Antibiosis, mycoparasitism, and colonization success for endophytic Trichoderma isolates with biological control potential in Theobroma cacao

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, pods of Theobroma species, and a liana (Banisteriopsis caapi). Fifteen isolates of Trichoderma, potentially representing seven species, were selected for characterization of the influence of seedling inoculation on the establishment of endophytic growth in cacao seedlings. An isolate of Colletotrichum gloeosporioides was also included. The isolates studied in vitro 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 pre-inoculated 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 (Trichoderma 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. 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. (c) 2008 Elsevier Inc. All rights reserved.