The variability within and among ectomycorrhizal species provides a su
bstantial genetic resource and the potential to increase forest produc
tivity and environmental sustainability. Two parallel and interacting
approaches, classical and molecular genetics, are being developed to a
cquire the genetic information underpinning selection of improved ecto
mycorrhizal strains. Determining the genetic traits of the fungi which
contribute to symbiosis and plant function are being followed using n
atural variability combined with classical and molecular genetic manip
ulations. Classical and molecular manipulations for breeding rely on k
ey information including sexual and parasexual reproduction, postmeiot
ic nuclear behaviour, mating-types and vegetative incompatibility mech
anisms. Progress in the manipulation of genomes of ectomycorrhizal fun
gi will depend on efficient methods for gene cloning and DNA transform
ation. Gene transfer into fungal cells have been shown to be successfu
l and include treatment of protoplasts and intact mycelium with naked
DNA in the presence of polyvalent cations, electroporation, and microb
ombardment. The merits and limitations of these methods are discussed.
Using this technology the expression of foreign DNA, the functional a
nalysis of fungal DNA sequences, as well as molecular exploitation for
commercial purposes can be carried out. This review concentrates on t
hese aspects' of fungal molecular biology and discusses the applicatio
ns of the experimental systems that are currently available to ectomyc
orrhizal fungi. As it is essential to be able to define the traits whi
ch a breeder is seeking to improve, availability of genetically define
d strains that are isogenic for a character or differ only in one char
acter and a thorough knowledge of the biochemistry of the symbiosis wi
ll be necessary before any genetic manipulation be carried out. Geneti
c variability of ectomycorrhizal strains has been assessed by DNA fing
erprinting. This approach allows the evaluation of DNA variability and
the exchange of genetic information in natural populations, the ident
ification of species and isolates by DNA polymorphisms, and tracking t
he environmental fate of the introduced fungi to determine their survi
val, growth, and dissemination within the soil.