One of the major common bean diseases devastating farmers’ fields unabated in Uganda is the common bean rust disease caused by Uromyces appendiculatus Pers. (Pers) Unger. To decipher the
economic importance of this disease, a study was conducted to quantify the yield loss caused by rust disease. Using a completely randomized block experimental design of Mancozeb fungicide treated and non-treated experimental plots, six common bean genotypes comprising of two rust resistant genotypes Redlands pioneer and Mexico 235, and four susceptible genotypes NABE 15, NABE 16, K132 and Masindi yellow were evaluated under field conditions in 2015B and 2016A planting seasons on station at NaCRRI-Namulonge. These genotypes responses were further validated on-station at BUZARDI-Hoima, and Mbarara-ZARDI during the 2016A season. The resistant genotypes recorded low rust disease severity and yield losses (5-33%) in both treated and non-treated plots whereas the susceptible genotypes had high disease severity and yield losses of up to 67% in non-treated plots.Rust severity and yield losses were highest in Mbarara-ZARDI, and lowest in the NaCRRI-Namulonge.

These findings will be valuable in the development of rust resistance in the farmer preferred bean genotypes and enhance the deployment of the integrated disease management strategy of rust
disease in Uganda.

Keywords: Phaseolus vulgaris, Uromyces appendiculatus, Mancozeb, fungicide, rust resistance, Disease management