natural-products-in-plant-pest-management

270 S. Hettiarachiarea. Similarly regenerated plants through micropropagation are extremelyimportant to relieve the pressure on the wild plants exerted by overexploitation.Depending on the tissue specificity of the product, the harvesting maybe destructive as vital parts, such as roots or bark, of the plant may have tobe removed in harvesting, imposing additional heavy pressure on wildpopulations.As mentioned in the review by Chaturavedi et al. (2007), the micropropagationand field establishment of Dioscorea floribandu in India has been a successstory. They calculate the number of plantlets that could be obtained within ayear starting from a single nodal cutting as 2,560,000 in comparison to a maximumof 10 plants from a single tuber which can be obtained after 3 years ofgrowth in the field. Thus there cannot be any doubt about the power of micropropagation,especially for those plants that cannot be rapidly propagatedotherwise. Even with those plants, the advantage of having propagation oftrue-to-type plants cannot be underestimated. The report criticizes the progressmade in India in the micropropagation of medicinal plants, despite thefact that experiments in various institutes have come up with protocols endingup in the field of a long list of medicinal plants. This fact is mentioned here inorder to highlight the inefficiency of technology transfer.The extraction of natural products from wild or field-grown plants, however,suffers from many impediments such as low production, and no uniformityof production from place to place, from time to time and from one plantvariety to another. Riker and Hildebrandt (1958) were probably the first scientistswho had vision of the power of plant tissue culture in natural productsynthesis. As tissue and cell cultures can be maintained under desirable cultureconditions, once culture media and culture conditions for optimumgrowth and optimum production have been worked out, the above problemscan be mitigated. When tissue is collected from cultivated or wild plants,there is a long waiting time from plantlet formation to product formationas extraction may be possible only after reaching maturity or some otherstatus.Among several other scientists working in the late 1970s and early 1980s,Berlin (1984) visualized plant tissue culture as a future potential process fornatural product synthesis and stressed that more research was needed for theelucidation of regulatory controls in biosynthetic pathways. Alfermann andPetersen (1995) demonstrated the potential of plant tissue and cell culturesfor natural product synthesis by referring to research by many scientists whowere able to produce various metabolites at the laboratory scale.It has been possible to manipulate biosynthesis through genetic manipulation,and overexpression and expression of new products has been possiblein cultured cells and organs. Organogenesis may be required for generatingcertain tissue-specific substances (Rout et al., 2000). The primary purpose ofplant tissue culture was the exploitation of the totipotency of the plant cellfor mass-scale propagation of useful varieties of plants. The plants obtainedare expected to be genetically identical and hence form a clone. However,variations occur within the clone due to somaclonal variations as a result ofreplication errors in mitotic cell divisions. While it seems undesirable, the