Quantification of an arbuscular mycorrhizal fungus, Glomus mosseae, within plant roots by competitive polymerase chain reaction

An assay based on the competitive polymerase chain reaction (PCR) was developed to quantify Glomus mosseae, an arbuscular mycorrhizal (AM) fungus, within plant roots. Using previously designed G. mosseae specific primers, a heterologous internal standard was constructed by amplifying Pseudomonas DNA under low stringency annealing conditions. Go-amplification of G. mosseae and internal standard DNA within leek root extracts provided accurate quantification of target DNA. Colonization of leek roots by G. mosseae was monitored in a comparative study by competitive PCR and microscopy, a conventional method of quantification. These two methods gave closely parallel data for G. mosseae colonization from three different inoculum levels over a 6 week period Results indicate that competitive PCR is a sensitive and accurate method of quantification. The major advantage of competitive PCR over microscopy is that it can quantify specific AM fungi.