Potential allelopathic effects of selected shade tree species on cocoa (Theobroma cacao)

Abstract Shade trees on cocoa farms have been recommended without properly understanding the potential of some shade trees to release chemicals which could be injurious to cocoa. This research sought to determine the effect of aqueous extract from selected shade trees cultivated on cocoa farms on germination and growth of cocoa seedlings. Mature leaves and roots of commonly used shade trees (Khaya anthotheca, Triplochiton scleroxylon, Melicia excelsa and Terminalia superba) were collected separately and grounded into powder. Aqueous extracts of shade trees of different concentrations (15g/lit., 30g/lit. and 45g/lit) were formulated and applied to seeds and seedlings of cocoa. The study was carried out in a greenhouse which mimic field conditions. The study revealed that germination of cocoa seeds declined with increasing concentrations of K. anthotheca, M. excelsa and T. scleroxlon, however, T. superba generally did not result in further decline in germination. Higher concentrations of T. superba reduced dry biomass whiles that of T. scleroxylon increased root length with respect to the control. Farmers ranked T. superba as their most preferred shade species which contradicts with the findings which preferably suggest the use of T. scleroxylon and M. excelsa as shade trees in cocoa agroforestry.