Irvingia, a forest host of the cocoa black‐pod pathogen, Phytophthora megakarya, in Cameroon

Abstract

Phytophthora megakarya is an increasingly important invasive pathogen of cocoa in West Africa, where it forms part of the black‐pod disease complex together with the more widespread, but less aggressive, P. palmivora. Its purported centre of diversity, based on evidence from molecular studies and mating types, lies on the Cameroon–Nigeria border, from where it has spread throughout both countries and more recently into Ghana and the Ivory Coast. A survey undertaken in an ancient primary forest (Korup National Park) in western Cameroon, adjacent to the Nigerian border, identified Irvingia sp., close to I. gabonensis (Irvingiaceae), as a wild host of P. megakarya, using both morphological and molecular characterization. ITS fingerprinting of two additional Phytophthora isolates, obtained during a supplementary survey in central Cameroon, showed identical banding patterns for the isolate from a cocoa pod, whilst the isolate from an unknown forest fruit proved to belong to P. heveae. This is the first authenticated record of P. heveae from the African continent. Subsequent AFLP analysis grouped the two P. megakarya isolates with other Cameroonian isolates held in the CABI Genetic Resource Collection, but separated them from the Ghanaian isolates.