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Monitoring the persistence of the ectomycorrhizal basidiomycete Laccaria bicolor S238N on Douglas-fir and Norway Spruce in nursery and forest sites by PCR

talk session 8
Céline Di Battista, Daniel Bouchard, Benoit Généré, Francis Martin, François Le Tacon
Equipe de Microbiologie Forestière-INRA Nancy, France 54280 Champenoux, CEMAGREF 45290 Nogent/Vernisson, France
ICOM1 Abstract
The growth of Douglas-fir (Pseudotsuga menziesii) and Norway spruce cuttings (Picea abies) is improved in nursery by artificial inoculation with the ectomycorrhizal strain Laccaria bicolor S238N. To evaluate its competitivity and its persistence after transplantation in forest, the mycorrhizal infection of Douglas fir and Norway spruce cuttings were determined morphologically and by ribotyping. The polymorphism of the internal transcribed spacer (ITS) and the intergenic spacer (IGS1) of the ribosomal DNA was assessed by RFLP of PCR amplified DNA. Eighty to 90% of mycorrhizal tips of the 1 or 2-year-old Douglas fir and Norway spruce cuttings, grown in nursery, were colonized by Laccaria bicolor S238N. The inoculated Norway spruce cuttings were outplanted on 2 forest sites (StGermain l'Herm, 1000m of altitude ; Vidaillat, 560m of altitude) where thecompetition with indigenous strains was higher than in nursery. InVidaillat, 1 year after outplanting, only 15% of mycorrhizae on inoculatedspruce cuttings were formed by L. bicolor S238N. Other mycorrhizal tips(85%) belonged to indigenous species. In St Germain l'Herm, 2 years afteroutplanting, only 18 % of the total mycorrhizal tips of the inoculatedNorway spruce cuttings were colonized by L. bicolor S238N. Four years afteroutplanting, only 3% of the mycorrhizal tips of L. bicolor S238N oninoculated spruce cuttings were still associated with the roots. In these sites, the introduced strain was rapidly replaced by local strain. However in other investigated forest sites, L. bicolor S238N associated with Douglas-fir persisted at least 10 years after transplantation. Persistence of the inoculated strain therefore depends on the host plant, the presence of competitive local strains, and/or edaphic and climatic conditions.