MORPHOLOGICAL ANALYSIS OF EARLY CONTACTS BETWEEN PINE ROOTS AND 2 ECTOMYCORRHIZAL SUILLUS STRAINS

Selection of ectomycorrhizal strains for application in forestry is mo stly based on the evaluation of symbiotic performance in small-scale e xperiments. Two Suillus collinitus strains isolated from a Mediterrane an and an alpine area were inoculated onto two pine tree species (Pinu s pinea and P. nigra ssp. laricio var. corsicana) typical of these two environments. The early events during contact between the cell surfac es of plant and fungal partners were analysed morphologically using ul trastructural and immunocytochemical techniques. All four plant-fungus combinations led to a similar degree of mycorrhizal infection and to a similar colonization pattern. The first contact of fungal hyphae wit h root cap cells usually involved breakdown of the outermost electron- opaque layer of the plant cell walls. Hyphae further developed between this layer and the underlying wall strata. Ultrastructural observatio ns revealed that S. collinitus strain J3-15-24, isolated from a Medite rranean area, induced a defence reaction in the roots of P. nigra, whi ch grows typically in alpine areas. These observations suggest functio nal differences between the two fungal strains in their mycorrhizal ca pabilities.