Biological control in vitro of Phytophtora megakarya, the causal organism of black-pod disease of cocoa (Theobroma cacao L.)

Potential fungal antagonists of Phytophtora megakarya were isolated from leaves, pods and soil rhizosphere of cocoa plant. Trichoderma harzianum and Trichoderma Koningii were isolated and tested for their ability to inhibit growth of P. megakarya on Potato Dextrose Agar (PDA). In-vitro screening was carried out using techniques of dual-culture analysis. The two isolates of Trichoderma effectively inhibited radial growth in P. megakarya through hyperparasitism iin vitro. The antagonists proliferated in the dual culture with P. megakarya and significantly reduced the growth of the mycelia when compared with the control. T. Koningii showed a better antagonistic effect than T. harzianum on P. megakarya. Results also indicated that introducing the antagonists before the pathogen gave better inhibitory effects than the other treatments (pathogen before antagonist and antagonist simultaneously with pathogen). Keywords: Biological control; Cocoa; Phytophtora megakarya, Trichoderma harzianum, Trichoderma koningii,Moor Journal of Agricultural Research Vol. 6 (1&2) 2005 pp. 87-9

Biological control of cacao diseases

This chapter discusses the advances in biological control of cacao diseases over the last 15 years. Most attention has been focused on biological control of frosty pod rot (Moniliophthora roreri), witches' broom (Moniliophthora perniciosa) and black pod disease (Phytophthora spp.). Research on biocontrol of other diseases in the cacao phyllosphere or rhizosphere is scarce or in its infancy. There is, however, a steady increase in information regarding the factors influencing and the mechanisms underlying biological control of cacao diseases as well as practical aspects such as inoculum production, formulation and application. There has been a clear shift away from inundative approaches using epiphytic BCAs towards more classical biocontrol approaches using bacterial and fungal endophytes as well as vesicular arbuscular mycorrhiza. These have the advantage that they can permanently establish themselves in the cacao tree. Moreover, besides direct competition for space and nutrients, antibiosis and mycoparasitism, through induced resistance and growth promotion, endophytes have a larger arsenal of mechanisms through which they can help protect their host. Endophytic BCAs could thus provide more effective and sustainable disease control. Recent advances in our understanding of the mechanisms through which endophytic biocontrol agents can reduce pest and disease impact provide possibilities for innovative disease control strategies, including combination therapies together with natural or chemical products. Continued work on production, formulation and application is also necessary in order for biocontrol to become economically interesting. However, biological control will not become a stand-alone solution for disease control but should become part of integrated pest management strategies, with cultural management as a central and reinforcing pillar. (Résumé d'auteur