Jpn. J. Trop. Agr. 49(1): 14•\20, 2005 Inflorescence and Flower Initiation and Development in Curcuma alismatifolia Gagnep (Zingiberaceae) Seiichi FUKAI and Waraporn UDOMDEE Horticultural Science, Faculty of Agriculture, Kagawa University, Miki-cho, Kagawa, 761-0795 Japan Abstract Morphological development of inflorescence and floral organs of Curcuma alismatifolia Gagnep (Zingiberaceae), native to northern Thailand, was determined using a scanning electron microscope. Inflorescence of C. alismatifolia was a mixed inflorescence named thyrse; the main axis was indeterminate and secondary axes were determinate. Apex of the main axis produced primary bracts continuously. On the other hand, the apex of each axil produced secondary bracts and terminated in the first flower. The secondary bract subtended the secondary axis that terminated in the second flower. Tertiary and higher order bracts and flowers appeared similarly, leading to the formation of a cincinnus. The flowers underwent a petaloid transformation of the stamen (petaloid staminode), which is one of the characteristics of Zingiberaceae. The flowers consisted of a gamosepalous calyx, three petals, a polliniferous stamen, a labellum developed from two petaloid staminodes, two lateral petaloid staminodes, and a pistil. Ovule primordia had a lobed appendix that developed into a large seed aril. Key Words: aril, cincinnus, petaloid staminode, thyrse flower development may enable to achieve effective Introduction flowering control and cut flower production with The genus Curcuma (Zingiberaceae) consists higher quality. of more than 50 species distributed in tropical Some Zingiberales-order plants undergo a Asia. Some Curcuma species have been used as petaloid transformation of the stamen (petaloid medicinal and aromatic plants. Curcuma species staminode) with considerable morphological have also a great potential as ornamental plants, variation (Kress, 1990; Weberling, 1989). The since they display a wide range of colors and family Zingiberaceae is one of eight families in morphological variations in their inflorescence. Zingiberales. Developmental studies on floral Curcuma alismatifolia Gagnep, native to northern organs in Zingiberales have been conducted for Thailand, was introduced to the world flower Cannaceae (Kirchoff, 1983), Costaceae (Kirchoff, market as a cut flower in the 1990s. Since the 1988), Lowiaceae (Kirchoff and Kunze, 1995), development of efficient propagation of this Marantaceae (Kirchoff, 1983), and Zingiberaceae species through tissue culture (Wannakrairoj, (Kirchoff 1997, 1998). The family Zingiberaceae 1997), a large number of corms with reasonable is sub-divided into four tribes, Hedychieae, price has become available for cut flower Globbeae, Zingibereae, and Alpinae. Each tribe production. Although the growth and flowering differs in floral morphology in terms of composition physiology of this species have been studied of floral organs. The androecia of Hedychieae (Azuma and Takano 1994; Hagiladi et al. 1997b; (the genus Curcuma belongs to this tribe) Krasaechai 1993; Kuehny et al. 2002; Ruamrungsri consists of a pollieniferous stamen, two petaloid et al. 2001; Takano and Azuma 1994), morphological staminodes forming a labellum, two lateral observations of the inflorescence and flower petaloid staminodes free from the labellum, and development in Curcuma have not been reported, an absent stamen (Kress 1990). except for a hand sketch drawn by Poobuapueon The objective of the present study was to et al. (1996). Elucidation of the inflorescence elucidate the morphological development of the and flower development is important for the inflorescence and floral organ of Curcuma alismatifo- analysis of the flowering physiology, because lia using a scanning electron microscope (SEM). better understanding of the inflorescence and Materials amd Methods Received Jun. 30, 2004 Accepted Dec. 18, 2004 Corms of C. alismatifolia 'Sharome Pink' and Fukai et al.: Inflorescence and floral development of Curcuma 15 ' Kimono Pink', derived from clonal propagation, thyrse: the main axis was indeterminate and the were planted in plastic boxes (20 x 60 x 15cm) secondary axes were determinate, cymose. containing a mixture of sandy soil: manure (3:1) Inflorescence with the same structure can be in March. They were grown in a greenhouse observed in Hedichieae species; Hedycium maintained at a minimum temperature of 15•Ž (Krirchof 1997) and Scaphochlamys (Krirchof under natural photoperiods, dug up in Decem- 1998). ber, and stored under dry conditions at room The primary bracts grew upward and covered temperature until next March. New shoots of the thyrse (Figure 1-E). The shoot apex of the ' Sharome Pink' at various developmental stages thyrse produced primary bracts continuously were collected during the period from April to (Figure 1-F) until the late stage of thyrse June in both 2002 and 2003 for morphological development. About 20 primary bracts devel- observations. oped at the flowering time. Primary bracts at Pollen of C. alismatifolia 'Kimono Pink' was lower positions on the thyrse (7.7 •} 0.12 primary mounted on the stigmas of 'Sharome Pink' bracts from the bottom, n=30) remained green because C. alismatifolia is self incompatible and the subsequent 11.5 •} 0.27 (n=30) primary (Fukai unpublised). The stigmas were harvested bracts became thin and displayed a pink color at 1, 2, 3, 5, and 7 days after pollination. referred to as 'coma bract'. Samples were fixed immediately with FAA (formalin: acetic acid: 70% ethanol; 5:5:90). The Development of cincinnus and flower specimens for SEM observation were dissected The secondary inflorescence developed in under a binocular microscope, dehydrated in an the axil of the primary bracts was a cincinnus ethanol-acetone series, dried at the critical point, (scopioid cyme): a cylindrical inflorescence, with coated with Pt, and observed with a SEM (5- axes on different planes, branching alternately 2150; Hitachi, Ltd.). Some other specimens for to one side and the other. fluorescence microscope observation were stained The swollen apex of the axil became rounded with 0.1% aniline blue for 24 h before observation. (Figure 2-A) and terminated in the first flower. The secondary bract appeared below the first Results and Discussion flower of the cincinnus (Figure 2-B). The direction Inflorescence initiation and development of the second bract development varried depending New shoots developed from corms produced on the position on the thyrse (Fig. 2-A and -B). 4 to 5 sheath leaves followed by 3 to 4 green The secondary bract was initiated in the opposite leaves before inflorescence initiation. The vegeta- direction of the raising of the phyllotactic helix tive shoot apex was flat and showed a triangular- in the first primary bract on the thyrse. However, shaped leaf primordium which surrounded more in higher primary bracts, the secondary bract than half of the apex with distichous phyllotaxy tended to be initiated in the direction of the (Figure 1-A). The first sign of inflorescence raising of the phyllotactic helix. The secondary initiation, dome formation (Figure 1-B), occurred bract subtended the secondary axis that produced when the shoot grew to a length of about 10 to a tertiary bract and terminated in the second 15 cm with considerable variation. Inflorescence flower of the cincinnus (Figure 2-C). The tertiary initiation occurred earlier in thicker stems, bract subtended the tertiary axis and the same which emerged from corms with larger storage sequence continued for higher order bracts and roots, as described by Hagiladi et al. (1997a). flowers, leading to the formation of the cincinnus The reproductive shoot apex produced (Figure 3). Cincinni of this genotype produced crescent-shaped leaves (Figure 1-C) (primary about seven to eight flowers. Nevertheless, only bracts) with spiral (2/5) phyllotaxy. An even ratio the first three to four flowers developed and of clockwise and counter-clockwise phyllotactic bloomed at lower positions on the thyrse. The helix was observed in the arrangement of the number of developed flowers in a cincinnus primary bracts. Each primary bract subtended decreased at the upper positions on the thyrse. an axillary bud that developed into a secondary The flower primordia produced three sepal inflorescence, leading to the formation of a primordia sequentially (Fig. 2-C): the first one mixed inflorescence (Figure 1-D). The structure appeared in the farthest corner of the flower of such a mixed inflorescence was referred to as primordia from the second flower, the second 16 Jpn. J. Trop. Agr. 49 (1) 2005 Fig. 1 Inflorescence initiation and development of C. alismatifolia 'Sharome Pink'. A; Vegetative shoot apex. Bar= 200ƒÊm. B; Dome formation and initiation of the first primary bract (arrow). Bar= 200ƒÊm. C; Reproductive shoot apex with crescent-shaped primary bracts. Bar = 200ƒÊm. D; Each bract subtended an axillary bud. Bar = 500ƒÊm. E; Primary bracts grew upward and covered the inflorescence. Bar = 500/ƒÊm. F; Shoot apex (arrow) of thyrse produced primary bracts continuously. Most primary bracts were removed in the picture. Bar =500ƒÊm. Fukai et al.: Inflorescence and floral development of Curcuma 17 Fig. 2 Development of cincinnus and flower of C. alismatifolia 'Sharome Pink'. A; Swollen apex of the axil. Bar = 100 ƒÊm. B; Secondary bract appeared below the first flower. Bar = 100/1 ƒÊm. C; Flower primordia producing sepal primordia. Arrows with numbers indicate the order of sepal primordium initiation.