Genetic variability of Pisolithus isolates associated with native hosts and exotic eucalyptus in the western Mediterranean region

. Genetic diversity and host specificity of Pisolithus is reported here in exotic (Eucalyptus) and native hosts in the western Mediterranean region. . Polymorphism in the internal transcribed spacer (ITS) sequences of the nu clear rDNA of Pisolithus was analysed. Sequences for 17 isolates associated with native Mediterranean hosts and Eucalyptus were compared with those in the GenBank DNA database using distance and parsimony methods. . Bootstrap analysis showed clustering of all Pisolithus isolates associate d with Mediterranean hosts. The ITS sequences suggest the occurrence of sev eral ecological species adapted to exploit different soil types (basic, aci d and clayey slate-derived soils), with specificity for particular indigeno us hosts. Isolates from eucalypt plantations in Brazil, Kenya and the Medit erranean grouped together with eucalypt-associated Australian isolates. Tra nsfer to native hosts did not occur; the host specificity range of these ex otic strains might prevent out-competition and interbreeding with local spe cies. . Pisolithus spp. in eucalypt plantations in the Mediterranean basin are of Australian origin; the co-introduction of the ectomycorrhizal fungi might explain the success of these exotic forest plantations.