Chitin and ergosterol content of extraradical and intraradical mycelium of the vesicular-arbuscular mycorrhizal fungus Glomus intraradices

A greenhouse experiment was carried out in order to compare microscopic estimations of hyphal length with chitin or ergosterol content of the vesicular-arbuscular mycorrhizal fungus (VAMF) Glomus intraradlces Schenck & Smith. Red clover ( Trifolium pratense L.) either inoculated or not with G. intraradices was grown in 30 ml plastic cylinders referred to as inoculum compartments (IC) containing the inoculum. The bottom of the IC was removed and substituted with a 40 μm nylon net which allowed the passage of mycorrhizal mycelia but prevented roots passing through. Two ICs were placed in a larger 200ml pot filled with washed sand of particle size ranging from 100 to 1000 μm. This design provided a root-free substratum (RFS) surrounding the IC from which VAM mycelia were collected using the extraradical mycelium extraction (EME) technique. The mycelia collected were used for chitin and ergosterol analysis and the mycelial length was also determined. Root colonization, chitin and ergosterol content in roots were also determined. Correlations were found between the two biochemical parameters (ergosterol and chitin content) and hyphal lengths in the RFS. Mycelial lengths in the RFS averaged 4.3 m g −1 growth medium. The concentration of chitin and ergosterol in extraradical mycelia collected from the RFS averaged 0.29 μg m −1 and 0.24 ng m −1, respectively. Considerably higher values of both substances were obtained from colonized roots growing in the IC, averaging 5.7 mg chitin g −1 root dry wt and 11.09 μg ergosterol g −1 root dry wt, indicating that most of the mycorrhizal biomass is located within the root domain. The advantages and disadvantages of each method for quantifying extraradical VAM mycelia are discussed.