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).
A summary of somatic chromosome numbers studied in Curcuma species.
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.
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