Study of Coffee Thread Blight Disease (Corticium koleroga (Cke) Hoehnel) in Ethiopia

Thread blight caused by Corticium koleroga is a devastating disease that causes severe damage to Coffea arabica in Ethiopia. However, it is one of the least researched diseases in Ethiopia. Therefore, the current work was designed with the objectives to (1) assess the intensity of the disease, (2) identify major factors associated with the disease intensity, (3) identify and characterize C. koleroga isolates and (4) determine the pathogenicity of C. koleroga isolates in southwest Ethiopia. For this purpose, field surveys were conducted on 180 farmers’ fields in 12 districts of southwest Ethiopia during 2017 cropping season. In addition, diseased samples were collected from 11 districts of southwestern Ethiopia during the study. The 11 C. koleroga isolates were characterized using macroscopic and microscopic features. The isolates were cultured on potato dextrose agar and incubated at 25 oC for ten days. The treatments were arranged in a completely randomized design with three replications. The average thread blight incidence varied from 0% to 46% while mean disease severity ranged from 0% to 44%. The thread blight disease incidence and severity were higher at areas representing highland and midland altitudes compared with lowland altitudes. Thread blight severity was positively and strongly associated with rainfall (r = 0.75) and relative humidity (r = 0.85), but the disease severity was negatively and strongly associated with mean temperature (r = -0.79) and shade level (r = -0.50), while it was positively and intermediately correlated to altitude (r = 0.44) and coffee production systems (r = 0.36). The colony color of C. koleroga isolates were from white to floral white, with circular to irregular form and filiform to entire in margin on PDA plates. Growth rate of the isolates varied between 6 and 9 mm/day in diameter. Average basidiospore size ranged from 10 to 13.75 × 3.75 to 5 μ. All isolates were pathogenic to C. arabica with different lesion sizes. The present study revealed the importance of coffee thread blight, identified factors associated with the disease intensity and morphological characteristics of C. koleroga existing in southwestern Ethiopia. Future research should be directed towards surveying more agro-ecologies to have a complete picture on the importance of thread blight disease across the country and molecular characterization of the pathogen to recommend disease management strategies.