Genetic variation and heavy metal tolerance in the ectomycorrhizal basidiomycete Suillus luteus

Twenty-one isolates of the ectomycorrhizal fungus Suillus luteus were scree ned for their tolerance to the heavy metals Zn, Cd, Cu and Ni, measured as inhibition of radial growth and biomass production. Two populations from ev en-aged pine stands were investigated: 10 isolates were obtained from an ar ea polluted with high levels of Zn, Cd and Cu, and ii isolates were obtaine d from a control population located in a nearby unpolluted area. RFLP patte rns of the internal transcribed spacer region of the isolates confirmed the morphological identification of the carpophores. All isolates were maintai ned on basic medium without elevated metals to avoid phenotypically acquire d metal tolerance. The in vitro Zn and Cd tolerance of the S. luteus isolat es from the polluted habitat were significantly higher than the tolerances measured in the isolates from the nonpolluted site. This observation sugges ts that the elevated soil metal concentrations might be responsible for the evolution of adaptive Zn and Cd tolerance. Tolerance was maintained in an isolate not exposed to elevated metals for 3 yr. The two S. luteus populati ons did not differ in tolerance to Cu and Ni. The mechanisms for the adapti ve Zn and Cd tolerance are not identical as there was no correlation betwee n response to the two metals; the most Zn-tolerant isolate was the most sen sitive for Cd in the metal-tolerant population. Zinc did not accumulate in basidiocarp tissue, whereas Cd levels in basidiocarps were significantly hi gher in the population on the polluted site. Inter-simple sequence-repeat f ingerprints showed that 90% of the isolates were from different individuals . The genetic variation in the population from the unpolluted site was cons iderably larger than that observed at the polluted site.