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Pollination Studies in Swertia chirayita - A Critically Endangered Medicinal Plant of Western Himalayas

Irfan Ali Shah*, Y. P. Sharma, R. Raina and R Rana

* Indira Gandhi National Forest Academy, FRI Campus, Dehra Dun, Uttarakhand, 248006.Dr Y S Parmar University of Horticulture and Forestry, Solan, Himachal Pradesh .173230

*Corresponding author: irfanalishahars@gmail.com,

Abstract:

Understanding breeding system of a sexually reproducing species is fundamental to undertake any crop improvement work with regard to development of better yielding agronomical types. Broadly, two main types of breeding systems i.e. self and cross pollination determine to a large extent the range of homo or heterozygosity for different characters expected in a population. Initiating a breeding program in a species would thus surely require determination of the type of pollination fertilization system prevalent in the species. Swertia chirayita (Family Gentianaceae) has been presumed to be cross pollinated on the basis of colorful corolla and presence of nectaries. The present studies showed that this species is mostly cross pollinated and although selfing is also present, it seems to be a feel safe strategy to meet the vagaries of nature.

Key words : Swertia chirayita, pollination, fruit set, seed set, breeding

Manuscript received: 17 August, 2011 Manuscript accepted: 30 December, 2011

Introduction

Swertia chirayita is a native of temperate Himalayas, found at an altitude of 4000 to 10,000 ft from Kashmir to Bhutan and in the Khasi Hills at 4000 to 5000 ft (Clarke, 1885; Blatter, 1984) The large continuous stem pith, dark green colour of stem and intensely bitter taste of leaves are sufficient to distinguish S. chirayita from other species of this genus, which are used as adulterants (Anonymous. 1976). The bitterness, antihelmintic, hypoglycemic and antipyretic properties are attributed to amarogentin, swerchirin and other active principles of herb.

Herbal medicines such as Ayush 64, Diabecon, Mensturyl syrup and Melicon ointment contain S. Chirayita extract in different quantities for its antipyretic, hypoglycemic, antifungal and antibacterial properties (Joshi & Dhawan, 2005). S. chirayita commands a pre-eminent position in several pharmacopoeias of the world and traditional systems of medicines like Ayurveda, Unani and Siddha etc. (Kirtikar & Basu, 1975). S. chirayita enjoys a good domestic and international market which is increasing at the rate of 10 per cent annually (Anonymous, 2008).

Despite considerable importance, the raw material of this species is still mainly harvested from wild, sparingly cultivated and negligible efforts have gone into developing proper agro-techniques as a crop. Moreover the perusal of literature reveals that there are discrepancies regarding the correct morphological features and habit of the plant. S. chirayita has already been categorized as critically endangered species by International Union for Conservation of Nature and Natural resources (Joshi & Dhawan, 2005). The

National Medicinal Plant Board, Government of India, New Delhi has already enlisted this species among 32 medicinal species prioritized for commercial cultivation in the country (Anonymous, 2008).

The phenological behaviour and breeding strategies operative in alpine medicinal plants like S. chirayita have far reaching consequences on their distribution, abundance and persistence in a geographical range affecting their pollination mode and conservation strategies, because it is the breeding system which eventually determines reproductive success and evolutionary fitness of a species (Mohi-ud-din et al., 2007).

Floral characteristics such as colorful corolla and presence of nectaries (Fig 1) support cross pollination in S. chirayita. Generally bees are the pollinators of S. chirayita (Joshi & Dhawan, 2005). Ironically, bee behavior (Fig. 2) suggests that fit, well resourced flowers bearing much nectar and pollen are more likely to be selfed or to suffer near relative matings than are poorly resourced flowers and it is accepted fact that repeated self fertilization rapidly results in a reduction in genetic variation within populations (Richards, 1997). Also fruit and seed settings are highly influenced by pollination mechanism. Poor fruit set, resultant low yield has been a serious problem in the commercial plantation in our country. This led to an intensive investigation into the causes which were initially approached by pollen fertility studies. To augment the research, breeding behavior, pollination efficiency and extent of fruit set using different pollination methods have been studied. With all these facts in view the present study was contemplated with the objective to

Open Access Journal of Medicinal and Aromatic Plants Vol. 2(1): 14-17)

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determine the pollination behaviour of this critically endangered medicinal herb in order to develop an better understanding of its reproductive biology.

Materials and methods

Raising of the crop

The crop of S. chirayita was raised in the Medicinal and Aromatic Plants Research Farm of the Department of Forest Product of Dr YS Parmar University at Shilly (1550 m amsl). The seeds were sown in the nursery during June 2006. The nursery raised seedlings were then planted in polybags at 6-8 true leaves stage during October, 2006. The seedlings were then transplanted in field at 8-10 true leaves stage in April, 2007 in field plots of size 3 m x 2 m with well prepared 45 cm x 45 cm spacing. Well rotten farm yard manure (FYM) was applied at the time of preparation of plots and no chemical fertilizers were used. Irrigation and weeding operations were regularly carried out as per requirement. The crop came in flowering in August-September, 2008 in the third year after seed sowing.

Pollination studies

The experiment was conducted in a randomized block design with three treatments replicated seven times. A minimum of 20 flowers were used for each replication. Different pollination mechanisms studied included open pollination wherein unopened buds on a plant were selected, tagged and left as such for natural pollination; selfing (by bagging) wherein unopened buds on a plant were selected, tagged and enclosed by butter paper bags to prevent pollinator activity and chance pollination by pollen from other plants and open cross pollination in which the unopened buds were carefully opened by removing petals and exposing the anthers. These anthers were carefully removed with the help of fine forceps without injury to any part of the flowers. These emasculated buds were then tagged and left as such. All the surrounding buds/flowers were removed to minimize the chances of geitenogamy. The bags of the selfed flowers were removed only after capsule development stage. Observations recorded included fruit set percentage which was calculated by counting the number of capsules produced in the treatment and seed yield per capsule which was calculated by allowing all the capsules resulting from each treatment/ replication to dry naturally and seeds obtained from them were separated and cleaned properly. Seed yield per capsule were then calculated in milligrams and reported as mean. Data were subjected to analysis of variance according to the methods described by Cochran and Cox (1967).

Results and Discussion

Results obtained revealed that under open cross pollination conditions (T

3) a significantly higher fruit

set percentage (80.10%) with 3.58 mg seed yield

per capsule(Fig. 3) was obtained as compared to 28.80 per cent fruit set with 1.17 mg seed yield per capsule observed under selfed (bagged flowers, Fig 4) conditions (T

2). However, under open (natural)

pollination conditions (T1) maximum fruit set of 91.37

per cent with 4.77 mg seed yield per capsule was obtained. These results indicate that this species is mostly cross pollinated, self incompatibility barriers are not strongly expressed as about 28 per cent fruit set was obtained under selfed conditions although with a lower seed yield per capsule, the maximum fruit set and seed yield per capsule obtained under open (natural) pollination conditions (T

1) may be due to the combined

effect of cross and self pollination and some seed may be definitely produced as a result of autogamous or geitenogamous pollination.

These conclusions are also supported by the floral architecture and phenology of the species and also the facts that the flowering in this species is staggered over a period of 2-3 months (August to October) and the life of individual flower does not exceed 7-15 days (from bud opening to withering). The flowers are characterized by a pair of large hairy nectaries at the base of each petal lobe, which provide a valuable reward to the pollinators in terms of nectar. Bawa (1974) postulated that without heterogeneity in the flowering pattern and duration of flowering there would be little inter plant movement of pollinators and hence little gene flow. Thus, the asynchronous flowering allows for maximum out crossing as is evident from the significantly higher fruit set (91.37%) and seed set (4.77 mg) in open pollination (T

1). Insects like honeybees, bees, beetles

etc. were frequently observed visiting these flowers often making foraging between flowers either on the same plant or different plants. Khoshoo and Tandon (1963) have also reported bees (Apoidae, hymenoptera) as the pollinators of this species. Considering the high fruit set with abundant seed yield per capsule under natural (T

1) and cross pollination (T

3; Fig. 5) conditions,

it appears that these insects apart from wind are acting as pollination vectors.

The behaviour of pollinators strongly influences pollen flow and the ways the plants have adapted to these behavioural characteristics play an overriding role in gene dispersal and the genetic structure of the plant populations. As S. chirayita has been reported to be mostly bee pollinated (Joshi and Dhawan, 2005), bee behaviour is likely to be important in determining the patterns of pollen flow and hence gene flow. Although the species appears to be mostly cross pollinated, but self pollination is also possible. This is of great advantage to this species because of its endangered status. Out crossing would ensure creation of new gene combinations which will help its stock in overcoming the vagaries of fast climate change. Production of inbred seed appears to be a “feel safe” strategy to produce seeds when pollinators are scarce as has been postulated by Rao et.al., (2002) in Pterocarpus santalinus.

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References

Anonymous,1976. Wealth of India, Vol X: Sp-W (Raw Materials), CSIR Publication, New Delhi, pp. 77-81.

Anonymous, 2008 .http://www.nmpb.nic.in : Official website of National Medicinal Plant Board (NMPB), New Delhi.

Bawa,K. S. 1974. Breeding systems of tree species of a lowland tropical community. Evolution 28: 85-92.

Bhattacharya, A., and Mandal, S. 2000. Pollination biology in Bombax ceiba Linn. Current Science 79 : 1706-1711.

Blatter, E. 1984. Beautiful Flowers of Kashmir. II, International Book Distributors (IBD) Publications, Dehradun, p. 204

Clarke, C. B. 1885.The Flora of British India, Vol. IV, Hooker, J. D. (ed) L. Reene and Co., London, p. 780

Cochran, W. G. and Cox, G. M. 1967. Experimental Designs, 3rd edition. ,Asia Publication House, Bombay, p. 611

Elliot, F. C.1958. Plant Breeding and Cytogenetics, Mc Graw Hill Book Company Inc, New York, p. 395

.Joshi,P. and Dhawan, V. 2005. Swertia chirayita – an overview. Current Science 89 : 635-640.

Khoshoo, T. N. and Tandon, S. R. 1963. Cytological, morphological and pollination studies on some Himalayan species of Swertia. Caryologia 16:445-477.

Kirtikar, K. R. and Basu, B. D. 1975. Indian Medicinal Plants. Vol III, 2nd edition. ,Bishen Singh Mahendra Pal Singh, Dehradun, p. 2391

Mohi-ud-din, G. G, Nawchoo, I.A. and Wafai, B. A. 2007. Reproductive biology of Picrorhiza kurrooa Royle Ex Benth.- An endangered medicinal plant of the North West Himalaya. Phytomorphology 57 : 100-116.

Rao, S. P. and Raju A. J. Solomon. 2002. Pollination ecology of the Red Sanders Pterocarpus santalinus (Fabaceae), an endemic and endangered tree species. Current Science 83: 1144-1148.

Richards, A. J. 1997. Plant Breeding Systems. 2nd edition, Chapman and Hall, London, p. 529

Weberling, F. 1989. Morphology of Flowers and Inflorescence, Cambridge University Press, New York, p. 405

Table 1: Effect of different pollination methods on fruit and seed set in S.chirayita

Parameters/Treatments Fruit set

(%)

Seed yield per

capsule (mg)

T1

(Open pollination) 91.37

(73.14)

4.77

T2 (Bagging) 28.80

(63.69)

1.17

T3 (Open cross) 80.10

(32.42)

3.85

CD. (p= 0.05) 4.51 0.24

(Figures in parentheses are Arc sine transformed values)

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Fig. 1

Fig. 4 Fig. 5

Fig. 2 Fig. 3

Figs. 1 to 5: Swertia Chirayita, insect pollination (fig.1); flowering branch showing closeup of a flower (fig.2); post fertilization ovary (fig.3); self pollination bag opened to show autogamous fruit setting (fig.4); fruit setting under open pollination conditions (fig.5)