Bringing medicinal plants into cultivation: opportunities and challenges for biotechnology

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Consumption of herbal medicines is widespread and increasing. Harvesting from the wild, the main source of raw material, is causing loss of genetic diversity and habitat destruction. Domestic cultivation is a viable alternative and offers the opportunity to overcome the problems that are inherent in herbal extracts: misidentification, genetic and phenotypic variability, extract variability and instability, toxic components and contaminants. The use of controlled environments can overcome cultivation difficulties and could be a means to manipulate phenotypic variation in bioactive compounds and toxins. Conventional plant-breeding methods can improve both agronomic and medicinal traits, and molecular marker assisted selection will be used increasingly. There has been significant progress in the use of tissue culture and genetic transformation to alter pathways for the biosynthesis of target metabolites. Obstacles to bringing medicinal plants into successful commercial cultivation include the difficulty of predicting which extracts will remain marketable and the likely market preference for what is seen as naturally sourced extracts.

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The growing pressures on wild medicinal plants

The World Health Organization has estimated that more than 80% of the world's population in developing countries depends primarily on herbal medicine for basic healthcare needs [1]. The use of herbal medicines in developed countries is also growing and 25% of the UK population takes herbal medicines regularly [1]. Approximately two-thirds of the 50 000 different medicinal plant species in use are collected from the wild [2] and, in Europe, only 10% of medicinal species used commercially are

The option of domestic cultivation

Although adequate protection of some species can be achieved through increased regulation and the introduction of sustainable wild harvesting methods, a more viable long-term alternative is to increase domestic cultivation of medicinal plants. Cultivation also opens up the possibility of using biotechnology to solve problems that are inherent in the production of herbal medicines. These include species misidentification, genetic and phenotypic variability, variability and instability of

Growth requirements of medicinal plants

Cultivation of some herbs has proved difficult because of low germination rates or specific ecological requirements [1]. There could simply be a lack of knowledge about the specific requirements for pollination, seed germination and growth. Low germination rates frequently result from fungal infection or mechanical damage to seeds and can be improved by seed treatments and by ensuring optimum storage conditions. Stratification, the artificial emulation of environmental conditions required for

Cultivation to control the content of active compounds

Controlled growth systems also make it feasible to contemplate manipulation of phenotypic variation in the concentration of medicinally important compounds present at harvest. The aim is to increase potency, reduce toxin levels and increase uniformity and predictability of extracts. The target compounds are almost invariably secondary metabolites, which, for the plant, frequently serve as adaptations to fluctuating temperature and light conditions (e.g. antioxidants), stress (e.g. proline),

Traditional breeding principles as applied to medicinal plants

By bringing herbs into cultivation, traditional and biotechnological plant-breeding techniques can be applied at the genetic level to improve yield and uniformity, and to modify potency or toxicity. Seed production and viability are target traits in which considerable success can be expected simply by selecting vigorous and fertile genotypes, a process that also establishes a population adapted to the growing conditions provided. Artificial selection is, however, time consuming and the process

Genetic transformation systems for medicinal plants

Direct manipulation of DNA sequences to alter gene expression in medicinal plants is an area that is ripe for expansion. Provided a trait can be related to one or a small number of genes, in principle, it is open to modification. Although the primary target for trait manipulation in medicinal plants is the content of active compounds, for development as crops, basic agronomic characters related to uniformity, stability, growth and development, and resistance to biotic and abiotic stresses, must

Pathway engineering in medicinal plants

Increasing the production of active phytochemical constituents is a well-established target for genetic manipulation but presents some severe challenges. In particular, the metabolic pathways by which active compounds are biosynthesized are mostly poorly understood, and relatively few genes for key enzymatic or regulatory steps have been isolated. Nevertheless, there are examples of pathway engineering leading to improvements of potential value in the breeding of medicinal plants (see reviews 42

Engineering agronomic traits in medicinal plants

Just as resistance to herbicides, pests and diseases are the characters that have led the way in the introduction of transgenic crop species, so too have these characters been among the first targets for medicinal plant biotechnology. Transgenic Atropa plants resistant to the herbicides bialaphos and glufosinate have been described [49] and Panax ginseng, resistant to the herbicide Basta, has been generated by transformation with the enzyme phosphinothricin acetyl transferase [50]. Resistant

Public perception of biotechnology: implications for medicinal plant cultivation

The commercial viability of bringing medicinal plants into domestic cultivation and the potential for increased use of modern biotechnologies are likely to be strongly influenced by the popular perceptions of both herbs and biotechnology. One of the main attractions of herbs as medicines is their ‘natural’ status and the associated, but erroneous, view that they must therefore be safe and intrinsically good for us. In stark contrast is the popular view of crops bred with the assistance of

Future prospects

In regions such as Western Europe, the trend away from commodity-type agriculture towards niche production of high-value species for non-food markets offers major opportunities for the application of plant biotechnology. Medicinal herbs are taking their place alongside the likes of bioenergy crops, sources of renewable industrial feedstocks and bioremedials as potential beneficiaries of technological solutions originally devised for the food chain. The twin political issues of world energy

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