A rapid staining technique for assessment of ectomycorrhizal infection of oak roots

Abstract

A staining procedure was developed to facilitate assessment of ectomycorrhizal infection on oak roots. Roots of northern red oak (Quercus rubra L.) seedlings previously inoculated with Pisolithus tinctorius (Pers.) Coker & Couch were stained with 0.1% Ponceau S (acid red 112) in 10% acetic acid. Mycorrhizal short roots were stained bright red by this procedure while nonmycorrhizal areas of the root remained unstained. To confirm the accuracy of the method, mycorrhizal and nonmycorrhizal oak root samples (as indicated by Ponceau S staining) were cleared and stained with trypan blue in lactophenol, a widely used procedure for confirming the presence of fungi on roots. For over 3000 short root samples, the two methods gave nearly identical results, with an error of only about 1%. The new method offers potential advantages for rapid assessment of mycorrhizal infection for several species of plants and fungi.