|Ismaiel, Ed - Ed|
Submitted to: Biological Control
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 8/18/2007
Publication Date: 11/1/2007
Citation: Tondje, P., Roberts, D.P., Bon, M., Widmer, T., Samuels, G.J., Ismaiel, A.A., Begoude, A.D., Tchana, T., Nyemb-Tshomb, E., Ndoumbe-Nkeng, M., Bateman, R., Fontem, D., Hebbar, K.P. 2007. Isolation and identification of mycoparasitic isolates of trichoderma asperellum with potential for supression of black pod disease of cacao in cameroon. Biological Control. 43:202-212. Interpretive Summary: Alternative measures are needed to control Phytophthora megakarya, the main causal agent of black pod disease in Africa as existing measures are time-consuming, and in many cases not economically feasible. Seventy percent of the world’s cacao crop comes from Africa. Cacao is an economically important crop as cacao beans are used in the manufacture of chocolate. Four strains of Trichoderma asperellum were isolated from soil in Cameroon and positively identified as this species using molecular taxonomic approaches. These four T. asperellum isolates were shown to be effective parasites of Phytophthora megakarya in laboratory studies and to effectively suppress black pod disease of cacao in two independent field trials in Cameroon. These T. asperellum isolates may ultimately be useful in disease management strategies targeting black pod of cacao in Cameroon. This information will be useful to scientists developing integrated pest management strategies for suppression of black pod disease of cacao.
Technical Abstract: Alternative measures are needed to control Phytophthora megakarya, the main causal agent of black pod disease in Africa. Precolonized plate and detached cacao pod assays were used to screen fungal isolates for mycoparasitism on P. megakarya. Only Trichoderma asperellum isolates 659-7, PR10, PR11, and PR12 were capable of necrotrophic mycoparasitism in both assays. Additional in vitro mycoparasitism assays demonstrated that T. asperellum 659-7, PR10, PR11, and PR12 were mycoparasitic on P. capsici, P. citrophthora, and P. palmivora; other causal agents of black pod worldwide. Sequence analysis of the gene for translation elongation factor 1 revealed two major phylogenetic lineages within T. asperellum. Isolates 659-7, PR10, PR11, and PR12 fell within the same lineage with PR10 distinct from the other three isolates within that lineage. These findings were strongly supported by RAPD and UP-PCR fingerprinting experiments. Cacao trees sprayed with T. asperellum 659-7, PR10, PR11, or PR12 had significantly lower percent diseased pod values than the untreated control in a short-term field trial and for at least a portion of a long-term field trial. Only treatments containing isolate PR11 resulted in values for percent diseased pods/tree that were significantly lower than those for the untreated control in the short-term field trial and all portions of the long-term field trial; although values for this treatment were not lower than the chemical treatment. We demonstrate for the first time the potential of mycoparasitic isolates of T. asperellum for suppression of black pod of cacao in Cameroon.