Submitted to: Biological Control
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 1/2/2008
Publication Date: 1/3/2008
Citation: Bailey, B.A., Bae, H., Strem, M.D., Crozier, J., Thomas, S.E., Samuels, G.J., Holmes, K.A. 2008. Antibiosis, mycoparasitism, and colonization sucess for endophytic Trichoderma isolates with biological control potential in Theobroma cacao. Biological Control. 46:24-35. Interpretive Summary: Cocoa is combined with agricultural commodities produced in the United States providing a direct benefit to the American farmer. Theobroma cacao (cacao), the source of cocoa, is attacked by several major pathogens resulting in severe yield reductions in most production areas. Traditional control measures are expensive to apply and often do not work. Control measures, including biocontrol, are being developed for cacao diseases in an effort to stabilize cocoa supplies. Biocontrol seeks to use beneficial organisms to control the damage caused by crop pests. The goal of this work was to identify beneficial organisms that protect cacao from pathogens and are able to maintain there presence in the cacao tree thereby limiting the requirement for repeated application and reducing the cost of disease control. Isolates of Trichoderma, a group of beneficial fungi, were identified that inhibit growth of the cacao pathogen that causes Frosty Pod. Frosty pod is a devastating disease of cacao often causing complete yield loss. The Trichoderma isolates inhibit the Frosty Pod pathogen by production of compounds toxic to the pathogen or by direct feeding on the pathogen. Some of these Trichoderma isolates were able to internally colonize cacao tissues in what is referred to as an endophytic association. Based on these results, some of these isolates will be further tested in the field for control of cacao diseases. By providing cacao farmers with sustainable, inexpensive disease control measures, cocoa supplies may be stabilized resulting in increased benefits to the cacao farmer, the cocoa industry, and the American farmer.
Technical Abstract: Theobroma cacao (cacao) suffers severe yield losses in many major production areas due to fungus-induced diseases. Cacao supports a complex endophytic microbial community that offers candidates for biocontrol of cacao diseases. Endophytic isolates of Trichoderma species were isolated from the live sapwood of trunks of Theobroma species and a liana (Banisteropsis caapi). Sixteen of these Trichoderma cultures, representing six species were selected for characterization of the influence of seedling inoculation on the establishment of endophytic growth in cacao seedlings. In addition, an isolate of T. asperellum and Colletotrichum gloeosporioides were included in the study. The isolates studied varied in their abilities to produce metabolites inhibitory to Moniliophthora roreri and in their abilities to parasitize M. roreri cultures. The five inoculation methods used were: 1- inoculation of germinating seed on agar plates; 2-plate inoculation followed by planting in sterile soil; 3-planting sterile seed in precolonized soil; 4-inoculation of emerged seedlings at the soil surface; and 5-inoculation of emerged seedlings between the cotyledon and stem. All the isolates studied were able to colonize Theobroma cacao seedlings but, isolates DIS 110a (T. cf. harzianum), DIS 219b (T. hamatum), DIS 219f (T. harzianum), and TA (T. asperellum) were the most efficient across inoculation methods. These same isolates also caused moderate to severe discoloration of roots of cacao seedlings germinated on water agar plates. Isolates DIS 173a (T. spirale), DIS 185c (T. stromaticum), and Col (Colletotrichum gloeosporioides) were inefficient colonizers of cacao. Methods that maximized exposure to the Trichoderma inoculum also maximized colonization of cacao. Method 2 (plate inoculation followed by planting in soil) resulted in the most complete colonization. Most of the isolates studied were able to establish an endophytic relationship with cacao by colonizing the above ground portions of the cacao seedling and exploitation of this characteristic could lead to the development of novel biocontrol strategies for control of cacao diseases.