Infectivity of vesicular-arbuscular mycorrhizal fungi: Influence of host-soil diluent combinations on MPN estimates and percentage colonization

Infectivity of vesicular-arbuscular mycorrhizal fungi, native to soils from four dissimilar habitats, was assessed by the “most probable number” (MPN) dilution method and by percentage mycorrhizal colonization. Inoculum from each site was tested in various host-soil diluent combinations. MPN estimates, percentage mycorrhizal colonization, intensity of colonization in infected root segments, sporulation, and the extent of extramatrical hyphae formation were greatest when host species and soil diluent most closely matched conditions at the site from which each inoculum was collected. Hence, the MPN method estimated infectivity of propagules best when the host and soil diluent properties permitted expression of all multiple factors conditioning infection processes. MPN estimates were directly proportional to percentage mycorrhizal colonization when the number of infectious propagules were low. regardless of host or soil diluent combination.