Diversity of Frankia nodule endophytes of the actinorhizal shrub Ceanothus as assessed by RFLP patterns from single nodule lobes

Root nodules of the actinorhizal shrub Ceanothus were collected from seven sites from its native range. DNA was extracted from individual nodule lobes using a cetyl trimethyl ammonium bromide (CTAB) extraction procedure. Three DNA probes were used in combination with two restriction endonucleases to evaluate the extent of restriction fragment length polymorphism (RFLP) diversity within and among populations of Ceanothus endophytes. We observed some diversity using a nif DH gene probe; however there was no correlation of RFLP pattern and geographic site. Using two random Frankia probes, we observed more diversity among the Ceanothus endophytes than with the nif probe. Differences in RFLP patterns were observed among plants at a single geographic site and between geographical sites. The results demonstrated that considerable diversity exists among Frankia strains symbiotic with Ceanothus, as has been shown for pure-cultured Frankia strains isolated from other actinorhizal genera. We have also demonstrated the usefulness of this method for the study of Frankia ecology in planta.