West African cocoa farms need shade overhaul to fight disease, study finds
Researchers in Sierra Leone have identified why cocoa black pod disease devastates some farms but spares others: excessive shade and dense tree cover create ideal breeding grounds for the fungus. The finding suggests smallholder farmers can cut losses by redesigning their agroforestry systems—a low-cost intervention that could protect a crop worth billions to West Africa's economy.
Originaltitel: Towards integrated pest management of cocoa black pod disease in Sierra Leone: host genetic diversity, agroforestry systems, and biological control
<p>Cacao (Theobroma cacao L.) is a key agricultural commodity in West Africa, which produces approximately 70 % of global cocoa. In Sierra Leone, cocoa provides vital income for smallholder farmers, but productivity is constrained by with diseases such as cocoa black pod disease (CBPD) caused by Phytophthora species. Accurate genetic identification is essential for effective resistance breeding programs, conservation efforts, and distribution of true-to-type planting materials to farmers. This thesis takes an integrated approach to management of CBPD combining an investigation into the genetic diversity of T. cacao, a survey of the agroforestry approaches used by farmers and testing of biological control solutions for sustainable CBPD control in Sierra Leone. Genetic characterization of cacao germplasm reveals substantial variability within populations, with most variation occurring within rather than between accessions. CBPD prevalence across Sierra Leone's cacaogrowing regions is strongly influenced by agroforestry system design. Dense shade and high canopy cover increase disease incidence through elevated humidity and reduced airflow, while greater tree-species diversity modestly reduces disease occurrence. Field applications of the biological control agent Trichoderma atroviride reduce CBDP incidence and increase yield, offering a promising sustainable alternative to the use of synthetic pesticides. The holistic approach taken in this thesis addresses key production constraints while promoting resilience and environmental sustainability in smallholder cacao systems.<br></p>