Rooting ability of cuttings from 1000-year-old Yaku-sugi (Cryptomeria japonica)

Yakushima in Japan was registered as a World Natural Heritage Site in 1993 for its ancient natural environment. On this island, extraordinarily long-lived Japanese cedars (Cryptomeria japonica D. Don), known as Yaku-sugi, can be found living to more than 1000 years old. It is estimated that there are now only 1000 specimens of these cedar trees because they have been felled during past 500 years for their irreplaceable value. In this study, clonal propagation of those long-lived Yaku-sugi was tried by cutting. Cuttings were obtained from four naturally occurring Yaku-sugi estimated at 880, 1150, 1340, 1480 years old, and one young planted 85-year-old Yaku-sugi. NAA treatments were carried out at 0, 100, 200, and 400ppm for 24 hrs prior to the planting of cuttings and the rooting rate, root number, and root length were examined after 5 months. Surprisingly, cuttings from the four long-lived Yaku-sugi rooted without NAA, though with low rooting rates below 30%, showing that they did have rooting-ability. Meanwhile, the young Yaku-sugi did not produce any roots, suggesting that there might be a genetic difference among the cedars examined. Variations in rooting rate, root number, and root length depended on the Yaku-sugi examined. The five cedars were classified into two groups, an easy rooting and a difficult rooting. The easy rooting group was highly sensitive to NAA concentration that is, nearly 100% of the cedars examined rooted at 100ppm NAA. Whereas the difficult rooting group was less sensitive to the concentration, that is, their rooting rate increased with an increase in concentration. Root number and root length increased with NAA concentration. All the cedars examined showed high rooting rates from 70% to 100% when treated with 400ppm NAA, enough for practical use. The sensitivity of the young 85-year-oid Yaku-sugi to NAA was similar to that of long-lived difficult rooting ones. This result suggests that the 85-year-old cedar may be applicable as a substitute material for the long-lived cedars in order to develop a clonal propagation technique.