MONITORING THE PERSISTENCE OF LACCARIA BICOLOR AS AN ECTOMYCORRHIZAL SYMBIONT OF NURSERY-GROWN DOUGLAS-FIR BY PCR OF THE RDNA INTERGENIC SPACER

The large-scale inoculation of selected beneficial ectomycorrhizal fun gi in forest nurseries has generated renewed interest in the ecology o f these symbiotic fungi. However, information on the dissemination and persistence of introduced symbionts is scarce due to the limitation o f the current identification methods. To identify ectomycorrhizal fung i on single root tips, we investigated the polymorphism of the PCR-amp lified ribosomal DNA intergenic spacer (IGS) from a wide range of ecto mycorrhizal fungi. To investigate the reliability of this molecular ap proach in large-scale surveys, the dissemination and persistence on Do uglas fir seedlings of the introduced Laccaria bicolor S238N were asse ssed in a forest nursery in the Massif Central (France). Several hundr ed ectomycorrhizas and fruiting bodies were sampled from plots where c ontrol and L. bicolor inoculated-Douglas fir seedlings were grown for 1.5 years. PCR typing of mycorrhizas indicated that trees inoculated w ith L. bicolor S238N remained exclusively colonized by that isolate (o r sexually derived isolates) for the entire test period. In contrast, control seedlings were infected by indigenous isolates of Laccaria lac cata and Thelephora terrestris. The molecular evidence for the persist ence of the introduced mycobiont despite the competition from indigeno us isolates of the same species provides further illustration of the p otential of exotic species for large-scale microbial application.