• VA mycorrhiza;
  • extra radical mycelium;
  • hyphal viability;
  • fluorescein diacetate


Clover (Trifolium repens L.) plants were inoculated with the vesicular-arbuscular mycorrhizal (VAM) fungus Glomus clarum Nicol. & Schenck in three experiments performed in similar environmental conditions. Extra radical mycelium was separated from soil by the membrane filter technique and its total length was measured; viable amounts were assessed after staining with the fluorescent dye fluorescein diacetate (FDA). Total mycelium increased steadily, and reached its maximum length 8 weeks after inoculation, unlike viability rate which decreased, from an initial value of about 100% to less than 15% after a period of 5 to 8 weeks. Consequently, the length of viable mycelium decreased after the first weeks following inoculation. The viability of extra radical mycelium may be an important factor influencing nutrient uptake and translocation by the VAM fungus.