Molecular and anatomical evidence for a three-way association between Pinus sylvestris and the ectomycorrhizal fungi Suillus bovinus and Gomphidius roseus

Many intimate associations between different species of ectomycorrhizal fun gi are inferred on the basis of the consistent cooccurrence of their fruit bodies. Suillus bovinus and Gomphidius roseus, where the latter never occur s without the former, is one example. This association was examined with PC R identification and light microscopy. S. bovinus and G. roseus were unambi guously separated on the basis of RFLPs of the PCR-amplified ITS region of ribosomal DNA. Tuberculate mycorrhizas of Pinus sylvestris sampled under fr uit bodies of G. roseus and S. bovinus were investigated and the majority w ere identified as mixed associations involving both G. roseus and S. bovinu s. Tuberculate mycorrhizas, which macroscopically resemble the ones of Suil lus species, contained typical chlamydospores of G. roseus and they had hau storia where G. roseus hyphae penetrated the cortical root cells. Pine seed lings collected near the fruit bodies of the two species were mainly coloni sed by S. bovinus. Mycelial rhizomorphs collected under the fruit bodies of G. roseus were identified as S. bovinus, while both fungal species were pr esent at the base of G. roseus fruit bodies. The significance of these obse rvations and the possibility that G. roseus acts as a parasite are discusse d.