All field-collected actinorhizae examined on Comptonia peregrina and Myrica pensylvanica in Maine are spore negative

The occurrence of spore-negative and spore-positive root nodules of Comptonia peregrina (sweet fern) and Myrica pensylvanica (bayberry) was examined in Maine, as well as the distribution of these nitrogen-fixing shrubs and selected characteristics of the environments in which they occur. Thirty-one widely distributed sweet fern sites were examined, and 16 of these were sampled intensively. The 16 sites were relatively open with < 30% tree cover, and their soil was coarse textured with pH ranging from 3.8 to 6.1. Bayberry nodules were examined at eight sites. All eight sites had the same characteristics as those of sweet fern except that soil pH ranged from 3.4 to 7.4. All nodules on both sweet fern and bayberry were spore negative. One possible explanation is host selection of spore-negative Frankia strains.