Assessment of the interaction between the spatial organization of citrus trees populations in cocoa agroforests and Phytophthora foot rot disease of citrus severity

Abstract

Complex agroforestry systems are known to be less conducive to the dispersion of plant pathogenic germs. These systems, which combine many species components provide a means of improving environmental and regulatory mechanisms of disease. The spatial structure, which is a basic characteristic of these systems, has often been indicated as one of the ecological pest control tool. This study was conducted to identify the interaction between the spatial structure of citrus in cocoa agroforests and the severity of Phytophthora foot rot disease of citrus (PFRDC) in the humid zones of Cameroon. The spatial structure of 19 cocoa based agroforests selected in three sites was analysed by L(r) Ripley modified function. The three sites were selected in two forest zones and in a savannah-forest transition zone. Disease severity was characterized on 438 citrus trees, during three rainy seasons and leaf flare periods. The biodiversity of this system was thus proven and in general, the spatial structure of citrus in the plots was random tend to be regular or aggregate. Plots with aggregate and random spatial structure were significantly attacked by PFRDC compared to regular spatial structure. This allows not only to demonstrate the involvement of the spatial structure of citrus on developing PFRDC in this culture system, but already opens a way for improvement of cocoa agroforests in terms of its structure.