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Efficacy of Trichoderma Asperellum oil formulations on the control of cocoa black pod disease (Phytophthora Megakarya)

Mbarga J.B., Ten Hoopen G.M., Begoude D., Trondje P.R., Kuaté J., Ambang Z., Amougou A., Schiffers B.. 2012. Communications in Agricultural and Applied Biological Sciences, 77 (3) : p. 65-73.

The objective of this study was therefore to develop a formulation of conidia of T. asperellum with the aim of improving its efficacy. The formulations developed were oily dispersions. It was a combination of solvents consisting of groundnut oil or palm oil with structural agents and emulsifying-dispersing agents. Emulsification tests were carried out and the stability of the emulsions evaluated. The evaluation of the effect of co-formulants on the growth of conidia of T. asperellum was done by reading the optical densities of the formulated samples on multi-plates using a plate reader. The test on detached cocoa pods was done by treating the cocoa pods with selected formulations at 1.107 conidia/ml and inoculation of the treated cocoa pods was done 24 hours later with zoospores of P. megakarya at 1.105 zoospores/ml. The growth of necrosis on the fruits was measured daily. The screening of co-formulants and emulsification tests ended up with the selection of two formulations. The first composed of conidia of T. asperellum, groundnut oil, Tensiofix NTM® and Tensiofix 869®. The second differed from the first by utilisation of palm oil as the solvent. These formulations proved stable when diluted in water with 1% and 0.5% of sedimentation respectively after 24 hours. The viability test of the conidia indicated that the different formulations selected did not have a fungitoxic effect. The test on detached cocoa pods showed an improved efficacy of T. asperellum to control the disease. The growth rates of necrosis were 6.29 mm/day, 7.25 mm/day and 31.6 mm/day for treatment with formulation 1, pure conidia and control treated with water respectively.

Mots-clés : theobroma cacao; phytophthora; trichoderma; lutte biologique; biopesticide; huile d'arachide; huile de palme; efficacité; formulation; cameroun; trichoderma asperellum; phytophthora megakarya; cabosse

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