Inhibition of Phytophthora palmivora, causal agent of cocoa black pod disease, by using three (3) species of Trichoderma in three (3) cocoa-producing regions inCôte d'Ivoire

Abstract

Cocoa black pod disease, caused by Phytophthora sp. leads to yield losses. In order to remedy such losses, the use of an antagonistic fungus such as Trichoderma is recommended. This study aims at contributing to cocoa yieldimprovement in Côte d'Ivoire by controlling Phytophthora sp. To this end, healthy cocoa pods, affected by black poddisease and soil from cocoa trees’ rhizosphere were collected. Trichoderma sp. and Phytophthora sp. wererespectively isolated from the soil and from the pods affected by black pod disease. PCR and amplicon sequencinganalyses were used to characterize Phytophthora and Trichoderma species. In vitro and in vivo comparisons werecarried out between Trichoderma sp. and Phytophthora sp. Three species of Trichoderma (T. harzianum, T. asperellum and T. virens) and three morphotypes of Phytophthora palmivora found in the cocoa orchards werecharacterized. Trichoderma species showed antagonistic activity towards Phytophthora palmivora with inhibitionrates ranging from 65 to 87.5% and from 75 to 88.7% on detached pods and on culture medium, respectively. Thesein vitro and in vivo tests showed that these Trichoderma strains have a strong inhibitory action in the presence of Phytophthora palmivora strains, in particular Trichoderma virens (with 87.5% inhibition rate). Keywords: Cocoa, Black pod disease, Phytophthora sp., Trichoderma sp.