|Ismaiel, Ed - Ed|
Submitted to: Biocontrol
Publication Type: Peer reviewed journal
Publication Acceptance Date: 8/15/2007
Publication Date: 8/24/2007
Citation: Tondje, P., Roberts, D.P., Bon, M., Widmer, T.L., Samuels, G.J., Ismaiel, A.A., Begoude, A., Tchana, T., Nyemb-Tshomb, E., Ndoumbe-Nkeng, M., Bateman, D., Fontem, D., Hebbar, K. 2007. Isolation and identification of mycoparasitic isolates of Trichoderma asperellum with potential for suppression of black pod disease of cacao in Cameroon. Biocontrol. Interpretive Summary: Alternative methods for controlling the plant pathogen that causes black pod disease in Central and West Africa are needed. Fungi that attack other fungi were screen for activity against this pathogen, resulting in identification of a single species that attacks the agents causing black pod disease in cacao. Molecular biology was used to confirm identification of the fungus. Field trials showed good efficacy against black pod disease, though not as good as chemical control measures.
Technical Abstract: Alternative measures to chemical fungicides are needed to control Phytophthora megakarya, the main causal agent of black pod diseasein Central and West Africa. Precolonized plate and detached cacao pod assays were used to screen fungal isolates for mycoparasitismon P. megakarya. Of over 200 isolates screened, only Trichoderma asperellum isolates 659-7, PR10, PR11, and PR12 were capableof necrotrophic mycoparasitism in both assays. Additional in vitro mycoparasitism assays demonstrated that T. asperellum 659-7, PR10, PR11, and PR12 were mycoparasitic on Phytophthora capsici, Phytophthora citrophthora, and Phytophthora palmivora; other causal agents of black pod worldwide. Culture filtrates from these T. asperellum isolates contained substantial laminarinase activity and lesser amounts of caboxymethylcellulase activity which could function in degrading cell walls of Phytophthora during mycoparasitism. Sequence analysis of the gene for translation elongation factor 1 (tef1) confirmed the identification of these isolates as T. asperellum. Molecular fingerprinting using RAPD and UP-PCR demonstrated high genetic similarity between isolates 659-7, PR11, and PR12 and high dissimilarity between PR10 and the other three isolates. Cacao trees sprayed with T. asperellum 659-7, PR10, PR11, or PR12 had a significantly lower percentage of diseased pods than the nontreated control in both short-term and long-term field screening experiments, but not lower than that for the chemical fungicide control treatment. Data presented here demonstrate for the first time the potential of mycoparasitic isolates of T. asperellum for suppression of black pod of cacao in Cameroon.