantly between Tanzania and Uganda. Generally, significant differences were observed in the incidence of major diseases between local or improved varieties. This is the first comprehensive sorghum disease survey report in over 15 years in both countries. INTRODUCTION - The last published comprehensive report listing sorghum diseases in Tanzania (de Milliano, 1992) and Uganda (Guiragossian, 1986; Hulluka and Esele, 1992) showed that 17 and 15 diseases, respectively, had been reported and confirmed. However, recent reports on the occurrence of individual diseases have been published (Bigirwa et al., 1998; Okori et al., 2004; Ramathani et al., 2011). From these recent reports, most have focused on leaf blight (Okori et al., 2004) and downy mildew (caused by Peronosclerospora sorghi) (Bigirwa et al., 1998) possibly because these diseases are increasing in importance. Shifts in the prevalence and severity over time are expected based on many factors such as changes in cropping patterns, varieties grown, climate. A survey was therefore carried out to identify and update information on diseases of sorghum across the major production areas in Tanzania and Uganda. RESULTS A A B B Figure 4. Occurrence and distribution of sorghum diseases in the Lake (A), Central (B) zones in Tanzania. Mean disease within each zone and for Tanzania are represented by dashed line and solid line graphs, respectively. Figure 5. Occurrence and distribution of sorghum diseases in Western (A), and Teso (B) agroecological zones in Uganda. Mean disease within agroecological zones and for Uganda are represented by dashed line and solid line graphs, respectively. MATERIALS AND METHODS - In Tanzania, the survey was conducted in June 2014 on farmers’ fields in Dodoma and Singida Provinces, and in Simiyu, Shinyanga, Mwanza, and Mara Provinces (Figure 1A). For Uganda, the survey was conducted in July to August 2014 in the Teso and Northern agroecologies; and December 2014, in the West Nile agroecology (Figure 1B). Farmers were purposefully selected, at least 30 plants per field along two diagonal transects were visually assessed for disease, and samples were taken to the laboratory to confirm the diseases observed. Fig 1. Maps of Tanzania (A) and Uganda (B) showing areas sampled during the survey. DISCUSSIONS– We identified 16 and 15 diseases in Tanzania and Uganda respectively. In Tanzania and Uganda, both anthracnose and leaf blight were significant and commonly prevalent. However, rust was more prevalent in Tanzania, and ladder leaf spot was more prevalent in Uganda. Previous reports (Hulluka and Esele, 1992; de Milliano, 1992) reported that ladder leaf spot had been reported in Tanzania but not confirmed, and had not been reported in Uganda. In our survey the prevalence of ladder leaf spot was higher in Uganda, but also present in the central drier zones of Tanzania. Of importance were observations that local land races had more diseases occurring on them than improved varieties. Improved varieties, for example KARI Mtama 1 in Tanzania was often infected with rust and leaf blight, but local landraces growing nearby would be affected by rust, leaf blight, anthracnose, head mold, ladder leaf spot, and tar leaf spot. This is the first comprehensive sorghum disease survey report in over 15 years in both countries. 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