Abstract

Orchid mycorrhizal fungi (OMF) play a crucial role in the germination and early development of orchids, particularly because orchid seeds lack energetic reserves and require OMF during germination. Soil conditions, as well as orchid and fungal identity, have been shown to significantly affect orchid germination. However, little is known about the role of interactions between fungal associates in this process. This study investigates the relationship between seed germination-inducing ability (symbiotic ability) and competitive ability under experimental in vitro conditions. We hypothesized a trade-off between these abilities, since fungal resources allocated to rapid growth and competitive ability may limit investment in symbiotic interactions. Thus, we expected that highly competitive OMF would exhibit reduced germination capacity, and that interspecific competition would negatively influence symbiotic germination outcomes. Using six Ceratobasidium strains isolated from Bipinnula fimbriata and B. plumosa from central Chile, we evaluated growth rates, competitive interactions, and the ability to induce germination of B. fimbriata seeds, both individually and through pairwise competition assays. Our findings revealed significant variability in competitive ability, which was positively correlated with growth rate. A quadratic relationship between competitive and symbiotic abilities suggests a complex trade-off, with intermediate competitors showing the highest symbiotic performance. The presence of a competitor significantly altered germination outcomes, depending on the fungal pairs. These results emphasize the complex dynamics of OMF interactions and their implications for orchid symbiotic germination, offering valuable insights to support orchid propagation and restoration programs.