Isolation of frankia strains from alder actinorhizal root nodules.

A simple procedure, based on the rapid filtration and washing of Frankia vesicle clusters, was devised for the isolation of Frankia strains from alder actinorhizal root nodules. Of 46 Alnus incana subsp. rugosa nodules prepared, 42 yielded isolates. A simple medium containing mineral salts, Casamino Acids, and sodium pyruvate proved to be the most effective for isolation. In general, colonies appeared 6 to 20 days after inoculation. On the basis of hyphal morphology, two distinct types of Frankia strains were characterized. Randomly selected isolates were tested for infectivity, and all formed root nodules on A. glutinosa. Because of its simplicity and efficiency, the procedure is an improved method for the study of Frankia diversity in alder root nodules.