Submitted to: Biological Control
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 1/7/2008
Publication Date: 6/1/2008
Citation: Desouza, J.T., Pomella, A.W., Bailey, B.A., Bae, H., Erbe, E.F., Murphy, C.A. 2008. Colonization of cacao seedlings by Trichoderma stromaticum, a mycoparasite of the witches’ broom pathogen, and its influence on plant growth and resistance. Biological Control 46:36-45. Interpretive Summary: Theobroma cacao (cacao), the source of cocoa, suffers from several major diseases and insect pests resulting in severe reductions in yield in many production areas. Cocoa is combined with United States agricultural commodities providing a direct benefit to the American farmer. Chemical and cultural control measures for cacao diseases are expensive to employ and are often ineffective. Biocontrol strategies using beneficial fungi to control the damage caused by diseases are being developed. As part of this work we characterized the interaction between the beneficial fungus Trichoderma stromaticum and cacao seedlings. Trichoderma stromaticum was able to grow on the surface and inside the cacao stem. Scientists may be able to optimize biocontrol strategies for Trichoderma stromaticum by taking advantage of its ability to colonize cacao tissues. By providing cacao farmers with sustainable, inexpensive biocontrol strategies for control of cacao diseases, cocoa supplies may be stabilized resulting in increased benefits to the cacao farmer, the cocoa industry, and the American farmer.
Technical Abstract: Trichoderma stromaticum is a mycoparasite of the cacao witches' broom pathogen Moniliophthora perniciosa. This beneficial fungus is being used in Bahia, Brazil to control the witches' broom disease under field conditions. The endophytic potential of this biocontrol agent was studied in both sterile and non-sterile cacao and bean seedlings. Agar plate and light and electron microscopy studies showed that T. stromaticum is able to colonize extensively both cacao and bean plants grown under sterile conditions. However, colonization was lower when plants were grown under non-sterile conditions. Recovery of T. stromaticum from field-grown trees showed that isolates belonging to genetic group II are more persistent as endophytes than isolates from group I. Endophytic colonization of cacao plants by T. stromaticum did not result in plant growth promotion nor induced resistance against M. perniciosa on seedlings that had been treated 30 days prior to the application of the pathogen. These results were confirmed by Northern Blot studies, where the fungus was unable to alter the expression of selected genes involved in plant defense such as ChiB, a putative class VII chitinase, Glu-1, a putative endo-1,4-beta-glucanase, Caf-1, a putative caffeine synthase, and Per-1 apoplastic quiacol peroxidase, genes involved in the regulation of growth TcORFX-1(fw2.2-like) and TcLhca-1(photosystem I 24 kDa protein) involved in energy production. This study indicates that induced resistance and growth promotion are not responsible for the activity of T. stromaticum in the biocontrol of the witches' broom pathogen.