Coffee tree architecture and its interactions with microclimates drive the dynamics of coffee berry disease in coffee trees

Coffee berry disease (CBD), which is widespread in Africa, has been responsible for massive yield losses of Coffea arabica. In Cameroon, C. arabica is mainly planted in agroforestry systems on smallholder farms, where low incomes hinder the use of chemicals to manage the disease. Novel agroecological strategies for controlling CBD are expected to be implemented and even increase in the current context of global changes. In this study, we showed that coffee tree architecture and its interactions with microclimates were important to CBD cluster symptom appearance (CSA), with notable CSA increasing along the tree branch away from the trunk to the tip of the branch. As shade trees can modify microclimates, we further investigated scenarios of various microclimatic conditions under shade to explore the effects of agroforestry systems on CBD dynamics in coffee trees. We showed that shade could result in contrasting effects on disease dynamics, decreasing CSA along the branch and increasing epidemic duration. We suggest that the contrasting effects of shade on disease dynamics need further evaluation of the possible trade-offs among the variables at play, and we recommend a combination of epidemiological and architectural modelling to help design more cost-effective and environmentally friendly CBD management strategies.