Diversity and pathogenicity of the Ceratocystidaceae associated with cacao agroforests in Cameroon

Abstract

Knowledge of the diversity and ecology of plant pathogenic fungi in cacao agroforests and surrounding natural ecosystems can inform the development of sustainable management strategies for new cacao disease outbreaks. In this study, we investigated the occurrence of fungi related to the Ceratocystisdaceae and their nitidulid beetle vectors in cacao agroforests in Cameroon, under diverse agroecological conditions. The fungi and their vectors were collected from artificially induced stem wounds on cacao and associated shade trees. Collections were also made from abandoned cacao pod husks and other tree wounds within and around plantations. Fungal isolates were identified using DNA sequence-based phylogenies and morphological comparisons, and two representatives of each species were evaluated for pathogenicity on cacao. Five species of Ceratocystidaceae were recovered, including Huntiella chlamydoformis sp. nov., H. pycnanthi sp. nov. and H. moniliformis, as well as Thielaviopsis cerberus and Th. ethacetica. The incidence of these fungi appeared to be influenced by the prevailing agroecological conditions. Nitidulid beetles in the genus Brachypeplus were found to be their most common insect associates on cacao. Both Th. ethacetica and H. pycnanthi produced extensive lesions after inoculation on branches of mature cacao trees, while Th. ethacetica also caused pod rot. Although their impact remains unknown, fungi in the Ceratocystidaceae and their nitidulid beetle vectors are common and likely contribute to the parasitic pressure in Cameroonian cacao agrosystems.