GENOTYPE NUTRITION INTERACTIONS IN THE ECTOMYCORRHIZAL FUNGUS HEBELOMA-CYLINDROSPORUM ROMAGNESI

Intraspecific variability in mycelial growth of the ectomycorrhizal basidiomycete Hebeloma cylindrosporum Romagnesi has been studied within 20 sib-monokaryons, each being the progeny of one wild dikaryon fruiting in vitro, and the 50 synthesized dikaryons obtained from all the compatible fusions of these monokaryons. The interaction between fungal diversity and nutrition was also studied. The range of variation in mycelial growth (expressed as mg protein per culture) among the sib-monokaryons was the same as that recorded among the synthesized dikaryons. The average growth of both mono- and dikaryons was highest on a synthetic medium containing nitrate as the sole nitrogen source, but showed the greatest variation. Fungal growth was approximately halved when nitrate was replaced by ammonium, and was intermediate on an organic nutrient-rich medium. A decrease from 24 mm to 24 mum concentration of phosphorus reduced the average growth of the mycelia 40-fold. The variation in mycelial growth in the synthesized dikaryons involved additive and non-additive genetic components. Their ratio was variable depending on the nutrient conditions. In all cases but one, the interactive component was higher than the additive one. From an ecological point of view, these results emphasize the tremendous effect of nutrition on the phenotypic expression of fungal growth. Their possible significance for the dynamics of natural populations of ectomycorrhizal fungi is discussed.