Abstract:“ Tateyama Mori no Kagayaki” is a male sterile Japanese cedar cultivar produced in Toyama Prefecture. Despite the purported“ male sterile”, due to the Mendelian laws of inheritance, pollen-producing seedlings occur at a frequency of approximately 50%. To select male sterile ones before shipment, we forcibly have seedlings induced male flowers by treating them with gibberellin. During this process, seedlings tend to elongate excessively owing to gibberellin treatment, growing to unseemly large sizes. In the present study, we aimed to adjust the sizes of elongated seedlings by cutting off the top sections（approx. 5 cm in length） and, at the same time, reuse the cut-off sections as cuttings to produce new male sterile seedlings. First, we cut off and collected top sections from 100 male sterile seedlings and then planted these cuttings in vermiculite medium. Later, all cuttings grew roots （100% rooting rate）．In the following year, we transplanted those new rooted cuttings into M-StAR containers. Consequently, the rooted cuttings grew to shippable sizes within the same year. While the original seedlings from which the top sections were cut off sprouted several shoots from the cut edges, they grew steadily without branching out as efforts were made to maintain only the main stalks. These results suggest that our method not only enables the simultaneous production of male sterile seedlings and cuttings but also improves the production efficiency and quality of seedlings through size adjustments by cutting. In short, this technique has proved promising.
Abstract: Clean Larch, which is a superior progeny ofthe F1 hybrid larch, is propagated by cuttings because seed production is inadequate. The original cutting method, whereby the stock plants are grown in the field and a paper pot is used as a growing tray for the cuttings, has two problems: a shortage of shoots for cuttings and an increased risk of root girdling. In this study, we investigated the effect of using a container, which doubled as a growing tray, for both the stock plant （ortet） and the cuttings. The number of rooted cuttings increased from 10.2 ± 4.4/ortet for the original method to 18.0 ± 3.8/ortet for the improved method. The mean root dry weight of a cutting incubated in a greenhouse until late October was 3.3 times the dry weight of the mean value of cuttings produced by the original method. The survival rate of rooted cuttings from the improved method was 12.8% higher than that from the original method in the year after the cuttings were taken. High plant density in the container in the improved method reduced the diameter of rooted cuttings.