Chromosome Numbers and Ploidy Levels of Chinese Curcuma Species

in HortScience

Curcuma L. is an economically important genus in the family Zingiberaceae. Many species are grown as medicinal, culinary, and ornamental crops. As a result of their high morphological diversity and small chromosome sizes, chromosome numbers and species relationships of Chinese Curcumas remain debated. This study examined chromosome numbers of 15 populations representing 11 species of Curcuma from China. Results showed that only Curcuma flaviflora S. Q. Tong was diploid with 2n = 2x = 42 and C. kwangsiensis S. G. Lee & C. F. Liang was tetraploid with 2n = 4x = 84. The other species were triploid (2n = 3x = 63). The study indicated that the basic chromosome number of Curcuma from China could be x = 21. The diploid C. flaviflora produced viable seeds, which was the main means for propagation. The tetraploid and the triploids produced no seeds and relied on rhizomes for propagation. Chromosome sizes of all species were small, ranging from 0.5 to 2.1 μm, which prevented karyotype analysis. The fact that nine of 11 species studied were triploid indicates that triploidy may have some type of competitive advantage over the diploid and tetraploid. In addition, the triploids are popular commercially because of abundant rhizome production and this may contribute to their wide distributions.

Abstract

Curcuma L. is an economically important genus in the family Zingiberaceae. Many species are grown as medicinal, culinary, and ornamental crops. As a result of their high morphological diversity and small chromosome sizes, chromosome numbers and species relationships of Chinese Curcumas remain debated. This study examined chromosome numbers of 15 populations representing 11 species of Curcuma from China. Results showed that only Curcuma flaviflora S. Q. Tong was diploid with 2n = 2x = 42 and C. kwangsiensis S. G. Lee & C. F. Liang was tetraploid with 2n = 4x = 84. The other species were triploid (2n = 3x = 63). The study indicated that the basic chromosome number of Curcuma from China could be x = 21. The diploid C. flaviflora produced viable seeds, which was the main means for propagation. The tetraploid and the triploids produced no seeds and relied on rhizomes for propagation. Chromosome sizes of all species were small, ranging from 0.5 to 2.1 μm, which prevented karyotype analysis. The fact that nine of 11 species studied were triploid indicates that triploidy may have some type of competitive advantage over the diploid and tetraploid. In addition, the triploids are popular commercially because of abundant rhizome production and this may contribute to their wide distributions.

The genus Curcuma L. is a member of the family Zingiberaceae consisting of ≈80 species distributed mainly in South and Southeast Asia with outposts in India and southern China (Larsen et al., 1998). Some species are also found in Australia and the South Pacific (Wu and Larsen, 2000). Curcuma species are important specialty crops produced as medicinal, culinary, and ornamental plants (Chen and Xia, 2011). For example, C. aromatica Salisb., C. kwangsiensis S. G. Lee & C. F. Liang, C. phaeocaulis Valeton, C. sichuanensis X. X. Chen, C. wenyujin Y. H. Chen & C. Ling, and C. zanthorrhiza Roxb. (Liu, 1985) are widely used as medicinal plants. C. long L. produces highly aromatic and antiseptic turmeric, which has been extensively used as a spice, a beauty care agent, and traditional medicine (Aggarwal et al., 2007). Some others are used as ornamental plants such as C. elata Roxb., which is popular as cut flowers (Škornicková et al., 2007).

Despite their economic importance, disagreements on chromosome numbers of Curcuma species still exists (Table 1). Somatic chromosome numbers of 2n = 40, 42, and 77 were documented for C. oligantha Trim. by Saensouk and Chantaranothai (2003), Eksomtramage et al. (2002), and Leong-Škorničková et al. (2007), respectively. The chromosome number of C. aromatica was reported to be 2n = 42 (Leong-Škorničková et al., 2007; Raghavan and Venkatsubban, 1943), 63 (Islam, 2004; Leong-Škorničková et al., 2007; Liu, 1985; Ramachandran, 1961), or 86 (Ramachandran, 1961). Variation also occurs in reports of the basic chromosome number, including x = 21 (Raghavan and Venkatsubban, 1943); x = 7 or 8 (Sato, 1960); and x = 7 (Leong-Škorničková et al., 2007). Thus far, x = 21 appears to be considered acceptable as the basic chromosome number (Eksomtramage et al., 2002; Islam, 2004; Joseph et al., 1999; Ramachandran, 1961, 1969). The ambiguity in chromosome numbers may be partially explained by potential misidentification of species. Curcuma species identification has been difficult as a result of the lack of a comprehensive taxonomic revision and the existence of numerous closely related species (Chen and Xia, 2011). So far, the number of species has been estimated at 50 (Wu and Larsen, 2000), 80 (Larsen et al., 1998), and 120 (Leong-Škorničková et al., 2007). High intra- and interpopulation variation also likely contributes to confusion in identification of Curcuma species (Chen and Xia, 2011).

Table 1.

A summary of somatic chromosome numbers studied in Curcuma species.

Table 1.

There are ≈12 Curcuma species in China, mainly distributed in Yunnan, Guangxi, Sichuan, Guangdong, and Zhejiang provinces (Wu and Larsen, 2000). Somatic chromosome numbers of some Chinese Curcumas have been examined. Liu (1985) reported 2n = 63 for C. aromatica, C. longa L., C. phaeocaulis, and C. yunnanensis N. Liu & C. Senjen and 2n = 64 for C. kwangsiensis. In contrast, Chen et al. (1988) stated 2n = 84 for C. kwangsiensis. Chromosome numbers of other Chinese Curcumas have not been documented such as C. flaviflora S. Q. Tong and C. sichuanensis.

Chromosome numbers and ploidy levels are important information for plant taxonomy, genetics, and evolution as well as essential for plant conservation and use (Bennett and Leitch, 2005). Cytogenetic characters have also been considered critical for defining intrageneric groups in Curcuma (Islam, 2004; Joseph et al., 1999; Leong-Škorničková et al., 2007; Ramachandran, 1961). To pursue a better understanding of Chinese Curcuma species, this study was intended to examine chromosome numbers of available Curcuma species in China, their ploidy levels, and their implications in distribution.

Materials and Methods

For this study, nine populations across eight species were collected from the wild in southwestern China. Six individuals of four species from Guangxi Botanical Garden of Medicinal Plants and South China Botanical Garden, Chinese Academy of Sciences, were examined (Table 2). Collected plants were grown outdoors in the ginger garden or were cultivated in containers in a greenhouse at the South China Botanical Garden. The plant specimens were identified with the help of Dr. De-Lin Wu at the South China Botanical Garden. Herbarium acronyms followed Index Herbariorum (Holmgren et al., 1990). Taxonomic names were in accordance with the classifications of Wu and Larsen (2000).

Table 2.

Chromosome numbers and vouchers of 11 species of Curcuma from China.

Table 2.

Actively growing root tips of the collected plants were taken and pretreated with 2.0 mm 8-hydroxyquinoline for 6 h, fixed in Carnoy I (three parts absolute ethanol and one part glacial acetic acid), macerated in 1 M HCl at 60 °C for 5 min, and stained with Carbol fuchsin. The root tips were squashed with forceps in a drop of 45% acetic acid on a glass slide, covered with a cover glass, and squashed again. Cover glasses were removed by freezing glass slides in liquid nitrogen. Slides were dried at room temperature and passed through three solutions: absolute ethanol; 1:1 ethyl ethanol:xylene; and xylene. Slides were sealed with permount mounting medium. Metaphase chromosomes were observed and photographs were taken under the OLYMPUS BX41 microscope (Olympus, Tokyo, Japan). Eight individual root tips from different plants of each Curcuma collection were studied. Chromosome numbers of a minimum of 20 cells of each collection were counted at the well-spread metaphase stage. Ploidy levels were determined based on x = 21 (Eksomtramage et al., 2002; Joseph et al., 1999; Ramachandran, 1961, 1969). All microscope slides were deposited in the South China Botanical Garden.

Reproductive strategies of different species were closely monitored and recorded, including seed propagation and asexual rhizome propagation. Seeds, if present, were collected and sowed. Rhizomes were also used for propagation.

Results

Chromosome numbers of 11 Curcuma species were determined (Table 2). Among them, C. amarissima Roscoe, C. aromatica, C. gulinqingensis N. H. Xia & J. Chen, C. elata, C. sichuanensis, C. phaeocaulis, C. rubrobracteata, C. wenyujin, and C. zanthorrhiza had the chromosome number 2n = 63 (Figs. 1A–H, 2J, and 2O), whereas C. kwangsiensis had 2n = 84 (Fig. 2K–N), and C. flaviflora had 2n = 42 (Fig. 2I). All plants examined were polyploids except for C. flaviflora, which was a diploid. The ploidy levels of all species fitted well with the primary number x = 21(Figs. 1 and 2).

Fig. 1.
Fig. 1.

Somatic metaphase chromosomes of Curcuma species. (A) Curcuma rubrobrateata (2n = 63); (B) C. aromatica (2n = 63); (C) C. sichuanensis (2n = 63); (D) C. elata (2n = 63); (E) C. wenyujin (2n = 63); and (F) C. phaeocaulis (2n = 63). Scale bar = 10 μm.

Citation: HortScience horts 48, 5; 10.21273/HORTSCI.48.5.525

Fig. 2.
Fig. 2.

Somatic metaphase chromosomes of Curcuma species. (G) Curcuma gulinqingensis (2n = 63); (H) C. zanthorrhiza (2n = 63); (I) C. flaviflora (2n = 42); (J) C. amarissima (2n = 63); (K) C. kwangsiensis 1 (2n = 84); (L) C. kwangsiensis 2 (2n = 84); (M) C. kwangsiensis 3 (2n = 84); (N) C. kwangsiensis 4 (2n = 84); and (O) C. wenyujin (2n = 63). Scale bar = 10 μm.

Citation: HortScience horts 48, 5; 10.21273/HORTSCI.48.5.525

All chromosomes of the studied Curcuma were very small, ranging from 0.5 to 2.1 μm in length; C. rubrobracteata (Fig. 1A) and C. zanthorrhiza (Fig. 2H) had the smallest chromosomes (0.5–1.3 μm). As a result of the small chromosome sizes, no clear morphological differences were observed. Centromeres were difficult to detect; thus, karyotype analysis was not performed.

Our study showed that C. flaviflora produced viable seeds and rhizomes, but seeds were the main method for propagation (Table 2; Fig. 3A–C). Tetraploid C. kwangsiensis appeared not able to produce seeds in the South China Botanical Garden, so it was propagated through rhizomes (Table 2; Fig. 3F–G) as were all of the triploids (Table 2; Fig. 3D–E).

Fig. 3.
Fig. 3.

Reproductive strategies of Curcuma species. (A–C) Spikes, seeds, and rhizomes of diploid species Curcuma flaviflora; (D–E) spikes and rhizomes of triploid species C. elata; and (F–G) spikes and rhizomes of tetraploid species C. kwangsiensis.

Citation: HortScience horts 48, 5; 10.21273/HORTSCI.48.5.525

The only diploid in the study, C. flaviflora, was found only in Yunnan province where it inhabits mountains or mountain margins. The majority of the triploids occurred in Southern China with the center of distribution in the Yunnan province. The tetraploids also had a wide geographical distribution, occurring in Yunnan, Guangxi, and Guangdong provinces (Table 2; Fig. 4).

Fig. 4.
Fig. 4.

The distribution of studied Curcuma in Guangdong, Guangxi, and Yunnan provinces, China. ★, ●, and ▲ represent the triploid, tetraploid, and diploid species, respectively.

Citation: HortScience horts 48, 5; 10.21273/HORTSCI.48.5.525

Discussion

This is the first report of chromosome counts for C. sichuanensis (Fig. 1C) and C. flaviflora (Fig. 2I). Before this study, no diploid chromosome counts have been reported for Chinese Curcumas (Chen and Chen, 1984; Chen et al., 1988; Liu, 1985). C. flaviflora produced viable seeds, which was the main method for propagation. The identification of C. flaviflora as a diploid species provided additional evidence supporting the claim that the basic chromosome number of Curcuma was 21. Sharma and Bhattacharya (1958) first reported x = 16 in the genus Curcuma. Sato (1960) proposed x = 7 and x = 8, and recently Leong-Škornicková et al. (2007) suggested that x = 7 should be considered a primary basic chromosome number for at least the majority of Indian Curcuma species (subgenus Curcuma). This proposal was based on the chromosome count of 2n = 77 in C. oligantha Trim by flow cytometry. On the other hand, the basic number x = 21 appeared too high to be the primary one. Raghavan and Venkatsubban (1943), Ramachandran (1961), and Venkatasubban (1946) believed that this basic number might have been derived either by dibasic amphidiploidy (by combination of lower basic numbers of nine and 12 found in some genera in the family) or by secondary polyploidy. Nevertheless, the chromosome numbers of all 11 species in the present study can be explained by the basic chromosome number x = 21.

The present study, in conjunction with an earlier investigation (Joseph et al., 1999), has demonstrated small and similar chromosome sizes in the genus Curcuma. Similar chromosome size was also prevalent in other genera characterized by x = 21 such as Caulokaempferia yunnanensis (Gagnep.) Smith and Hitchenia (Chen et al., 1988; Leong-Škornicková et al., 2007; Ramachandran, 1969). The chromosomes of Curcuma were as small as those of other genera of the subfamily Zingiberoideae such as Globba, Hedychium and Cornukaempferia (Eksomtramage et al., 2002; Ramachandran, 1969). Stebbins (1966) pointed out that variation in chromosome size was correlated with climatic adaptation: the genera having smaller chromosomes were predominantly tropical or subtropical, whereas the large chromosomes were found exclusively in temperate climates. The genus Curcuma, one of many genera of the Zingiberaceae mainly occurring in tropical and subtropical habitats (Islam, 2004), may bear smaller chromosomes for adaptation to its habitat.

The triploids and tetraploids were located in areas either rich in water or influenced by human activities. Triploids probably originated by a fusion of reduced and unreduced gametes of diploids within or between species (Leong-Škornicková et al., 2007; Rieseberg and Willis, 2007). Given the continuum of traits in polyploid taxa, hybridization may have also played an important role (Rehse, 2005). Nevertheless, the fact that the majority of species in China were triploid indicates that triploids may have some type of competitive advantage over diploids and tetraploids. The triploids are sterile and do not require seed production, their abundant rhizomes (Fig. 3D–E) make them popular in production, and subsequent selection may contribute to their wide distribution.

Literature Cited

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Contributor Notes

This research was supported by National Natural Science Foundation of China (Grant no. 31170185 and no. 31200161).We are grateful to Drs. Qin-er Yang and Yuan Qiong for their technical assistance in conducting this research. We also thank Mr. Yushi Ye for his help during field work.

To whom reprint requests should be addressed; e-mail chenjuan101@scib.ac.cn; nhxia@scib.ac.cn.

  • View in gallery

    Somatic metaphase chromosomes of Curcuma species. (A) Curcuma rubrobrateata (2n = 63); (B) C. aromatica (2n = 63); (C) C. sichuanensis (2n = 63); (D) C. elata (2n = 63); (E) C. wenyujin (2n = 63); and (F) C. phaeocaulis (2n = 63). Scale bar = 10 μm.

  • View in gallery

    Somatic metaphase chromosomes of Curcuma species. (G) Curcuma gulinqingensis (2n = 63); (H) C. zanthorrhiza (2n = 63); (I) C. flaviflora (2n = 42); (J) C. amarissima (2n = 63); (K) C. kwangsiensis 1 (2n = 84); (L) C. kwangsiensis 2 (2n = 84); (M) C. kwangsiensis 3 (2n = 84); (N) C. kwangsiensis 4 (2n = 84); and (O) C. wenyujin (2n = 63). Scale bar = 10 μm.

  • View in gallery

    Reproductive strategies of Curcuma species. (A–C) Spikes, seeds, and rhizomes of diploid species Curcuma flaviflora; (D–E) spikes and rhizomes of triploid species C. elata; and (F–G) spikes and rhizomes of tetraploid species C. kwangsiensis.

  • View in gallery

    The distribution of studied Curcuma in Guangdong, Guangxi, and Yunnan provinces, China. ★, ●, and ▲ represent the triploid, tetraploid, and diploid species, respectively.

  • AggarwalB.B.SurhY.ShishodiaS.2007The molecular targets and therapeutic uses of curcumin in health and disease. Springer Science + Business Media LLC New York NY

  • BennettM.D.LeitchI.J.2005Nuclear DNA amounts in angiosperms: Progress, problems, and prospectsAnn. Bot. (Lond.)954590

  • ChenJ.XiaN.H.2010Chromosome cytology, leaf epidermal morphology and palynology of Curcuma rubrobracteata (Zingiberaceae)Nord. J. Bot.28212215

    • Search Google Scholar
    • Export Citation
  • ChenJ.XiaN.H.2011Pollen morphology of Chinese Curcuma L. and Boesenbergia Kuntz (Zingiberaceae): Taxonomic implicationsFlora206458467

  • ChenZ.Y.ChenS.J.1984A report on chromosome numbers of Chinese Zingiberaceae (2)Guihaia41318[in Chinese with English summary]

  • ChenZ.Y.ChenS.J.HuangX.X.HuangS.P.1988A report on chromosome numbers on Chinese Zingiberaceae (5)Guihaia8143147[in Chinese with English summary]

    • Search Google Scholar
    • Export Citation
  • EksomtramageL.SirirugsaP.JivanitP.MaknoiC.2002Chromosome counts of some Zingiberaceae species from ThailandSongklanakarin. J. Sci. Technol.24311319

    • Search Google Scholar
    • Export Citation
  • Holmgren P.K. N.H. Holmgren and L.C. Barnett (eds.). 1990. Index herbariorum. Part I The herbaria of the world. 8th Ed. New York Botanic Garden Bronx NY

  • HuangJ.ZhaoY.X.LiuX.H.WangJ.2010Chromosome karyotype analysis of Curcuma kwangsiensisJ. Anhui Agr. Sci.381553815539[in Chinese with English summary]

    • Search Google Scholar
    • Export Citation
  • IslamM.A.2004Genetic diversity of the genus Curcuma in Bangladesh and further biotechnological approaches for in vitro regeneration and long-term conservation of C. longa germplasm. PhD thesis University of Hannover Hannover Germany

  • JosephR.JosephT.JosephJ.1999Karyomorphological studies in the genus Curcuma LinnCytologia (Tokyo)33313317

  • LarsenK.LockJ.M.MaasH.MaasP.J.M.1998Zingiberaceae p. 474–495. In: Kubitzki K. (ed.). The families and genera of vascular plants. Springer-Verlag Berlin Germany

  • Leong-ŠkorničkováJ.ŠídaO.JarolímováV.SabuM.FérT.TrávníčekP.SudaJ.2007Chromosome numbers and genome size variation in Indian species of Curcuma (Zingiberaceae)Ann. Bot. (Lond.)100505526

    • Search Google Scholar
    • Export Citation
  • LiuN.1985The taxonomic study of Curcuma L. from China. MSc thesis South China Botanical Garden Guangzhou China [in Chinese]

  • RaghavanT.S.VenkatsubbanK.R.1943Cytological studies in the family Zingiberaceae with special reference to chromosome number and cyto-taxonomyProc. Indian Acad. Sci. B17118132

    • Search Google Scholar
    • Export Citation
  • RamachandranK.1961Chromosome numbers in the genus CurcumaLinn. Curr. Sci.30194196

  • RamachandranK.1969Chromosome numbers in ZingiberaceaeCytologia (Tokyo)34213221

  • RehseT.M.2005Phylogenetics and classification of Curcuma (Zingiberaceae): Polyploidy reticulation and species complexes. MSc thesis Duke University Durham NC

  • RiesebergL.H.WillisJ.H.2007Plant speciationScience317910914

  • SaensoukS.ChantaranothaiP.2003The family Zingiberaceae in Phu Phan National Park. Proc. of the 3rd Symposium on the Family Zingiberaceae. Applied Taxonomic Research Centre Khon Kean University Khon Kaen Thailand. p. 16–25

  • SatoD.1960The karyotype analysis in Zingiberales with special reference to the protokaryotype and stable karyotypeSci. Papers Coll. Gen. Educ. Univ. Tokyo10225243

    • Search Google Scholar
    • Export Citation
  • SharmaA.K.BhattacharyaN.K.1958Cytology of several members of Zingiberaceae and a study of the inconstancy of their chromosome complementsCellule59299346

    • Search Google Scholar
    • Export Citation
  • ŠkornickováJ.RehseT.SabuM.2007Other economically important Curcuma species p. 451–467. In: Ravindra P.N. K.N. Babu and K. Sivaraman (eds.). Tumeric: The genus Curcuma (Medicinal and Aromatic Plants—Industrial Profiles). Vol. 45. CRC Press Taylor & Francis Group Boca Raton FL

  • SoontornchainaksaengP.Anamthawat-JónssonK.2011Ribosomal FISH mapping reveals hybridity in phytoestrogen producing Curcuma species from ThailandPlant Syst. Evol.2924149

    • Search Google Scholar
    • Export Citation
  • StebbinsG.L.1966Chromosomal variation and evolutionScience15214631467

  • SugiuraT.1936Studies on the chromosome number of higher plantsCytologia (Tokyo)7544595

  • VenkatasubbanK.R.1946A preliminary survey of chromosome numbers in Scitamineae of Bentham & HookerProc. Indian Acad. Sci. B23281300

  • WuD.L.LarsenK.2000Zingiberiaceae p. 322–377. In: Wu Z.Y. P. Raven and D.Y. Hong (eds.). Flora of China. Vol. 24. Science Press Beijing China and Missouri Botanical Garden Press St. Louis MO

  • YeX.B.ChenJ.LiuN.2008Curcuma nankunshanensis (Zingiberaceae), a new species from ChinaJ. Trop. Subtrop. Bot.16472476

  • ZhaoL.J.TangF.F.LiuL.K.2011Karyotype analysis of Curcuma zedoaria (Christm.) roscoe by using CPD staining and FISH with 45S rDNAChin. Agri. Sci. Bull.27190194[in Chinese with English summary]

    • Search Google Scholar
    • Export Citation
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