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Résumé :
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Ectomycorrhizas are symbiotic associations between Basidiomycetes or Ascomycetes fungi and the roots of temperate forest trees. Ectomycorrhizal fungi enhance the growth of trees, mostly by improving their mineral nutrition. For this reason, they play a key role in forest ecosystems and they can be used in forest practice to improve the growth of trees issued form seedlings or cuttings. Numerous investigations have shown that there are many situations where growth of plantations trees can be enhanced by the inoculation of seedlings with selected mycorrhizal fungi. The adaptation of this technique to genetically improved cuttings was a new challenge. The objective of the project for was to associate genetically improved cuttings, selected because of their superior form and vigour or wood quality, with superior strains of ectomycorrhizal fungi or bacteria, with the aim of increasing the growth of forest plantations on poor acid lands which have been or which will be abandoned by agriculture. The research proposed in this project concerned the main species used for reforestation in Europe : Douglas fir, Norway spruce, Sitka spruce, maritime pine, oak and European chestnut. The objective for European Chestnut was to produce mircopropagated plants well adapted to field conditions and more resistant to root pathogens. This project had also two different scientific aspects : 1 - a better knowledge of the interactions between micro-organisms and tree metabolism on the physiology of IAA production and the control of rhizogenesis processes ; characterisation of hormone production, especially IAA, by different fungal or bacterial strains in pure culture and at different stages of the establishment of the association ; inter- and intraspecific variation of IAA synthesising activity within fungal genera and improvement of fungal IAA production by the way of chromosomal genetics ; isolation and characterisation of fungal IAA overproducer mutants ; determination of plant hormones and metabolites and immunolocalization of growth regulators during the formation of roots and the establishment of mycorrhizas ; 2- a better knowledge of the survival of the articicially inoculated ectomycorrhizal and bacterial strains by new methods, such as isozyme analysis, RFLP (Restriction fragment length polymorphism), PCR (polymerase chain reactin), RAPD (Randon amplified polymorphic DNA) and DNA probes.
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