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India is a known mega-diversity centre harbouring a multitude of medicinal plant species each presumably studded with as yet unknown genetic and chemical variations of economic importance. Out of an estimated 17,000 higher plant species occurring in India, more than 1000 species are used over several centuries in the traditional systems of medicine viz. Ayurveda, Siddha, Unani and Amchi. The villagers and tribal folks spread across the length and breadth of the country make use of more than 7000 plant species through oral traditions (Pushpangadan et al., 1997). Nearly 3/4 of the herbal drugs and perfumery products used in the world are available in natural state in India. Therefore, the rich and varied plant diversity, especially the genetic diversity of medicinal and aromatic plants, is one of India's important strengths and is the bedrock for all future bioindustrial developments. Unfortunately, the renowned medicinal plant wealth of India has seldom been subjected to genetic scrutiny keeping in mind the latent and patentable properties and economic utility of the selected plant types. As severe habitat losses and consequent endangerment and extinction of known and hitherto lesser known species of economic value are not uncommon in the Indian subcontinent, it is imperative that heritable variations within the otherwise unimproved natural populations of prospective taxa are studied for selection, improvement and development of suitable cultivars. Otherwise called bioprospecting, this line of research is essential to fish out useful genes and gene products for commercialisation in the now unfolded patent regime. Knowledge of the genetic diversity is also a prerequisite for any in situ and ex situ conservation schemes (Hamrick et al., 1991) as it is not practical to conserve all genotypes of a given species against the mass extinction spasm projected for the 21st century (Raven, 1999).

Andrographis paniculata Nees (Acanthaceae), the Kalmegh of Ayurveda selected for the present investigation is an erect annual herb (Fig. 1.1) extremely bitter in taste in each and every part of the plant body. The plant is known in north-eastern India as ‘Maha-tita’, literally ‘king of bitters’ and known by various vernacular names (Table 1.1). It is also known as ‘Bhui-neem’, since the plant, though much smaller in size, shows similar appearance and has bitter taste as that of Neem (Azadirachta indica). Incidentally, the genus Andrographis consists of 28 species of small annual shrubs essentially distributed in tropical Asia (Fig 1.2). Only a few species are medicinal, of which A. paniculata is the most popular.

It grows erect to a height of 30-110 cm in moist shady places with glabrous leaves and white flowers with rose-purple spots on the petals. Since ancient times, A. paniculata is used as a wonder drug in traditional Siddha and Ayurvedic systems of medicine as well as in tribal medicine in India and some other countries for multiple clinical applications. The therapeutic value of Kalmegh is due to its mechanism of action which is perhaps by enzyme induction. The plant extract exhibits antityphoid and antifungal activities (Anonymous, 1985). Kalmegh is also reported to possess antihepatotoxic, antibiotic, antimalarial, antihepatitic, antithrombogenic, antiinflammatory, antisnakevenom, and antipyretic properties to mention a few, besides its general use as an immunostimulant agent (Table 1.2). A recent study conducted at Bastyr University, USA confirms anti-HIV activity of andrographolide (Calabrese et al., 2000).

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