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Title: TRICHODERMA OVALISPORUM, A NOVEL BIOCONTROL AGENT OF FROSTY POD ROT (MONILIOPHTHORA RORERI) OF COCOA (THEOBROMA CACAO): FROM DISCOVERY TO FIELD

Author
item HOLMES, KEITH - CABI, UNITED KINGDOM
item KRAUSS, ULRIKE - TURRIALBA, COSTA RICA
item Samuels, Gary

Submitted to: Book Chapter
Publication Type: Proceedings
Publication Acceptance Date: 7/23/2005
Publication Date: 9/10/2006
Citation: Holmes, K.A., Krauss, U., Samuels, G.J. 2006. Trichoderma ovalisporum, a novel biocontrol agent of frosty pod rot (moniliophthora roreri) of cocoa (theobroma cacao): from discovery to field. Proceedings of the 1st International Conference on Plant Microbe Interactions: Endophytes and Biocontrol Agents. Saariselka, Lapland, Finland 18-22nd April 2005. Eds Sorvari S and Toldi O. PP. 54-65.

Interpretive Summary: Cocoa is the major ingredient in chocolate, a major U.S. industry involving many agricultural commodities. Two problems with cocoa production are the diseases known as frosty pod rot and witches’ broom, which threaten the production of this crop in Central and South America. Safe and effective methods of combating the fungi that cause these diseases are urgently needed. Beneficial fungi called Trichoderma are known to control these diseases but are relatively unknown because they are small and occur primarily inside plants. During exploration in the Amazonian regions of Ecuador and Brazil, a new species of Trichoderma was discovered. In this research, this new species is described, illustrated, and characterized for its biocontrol potential. The new fungus was shown to colonize seedlings and pods of cocoa and inhibit growth of the fungi that cause witches’ broom and frosty pod rot. The results are significant because they provide a new potential weapon for combating diseases of cocoa. Therefore, this research will be used by scientists working to control diseases of cocoa and other crops.

Technical Abstract: A multi-national research programme was initiated in 1998 to identify and develop biocontrol agents of the fungal disease frosty pod rot (Moniliophthora roreri) of cocoa (Theobroma cacao) in Latin America. As part of this study, surveys were carried out in the centre of origin of cocoa, other Theobroma species and what was subsequently discovered to be the con-generic witches’ broom pathogen (Crinipellis perniciosa). Surveys were carried out in the Amazonian regions of Ecuador and Brazil, where endophytic fungi were collected as potential classical biological control agents. A new Trichoderma species was isolated as a stem endophyte from Theobroma grandiflorum and from T. speciosum in Para State, Brazil, and from a witches’ broom-infected liana (Banisteriopsis caapi) from Sucumbios Province, Ecuador. In morphological and molecular studies, we identified the new species of Trichoderma, T.ovalisporum, as a very close relative of T. koningii, but it differed in morphology, growth rate and was a tropical rather than temperate species. T. ovalisporum was screened against the frosty pod rot pathogen, M. roreri, in vitro using a pre-colonised plate method. Mycoparasitism of the M. roreri pseudostroma was observed. Glasshouse/laboratory studies were carried out to assess its endophytic ability. T. ovalisporum was found to be able to colonise the meristematic tissue of cocoa seedlings. In subsequent small-scale field studies in Costa Rica, T. ovalisporum, when applied to pod surfaces, was reisolated from surface and internal pod tissue after 12 weeks. Given the ability of T. ovalisporum to colonise both seedlings and pods of cocoa, and its mycoparasitic activity against the frosty pod pathogen, we carried out a full-scale field trial to assess the biocontrol efficacy of T. ovalisporum against frosty pod rot. In a full-scale field trial T. ovalisporum, when formulated with the sticker NP-7, appeared to increase yield to a similar level to that of the fungicide treatments copper hydroxide and flutolanil. The potential of T. ovalisporum as a biocontrol agent of the frosty pod pathogen of cocoa and future studies are discussed.