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Cytogenetics of Four Rare Species of the Genus Alocasia in Thailand
2023 年 88 巻 1 号 p. 21-25
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2023 年 88 巻 1 号 p. 21-25
Four rare species of genus Alocasia in Thailand were cytologically studied. The somatic chromosome number and karyotypes of four rare species are 2n=28=12m+12sm+4st (A. heterophylla), 2n=28=16m+8sm+4st (A. hypoleuca), 2n=56=34m+12sm+10st (A. princeps ‘Purple Cloak’) and 2n=26=12m+10sm+4st (A. nebula), respectively. The somatic chromosome numbers of all species were reported for the first time except A. princeps ‘Purple Cloak.’ The NF and karyotype of all species were reported for the first time. The cytogenetic data in this study can be used for the identification of each species.
One of the largest monocots family was Araceae includes about 144 genera and 3,645 species worldwide (Boyce and Sookchaloem 2012, World checklist of selected plant families (WCSP). http://apps.kew.org/wcsp/). Most of the species are distributed in the tropical New World. Some are in the tropics of the Old World and northern temperate regions. All parts contain clear latex containing calcium oxalate crystals, which are toxic to human and animal skin. If touched, it can itch or swell. The spadix in the inflorescence is a dominant character of the family Araceae (Boyce and Sookchaloem 2012). It has been utilized in terms of ornamental flowers, food plants, and various herbaceous plants (Hetterscheid and Ittenbach 1996).
Alocasia (Schott) G.Don is an accepted genus in the family Araceae and includes 89 accepted species (Boyce and Sookchaloem 2012). This genus is distributed range from tropical and subtropical Asia to East Australia. Alocasia has the potential as a landscaping ornamental (Boyce 2008).
The chromosome numbers of species in the Alocasia as 2n=28 to 58 were studied by several scientists i.e., A. cucullata (Lour.) G.Don as 2n=28 (Ito 1942, Darlington and Wylie 1955, Marchant 1971, Bhattacharya 1974, Ankei 1987, Ishida 2001, She 2016, Senavongse et al. 2020), A. longiloba Miq. as 2n=56 (Sharma 1970, Bhattacharya 1974, Senavongse et al. 2020), A. macrorrhizos (L.) G. Don as 2n=28 (Ishida 2001, Senavongse et al. 2020). Few scientists have studied the karyotype of three Alocasia species A. cucullata (Lour.) G.Don, A. longiloba Miq. and A. macrorrhizos (L.) G.Don (She 2016, Senavongse et al. 2020).
Whereas, we collected Alocasia species in Thailand during 2020–2021. We found four rare Alocasia species include: A. heterophylla (C.Presl) Merr., A. hypoleuca P.C. Boyce, A. princeps W.Bull ‘Purple Cloak,’ and A. nebula A.Hay. These rare Alocasia species have not been studied cytogenetically. Therefore, this study aimed to provide the chromosome number, NF, and karyotype in four rare species of the genus Alocasia, family Araceae in Thailand.
Four rare species of the genus Alocasia in Thailand—A. heterophylla (coll. no. Saensouk 3500), A. hypoleuca (coll. no. Saensouk 3501), A. princeps ‘Purple Cloak’ (coll. no. Saensouk 3502), and A. nebula (coll. no. Saensouk 3503) were collected from several parts in Thailand, and all species were cultivated in a nursery at Mahasarakham University, Maha Sarakham Province, Thailand (Table 1).
| Species | 2n | NF | Karyotype formula | Conservation status (based on WCSP) | Location (Provinces) | Reference |
|---|---|---|---|---|---|---|
| A. heterophylla | 28* | 56* | 12m+12sm+4st* | Rare species | Chiangmai | Present study |
| A. hypoleuca | 28* | 56* | 16m+8sm+4st* | Rare and endemic species | Tak | Present study |
| A. princeps ‘Purple Cloak’ | 56 | 112* | 34m+12sm+10st* | Rare species | Songkla | Present study |
| 28 | — | — | — | Hiroshima | Ishida (2001) | |
| A. nebula | 26* | 52* | 12m+10sm+4st* | Rare species | Satun | Present study |
* First-time report
Root tips (1–1.5 cm long) from four cultivated species were observed for mitotic chromosomes. All samples 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 then stored at 4°C. These samples were washed with distilled water, then hydrolyzed in 1M HCl for 5 min at 60°C, and washed twice in distilled water. After that root tips were stained and squashed in 2% aceto-orcein, and then the chromosomes were observed using a light microscope (Zeiss: Axiostar plus). The chromosome number study followed Senavongse et al. (2018, 2020) and Saensouk et al. (2019). The nomenclature of the chromosome morphology followed Levan et al. (1964). The chromosome number, chromosome length, arm ratio, relative length, and karyotype formula were recognized from 10 metaphase cells in each species. For the arrangement of the chromosomes in the karyotypes, the parameters for the average length of the short arm (Ls), the average length of the long arm (Ll), length of each chromosome (LT), average relative length (RL), chromosome index (CI) and standard deviations (SD) of the RL and CI from metaphase chromosomes were calculated following the methods of Senavongse et al. (2018, 2020).
The four species of the Alocasia form Thailand, i.e., A. heterophylla, A. hypoleuca, A. princeps ‘Purple Cloak,’ and A. nebula Table 1 were rare species in Thailand based on the database of WCSP. While only A. hypoleuca was reported as an endemic species in Thailand. The somatic chromosome numbers from the root tips of four rare Alocasia species are summarized in Table 1. The chromosome numbers ranged from 2n=26 to 56 (Table 1, Fig. 1), and the characteristics of the karyotypes of four rare species in Alocasia are provided in Table 1 and Fig. 2.
The somatic chromosome number of A. heterophylla was 2n=28 with NF=56 (Fig. 1A). The karyotype had six pairs of metacentric chromosomes, six pairs of submetacentric chromosomes, and two pairs of subtelocentric chromosomes. The karyotype formula 12m+12sm+4st was an asymmetrical karyotype (Table 2, Fig. 2A). The short arm length ranged from 0.99±0.01 to 2.25±0.03 µm, the long arm length ranged from 2.29±0.03 to 3.83±0.04 µm and the total chromosome length ranged from 3.39±0.04 to 5.77±0.07 µm. The RL ranged from 5.34±0.00 to 9.09±0.01% and the chromosomes according to the CI ranged from 0.54±0.04 to 0.72±0.05 (Table 2). The somatic chromosome number, NF, and karyotype of A. heterophylla were studied for the first time.
| Chromosome pair | Ls±SD (µm) | Ll±SD (µm) | LT±SD (µm) | RL (%) | CI | Chromosome type |
|---|---|---|---|---|---|---|
| 1 | 1.93±0.02 | 3.83±0.04 | 5.77±0.07 | 9.09±0.03 | 0.67±0.04 | Submetacentric |
| 2 | 1.45±0.02 | 3.81±0.04 | 5.26±0.06 | 8.29±0.02 | 0.72±0.05 | Subtelocentric |
| 3 | 1.92±0.02 | 3.04±0.04 | 4.96±0.06 | 7.82±0.02 | 0.61±0.04 | Submetacentric |
| 4 | 2.25±0.03 | 2.71±0.03 | 4.96±0.06 | 7.82±0.02 | 0.55±0.04 | Metacentric |
| 5 | 1.55±0.02 | 3.38±0.04 | 4.93±0.06 | 7.77±0.02 | 0.68±0.04 | Submetacentric |
| 6 | 1.62±0.02 | 3.11±0.04 | 4.73±0.05 | 7.46±0.02 | 0.66±0.04 | Submetacentric |
| 7 | 2.15±0.02 | 2.54±0.03 | 4.69±0.05 | 7.39±0.02 | 0.54±0.04 | Metacentric |
| 8 | 2.11±0.02 | 2.47±0.03 | 4.58±0.05 | 7.21±0.02 | 0.54±0.04 | Metacentric |
| 9 | 1.37±0.02 | 2.92±0.03 | 4.29±0.05 | 6.76±0.02 | 0.68±0.04 | Submetacentric |
| 10 | 1.87±0.02 | 2.42±0.03 | 4.29±0.05 | 6.76±0.02 | 0.57±0.04 | Metacentric |
| 11 | 1.68±0.02 | 2.40±0.03 | 4.07±0.05 | 6.42±0.02 | 0.59±0.04 | Metacentric |
| 12 | 1.67±0.02 | 2.34±0.03 | 4.01±0.05 | 6.32±0.02 | 0.58±0.04 | Metacentric |
| 13 | 0.99±0.01 | 2.52±0.03 | 3.51±0.04 | 5.53±0.02 | 0.72±0.04 | Subtelocentric |
| 14 | 1.10±0.01 | 2.29±0.03 | 3.39±0.04 | 5.34±0.02 | 0.68±0.04 | Submetacentric |
The somatic chromosome number of A. hypoleuca was 2n=28 with NF=56 (Fig. 1B). The karyotype had eight pairs of metacentric chromosomes, four pairs of submetacentric chromosomes, and two pairs of subtelocentric chromosomes. The karyotype formula was 16m+8sm +4st, which was an asymmetrical karyotype (Table 3, Fig. 2B). The short arm length ranged from 1.00±0.01 to 2.68±0.03 µm, the long arm length ranged from 4.08±0.05 to 2.34±0.03 µm and the total chromosome length ranged from 3.67±0.04 to 6.17±0.07 µm. The RL ranged from 5.27±0.00 to 8.86±0.01% and the chromosomes according to the CI ranged from 0.53±0.03 to 0.74±0.01 (Table 3). The somatic chromosome number, NF, and karyotype of A. hypoleuca were studied for the first time.
| Chromosome pair | Ls±SD (µm) | Ll±SD (µm) | LT±SD (µm) | RL (%) | CI | Chromosome type |
|---|---|---|---|---|---|---|
| 1 | 2.09±0.02 | 4.08±0.05 | 6.17±0.07 | 8.86±0.03 | 0.66±0.02 | Submetacentric |
| 2 | 1.83±0.02 | 3.98±0.05 | 5.82±0.07 | 8.36±0.02 | 0.68±0.02 | Submetacentric |
| 3 | 2.68±0.03 | 2.96±0.03 | 5.64±0.07 | 8.10±0.02 | 0.53±0.03 | Metacentric |
| 4 | 2.38±0.03 | 3.24±0.04 | 5.62±0.06 | 8.07±0.02 | 0.58±0.03 | Metacentric |
| 5 | 2.57±0.03 | 3.02±0.03 | 5.60±0.06 | 8.04±0.02 | 0.54±0.03 | Metacentric |
| 6 | 1.56±0.02 | 3.81±0.04 | 5.37±0.06 | 7.71±0.02 | 0.71±0.02 | Subtelocentric |
| 7 | 2.31±0.03 | 3.05±0.04 | 5.36±0.06 | 7.70±0.02 | 0.57±0.03 | Metacentric |
| 8 | 2.02±0.02 | 2.82±0.03 | 4.83±0.06 | 6.95±0.02 | 0.58±0.03 | Metacentric |
| 9 | 1.64±0.02 | 3.04±0.04 | 4.67±0.05 | 6.72±0.02 | 0.65±0.02 | Submetacentric |
| 10 | 1.85±0.02 | 2.75±0.03 | 4.60±0.05 | 6.60±0.02 | 0.60±0.02 | Metacentric |
| 11 | 1.84±0.02 | 2.51±0.03 | 4.35±0.05 | 6.25±0.02 | 0.58±0.03 | Metacentric |
| 12 | 1.70±0.02 | 2.34±0.03 | 4.04±0.05 | 5.81±0.01 | 0.58±0.03 | Metacentric |
| 13 | 1.00±0.01 | 2.87±0.03 | 3.87±0.04 | 5.57±0.01 | 0.74±0.01 | Subtelocentric |
| 14 | 1.15±0.01 | 2.52±0.03 | 3.67±0.04 | 5.27±0.01 | 0.69±0.01 | Submetacentric |
The somatic chromosome number of A. princeps ‘Purple Cloak’ was 2n=56 with NF=112 (Fig. 1C). The karyotype had seventeen pairs of metacentric chromosomes, six pairs of submetacentric chromosomes, and five pairs of subtelocentric chromosomes. The karyotype formula 34 m+12sm +10st was an asymmetrical karyotype (Table 4, Fig. 2C). The short arm length ranged from 0.74±0.01 to 2.12±0.02 µm, the long arm length ranged from 1.32±0.02 to 2.97±0.03 µm and the total chromosome length ranged from 2.19±0.03 to 4.52±0.05 µm. The RL ranged from 2.22±0.01 to 4.58±0.02% and the chromosomes according to the CI ranged from 0.52±0.01 to 0.76±0.01 (Table 4). The somatic chromosome numbers of this species as 2n=56 which differed from a previous report (2n=28) from Hiroshima, Japan by Ishida (2001) due to environmental factors. Whereas, NF and karyotype of A. princeps ‘Purple Cloak’ were studied for the first time.
| Chromosome pair | Ls±SD (µm) | Ll±SD (µm) | LT±SD (µm) | RL (%) | CI | Chromosome type |
|---|---|---|---|---|---|---|
| 1 | 2.04±0.02 | 2.49±0.03 | 4.52±0.05 | 4.58±0.02 | 0.55±0.01 | Metacentric |
| 2 | 2.12±0.02 | 2.35±0.03 | 4.46±0.05 | 4.52±0.02 | 0.53±0.01 | Metacentric |
| 3 | 1.72±0.02 | 2.40±0.03 | 4.11±0.05 | 4.17±0.02 | 0.58±0.01 | Metacentric |
| 4 | 1.91±0.02 | 2.11±0.02 | 4.02±0.05 | 4.07±0.02 | 0.53±0.01 | Metacentric |
| 5 | 1.77±0.02 | 2.25±0.03 | 4.01±0.05 | 4.06±0.02 | 0.56±0.01 | Metacentric |
| 6 | 1.90±0.02 | 2.10±0.02 | 4.01±0.05 | 4.06±0.02 | 0.53±0.01 | Metacentric |
| 7 | 0.93±0.01 | 2.97±0.03 | 3.90±0.05 | 3.95±0.01 | 0.76±0.01 | Subtelocentric |
| 8 | 1.47±0.02 | 2.36±0.03 | 3.83±0.04 | 3.88±0.02 | 0.62±0.01 | Submetacentric |
| 9 | 1.39±0.02 | 2.42±0.03 | 3.82±0.04 | 3.86±0.02 | 0.64±0.01 | Submetacentric |
| 10 | 1.71±0.02 | 2.10±0.02 | 3.80±0.04 | 3.85±0.02 | 0.55±0.01 | Metacentric |
| 11 | 1.51±0.02 | 2.27±0.03 | 3.78±0.04 | 3.83±0.02 | 0.60±0.01 | Metacentric |
| 12 | 1.46±0.02 | 2.28±0.03 | 3.74±0.04 | 3.79±0.02 | 0.61±0.01 | Submetacentric |
| 13 | 1.68±0.02 | 2.01±0.02 | 3.69±0.04 | 3.74±0.02 | 0.54±0.01 | Metacentric |
| 14 | 1.07±0.01 | 2.62±0.03 | 3.69±0.04 | 3.73±0.01 | 0.71±0.01 | Subtelocentric |
| 15 | 1.75±0.02 | 1.90±0.02 | 3.65±0.04 | 3.70±0.02 | 0.52±0.01 | Metacentric |
| 16 | 1.63±0.02 | 2.02±0.02 | 3.64±0.04 | 3.69±0.02 | 0.55±0.01 | Metacentric |
| 17 | 1.51±0.02 | 1.86±0.02 | 3.38±0.04 | 3.42±0.02 | 0.55±0.01 | Metacentric |
| 18 | 1.20±0.01 | 2.10±0.02 | 3.30±0.04 | 3.34±0.01 | 0.64±0.01 | Submetacentric |
| 19 | 1.50±0.02 | 1.79±0.02 | 3.29±0.04 | 3.34±0.02 | 0.54±0.01 | Metacentric |
| 20 | 1.18±0.01 | 2.10±0.02 | 3.28±0.04 | 3.33±0.01 | 0.64±0.01 | Submetacentric |
| 21 | 1.30±0.02 | 1.90±0.02 | 3.20±0.04 | 3.24±0.02 | 0.59±0.01 | Metacentric |
| 22 | 0.80±0.01 | 2.31±0.03 | 3.10±0.04 | 3.14±0.01 | 0.74±0.01 | Subtelocentric |
| 23 | 1.01±0.01 | 1.99±0.02 | 2.99±0.03 | 3.03±0.01 | 0.66±0.01 | Submetacentric |
| 24 | 0.81±0.01 | 2.17±0.03 | 2.98±0.03 | 3.02±0.01 | 0.73±0.01 | Subtelocentric |
| 25 | 1.23±0.01 | 1.64±0.02 | 2.87±0.03 | 2.91±0.01 | 0.57±0.01 | Metacentric |
| 26 | 1.25±0.01 | 1.56±0.02 | 2.81±0.03 | 2.85±0.01 | 0.56±0.01 | Metacentric |
| 27 | 0.74±0.01 | 1.91±0.02 | 2.65±0.03 | 2.68±0.01 | 0.72±0.01 | Subtelocentric |
| 28 | 0.88±0.01 | 1.32±0.02 | 2.19±0.03 | 2.22±0.01 | 0.60±0.01 | Metacentric |
The somatic chromosome number of A. nebula was 2n=28 with NF=26 (Fig. 1D). The karyotype had six pairs of metacentric chromosomes, five pairs of submetacentric chromosomes, and two pairs of subtelocentric chromosomes. The karyotype formula was found to be 12m+10sm+4st, which was an asymmetrical karyotype (Table 5, Fig. 2D). The short arm length ranged from 1.10±0.01 to 2.69±0.03 µm, the long arm length ranged from 2.61±0.03 to 6.21±0.07 µm and the total chromosome length ranged from 3.94±0.05 to 8.90±0.10 µm. The RL ranged from 5.52±0.00 to 12.48±0.01% and the chromosomes according to the CI ranged from 0.54±0.01 to 0.74±0.01 (Table 5). The somatic chromosome number, NF, and karyotype of A. nebula were studied for the first time.
| Chromosome pair | Ls±SD (µm) | Ll±SD (µm) | LT±SD (µm) | RL (%) | CI | Chromosome type |
|---|---|---|---|---|---|---|
| 1 | 2.69±0.03 | 6.21±0.07 | 8.90±0.10 | 12.48±0.04 | 0.70±0.02 | Submetacentric |
| 2 | 2.68±0.03 | 4.13±0.05 | 6.81±0.08 | 9.54±0.03 | 0.61±0.01 | Submetacentric |
| 3 | 2.64±0.03 | 3.73±0.04 | 6.36±0.07 | 8.92±0.03 | 0.59±0.01 | Metacentric |
| 4 | 2.68±0.03 | 3.29±0.04 | 5.98±0.07 | 8.38±0.03 | 0.55±0.02 | Metacentric |
| 5 | 1.41±0.02 | 4.06±0.05 | 5.48±0.06 | 7.68±0.02 | 0.74±0.01 | Subtelocentric |
| 6 | 2.24±0.03 | 3.10±0.04 | 5.34±0.06 | 7.49±0.02 | 0.58±0.02 | Metacentric |
| 7 | 2.44±0.03 | 2.85±0.03 | 5.29±0.06 | 7.41±0.02 | 0.54±0.01 | Metacentric |
| 8 | 2.03±0.02 | 3.09±0.04 | 5.12±0.06 | 7.18±0.02 | 0.60±0.02 | Submetacentric |
| 9 | 2.16±0.02 | 2.77±0.03 | 4.93±0.06 | 6.91±0.02 | 0.56±0.02 | Metacentric |
| 10 | 1.92±0.02 | 2.61±0.03 | 4.53±0.05 | 6.35±0.02 | 0.58±0.02 | Metacentric |
| 11 | 1.64±0.02 | 2.82±0.03 | 4.46±0.05 | 6.25±0.01 | 0.63±0.01 | Submetacentric |
| 12 | 1.31±0.02 | 2.88±0.03 | 4.20±0.05 | 5.89±0.01 | 0.69±0.01 | Submetacentric |
| 13 | 1.10±0.01 | 2.83±0.03 | 3.94±0.05 | 5.52±0.01 | 0.72±0.01 | Subtelocentric |
Petersen (1989) and several scientists reported the basic chromosome number as x=7 including somatic chromosome numbers 2n=14 (as diploid), 2n=28 (as tetraploid), 2n=42 (as hexaploidy), and 2n=56 (as octoploid) for this genus Alocasia. However, the chromosome numbers 2n=28 and 56 shown in this study completely agree with the basic chromosome number of x=7. Therefore, the present three species may be considered tetraploid (2n=4x=28) for A. heterophylla, A. hypoleuca, and octoploid (2n=8x=56) for A. princeps ‘Purple Cloak.’ The chromosome number of A. nebula was 2n=26 which was not the basic chromosome number x=7. All species in this study except for A. princeps ‘Purple Cloak’ had their cytogenetics studied for the first time. The results showed that the chromosome morphology and karyotype formulae of four rare Alocasia species from Thailand can be used for the identification of each species, which was consistent with Santhosh (1999) who could identify plants by the chromosome morphological characteristics of the plants.
This research project was financially supported by Thailand Science Research and Innovation (TSRI). We are grateful to Mahasarakham University and Walai Rukhavej Botanical Research Institute, Maha Sarakham Province, Thailand for their facilities during this study. Many thanks to our students for their help with laboratory techniques.
