Occurrence of potato taste defect in coffee and its relations with management practices in Rwanda

Coffee production is a critical export for Rwanda and a direct income source for many rural farmers. An undesirable raw potato-like smell found in parchment, green and roasted coffee beans and in brewed cups of coffee referred to as “potato taste defect” (PTD) affects coffee across the Africa Great Lakes Region. Two main insect pests of coffee, antestia bug (Antestiopsis thunbergii) and coffee berry borer (Hypothenemus hampei) occur in the same region and may be directly or indirectly responsible for the spread of PTD. The objectives of this study were to determine the distribution of PTD in Rwanda and to evaluate how crop management practices influence the occurrence of this defect in coffee. A stratified random sample of 338 coffee farms was selected and the density of antestia bug and damage to coffee berries attributed to antestia bug or coffee berry borer (CBB) were quantified. Management practices such as pruning, intercropping and insecticides application were recorded. A random sample of three kg of ripe cherries was collected from each farm, hand pulped, fermented for 24 h, washed, dried and tested. Processing did not include sorting by floatation or removal of insect - infested cherries. Potato taste defect was detected in about 5% of the samples. The PTD was distributed throughout the coffee producing regions of Rwanda with the highest incidence in the Central Plateau, Granitic Ridges and Eastern Plateau. Occurrence of PTD was significantly correlated with antestia bug density and damage but not to CBB infestation. Pruning significantly reduced the occurrence of PTD but intercropping did not affect the occurrence of this defect in coffee. This study suggests that PTD could be significantly reduced through proper control of antestia bug, but its elimination would also require understanding its mechanisms of infection.