A molecular approach to explore the extent of the threatened fungus Hypocreopsis rhododendri within wood

Hypocreopsisrhododendri is a rare fungus that grows on woody stems in hyperoceanic climax scrub on the west coasts of Britain, Ireland, and France. Knowledge of the distribution and abundance of the fungus is based entirely on sporocarp records; it does not account for any occurrence as vegetative mycelia. To address this issue, aH. rhododendri-specific polymerase chain reaction (PCR) was developed and used to assay Corylus avellana (hazel) stems for the presence of H. rhododendri mycelia. The primers ITSHrF and ITSHrR were designed within the internal transcribed spacer 2 region, and their specificity to H. rhododendri was established by their failure to amplify DNA extracted from 14 other Hypocreaceae species. The sensitivity of the assay was demonstrated by amplifying DNA extracted from 4 mg C. avellanawood spiked with 0.0013 % H. rhododendri mycelium. Samples of wood and bark were then taken from around and directly underneath 11 H. rhododendri sporocarps and assayed for the presence of H. rhododendri. PCR products were obtained from a third of the surface bark samples, but only one faint product was obtained from 70 samples taken from beneath the outer bark. The results support the view that H. rhododendri does not form mycelia within stems. We suggest that H. rhododendri is not a saprotrophic fungus, but instead appears to be a parasitic on the wood decay fungusHymenochaete corrugata, with which it always occurs. Evidence that tissue of H. corrugata is present within the sporocarps of H. rhododendri is discussed.