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Résumé :
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As in 1994 and 1995, all the experiments, in laboratory conditions or in nursery or field conditions, started or continued as planned. We also continue to use nursery or field experiments which have been settled during the negotiation phase of the actual contract or just before.The results of this third year of work continue to be scientifically interesting. We have started to better understand the relationships between micro-organisms, rhizogenesis processes and mycorrhizal infection. In 1994, if it was relatively easy to identify a specific strain by PCR typing in pure culture or in association with the host in nursery conditions, it was much more difficult to use this method in field situation. In 1995, we have solved this problem and we are now able to identify ectomycorrhizal strains in field situations. In 1996 we were able to track Laccaria s 238 N. The final objective which is to associate clones selected because of their superior form and vigour or wood quality, with superior strains of ectomycorrhizal fungi or bacteria seams still feasible at least for Douglas fir. We have solved several difficulties and now we are able to get a good mycorrhizal infection in in vitro conditions, except for oak, and in non axenic conditions, during or after the rooting phase of the cuttings. We almost always got an improvement of the performances of the cuttings during the nursery phase. In 1995, we had no positive effects of nursery inoculation on the performances of the cuttings after outplanting. For field experiment, the year 1996 was interesting with two examples of effects of nursery inoculation. A positive effect, at Sully, confirms that the association between Laccaria S 238 and Douglas-fir can be profitable in the field as well as in the nursery. Such results were already known on seedlings and their application to cuttings are more and more probable. A detrimental effect of Laccaria S 238 on second-year growth, at Trévillers, was observed on Norway-spruce. On this forest species, if a positive effect of inoculation on growth or survival can happen during the growing phase, it never happened clearly after planting, except a brief positive effect on second-year growth, at Vidaillat. In Great Britain, there is still an indication that inoculating Sitka spruce cuttings with Laccaria bicolor (S 238) improves height growth in the second year after outplanting and growth appears to be correlated with the mycorrhizal status of the cuttings, as measured at the time of planting. From these experiments, it appears that several years are necessary to get comprehensible results after transplantation in forest conditions. The molecular characterisation of Paxillus involutus strains was successfully achieved in 1996 by PCR products, RFLPs and by sequencing the IGS region. The results obtained by sequencing confirmed and helped to explain the findings obtained by RFLPs. Both methods can therefore be used to characterise and re identify strains of ectomycorrhizal fungi by molecular characteristics of the IGS region. Although we were not able to construct a specific primer for the most efficient P. involutus strains, the knowledge obtained by sequencing came out to be very useful in controlling mycorrhization potential and persistency of fungal strains when applied to inoculation practice in nurseries.
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