Ceratobasidium includes orchid mycorrhizal symbionts, plant pathogens and biocontrol agents of soilborne plant pathogens. It is not known to what extent members of the first guild also can participate in the others. Ceratobasidium spp. were isolated from roots of Colombian orchids and identified by phylogeny based on nrITS sequences. Phylogenetic grouping of Ceratobasidium spp. isolates corresponded to orchid host substrate (epiphytic vs. terrestrial). Isolates were tested for virulence on rice and for biocontrol of Rhizoctonia solani, causal agent of sheath blight of rice. All Ceratobasidium spp. isolates caused some signs of sheath blight but significantly less than a pathogenic R. solani used as a positive control. When Ceratobasidium spp. isolates were inoculated on rice seedlings 3 d before R. solani, they significantly reduced disease expression compared to controls inoculated with R. solani alone. The use of Ceratobasidium spp. from orchids for biological control is novel, and biodiverse countries such as Colombia are promising places to look for new biocontrol agents.

PREMISE OF THE STUDY: Oeceoclades maculata is a naturalized, invasive, terrestrial orchid in Puerto Rico and elsewhere in the neotropics. We asked whether its success might be partly explained by its mycorrhizal associations, hypothesizing a relationship with many fungal partners or with one widely distributed partner.METHODS: Oeceoclades maculata roots were collected throughout Puerto Rico, and the degree of mycorrhizal colonization was measured. For identification of fungi, the ITS region was sequenced from pure cultures and directly from roots. Representative fungi were used for symbiotic seed germination experiments.KEY RESULTS: Colonization of O. maculata roots was very variable. The most common fungus identified by BLAST searches was Psathyrella cf. candolleana, but typical orchid mycorrhizal fungi (Ceratobasidium and Tulasnella) were also found, as were a range of saprotrophs. Seeds germinated in vitro only in the presence of Psathyrella.CONCLUSIONS: These results are surprising in two respects. First, O. maculata appears to be highly specific for fungi during seed germination, but unusually promiscuous as adult plants. Second, mycorrhizal associations with Psathyrella and with other saprotrophic fungi have been previously reported, but only from mycoheterotrophic (i.e., nonphotosynthetic) orchids, not from green orchids like Oeceoclades. This combination may partly explain the success of Oeceoclades.

The natural vanilla essence is obtained principally from the fruits of the species Vanilla planifolia, a member of the Vanilla aromatic clade, and native to the neo-tropics. Colombia is an important center of diversity for the genus with 22 Vanilla species reported, of which 18 belong to the aromatic clade. Colombian native Vanilla species comprise important genetic resources for the vanilla crop. Although there is no tradition of cultivation of vanilla in the country, these species have potential for establishment in sustainable agroforestry systems. Nonetheless, Vanilla, like many orchid species, is subject to both intrinsic and extrinsic conservation threats. This article outlines an integrated strategy for conservation, incorporating in situ, ex situ and circa situm measures to ensure the conservation of Vanilla species in Colombia, and to promote their sustainable use in community-based cultivation programs. This proposed strategy is also relevant for conservation managers in other countries with native Vanilla species.

Vanilla is an economically important crop for low-lying humid tropical regions. World demand for natural vanilla is increasing, but cultivated plants face serious phytosanitary problems. The disease known as Fusarium wilt is mainly related to the fungus Fusarium oxysporum f. sp. vanillae, and for its management, the pathogen–host relationship must be understood. Four in vitro multiplied vanilla accessions were evaluated: two Vanilla planifolia from Colombia and Mexico, one from V. odorata, and one (1) F1 hybrid (V. rivasii × V. trigonocarpa). In addition, three isolates of Fusarium from different symptomatic plants present in small-scale agroforestry systems: (1Fov) F. oxysporum f. sp. vanillae from leaf, (2Fov) F. oxysporum f. sp. vanillae from root and (3Fs) F. solani also from root. Plants with two months of growth were inoculated in vitro by immersion of roots, and the development of Fusarium wilt was recorded for 15 days, using a severity scale to describe symptoms and to calculate the area under the disease progress curve (AUDPC). No statistical differences were found when analyzing the interaction between Fusarium isolates and vanilla accessions. However, when independently analyzing the design factor Fusarium isolates, there were significant differences; the 1Fov isolate of F. oxysporum f. sp. vanillae induced the highest symptoms as well as death in some plants of all accessions, while F. solani was considered a secondary pathogen. There were no statistical differences for the vanilla accessions factor, but the values of AUDPC and symptoms observed suggest a slight resistance in all the accessions. Therefore, it is suggested to explore the vanilla gene pool to generate multiplication material with resistance genes and to contribute with genetic improvement to successfully integrate the management of Fusarium wilt in commercial systems.

Para su germinación, las orquídeas dependen de hongos micorrízicos y muchas de las características únicas de estas plantas están asociadas con el hongo que las coloniza. En este trabajo se evaluó la germinación de semillas de la orquídea Comparettia falcata en condiciones de laboratorio utilizando los métodos simbióticos: dos hongos micorrízicos de orquídeas de diferentes especies y un aislamiento patogénico de Rhizoctonia solani obtenido de arroz,y los asimbioticos: formulación de Knudson C y MS (Murashie & Skood). Se encontraron diferencias (P < 0.05) entre tratamientos, resultando mejor el método asimbiótico con la formulación Knudson C y el simbiótico con R. solani, patógeno de arroz. Además, se encontró que los tratamientos donde se implementó la metodología simbiótica tuvieron menor porcentaje de contaminación por microorganismos que los tratamientos de tipo asimbiótico.

Fusarium wilt, caused by the fungus Fusarium oxysporum f. sp. vanillae (Fov), is a disease that results in significant losses in commercial vanilla production. The genera Ceratobasidium (Ceratobasidiaceae) and Tulasnella (Tulasnellaceae), which are often reported as mutualistic symbionts in orchids, belong to the form genus Rhizoctonia, a paraphyletic group of fungi with potential for pathogen biocontrol. We assayed the antagonistic properties of the form genus Rhizoctonia from the roots of neotropical orchids: two Tulasnella spp. isolates (Bv3 and Er1) and one Ceratobasidium sp. (Er19). In a dual culture, we found that form genus Rhizoctonia isolates can generate a biocontrol effect against Fusarium 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 Vanilla planifolia accessions multiplied in vitro (NSF021 and NSF092). However, in plant assays, the form genus Rhizoctonia 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.