| Summary: | Fusarium wilt, caused by the fungus <i>Fusarium oxysporum</i> f. sp. <i>vanillae</i> (Fov), is a disease that results in significant losses in commercial vanilla production. The genera <i>Ceratobasidium</i> (Ceratobasidiaceae) and <i>Tulasnella</i> (Tulasnellaceae), which are often reported as mutualistic symbionts in orchids, belong to the form genus <i>Rhizoctonia</i>, a paraphyletic group of fungi with potential for pathogen biocontrol. We assayed the antagonistic properties of the form genus <i>Rhizoctonia</i> from the roots of neotropical orchids: two <i>Tulasnella</i> spp. isolates (Bv3 and Er1) and one <i>Ceratobasidium</i> sp. (Er19). In a dual culture, we found that form genus <i>Rhizoctonia</i> isolates can generate a biocontrol effect against <i>Fusarium</i> through the mechanisms of antibiosis and competition for space and nutrients. On histological observations, orchid root endophytes also demonstrated potential for mutualistic symbiosis development by establishing themselves on the surface and within the root tissue of <i>Vanilla planifolia</i> accessions multiplied in vitro (NSF021 and NSF092). However, in plant assays, the form genus <i>Rhizoctonia</i> isolates did not reduce symptom expression or disease development due to infection by Fov in the host. These results contribute to the knowledge of the interactions between tropical orchids and their microbiota and demonstrate the need for multidisciplinary studies for the implementation of integrated management strategies for Fusarium disease in commercial systems.
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