India is endowed with a rich wealth of medicinal plants.These plants have made a good contribution to the development of ancient Indian materia medica. One of the earliest treatises on Indian medicine,the Charak Samhita(1000 B.C),records the use of over 340 drugs of vegetable origin. Most of these continue to be gathered from wild plants to meet the demand of the medical profession.Thus, despite the rich heritage of knowledge on the use of plant drugs, little attention had been paid to grow them as field crops in the country till the latter part of the nineteenth century.
During the past seven or eight decades, there has been a rapid extension of the allopathic system of medical treatment in India. It generated a commercial demand for pharmacopoeial drugs and products in the country, Thus efforts were made to introduce many of these drug plants into Indian agriculture, and studies on the cultivation practices were undertaken for those plant which were found suitable and remunerative for commerical cultivation. In general, agronomic practices for growing poppy, isabgol, senna, cinchona, ipecac, belladonna, ergot and a few others have been developed and there is now localized cultivation of these medicinal plants commercially. The average annual foreign trade in crude drugs and their phytochemicals is between 60 and 80 million rupees and this accounts for a little over 0.5 per cent of the world trade in these commodities.
The curative properties of drugs are due to the presence of complex chemical substances of varied composition (present as secondary plant metabolites) in one or more parts of these plants. These plant metabolites in one, according to their composition, are grouped as alkaloids, glycosides, corticosteroids, essential oils, etc. The alkaloids form the largest group, which includes morphine and codein (poppy), strychnine and brucine(nux vomica), quinine(cinchona), ergotamine(ergot), hypocyamine,(beeladona) ,scolapomine(datura), emetine(ipecac), cocaine(coco), ephedrine(ephedra), reserpine(Rauwolfia), caffeine(tea dust), aconitine(aconite), vascine(vasaca). santonin(Aremisia), lobelin(Lobelia) and a large number of others. Glycosides form another important group represented by digoxin(foxglove), stropanthin(strophanthus), glycyrrhizin(liquorice), barbolin (aloe), sennocides (senna),etc. Corticosteroids have come into prominence recently and diosgenin(Dioscorea), solasodin(Solanum sp.),etc. now command a large world demand. Some essential oils such as those of valerian kutch and peppermint also possess medicating properties and are used in pharmaceutical industry. However, it should be stated in all fairness that our knowledge of the genetic and physiological make-up of most of the medicinal plants is poor and we know still less about the biosynthetic pathways leading to the formation of active constituents for which these crops are valued.
During the last two decades, the pharmaceutical industry has made massive investments on pharmacological, clinical and chemical researches all over the world in an effort to discover and still more potent plant drugs ; in fact, a few new drug plant have suceessfully passed the tests of commercial screening. However, benefits of this labour would reach the masses when the corresponding support for agricultural studies for commercial cultivation is provided. Infact, agricultural studies on medicinal plants, by its very nature, demand an equally large investment and higher priority. India, in particular, has a big scope for the development of the pharmaceutical and phytochemical industry.
The Indian Pharmacopoeia(1966) recognizes eighty five drug plants whose ingredients are used in various pharmaceutical preparations. We shall, however, confine our treatment to a few important commercially grown medicinal plants whose cultivation deserves priority in out national economy.