Colonization of conifer needles by aquatic hyphomycetes

Abstract

Dead needles of Abies alba, Pinus sylvestris, P. leucodermis, and Sequoia gigantea were immersed in a stream for 28 days and then examined for conidiophores of aquatic hyphomycetes. Contrary to statements in the literature, these fungi were found to colonize untreated needles. However, numbers of species and conidiophores were significantly higher on needles treated with steam before immersion than on untreated needles; both values were also higher on cut surfaces (mesophyll) than on intact surfaces (epidermis with cuticle) of longitudinally halved needles.Addition of untreated needle powder (Sequoia, P. leucodermis) to malt extract agar depressed linear growth of pure cultures of five aquatic hyphomycetes. The inhibition persisted when a 0.2-μm membrane filter was placed between medium and fungal cultures. On water agar, by itself unsuitable for fungal growth, low doses of needle powder allowed growth of the same fungi. At higher doses, inhibition again became predominant. Steam distillation of needle powder yielded three fractions: solid residue, soluble residue, and steam distillate. Steam distillate did not influence fungal growth on the two media, while the other two fractions supported growth on water agar but did not lead to a clear dosage–effect curve on malt extract agar.