Micropropagation of Plants

Micropropagation (or in vitro propagation) is the most common term used for clonal, true-to-type propagation of plants by a variety of tissue, cell and organ culture methods. It implies the aseptic culture of small sections (i.e., explants) of tissues and organs, in closed vessels with defined culture media and under controlled environmental conditions. Micropropagation, in addition to genetic engineering, is at present the most commercially efficient and practically-oriented plant biotechnology, resulting in rapid generation of a large number of clonal plants of many plant species, which are in many cases also virus- or other pathogen-free. It is now the technical link in the generation of transgenic plants and somatically-bred plants. Following a brief history and a presentation of the objectives of micropropagation and related applications, we discuss the basic biological principles of micropropagation, including totipotency of plant cells, cell division and callus formation, and the major forms of differentiation and regeneration (axillary bud proliferation, organogenesis, and somatic embryogenesis). The practice of micropropagation is dependent on precise implementation of several technical aspects and developmental/growth stages, including the use of proper explants, asepsis (axenic culture), culture media composition and use of appropriate growth vessels, and the monitoring and control of macro- and micro-environmental conditions within the laboratory and acclimatization facility. We include a review of the design and maintenance of the laboratory and further discuss the advantages and disadvantages of micropropagation and the organizational, economic and financial aspects of commercial micropropagation. In addition, we address critical limiting factors such as recalcitrance, somatic variation and trueness-to-type, and contamination. New trends in improving the efficiency of micropropagation conclude this chapter.