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) f ungus, within plant roots. Using previously designed G. mosseae specif ic primers, a heterologous internal standard was constructed by amplif ying Pseudomonas DNA under low stringency annealing conditions. Go-amp lification of G. mosseae and internal standard DNA within leek root ex tracts provided accurate quantification of target DNA. Colonization of leek roots by G. mosseae was monitored in a comparative study by comp etitive PCR and microscopy, a conventional method of quantification. T hese two methods gave closely parallel data for G. mosseae colonizatio n from three different inoculum levels over a 6 week period Results in dicate that competitive PCR is a sensitive and accurate method of quan tification. The major advantage of competitive PCR over microscopy is that it can quantify specific AM fungi.