Karyomorphological Analysis of Hildegardia populifolia (Malvaceae): An Endemic Species from the Eastern Ghats, India

Abstract

Hildegardia populifolia (Malvaceae) is one of the endemic and rare species of Eastern Ghats. The mitotic chromosome counts 2n=40 and basic karyomorphology of H. populifolia is reported for the first time. The karyotype formula is 20 m. The karyotype is 1A of the Stebbins category.

The genus Hildegardia Schott & Endl. belonging to the family Malvaceae, subfamily Sterculoideae, tribe Sterculieae is represented by 11 species in the World (Mabberley 2017) of which one occurs in Cuba, three each in Africa, Madagascar, and Indomalaya, and one in Australia. H. populifolia, a deciduous forest tree species was earlier known to be represented by a sole surviving population comprising about 20 trees in Kalarayan Hills of Tamil Nadu (Ahmedullah 1990). Its conservation status has been variously assessed as Critically Endangered by Sarcar and Sarcar (2002) and Endangered by Ahmedullah (1990), Walter and Gillet (1998), and Rao et al. (2003). Rao et al. (1998) recognized five subpopulations of this endangered species in the Rayalaseema District of Andhra Pradesh. Sudhakar et al. (2001) categorized species as Vulnerable. The World Conservation Monitoring Centre (1998) assessed the conservation status of this species as Critically Endangered.

H. populifolia is an endemic species to the southern Eastern Ghats for which there is no chromosome report so far. The present paper provides mitotic chromosome count and karyotype analysis of this species.

Materials and methods

Saplings of H. populifolia, were collected from the Department of Botany, Yogi Vemana University, Kadapa 516003, Andhra Pradesh, India. The voucher specimen is deposited in the Herbarium, Department of Botany, Yogi Vemana University (YVUH).

Mitosis was studied from the root tips of saplings. Root-tips of 6–10 mm length were pre-treated with 2 mM 8-hydroxyquinoline for 8–10°C for 3–4 h. The root tips were squashed in 2% propionic orcein. Ten well spread somatic chromosome plates were used for karyotype analysis. The well-spread chromosome plates were photographed with a Carl Zeiss Axio Imager A2 attached with a camera.

Types of chromosomes were evaluated by using centromeric index (i) (Levan et al. 1964), Karyotype morphometric characters were evaluated by calculating haploid complement length together with intrachromosomal asymmetry index (A1) and interchromosomal asymmetry index (A2) as given by Zarco (1986).

Results and discussion

Somatic chromosome number 2n=40 was observed in H. populifolia (Fig. 1A). Chromosomes ranged from 2.53±0.34 to 4.97±0.81 µm in length and all of them were observed to be median (m) (Table 1). The total chromosome length of the haploid complement (TCLH) was 74.14±0.61 µm. The total form percentage (TF%) was 43.12. The symmetric index (SI) was 75.81 and the gradient index (GI) was 71.92. The coefficient of variation of chromosome lengths (CVcl) and Coefficient of variation of the centromeric index (CVci) were 17.22 and 3.30, respectively. A1 and A2 were 0.24 and 0.17, respectively. The karyotype formula was 20 m belonging to 1A asymmetric category (Stebbins 1971). Figure 1B illustrates the karyogram.

Fig. 1. H. populifolia: A. Somatic chromosome plate, B. Karyotype.

Table 1. Karyotypic analysis of H. populifolia.

Chr. No.	Long arm (L)±SD (µm)	Short arm (s)±SD (µm)	Total length c=l+s±SD (µm)	d=l−s	r=l/s	i=s/c ×100	Centromeric position
1	2.81±0.38	2.16±0.47	4.97±0.81	0.65±0.25	1.33±0.16	43.15±3.00	m
2	2.72±0.37	1.92±0.37	4.64±0.68	0.81±0.30	1.44±0.21	41.16±3.35	m
3	2.51±0.38	1.94±0.33	4.44±0.65	0.57±0.30	1.30±0.18	43.63±3.48	m
4	2.40±0.24	1.96±0.29	4.36±0.50	0.44±0.18	1.23±0.11	44.87±2.19	m
5	2.40±0.43	1.81±0.14	4.20±0.50	0.59±0.40	1.33±0.23	43.34±4.16	m
6	2.35±0.42	1.74±0.19	4.10±0.53	0.61±0.40	1.36±0.26	42.82±4.32	m
7	2.16±0.37	1.79±0.23	3.94±0.54	0.37±0.29	1.21±0.16	45.44±3.34	m
8	2.27±0.44	1.57±0.26	3.83±0.62	0.70±0.37	1.46±0.27	41.06±4.07	m
9	2.11±0.31	1.59±0.23	3.70±0.53	0.52±0.15	1.33±0.9	42.95±1.56	m
10	2.16±0.38	1.50±0.24	3.66±0.52	0.65±0.37	1.45±0.28	41.20±4.27	m
11	2.07±0.35	1.50±0.20	3.57±0.47	0.57±0.31	1.38±0.21	42.22±3.48	m
12	1.98±0.30	1.55±0.22	3.53±0.44	0.44±0.29	1.30±0.20	43.87±3.87	m
13	2.03±0.33	1.50±0.16	3.53±0.44	0.52±0.27	1.35±0.18	42.75±2.79	m
14	1.96±0.27	1.46±0.21	3.42±0.45	0.50±0.18	1.35±0.14	42.70±2.45	m
15	1.92±0.35	1.44±0.19	3.35±0.46	0.48±0.32	1.34±0.25	43.12±4.05	m
16	1.87±0.34	1.42±0.19	3.29±0.45	0.46±0.33	1.33±0.24	43.29±4.42	m
17	1.81±0.30	1.33±0.19	3.14±0.39	0.48±0.31	1.38±0.24	42.47±4.52	m
18	1.74±0.25	1.33±0.16	3.07±0.69	0.41±0.16	1.31±0.12	43.34±2.49	m
19	1.55±0.22	1.33±0.16	2.87±0.35	0.22±0.15	1.17±0.11	46.28±2.43	m
20	1.37±0.20	1.15±0.21	2.53±0.34	0.22±0.23	1.22±0.24	45.59±4.58	m

c: Total length, d: difference, r: arm ratio and i: centromeric index

Out of 11 species of Hildegardia, H. barteri (Mast.) Kosterm. is the only species in which chromosome number 2n=40 is reported (Mangenot and Mangenot 1958). The present study also revealed that the species of Hildegardia exhibit a somatic chromosome count of 2n=40 and there is a need for further cytological study in remaining species for further cytological understanding and relationships among species in a genus.

Acknowledgments

The authors are grateful to the Head of the Department of Botany, Shivaji University, Kolhapur for providing research facilities. Rohit N. Mane is grateful to Rajiv Gandhi Science and Technology Commission (RGSTC), Government of Maharashtra for financial assistance (RGSTC/ File-2007/DPP-054/CR-028). Chennuru Nagendra and A. Madhusudhana Reddy are gratefully acknowledging the ministry of Environment Forest and Climate change (MoEF and CC) (no. 10/16/2016-CS/BG) for financial support under the ABG, scheme.

References

• Ahmedullah, M. 1990. Hildegardia populifolia. In: Nayar, M. P. and Sastry, A. R. K. (eds.). Red Data Book of Indian Plants Vol. 3. Botanical Survey of India, Calcutta, pp. 251–253.
• Levan, A., Fredga, K. and Sandberg, A. A. 1964. Nomenclature for centromeric position on chromosomes. Hereditas 52: 201–220.
• Mabberley, D. J. 2017. The Plant–Book: A Portable Dictionary of Plants, Their Classification and Uses 4th Edn. Cambridge University Press, Cambridge.
• Mangenot, S. and Mangenot, G. 1958. Deuxieme liste de nombres chromosomiques nouveaux chez diverse dicotyledons et monocotyledones d’Afrique occidentale. Bull. Jard. Bot. Etat. 28: 315–329.
• Rao, C. K., Geetha, B. L. and Suresh, G. 2003. Red List of Threatened Vascular Plant Species in India. Botanical Survey of India, Calcutta.
• Rao, B. R. P., Sunitha, S. and Reddy, A. M. 1998. Notes on Hildegardia populifolia (Roxb.) Schott & Endl. (Sterculiaceae), an endemic and endangered species. Eighth Annual Conference of IAAT and National Seminar on Biodiversity, Conservation and Taxonomy of Tropical Flowering Plants, Calicut. p. 47.
• Sarcar, M. K. and Sarcar, A. B. 2002. Status, botanical description, natural distribution zone, propagation practices and conservation efforts of Hildegardia populifolia (Roxb.) Schott & Endl.: A threatened tree species of dry tropical forests in India. Indian For. 128: 757–770.
• Stebbins, G. L. 1971. Chromosomal Evolution in Higher Plants. Edward Arnold Publisher, London.
• Sudhakar, R. C., Jadhav, S. N., Ved, D. K., Ghate, U. and Reddy, K. 2001. Proceedings of the Workshop in Conservation Assessment and Management Planning for Medicinal Plants of Andhra Pradesh. FRLHT, Bangalore.
• Walter, K. S. and Gillet, H. J. 1998. 1997 IUCN Red List of Threatened Plants. IUCN Publishing Service, Cambridge.
• Zarco, C. R. 1986. A new method for estimating karyotype asymmetry. Taxon 35: 526–530.