Most Probable Number assay at BCCM/MUCL

The objective of this bioassay is to evaluate the number of infective propagules of arbuscular mycorrhizal fungi (AMF) in a specific substrate using the Most Probable Number (MPN) method.

The MPN method involves taking the original sample, diluting it by orders of magnitude (frequently 10x, 4x, 2x), and assessing the presence/absence of colonization in roots of trap plants.


The method consist in growing plants on a dilution series of the substrate and assessing the presence/absence of contact points between germinating hyphae and plant.

In practice:

  • Plants are grown during at least 6 weeks under controlled conditions.

  • Roots are then harvested, stained (Walker 2005) and observed under microscope to record the number of plants showing presence of AMF.

  • The MPN is then estimate using a mathematical model (Jarvis et al. 2010).



Sylvie Cranenbrouck


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  • Jarvis B, Wilrich C, Wilrich P-T 2010 Reconsideration of the derivation of Most Probable Numbers, their standard deviations, confidence bounds and rarity values. Journal of Applied Microbiology 109: 1660-1667.
  • Walker C 2005 A simple blue staining technique for arbuscular mycorrhizal and other root-inhabiting fungi. Inoculum 56(4).
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