Nursery and field response to ectomycorrhizal inoculation of
forest trees in western Europe
François Le Tacon
Equipe de Microbiologie Forestiere, INRA-Nancy, 54280 Champenoux, France
Abstract
It is essential for afforestation or reforestation to produce tree
seedlings with efficient mycorrhizal associations enhancing tree growth
and survival after transplantation. However, ectomycorrhizal
deficiencies are frequent in forest nurseries, as different practices
inhibit mycorrhizal development. Techniques of ectomycorrhizal
inoculation of bare-root seedlings in classical nurseries after soil
fumigation, or for the production of inoculated containerized seedlings
on artificial substrate are now available. Sixty field experiments are
presently available in western Europe. In almost all of them, several
years after outplanting, there is an effect, positive or negative, of
the mycorrhizal status inherited from the nursery phase. To improve
field responses quantitatively and to enlarge the number of sites where
a positive response can be obtained, efforts should be concentrated in
three areas: the competitive ability, the efficiency and the stability
of the artificially introduced fungi. The differences in effectiveness
and competitivity between fungal species and strains is the basis of
practical application. A major problem is the delineation and management
of stable strains, and the recognition of these strains in field
situations.
Even without sexual reproduction, ectomycorrhizal strains often present
variations which could be of epigenetic or genetic origin. Moreover,
most of the time, introduced and natural strains produce meiotic
spores. The consequence is that introgression of the introduced genes in
the local population is possible.
Competition and stability studies are now possible in long term
experiments with new methods such as RFLP and PCR, gene sequencing and
DNA probes.