Influence of mycorrhizal fungi, cocoa pod husk biochar and pig manure on the growth and health status of cocoa plants (Theobroma cacao L.) in nursery

The effective restoration and development of cocoa orchards depends in large part on the growth and health of young cocoa trees in the nursery. Our work aims to investigate possibilities for improving the quality of cocoa tree seedlings in nurseries by investigating the impact of arbuscular mycorrhizal fungi (AMF) in combination with cocoa pod husk biochar and pig manure on the growth performance and health status of cocoa seedlings. The experiment was carried out in a farming environment in Nkolandom, (Southern Cameroon region). A two factors completely randomized block design was used. Treatments resulted from the combination of two factors: the presence or absence of mycorrhizal fungi and the type of organic fertilizer added to the substrate (simple substrate, substrate + 9 g of biochar per kg of soil, and substrate + 30 g of pig manure per kg of soil). The growth of cocoa seedlings was significantly (p < 0.05) improved by biochar and the mycorrhizae-biochar combination, which showed the best results in terms of height (26.62 and 24.63 cm respectively), stem circumference (1.7 and 1.6 cm), leaf area (743.51 and 532.98 cm2), fresh biomass and seedling vigor index compared to the control and pig manure after twelve weeks in the nursery. Evaluation of health status revealed that mycorrhizal and non-mycorrhizal plants, in combination with biochar, were the least susceptible to the observed symptoms (leaf necrosis and stem lesions) in contrast to pig manure treated plants and the control. The results imply that mycorrhizal fungi and cocoa pod husk biochar can positively improve the growth and health status of cocoa trees in the nursery, which is an important basis for promoting the adaptability of transplanted cocoa trees in their future agro-ecosystem.

Keywords: Cocoa nursery, Cocoa seedling health, Mycorrhizal fungi, Biochar, Pig manure