Seed Viability and Symbiotic Seed Germination in Vanilla spp. (Orchidaceae)

Background: Mycorrhizal interactions are ecologically important to understand the orchid biology since orchids depend on mycorrhizal fungi for seed germination. Objective: The aim of this study was to evaluate the ability of fungi isolated from the roots of Vanilla adult plants to induce symbiotic seed germination. Materials and Methods: Fruits from three native species of Vanilla from Colombia were collected to test symbiotic seed germination through experiments in vitro. First, the viability of the seeds was determined through scarification of the seeds using sand-paper and immersion of the embryos in a 1% tetrazolium chloride solution. Second, a surface-sterilized seeds suspension was added to the petri dishes that had an isolated fungus previously obtained from adult plants. Finally, the percentage of seed germination and the index of growth were calculated and the germination stages were morphologically characterized. A one-way analysis of variance (ANOVA) for evaluate differences among species was realized for seed viability variable. For seed germination trails, a factorial design was used and a generalized linear model with a gamma distribution and link function “Log” was performed. Results: With Ceratobasidium strains percentages of germination close to 80% were reached whereas, Tulasnella isolates promoted percentages close to 60%. At Vanilla species level, V. rivasii had the best performance for the variables evaluated. Conclusion: This study presented a new procedure for measuring Vanilla seed viability, as well as, it provided relevant information about seed development. Both Ceratobasidium and Tulasnella isolates can promote germination in Vanilla seeds. However, with the Ceratobasidium strains, higher stages of development were reached.