Mycorrhizal association and symbiotic germination of the terrestrial orchid Bipinnula fimbriata (Poepp.) Johnst (Orchidaceae)

In this study mycorrhizal fungi were isolated from the roots of the endemic terrestrial orchid . Bipinnula fimbriata. Seven isolates were previously identified as the form-genus . Rhizoctonia, a polyphyletic group known to form mycorrhizal associations with Orchidaceae. Two other isolates were included in the study: #793 isolated from . Chloraea crispa, and #1325 . Rhizoctonia solani, isolated from potato. After morphological and molecular characterization of the nine isolates, they were divided into three groups, . Ceratobasidium sp., . Tulasnella calospora and . Thanatephorus cucumeris, to determine the diversity between isolates. Consensus ITS sequences were used for a blast search on the GenBank database, which confirmed the results of the morphological observations. Once the isolates were identified, an . in vitro germination test was done with four plates of oatmeal agar inoculated with each fungus, plus an asymbiotic control. The germination stages of the seeds were recorded 30 days after sowing. All isolates obtained from . B. fimbriata, and the isolate #793 from . Chloraea crispa, promoted seed germination. However, the isolate #1325 . Rhizoctonia solani, which is known as both a pathogen and an orchid symbiont, did not promote germination. This shows that . B. fimbriata is associated with more than one mycorrhizal fungus in its habitat and has a broader potential specificity . in vitro. The results support the hypothesis that at least one fungal isolate promotes the germination of . B. fimbriata, permitting the conservation of this species in . ex situ conditions.