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Mapping and Conserving the Genetic Diversity of Medicinal Plant Species through the Establishment of Forest Gene Bank Models
by Madhugiri Nageswara-Rao^1,3, K.N. Ganeshaiah³, R. Uma Shaanker²

¹University of Florida, IFAS, Citrus Research and Education Centre, 700 Experiment Station Road, Lake Alfred, FL33850, USA.
Department of ²Crop Physiology and ³Genetics and Plant Breeding, University of Agricultural Sciences, Bangalore- 560065, India.

¹Correspondence: E-mail: mnrao@crec.ifas.ufl.edu

The tropical forests are home for nearly 25% of the world’s most prescribed drugs (Miller 1994; Ved et al., 2001). About 70% of the 3,000 plants identified by the National Cancer Institute (NCI) as sources of cancer-fighting chemicals come from tropical forests alone. Commercial sale of these drugs account for more than $ 40 billion per year (Myers 1994; Ved et al., 2001). According to estimates, in the Indian subcontinent alone over 7000 species of plants are used for medicinal purposes (Uma Shaanker et al., 2001; Ved et al., 1998) and more than 95% of these medicinal plants are extracted from their wild habitats (FRLHT 1999). Because of the increased demand for these medicinal plant resources by the pharmaceutical industries (domestic as well as international) there is a growing threat to these medicinal plant species both globally as well as within the country (Uma Shaanker et al., 2001). Despite these threats, little is known of the possible impacts that such extraction has on the genetic diversity of the species (Uma Shaanker et al., 2001; Padmini et al., 2001; Nageswara Rao et al., 2000, 2007 a & b, 2008). Interests to maintain the genetic diversity of harvested populations are motivated in general by the need to conserve the array of gene assemblages that have evolved over millennia. These genes and their assemblages confer fitness advantage to the individuals and populations.

The existing conservation programs on such threatened economically important medicinal plants rely mainly on field banks, ex situ and in situ conservation methods. These approaches suffer from several limitations, as they represent only a proportion of global genetic variability (in situ) or relative isolation of the populations with a narrow genetic base (ex situ and field banks). Uma Shaanker and Ganeshaiah (1997) and Uma Shaanker et al. (2002) proposed a comprehensive ‘Forest Gene Bank’ (FGB) model aimed at conserving the widest possible spectrum of the genetic variability on a long-term basis which combines and compliments the virtues of in situ and ex situ methods of conservation. According to this model the genetic resources of a species are conserved in situ at a “sink” site into which the gene pool from various “source” sites are infused periodically and thus facilitate the continuous turn over of the genetic material

Forest Gene Bank model for sandal (Santalum album L.) in south India.
Source populations (WG = Western Ghats and EG= Eastern Ghats); Sink populations (DP= Deccan plateau). Populations circumscribed in the light aqua color zone in the map have high genetic conservation value.

We have proposed the establishment of the FGB model for the conservation of the genetic resources of Santalum album L., an economically important medicinal plant of southeast Asia. The sandal tree is generally known as the ‘Dollar earning parasite’, its wood is commercially known as ‘East Indian Sandalwood’ and its fragrant oil is known as ‘Queen of Essential oil’ (Nageswara Rao et al., 2008). India is among the chief exporters of sandalwood and oil in the world. Sandalwood oil is considered to be unique and is preferred for the preparation of top-class and sophisticated perfumes, formulations, flavors, cosmetics, toiletries, beauty aids and in medicines. Sandalwood is useful in treating nervous conditions that result from stressful situations or stress inducing activities. Some of these conditions include insomnia, depression or anxiety (Whittle, 2007).

We analyzed the genetic diversity of populations of the species in south India (using biochemical molecular markers) and identified the ‘hot-spots’ of genetic variability (Nageswara Rao et al., 2007a, 2008). Conventionally, conservation of the genetic variability would tend to be focused on the hot-spots, where perhaps in situ sites will be located. However, we found that through this approach, a large proportion of the principal component space of the distribution of genetic variability would go underrepresented. Uma Shaanker and Ganeshaiah (1997) and Uma Shaanker et al. (2001) proposed that under these circumstances, it might be worthwhile to establish an FGB, which would encompass a wider spectrum of genetic variability. The establishment of the FGB requires the identification of a “sink” population into which genes from identified “source” populations can be infused periodically. Sink populations could be among those whose mean genetic distance with the rest of the populations is the least; these populations would then be the most representative of the “global” population, while the source populations could be those which represent distinct genetic clusters (or provenances). Our analysis indicated that the population at Deccan plateau, which are the most representative of the studied populations could serve as the “sink” population into which genes (either through pollen grains or seed dispersal) can be infused from other sites, “source”, at Western Ghats and Eastern Ghats (which account for distinct PCA-space). We propose that long-term monitoring and management of such FGB’s can help conserve the genetic resources of tree species in a cost-effective manner. The FGB is especially important in the conservation of genetic resources of trees whose populations are highly fragmented and sparse, a recurrent feature of many economically important and rare and threatened plants in the tropics.

Steps involved in establishment of Forest Gene Bank (Uma Shaanker et al., 2002)

Step 1: Mapping the geographic distribution of given species
Step 2: Mapping the genetic variability distribution and identification of distinct genetic populations
Step 3: Identification of "SINK" (recipient) and "SOURCE" (donor) populations
Step 4: Genetic enhancement of threatened/critically endangered species through enrichment planting (or pollen additions)
Step 5: Step 4 to be repeated periodically involving existing populations/new populations/populations threatened
Step 6: Periodic monitoring of gene frequency and other genetic diversity parameters in sink populations

References:

FRLHT (1999) The key role of forestry sector in conserving India’s medicinal plants: conceptual and operational features, pp 1-31, Published by FRLHT, Bangalore, India.

Miller GT, ed. (1994) Living in the environment, pp. 1-701, International Thomson Publishing, Bemont, California, USA.

Myers N (1994) Tropical forests and their species: going, going ? pp 288-289. Living in the environment, Miller GT (ed.), International Thomson Publishing, Bemont, California, USA.

Nageswara Rao M, Padmini S, Ganeshaiah KN, Uma Shaanker R (2000) Genetic diversity of Terminalia bellerica and T. chebula in deciduous forests of south India: Impact of harvesting and other anthropogenic pressures. National seminar on the Frontiers of Research and Development of Medicinal Plants, JMPAS, Sep-1, Vol 22: pp 58, CIMAP, CSIR, Lucknow-226 015.

Nageswara Rao M, Ganeshaiah KN, Uma Shaanker R (2007a) Assessing threats and mapping sandal (Santalum album L.) resources in peninsular India: Identification of genetic hot-spot for in-situ conservation. Conservation Genetics, 8:925–935.

Nageswara Rao M, Ramesha BT, Ravikanth G, Ganeshaiah KN, Uma Shaanker R (2007b) Cross-species amplification of Coconut micro satellite markers in Rattans. Silvae Genetica, 56:(6)282-286.

Nageswara Rao M, Ganeshaiah KN, Uma Shaanker R (2008) Fading fragrance? Deccan Herald, Science and Technology, May 6th, 2008 http://www.deccanherald.com/Content/May62008/snt2008050566414.asp

Padmini S, Nageswara Rao M, Ganeshaiah KN, Uma Shaanker R (2001) Genetic diversity of Phyllanthus emblica in tropical forests of South India: Impact of anthropogenic pressures. Journal of Tropical Forest Science, 13(2):297-310.

Uma Shaanker R, Ganeshaiah KN (1997) Mapping genetic diversity of Phyllanthus emblica: Forest gene banks as a new approach for in situ conservation of genetic resources. Current Science, 73: 163-168.

Uma Shaanker R, Ganashaiah KN, Bawa KS (eds.) (2001) Forest Genetic Resources: Status, Threats and Conservation Strategies, Oxford and IBH, NEW Delhi, India.

Uma Shaanker R, Ganeshaiah KN, Nageswara Rao M, Ravikanth G, (2002) Forest gene banks - a new integrated approach for the conservation of forest tree genetic resources, pp 229-235, Managing Plant Genetic Resources, Engels JMM, Brown AHD and Jackson MT (eds.), CABI Publishing, Nosworthy. Wallingford. Oxon. UK.

Ved DK, Prathima CL, Mortan N, Shankar D (2001) Conservation of India’s medicinal plant diversity through a novel approach of establishing a network of in situ Gene Banks, Uma Shaanker R, Ganashaiah KN, Bawa KS (eds.), Forest Genetic Resources: Status, Threats and Conservation Strategies, pp. 183.95. Oxford and IBH, New Delhi, India.

Ved DK, Vijay Barve, Noorussisa Begum, Latha R (1998) Eco-distribution mapping of the priory medicinal plants of southern India. Current Science, 75(3): 205-208.

Whittle A (2007) Therapeutic Properties of Sandalwood Essential Oil, EZine articles http://ezinearticles.com/?Therapeutic-Properties-of-Sandalwood-Essential-Oil&id=845206.

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