Aislamiento e identificación de hongos micorrizógenos promotores de germinación y desarrollo inicial de Epidendrum radicans Pav. ex Lindl

Background. Seeds of the Orchidaceae family lack an endosperm with sufficient reserves to meet the carbon demands required during germination and the pre-autotrophic developmental stage. This limitation is compensated through symbiotic relationships with orchid mycorrhizal fungi (OMF). The roots of adult orchids also establish symbiotic relationships with OMF, some of which can extend their hyphae to colonize new seeds. Epidendrum radicans is a hemiepiphytic lithophytic, or terrestrial orchid native to Mexico, widely used as an ornamental species; and its fruits produce thousands of seeds. Objective. To isolate fungi that promote germination and early development of E. radicans, using roots from adult plants as the source. Methodology. The presence of OMF structures in E. radicans roots was verified using trypan blue staining. An in vitro co-culture system was designed to induce germination by pairing seeds and OMF-colonized roots. Hyphae associated with germinated orchids were isolated and cultured. One representative isolate from each identified genus was selected and evaluated for its colonization capacity and ability to promote germination, using stained protocorms obtained from co-culture. Results. Sixteen isolates were obtained and morphologically characterized, belonging to the genera Fusarium (14), Rhizoctonia (1), and Ceratobasidium (1). The selected Fusarium sp. isolate did not promote seed germination. In contrast, Ceratobasidium sp. and Rhizoctonia sp. facilitated both germination and early plant development. The number of leaf-bearing plantlets generated by Ceratobasidium sp. was 5.7 times higher than that obtained with Rhizoctonia sp. Seedlings and protocorms germinated in co-culture with both genera exhibited characteristic orchid mycorrhizal colonization structures. Implications. The co-culture protocols used for isolating germination-promoting OMF, along with the modified staining protocol for roots and protocorms, offer valuable tools for enhancing sexual propagation of orchids in breeding programs or conservation efforts targeting species at risk of genetic erosion. Conclusion: The co-culture protocol developed in this study enabled the isolation of two OMF species capable of promoting germination and early development of E. radicans.