This study was conducted to determine physiological and morphological variation of strains of the ectomycorrhizal fungus Hebeloma cylindrosporum associated with Pinus pinaster and its consequence on the symbiotic processes in coastal forests adjacent to Bordeaux, south west France, from 2003-2005. Mycelial cultures were conducted in the laboratory on a rich medium (YMG). Diploid fungal strains from the field as well as hybrid strains, originating from laboratory crosses between haploid isolates, were compared for growth rate at 12oC and 22oC. At 12oC there were significant differences between strains collected in coastal forests with the other strains. Metabolic abilities and growth rates were also investigated for mutant fungal strains that had incorporated in their genome a T-DNA from the phytophatogenic bacterium Agrobacterium tumefaciens. The data indicates that mutations induced by T-DNAs result in phenotypes that could affect symbiotic processes. The possible application of these findings in cultivation of trees in non productive coastal lands is discussed.