Cultivation of Herbal Drugs, Biotechnology, and In Vitro Production of Secondary Metabolites, High-Value Medicinal Plants, Herbal Wealth, and Herbal Trade

Abstract

Medicinal plants are used directly as therapeutic agents in various traditional practices, and medicinal plants like Dioscorea deltoidea, Papaver somniferum, Atropa belladonna, Rauvolfia serpentina, Hyoscyamus niger, Digitalis lanata, Datura metel, Digitalis purpurea, Pilocarpusa bonandi, Cinchona ledgeriana are contributing directly several prescribed medicinals. The ever-increasing trend in the use of medicinal herbs and herbal products in therapeutic purpose, research, and trade has created tremendous pressure on supply from their wild source. Under the circumstances of increasing demand, indiscriminate and over extraction from the wild, habitat destruction, etc., many of the naturally growing medicinal herbs are on the verge of extinction and thus unsustainability in the supply of medicinal plants from natural source. Systematic cultivation of medicinal herbs would be a viable alternative to overcome this unsustainability problem of medicinal plants from the wild source and cultivation offers opportunity to optimize yield and achieve a uniform, high-quality product. Several drugs like cardamom, cannabis, cinnamon, ginger, cinchona, opium, linseed, and fennel are now obtained almost exclusively from cultivation source. Benefits of cultivation of medicinal plants are widely viewed as a means for meeting current and future demands for large volume production of plant-based drugs; cultivation can reduce growing pressures on wild medicinal plants and ensure pure and smooth supply; means of earning livelihood, etc. The WHO has published wide-spectrum guidelines for good agricultural and collection practices for sustainable production of raw material of quality and standardized herbal ingredients to ensure quality of herbal medicines. Medicinal plants may be cultivated by the following: (a) agricultural practice at field level and (b) in vitro production of secondary metabolites. Commercial cultivation at field level (open field, homestead garden, forest floor) is an agronomic practice and offers the opportunity to overcome the problems that are inherent in herbal extracts like misidentification, genetic and phenotypic variability, extract variability and instability, toxic components, and contaminants. The agronomic method of crop cultivation includes systematically the steps like site and season selection, selection of crop, true seed or vegetative propagule, land preparation and basal manuring and fertilization, spacing, seed sowing or seedling transplantation, split application of fertilizer, irrigation, intercultural operation, and weed control and harvesting. Large-scale plant tissue or organ culture for the production of secondary metabolites is an attractive alternative approach to traditional methods of cultivation of drug plants. The advantages of this method are many; it is independent of soil, paste, climatic interference, geographical location, and it can ultimately provide a continuous and reliable source of natural products. Considering the cost involvement, plant tissue culture for secondary metabolites is now limited to only high-value compounds such as diosgenin-derived steroid hormone precursors, digitalis glycosides, berberine isoquinoline alkaloid, taxol, paclitaxel, and several other toxoids—complex diterpene alkaloids. Herbal plants have global market worth about US$62 billion per annum, and so they may be a good export item and wealth of a country and should be cultivated in commercial scale like any other conventional cash crops. As cultivation of medicinal plants at commercial scale is comparatively a new concept in many countries to meet the demand of internal and foreign markets and earning livelihood of the rural people, medicinal plants are important natural wealth and herbal wealth, play significant role in providing primary health-care services to rural people, and serve as raw material in traditional and modern pharmaceutical as well as in cosmetic, agricultural, and food industries. Substantial amount of foreign exchange can be earned by exporting medicinal plants to other countries. In this way, indigenous medicinal plants may play a significant role in the economy of a country.