Fungal endophytes isolated from healthy Theobroma cacao tissues were screened in vitro for antagonism against major pathogens of cacao. Of tested endophytic morphospecies, 40% (21/52), 65% (28/43) and 27% percent (4/15) showed in vitro antagonism against Moniliophthora roreri (frosty pod rot), Phytophthora palmivora (black pod rot) and Moniliophthora perniciosa (witches broom), respectively. The most common antagonistic mechanism was simple competition for substrate. Nonetheless, 13%, 21%, and 0% of tested morphospecies showed clear antibiosis against M. roreri, P. palmivora, and M. perniciosa, respectively. One isolate of Trichoderma was observed to be parasitic on M. roreri. Endophyte species that were common in the host plants under natural conditions often are good colonizers and grow fast in vitro whereas antibiosis producers usually appear to be relatively rare in nature, tend to grow slowly in vitro, and often are not good colonizers. We suggest that there is an inherent general trade-off between fast growth (high colonization) and production of chemicals that produce antibiosis reactions. Finally, field trials assessing the effects of three endophytic fungi (Colletotrichum gloeosporioides, Clonostachys rosea and Botryosphaeria ribis) on pod loss due to M. roreri and Phytophthora spp. were conducted at four farms in Panama. Although the overall incidence of black pod rot was very low during the tests, treatment with C gloeosporioides significantly decreased pod loss due to that disease. We observed no decrease in pod loss due to frosty pod rot, but treatment with C rosea reduced the incidence of cacao pods with sporulating lesions of M. roreri by 10%. The observed reduction in pod loss due to Phytophthora spp., and sporulation by M. roreri, supports the potential of fungal endophytes as biological control agents. Further, these studies suggest that combined information from field censuses of endophytic fungi, in vitro studies, and greenhouse experiments can provide useful a priori criteria for identifying desirable attributes for potential biocontrol agents. (c) 2008 Elsevier Inc. All rights reserved.