Isolation and identification of mycoparasitic isolates of Trichoderma asperellum with potential for suppression of black pod disease of cacao in Cameroon

Alternative measures to chemical fungicides are needed to control Phytophthora megakarya, the main causal agent of black pod disease in Central and West Africa. Precolonized plate and detached cacao pod assays were used to screen fungal isolates for mycoparasitism on P. megakarya. Of over 200 isolates screened, 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 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.