Regular Article
Karyological Study in Three Thailand Species of Colocasia (Araceae)
2019 年 84 巻 2 号 p. 179-182
詳細
2019 年 84 巻 2 号 p. 179-182
Cytogenetical studies in three Thailand species of genus Colocasia Schott, C. fallex, C. gigantea and C. lihengiae, were reported. The species had the same chromosomes number of 2n=28 and their karyotypes were formulated as 24m+4sm, 20m+6sm+2st (2 sat) and 18m+2sm+8st, respectively. Differences among three species appeared in the number of m, sm and st chromosomes as well as satellite. These karyological data were discussed intra- and inter-specific variation in the Colocasia species.
Araceae is a large family in monocots and is distributed in tropical regions worldwide, consisting of 120 genera with more than 3800 species. Thirty genera with about 210 species of Araceae are reported in Thailand (Boyce et al. 2012). The genus Colocasia Schott (Araceae) is represented by 20 species that are mainly distributed from the subtropical eastern Himalayas throughout subtropical and tropical Asia into the tropical western Pacific, the Polynesian islands, eastern Australia, parts of Africa and Oceania (Boyce and Sookchaloem 2012). In Thailand, four species are growing in humid areas, brook, waterfront, swamp, canal, and marsh. (Boyce and Sookchaloem 2012).
Since the first cytological contribution on C. gigantea by Nakajima (1936) Colocasia species were extensively studied on their chromosome numbers. Karyotypes were reported in eight species (Okada and Hambali 1989, Sreekumari and Mathew 1991, Cao and Long 2003, 2004, 2006, Yang et al. 2003, Parvin et al. 2008, Das et al. 2015, Senavongse et al. 2018). In the three species of C. fallax, C. gigantean, and C. lihengiae, chromosome number and karyotype have been reported (Nakajima 1936, Larsen 1969, Moore 1973, Tanimoto and Matsumoto 1986, Okada and Hambali 1989, Long and Liu 2001, Yang et al. 2003, Cao and Long 2004, Begum and Alam 2009) (Table 1). The aim of this study is to establish the karyotypes in three species of Colocasia from Thailand for identification of species and strains.
| Species | 2n | NF | Karyotype formula | Satellite | Country | Reference |
|---|---|---|---|---|---|---|
| C. fallax | 28 | — | — | — | Bangladesh | Begum and Alam (2009) |
| 28 | 56 | 24m+4sm | Thailand | Present study | ||
| C. gigantea | 42 | — | — | — | Japan | Nakajima (1936) |
| 28 | — | — | — | Canada | Moore (1973) | |
| 28 | — | — | — | Japan | Tanimoto and Matsumoto (1986) | |
| 28 | — | — | — | Indonesia | Okada and Hambali (1989) | |
| 28 | 56 | 20m+8sm | — | China | Yang et al. (2003) | |
| 28 | 54 | 22m+4sm+2st | — | China | Cao and Long (2004) | |
| 28 | 56 | 20m+6sm+2a | 2 (STR) | Thailand | Present study | |
| C. lihengiae | 28 | 56 | — | — | China | Long and Liu (2001) |
| 28 | 52 | 18m+6sm+4st | 1 (SCR) | China | Cao and Long (2004) | |
| 28 | 56 | 18m+4sm+6a | — | Thailand | Present study |
STR=Subtelomeric region, SCR=subcentromeric regions, ̶=not available.
Three Colocasia species of C. fallax Schott, C. gigantea (Blume) Hook. f. and C. lihengiae C. L. Long & K. M. Liu were collected from fields in Thailand and grown in a nursery at the Walai Rukhavej Botanical Research Institute, Mahasarakham University, Thailand. Their root tips were pretreated with 2 mM 8-hydroxyquinoline for 8 h at 4°C, fixed in ethanol–acetic acid (3 : 1, v : v) for 30 min at room temperature and stored at 4°C or immediately used. Samples were washed in distilled water, then hydrolyzed in 1 M HCl for 5 min at 60°C and washed again in distilled water. The root tips were stained and squashed in 2% aceto-orcein and observed under a microscope. Karyotype formulas were derived from measurements of the metaphase chromosomes in photomicrographs. The nomenclature of chromosome shape for karyotype description followed Levan et al. (1964). The classification of the karyotype symmetry followed Stebbins (1971).
The somatic chromosome number of C. fallax is 2n=28 and NF=56 (Fig. 1). The karyotype including 24 metacentric (m) pairs and four submetacentric (sm) pairs and its formula was 24m+4sm and symmetric. The relative length in the karyotype is a value between 5.1 to 9.8% (Tables 1, 2 and Figs. 1A, 2A). Which is consistent with Begum and Alam (2009) reported that somatic karyotypes of C. fallex three morphological forms including deep purple petiole form (2n=28, NF=56, 24m+4sm), but while two forms differed in green petiole form (2n=28=20m+8sm) and light purple petiole form (2n=30=26m+2sm+2st), respectively.
| Chromosome pair | Ls±SD (µm) | Ll±SD (µm) | LT±SD (µm) | RL (%) | CI | Chromosome type |
|---|---|---|---|---|---|---|
| 1 | 3.54±0.04 | 3.61±0.01 | 7.15±0.05 | 9.75 | 0.51 | Metacentric |
| 2 | 2.73±0.03 | 3.72±0.01 | 6.45±0.06 | 8.80 | 0.58 | Metacentric |
| 3 | 2.73±0.00 | 3.22±0.01 | 5.95±0.03 | 8.12 | 0.54 | Metacentric |
| 4 | 2.73±0.01 | 3.00±0.01 | 5.73±0.02 | 7.82 | 0.52 | Metacentric |
| 5 | 2.64±0.01 | 2.95±0.01 | 5.60±0.02 | 7.63 | 0.53 | Metacentric |
| 6 | 2.55±0.01 | 2.95±0.02 | 5.50±0.02 | 7.51 | 0.54 | Metacentric |
| 7 | 2.46±0.02 | 2.95±0.02 | 5.42±0.03 | 7.38 | 0.55 | Metacentric |
| 8 | 2.38±0.02 | 2.95±0.02 | 5.34±0.03 | 7.28 | 0.55 | Metacentric |
| 9 | 2.31±0.02 | 2.95±0.02 | 5.26±0.04 | 7.18 | 0.56 | Metacentric |
| 10 | 2.19±0.01 | 2.47±0.09 | 4.65±0.10 | 6.34 | 0.53 | Metacentric |
| 11 | 2.08±0.11 | 2.44±0.10 | 4.53±0.20 | 6.17 | 0.54 | Metacentric |
| 12 | 1.71±0.02 | 2.42±0.03 | 4.13±0.04 | 5.63 | 0.59 | Metacentric |
| 13 | 1.46±0.03 | 2.44±0.03 | 3.90±0.07 | 5.32 | 0.63 | Submetacentric |
| 14 | 1.33±0.02 | 2.39±0.04 | 3.73±0.06 | 5.08 | 0.64 | Submetacentric |
The chromosome number of C. gigantea is 2n=28 and NF=56. The karyotype of this species including 10 metacentric pairs, three submetacentric pairs and one subtelocentric (st) pair was asymmetric with a formula as 20m+6sm+2st. The relative length is a value between 4.8 to 8.6% and satellites present on two m chromosomes (Tables 1, 3 and Figs. 1B, 2B). The present results agreed with the previous chromosome number reports of Moore (1973), Tanimoto and Matsumoto (1986), Okada and Hambali (1989), Yang et al. (2003) and, Cao and Long (2004), but it differs of 2n=42 by Nakajima (1936).
| Chromosome pair | Ls±SD (µm) | Ll±SD (µm) | LT±SD (µm) | RL (%) | CI | Chromosome type |
|---|---|---|---|---|---|---|
| 1 | 3.46±0.01 | 3.89±0.02 | 7.35±0.03 | 8.58 | 0.53 | Metacentric |
| 2 | 2.73±0.06 | 4.33±0.05 | 7.06±0.10 | 8.24 | 0.61 | Submetacentric |
| 3 | 3.14±0.03 | 3.87±0.02 | 7.00±0.04 | 8.18 | 0.55 | Metacentric |
| 4 | 3.34±0.02 | 3.43±0.04 | 6.77±0.05 | 7.90 | 0.51 | Metacentric |
| 5 | 2.95±0.02 | 3.55±0.02 | 6.51±0.03 | 7.60 | 0.55 | Metacentric |
| 6 | 3.16±0.06 | 3.29±0.02 | 6.45±0.07 | 7.53 | 0.51 | Metacentric |
| 7 | 2.89±0.03 | 3.52±0.02 | 6.41±0.04 | 7.48 | 0.55 | Metacentric |
| 8 | 2.61±0.03 | 3.56±0.04 | 6.16±0.05 | 7.19 | 0.58 | Metacentric |
| 9 | 2.82±0.01 | 3.27±0.02 | 6.09±0.02 | 7.11 | 0.54 | Metacentric |
| *10 | 3.61±0.04 | 2.21±0.06 | 5.81±0.08 | 6.79 | 0.58 | Metacentric |
| 11 | 2.26±0.04 | 3.27±0.04 | 5.63±0.06 | 6.57 | 0.61 | Submetacentric |
| 12 | 2.51±0.01 | 2.95±0.02 | 5.46±0.03 | 6.38 | 0.54 | Metacentric |
| 13 | 1.36±0.07 | 3.51±0.08 | 4.86±0.12 | 5.68 | 0.72 | Subtelocentric |
| 14 | 1.43±0.05 | 2.67±0.04 | 4.10±0.07 | 4.79 | 0.65 | Submetacentric |
*=Satellite chromosome.
The chromosome number of C. lihengiae is 2n=28 and NF=56. The karyotype of this species including nine metacentric pairs, one submetacentric pair, and four subtelocentric pairs was asymmetrical and its formula was 18m+2sm+8st. The relative length is a value between 4.8 to 9.7% (Tables 1, 4 and Figs. 1C, 2C). This is inconsistent with chromosome number 2n=28 reported by Long and Liu (2001) and Cao and Long (2004) (Table 1). In addition, Cao and Long (2004) reported the karyotype formula of 18m+6sm+4st and with one satellite that is different karyotype formula of this study.
| Chromosome pair | Ls±SD (µm) | Ll±SD (µm) | LT±SD (µm) | RL (%) | CI | Chromosome type |
|---|---|---|---|---|---|---|
| 1 | 3.50±0.01 | 3.62±0.01 | 7.12±0.01 | 9.65 | 0.51 | Metacentric |
| 2 | 2.96±0.01 | 3.43±0.07 | 6.40±0.12 | 8.67 | 0.54 | Metacentric |
| 3 | 2.10±0.04 | 4.21±0.04 | 6.31±0.07 | 8.55 | 0.67 | Submetacentric |
| 4 | 2.70±0.09 | 3.20±0.09 | 5.90±0.18 | 8.00 | 0.54 | Metacentric |
| 5 | 2.58±0.01 | 2.95±0.01 | 5.54±0.02 | 7.51 | 0.73 | Subtelocentric |
| 6 | 1.75±0.07 | 3.70±0.06 | 5.45±0.11 | 7.39 | 0.78 | Subtelocentric |
| 7 | 2.49±0.02 | 2.95±0.01 | 5.44±0.03 | 7.38 | 0.54 | Metacentric |
| 8 | 2.38±0.02 | 2.99±0.02 | 5.37±0.04 | 7.28 | 0.56 | Metacentric |
| 9 | 1.72±0.06 | 3.53±0.06 | 5.25±0.11 | 7.12 | 0.77 | Subtelocentric |
| 10 | 1.61±0.05 | 3.07±0.05 | 4.68±0.08 | 6.34 | 0.76 | Subtelocentric |
| 11 | 1.91±0.03 | 2.50±0.02 | 4.40±0.04 | 5.97 | 0.57 | Metacentric |
| 12 | 1.94±0.01 | 2.36±0.02 | 4.30±0.02 | 5.83 | 0.55 | Metacentric |
| 13 | 1.76±0.02 | 2.30±0.01 | 4.05±0.03 | 5.49 | 0.57 | Metacentric |
| 14 | 1.52±0.02 | 2.01±0.01 | 3.54±0.03 | 9.65 | 0.57 | Metacentric |
Many reports on chromosomes in Colocasia species reveal a diversity of chromosome numbers (2n=26, 28, 36, 38, 42 and 56), proposed basic chromosome numbers of x=7, 12, 13, 14 and 19, and polyploid cytotypes of 2x, 3x, and 4x in C. antiquorum, C. esculenta, C. gaoligongensis and C. gigantea (Nakajima 1936, Rao 1947, Delay 1951, Darlington and Wylie 1955, Marchant 1971, Ramachandran 1978, Coates et al. 1988, Okada et al. 1989, Yang 2003, Wang et al. 2017). Species of Araceae are difficult to identify because of the large variation of each species such as C. esculenta (three and five varieties), C. fallax (three varieties), Lasia spinosa (three varieties) and Xanthosoma violaceum (two varieties). Therefore, several cytologists such as Alam and Deen (2002), Sultana et al. (2006), Begum and Alam (2009), Deen and Alam (2002) and Senavongse et al. (2018) are studied chromosomes for classification of varieties of certain species. In the case of closely related species with the same number of chromosomes, karyotypes were used to identification of species. In addition, the characteristics of satellites and chromosome lengths can also be used to identify the species. However, all species in the genus have the same chromosome numbers, which could not be used to identify species. Some chromosome characters such as satellite (Yu et al. 2009) may be used to identify species in certain genera. While the result of this study found that clear satellites appeared in C. gigantea, which can be distinguished from C. fallex and C. lihengiae, even with the same chromosomes number (Fig. 2). Most of the satellite relates with NOR, visible or invisible of satellites should be carefully analyzed not only by conventional staining but also by bandings and/or FISH using rDNA prove.
When the study of karyotypes are reported in the same condition in most species and varieties of Colocasia species in Thailand, the karyotype analysis may be good tools for identification of intra- and/or inter-species variation in the Colocasia species. Therefore, the karyotypes in three species of Colocasia from Thailand are expected to the basic information to study family Araceae in the future.
This research has financially supported by Mahasarakham University and National Research Council of Thailand. We are grateful to the WalaiRukhavej Botanical Research Institute, Mahasarakham University, Thailand, for their facilities during this study. Many thanks to my family and friends for their supports and helps in the field. In addition, thanks to Dr. Jolyon Dodgson for language editing and suggestions to improve the manuscript.
