Efficacité en pépinière forestière d'un inoculum de champignon ectomycorhizien produit en fermenteur et inclus dans une matrice de polymères

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Pure culture inocula of ectomycorrhizal fungi are usually produced on a vermiculite peat mixture. They can also be prepared by cultivating the fungus in a fermentor and entrapping it in a polymeric gel as proposed by Dommergues et al. (1979) for bacteria and Jung et al. (1981) for different microorganisms. We have prepared different types of inoculum of Hebeloma cylindrosporum as follows: non washed peat vermiculite inoculum; washed peat vermiculite inoculum; pellets of mycelium cultivated in a fermentor of 800 liters; pellets of mycelium cultivated in a fermentor and included in an alginate gel; pellets of mycelium cultivated in a fermentor, included in an alginate gel and mixed with macropourous silica; pellets of mycelium cultivated in a fermentor, included in a gel of xanthane and 1-4 galactomannan (caroube gel) and mixed with macropourous silica. These different types of inoculum have been tested with spruce (Picea exelsa) and douglas fir (Pseudotsuga douglasii) in fumigated and non fumigated nursery soil. In non fumigated soil it is impossible to obtain a good mycorrhizal development by Hebeloma cylindrosporum with any of the above types of inoculum. In fumigated soil we have obtained a good mycorrhizal development of the two species with Hebeloma cylindrosporum. The mycelium entrapped in the three types of polymers (alginate, alginate and macropourous silica, xanthane, galactomannan and macropourous silica) is a better inoculum than the non entrapped mycelium or the mycelium produced on peat and vermiculite. This method of producing mycelium of an ectomycorrhizal fungus in fermentor and entrapping it in a polymeric gel seems to be a suitable way for producing large quantities of commercial inoculum