in Ginger (Zingiber officinale

J. Japan. Soc. Hort. Sci. 58(3) ; 649-656. 1989. Effects of Day Length on Flowering and in Ginger (Zingiber officinale Rhizome Swelling Roscoe) Shlnlchl ADANIYA1, MOrlyukl SHODA1 and Kunlnlltsu 1 Faculty of Agriculture, University of the Ryukyus, Nishihara, 2 Faculty of Agriculture, Kyusyu University, Fukuoka 812 FUJIEDA2 Okinawa 903-01 Summary Photoperiodic treatments were carried out with three Japanese cultivars (`Kintoki', `Sanshu' and `Oshoga') of ginger (Zingiber officinale Roscoe). As day length was increased from 10 h to 16 h, the vegetative growth of the plants was enhanced, whereas it was inhibited and rhizome swelling was promoted as the day length was decreased from 16 h to 10 h. Further increase in day length from 16 h to 19 h did not give any rhizome swelling, and resulted in the lowering of the growth increment. The cultivar `Sanshu' was most sensitive to photoperiod for rhizome swelling, but `Oshoga' was relatively insensitive. In `Sanshu' and `Oshoga', many flower stalks bolted under the day length of 13 h and 16 h, but they emerged slightly or not at all under the day length of 10 h, ND (decreasing natural daylength) and 19 h. The photoperiodic response to flowering of `Kintoki' was not very clear. Introduction Little is still known about factors affecting the flowering and rhizome swelling of ginger, although factors affecting the yield of the plant such as nutrition, temperature and moisture of soil, planting space, size of seed pieces and planting and harvesting times have been well investigated(1, 4, 8, 9,12,15). On the other hand, the cross breeding of ginger is difficult because it rarely sets seeds. However, there are some reports(5, 7,11,13) suggesting the possibility of setting. As the first step to activate the development of ginger breeding, it is necessary to clarify the environmental factors promoting flowering and swelling of rhizomes. In this paper, effects of photoperiod on flowering induction and rhizome swelling in ginger are described. Materials and Methods The ginger cultivars in Japan are classified into three groups(10) : type 1, small-sized group with many tillers and small rhizome knobs ; type 2, medium-sized group with inter- Received for publication October 28, 1988 mediate number of tillers and medium-sized rhizome knobs ; and type 3, large-sized group with fewer tiller plant height and larger rhizome knobs. On May 5, 1986, the rhizomes of `Kintoki' (type 1), `Sanshu' (type 2) and `Oshoga' (type 3) were trimmed into pieces of about 60, 80 and 100 g, respectively, and were preplanted in a greenhouse at the University of the Ryukyus, Okinawa Island (26 13' N Latitude). After incubation for one month, shoots with one leaf and roots were carefully excised from each rhizome, and were planted in a mixture of manure and soil (1: 3) in containers. Twenty plants were used for each treatment. The plants in the greenhouse were shaded with black cheesecloth with 500 light penetration during July to September. Compound fertilizer (OK-F 1) diluted with 700 fold of water was applied at 4-day intervals. Average daily maximum and minimum temperatures in the greenhouse during the experiment were 34.6 ±0. 5 C and 24.1±0. 4 C, respectively. The photoperiodic treatment was conducted with five treatments of day length :10 h (covered with opaque polyethylene films), 13 h (covered with the films until August 16, and the natural 649

650 S. ADANIYA, M. SHODA AND K. FUJIEDA day length (ND) supplemented with candescent light afterward), 16 and 19 h (ND supplemented with candescent light during the experiments), and ND (decreasing day length from 13.40 h on June 29 to 10. 41 h on November 26). The light intensity by 75 watt tungsten lamps was ca. 1, 8x10-3 cal cm-2 min-1 at the top of the plants. The treatment started on June 29 and the plants were lifted on November 26. Plant height, number of tillers per plant, and the percentage of flag leaves formed per plant were recorded at two-week intervals. The weights of whole plants, roots and rhizomes per plant, number of primary roots per plant, and the percentage of swollen primary roots formed per plant were recorded all at harvest. The flag leaf was defined when no more new leaves emerged thereafter. The swollen primary root was determined when the cross sectional diameter at the basal part of the primary root was more than three times as large as that of the standard one. Results 1. Effect of photoperiod on shoot growth Flag leaves were formed in almost all the shoots tillered under 10 h and ND in the three cultivars, and under 13 h in `Sanshu' ; but they were scarce in the other treatments (Fig. 1). They were always formed earlier under 10 h day length than under ND in all the cultivars, and `Sanshuf' formed them earliest of all. Cessation of the increase in plant height occurred earliest under 10 h day length in all the cultivars, whereas all the cultivars under the day length of 13 h, 16 h and 19 h, except `Sanshu' under 13 h, continuously increased their plant height until harvest day (Fig. 2). In `Kintoki' and `Sanshu', the striking cessation of tillering was observed only under 10 h and ND, under which cessation began 90 days after the beginning of the treatments; the number of tillers under 10 h was always less than that under ND (Fig. 3). Under the day-length of 13 h, 16 h and 19 h, the number of tillers increased linearly until harvest day. In `Oshoga', on the other hand, no significant difference in the number was observed in any treatment. In `Kintoki' and `Sanshu', the weights of whole plants and of the shoots per plant decreased as the day length was decreased from 16h to 10 h (Table 1). In `Oshoga', the weights were also lowest under 10 h, but there was no significant difference in the weights between the other treatments. In `Sanshu' and `Oshoga', the diameter at the base of the shoot increased as the day length was extended from 10 h to 16 h, and it decreased under 19 h ; but in `Kintoki', it did not follow the daylength extension. 2. Effect of photoperiod on the growth of underground parts In `Sanshu' and `Oshoga', the number of rhizome knobs per plant increased with daylength extension from 10 to 13 h or 16 h, and Fig. 1. Effect of photoperiod on flag leaf formation. -~ : 10 h, Q-0 : 13h, o-p : 16h, 19h and v-y : natural day length.

EFFECTS OF DAY LENGTH ON FLOWERING AND RHIZOME SWELLING IN GINGER 651 Fig. 2. Effect of photoperiod on plant height. Symbols are as in Fig. 1. Fig. 3. Effect of photoperiod on the tillering of shoots. Symbols are as in Fig. 1. Table 1. Effect of photoperiod on the weight of a whole plant and the weight and diameter of shoots.

652 S. ADANIYA, M. SHODA AND K. FUJIEDA Fig. 4. Effect of photoperiod on the growth of underground parts of A: loh, B: natural day length, C : 13h, D : 16h and E : 19h. Arrows "a" indicate swollen primary roots, "b" sprouting shoots. `Sansyu'. Table 2. Effect of photoperiod on the growth of underground parts.

EFFECTS OF DAY LENGTH ON FLOWERING AND RHIZOME SWELLING IN GINGER 653 Table 3. Effect of photoperiod on the bolting of flower stalks. the number decreased as the day length was further extended from 13 h or 16 h to 19 h ; whereas, in `Kintoki', no difference in the number was observed between the treatments (Table 2). In `Kintoki', the maximum and minimum rhizome weights per plant were obtained under 16 h and 10 h, respectively, and there was no significant difference in the weight between the treatments of ND, 13 h, 16 h and 19 h. Rhizome weights in `Sanshu' and `Oshoga' increased with the day-length extension from 10 h to 16 h and from 10 h to 13 h, respectively. The photoperiodic response of rhizome knob weight was similar to that of rhizome weight, except that the rhizome knob weight did not significantly decrease when the day length changed from 16 h to 19 h. In the three cultivars, the rhizomes formed under 10 h and ND had roundish knobs, while those under 16 h and 19 h had slender knobs from which some new shoots were still sprouting on harvest day (Fig. 4). In `Kintoki' and `Sanshu', the number of primary roots increased as the day length was extended from 10 h to 16 h, and they decreased under 19 h. Their color changed gradually from brown into white with day-length extension. Furthermore, as shown in Fig. 4, their whitish rootlets also increased in number with day-length extension. In `Oshoga', the photoperiod did not significantly affect the number of primary roots in the four treatments, except that the number was significantly low under 10 h day length. The primary roots swelled under 10 h, ND and 13 h in `Kintoki' and `Sanshu' ; and under 10 h and ND in `Oshoga' (Table 2, Fig. 4). In `Kintoki', the percentage of swollen primary roots formed per plant was highest under 10 h, and it was higher under 10 h and ND than under 13 h. In `Sanshu', the percentage was also higher under 10 h and ND than under 13 h. In `Oshoga', the percentage of swollen primary roots, which were formed only under 10 h and ND, was lower than that of the other two cultivars under the same day lengths. 3. Effect of photoperiod on flowering As Table 3 shows, no flower stalks bolted under 10 h day length in `Kintoki' and `Sanshu', and under 10 h, ND and 19 h in `Oshoga'. In `Kintoki', although the flower stalk bolting was delayed as day length was extended from ND to 19 h, the photoperiodic effect on the total number of flower stalks was not clear. In `Sanshu', flower stalks emerged 90 days after the beginning of the treatments under

654 S. ADANIYA, M. SHODA AND K. FUJIEDA Fig. 5. A the day length of ND, 13 h and 16 h, and the number of flower stalks emerged by this day was largest under 13 h among the three photoperiods, but the number of flower stalks under 13 h did not markedly increase thereafter. However, the number under 16 h increased rapidly from 105 days after the beginning of the treatments and was the highest among the treatments. In `Oshoga', flower stalks emerged under 13 h and 16 h in 120 days after the beginning of treatments, and their numbers increased steadily thereafter. Figure 5 shows that under 16 h day length, spike size was smallest in `Kintoki', and largest in `Oshoga'. Spikes of ginger formed under 16 h day length. `Kintoki', B: `Sanshu' and C: `Oshoga'. Discussion In the three cultivars, as day length was decreased from 16 h to 10 h, vegetative growth in the shoots and underground parts was inhibited, and the rhizome knobs became more roundish and smaller. As the day length was increased to 16 h, the plants grew more vigorously and their rhizome knobs, from which new shoots were still sprouting on the harvest day, became slenderer and larger. When the day length was further extended to 19 h, the growth increment of the shoots and underground parts was lowered to an extent similar to that under ND or 13 h. However, the morphology of the plants under 19 h differed apparently from that under ND or 13 h ; no plants under 19 h formed any swollen roots, and they formed a few flag leaves and the slender knobs from which new shoots were still sprouting on harvest day. These facts suggest that the vegetative growth of ginger was promoted under relatively long day length and rhizome swelling was accelerated under relatively short day length. In `Sanshu', flowering occurred independently of the day-length treatments, except for 10 h. Under 13 h day length, however, the bolting of flower stalks and development of spikes were promoted at the early time of flowering, and the number of flower stalks barely increased thereafter. On the other hand, under 16 h day length only one flower stalk bolted at the early time of flowering, and then the number of flower stalks increased rapidly and continuously up to the harvest day. Under 19 h day length the bolting of flower stalks was further retarded, and four flower stalks bolted just on harvest day. The above results suggest that relatively short day length accelerated the progression of the reproductive growth, while relatively long day length decelerated it. For example, under ND and 13 h, the bolting or the spikes development, or both, were promoted at the early time of flowering, but the number of flower stalks did not increase thereafter. This is most likely due to rapid progress of the growth toward the reproductive phase and to the subsequent rapid degradation of plant activity. On the other hand, the linear increase in the number of flower stalks under 16 h day length can be ascribed to sufficient foliage for flowering being ensured by the vigorous growth and the reproductive stage being maintained for long period by the gradual progression toward maturity. In addition, Sivan(12) and Whiley(14) reported that the fibre content in the rhizome of ginger increased rapidly during flowering time, and the net assimilation rate decreased during the same time. Probably, the plants under 16 h day length accumulate fibre content very slowly, while those under the day length of 10 h, ND and 13 h accumulate it rapidly during the flowering time. Therefore, ginger possibly flowers under any day-length conditions, except for extremely short or long day length, when the plant has reached a certain growth stage. Thus, ginger

EFFECTS OF DAY LENGTH ON FLOW ERIN G AND RHIZOME SWELLING IN GINGER 655 must be a quantitative short-day plant for flowering and rhizome knob swelling. Such photoperiodic response in ginger was very similar to that in Z. mioga Roscoe(2) and the dahlia(6). Our results suggest that ginger has a certain intraspecific variation on photoperiodic response : `Sanshu' responded most sensitively to photopeiod for the flowering and rhizome knob swelling; `Kintoki' was more sensitive to photoperiod for rhizome knob swelling than `Oshoga'. Such a photoperiodic difference among the cultivars may be related to their traditional classification and geographical distribution in Japan ; `Kintoki' and `Sanshu' are classified as early cultivars and adapted over the northern part (mainly in Kanto district), and `Oshoga' is classified as a late cultivar and adapted over southern part (from Okinawa to Shikoku district). Ginger rarely flowers in temperate regions, but in Japan, it flowers when grown in a heated greenhouse during autumn (10). Moreover, ginger flowers commonly in subtropical and near subtropical regions such as Okinawa Island, Kwangtung(7), Queensland(14), Jamaica(7) and Fiji(12) ; but in this experiment the remarkable inhibition of bolting under ND must be due to trimming the plant materials into small-sized ones. On the other hand, the ginger plant very rarely flowers in tropical region such as Malaya (3). These facts also suggest that it is difficult for ginger to flower under short-day conditions such as around 12 h. Our results show a possibility to obtain ginger flowers by day-length treatment even with difficult-to-flower cultivars and even in difficult-to-flower regions. Further studies on other factors such as temperature which may affect the flowering are needed. Acknowledgement We thank Dr. Takashi Aoba, ex-prof. of Chiba University, for his helpful suggestions, and also thank Dr. Michio Shiroma, Prof. of University of the Ryukyu and Dr. Hiroshi Okubo, Assistant Prof. of Kyushu University, for reading and correcting the manuscript. Literature Cited 1. ACLAN, F. and E.G. QUISUMBING. 1976. Fertilizer requirement, mulch and light attenuation on the yield and quality of ginger. Phil. Agr. 60: 183-191. 2. ADANIYA, S. 1985. Studies on the breeding of Zingiber mioga Roscoe. 1. Effect of photoperiod on the rhizome and tuberous root formation, and the flower bud initiation and development. Abstr. Japan. Soc. Hort. Sci. Autumn Meet. p. 180-181. (In Japanese) 3. BURKILL, I.H. 1935. A dictionary of the economic products of Malay Peninsula. p. 2338-2344. 4. EVANSON, J.P., J.P. BRYANT and C.J. ASHER. 1978. Germination and early growth of ginger (Zingiber officinale Roscoe). 1. Effects of constant and fluctuating soil temperature. Trop. Agr. 55: 1-7. 5. IWASA, S. 1984. Vegetables in tropics. p. 224-254. Yokendo, Tokyo. (In Japanese) 6. KONISHI, K. and K. INABA. 1967. Studies on flowering control of dahlia. VII]. Effect of daylength on dormancy in axillary bud. J. Japan Soc. Hort. Sci. 36: 243-249. (In Japanese with English summary) 7. LAWRENCE, B.M. 1984. Major tropical species, Ginger (Zingiber offacinale Rosc.). Perfumer & Flavorist 9: 1-40. 8. LEE, M.T., C. J. ASHER and A.W. WHILEY. 1981. Nitrogen nutrition of ginger (Zingiber officinale). 1. Effects of nitrogen supply on growth and development. Field Crop Res. 4: 55-68. 9. OGAWA, T., N. MATSUBARA, N. MORI and A. IWANAGA. 1974. On the stabilizing production of seed ginger. Nagasaki Agr. Exp. Sta. Bull. 3-30. (In Japanese) 10. OGAWA, T. 1977. Ginger. p. 1060-1066. In: S. Shimizu (ed), Encyclopedia on vegetable gardening. Yokendo, Tokyo. (In Japanese). 11. RAMACHANDRAN, K. 1982. Polyploidy induced in ginger by colchicine treatment. Current Science 51: 18-19. 12. SIVAN, P. 1979. Growth, Spacing, time of lifting and production of early harvest ginger in Fiji. Fiji Agr. J. 42: 37-43. 13. PILLAI, P.K.T., G. VIJAYAKUMAR and M.C. NAMBIAR. 1987. Flowering behaviour, cytology and pollen germination in ginger (Zingiber offccinale Rosc.). J. Plantation Crop 6: 12-13. 14. WHILEY, A.W. 1980. Growth and fibre development of ginger (Zingiber officinale Rosc.). in south-east Queensland. Aust. J. Exp. Agr. Anim. Husb. 20: 608-612. 15. WHILEY, A.W. 1981. Eflect of plant density on time to first harvest maturity, knob size and yield in two cultivars of ginger (Zingiber

656 S. ADANIYA, M. SHODA AND K. FUJIEDA oicinale Rosc.) growth in southeast Queensland. Trop. Agr. 58: 245-251.