Effect of Potential Allelochemicals From Shade Trees on Cocoa Seedlings' Performance

Shade trees are important in cocoa cropping systems, as they affect the growth of cocoa. However, there is a dearth of information on allelochemicals produced by different tissues of these shade trees and how these compounds affect cocoa growth. This study builds on studies by Danso et al. (2024), who assessed the impact of bark aqueous extracts from 11 common shade trees on the performance of cocoa seedlings. However, the current study focuses on the effects of allelochemicals from the leaves of these same shade trees used in the cocoa landscape in Ghana. The study was carried out during the 2020/2021 and 2021/2022 cocoa cropping season at Akim Tafo, in the Eastern region of Ghana. A factorial experiment was set up to evaluate the effects of aqueous leaf extracts from different tree species on the growth of cocoa seedlings in nursery. The treatments were aqueous leaf extracts from 11 tree species at four concentrations (0, 50, 75 and 100 mg mL⁻¹). Treatments were arranged in a Completely Randomised Design with four replications. The effect of tree species and extract concentration on the foliar chlorophyll content and stem diameter of cocoa seedlings varied with time, with both tree species and leaf extract concentrations having a promotional effect on chlorophyll content but suppressing stem diameter. Only the 75 mg mL⁻¹ concentration had a promotional effect on plant height. There was no significant effect of tree species and leaf extract concentration as well as their interaction on net assimilation rate. The effect of leaf extract concentration on stem dry weight was more pronounced than the root dry weight. In general, leaf extract concentration at a higher rate (100 mg mL⁻¹) had suppression effects on most phenotypic growth parameters compared to lower rates. The tree species effect depended on the cocoa seedling parameter assessed. The findings of this study will provide further guidelines for shade tree selection in cocoa production.