Symbiotic germination and development of the myco-heterotrophic orchid Neottia nidus-avis in nature and its requirement for locally distributed Sebacina spp.

Symbiotic germination and development of the fully myco-heterotrophic orchid Neottia nidus-avis were studied in 'packets' of seed placed adjacent to, or at varying distances from, adult plants in a Fagus sylvatica woodland. The distribution and identity of the fungal partner(s) of N. nidus-avis were investigated by internal transcribed spacer (ITS)-restriction fragment length polymorphism (RFLP) and sequence analysis of part of the 28S gene in fungal DNA extracted from adult plants from the UK and Germany, and from seedlings germinated in situ. Germination commenced in the spring, but only in the presence of a specific fungus, and occurred most frequently in plots containing adults of N. nidus-avis. Seedlings grew best in packets in which a large number of seeds germinated. Adults and seedlings of UK origin contained the same fungal partner whose 28S sequence most closely matched Sebacina dimitica. Plants of German origin contained a closely related, but distinct, fungus. The results provide the first definitive chronology of the development of N. nidus-avis and establish its critical dependence upon, and specificity for, the locally distributed Sebacina-like fungus that is required for germination and growth.