In order to develop the rapid cultivation of potted seedlings of Alnus hirsuta, we selected Frankia spp. favorable for the growth of A. hirsuta. The growth of A. hirsuta seedlings inoculated with suspension of root nodules of the species for two years after germination was different among the root nodule suspensions derived from natural seedlings collected from different four sites. Using the root nodule suspensions re-derived from the seedlings with the best and worse growth-performances revealed by the experiments, repeatable results were obtained, where the average size of the 28 potted seedlings with the best growth-performance exceeded 30cm in the middle of September and the proportion of seedlings higher than 30cm was about 70%. This study demonstrated that A. hirsuta seedlings grew to the size suitable for shipping, for about five months, by the inoculation of Frankia spp. with high growth promoting effects as selected in this study, into germinated seedlings.
