Dispersal and distribution of Phytophthora megakarya in young cacao plantations

The arrival and subsequent dispersal of Phytophthora megakarya within young cacao plantations, previously free of black pod and containing cacao germplasm that is evaluated for its resistance to P. megakarya, is the subject of an ongoing study in Cameroon. A total of 12 plantations, established in 2006 on lands free of cacao cultivation for at least 20 years have been closely monitored on a weekly basis since June 2009. Near the end of 2009, the first infections were observed in three plantations, with a slow but gradual increase over 2010 and 2011 in the number of plantations, trees and pods that were affected. The spatial as well as temporal distributions of infections seem to indicate that multiple P. megakarya introductions occurred and that dispersal by humans plays an important role. Moreover, spatial distribution is not only a function of dispersal mechanism(s) but also depends on other factors such as microclimate and cacao genotype. Understanding the factors that govern the establishment and subsequent dispersal of P. megakarya in newly established cacao plantations will help farmers to delay the onset of cacao black pod epidemics. (Résumé d'auteur