Mathematical modeling to improve control strategies in the cocoa and black pod disease pathosystem

Black pod rot of cocoa, due to Phytophthora spp. is a major concern in cocoa production and much research attention has been dedicated to it. However, there are still many questions regarding the factors that govern the disease's dynamics. Here, we explore the use of mathematical modelling to understand the spatial dynamics of black pod disease caused by P. megakarya and notably the impact of shade on disease dynamics. The results were exploited as a base for an in-vitro investigation on the impact of light on growth and sporulation of P. megakarya. A mechanistic–statistical approach was used to estimate spatio-temporal model parameters from real observations of a specific cocoa plot. Shading data collected in the cocoa plot led to refined numerical simulations of disease dispersion and to identify a greater number of infected pods located in areas of the plot with higher shading values. Following the investigation on the effect of shading on system dynamics, the effects of different light wavelengths on P. megakarya biology (growth and sporulation) was assessed. Experiments revealed that all the studied strains grew relatively better in the dark compared with exposure to light. However, it was noted that in general, light was a stimulating factor for P. megakarya sporulation. The increase in the growth rate of P. megakarya in the dark and increased sporulation under light conditions may help explain why shaded or heterogeneously shaded systems are more favorable to P. megakarya development. Based on these findings recommendations in terms of cocoa farming systems with specific (homogenous) shading regimes are discussed

Keywords: Cocoa, black pod disease, epidemiological model, shade, light