Induction and Rapid Propagation of Shoot Primordia from Shoot Apices of Lilium japonicum.

Since Lilium is economically very important with tremendous popularity in the horticulture world, various tissue culture methods have been applied to develop new cultivars, virus-free, clonal micropropagation, and so on1-9). However, the cultured shoot primordium method of tissue culture discovered by Tanaka and Ikeda10) (Patents of Canada, France, and Germany; Patent of Japan officially announced) has not yet been studied in Lilium. The shoot primordium is a dome-shaped tissue which occurs during pref ormation of the shoot tip of a plant and which can be maintained without any regeneration into plantlets only in liquid media stirred in test tubes by rotary culture equipment (2 cycles/minute)10). This method can have the advantage of saving clonally genetic resources of endangered and threatened plant species11) and economically important dioecious and annual plant species12). Lilium japonicum Thunberg leaves are highly variable with deep to shallow veins and the flowers vary in color from purplish-pink to white within the natural population. Since this species is difficult to grow in well-managed cultivated fields, the commercialized cut-flowers of L. japonicum have been harvested only from natural populations. This species is meeting with problems of decrease in the natural population, devastation of their habitat, and so on. In this study, the shoot primordium method was applied to store the genetic diversity of Lilium japonicum. Apical domes of shoot tips approximately 1 mm long were harvested from shoots that appeared from the sterilized bulb scales which were used for starting material for the culture and placed in test tubes (30mmx200mm, 25ml) containing Murashige and Skoog media (MS) 13) supplemented with auxin [1-naphthaleneacetic acid (NAA)] at concentrations of 0, 0.02, 0.2, 2.0 and 4.0mg/l and cytokinin [6-benzylaminopurine (BAP)] at concentrations of 0, 0.2 and 2.0mg/l at pH 5.8 for shoot primordia induction. The cultures were incubated at 22C under 10,000 lux illumination by mercury lamp for a whole day and shaken at 2 cycles/minute on a rotary culture equipment (1m diameter). They were subcultured at two week intervals. Masses of shoot primordia of Lilium japonicum were induced and proliferated in MS liquid media supplemented with NAA at concentrations of 0.02, 0.2, 2.0 or 4.0mg/ l and BAP at concentrations of 0.2 or 2.0mg/l three months after the beginning of primary culture (Table 1). Thus, the best growth and shape of shoot primordia of this species were exhibited in MS liquid media containing 2.0mg/l NAA and 0.2mg/l BAP or containing 4.0mg/l NAA and 2.0mg/l BAP (Table 1, Fig. 1A, B).