GENETICS OF ECTOMYCORRHIZAL FUNGI - PROGRESS AND PROSPECTS

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.