MICROPROPAGATION OF PLANTS BETH LOBERANT 1 and ARIE ALTMAN 2 1 Desert Labs, Kibbutz Yotvata, Israel 2 Robert H. Smith Institute of Plant Sciences and Genetics in Agriculture, The Hebrew University of Jerusalem, Rehovot, Israel INTRODUCTION Terminology Micropropagation (other synonyms include: in vitro propagation) is the most common term used for clonal, true-to-type propagation of plants by a variety of tissue, and cell and organ culture methods. The terms axenic or aseptic culture and plant tissue culture refer to other applications of plant tissue culture which are not necessarily strictly propagation. Micropropagation 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 commer- cially efficient and practically oriented plant biotechnol- ogy, 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. Moreover, micro- propagation is now the technical link in the generation of transgenic plants and otherwise somatically bred plants. Efficient production of transgenic plants relies heavily, if not exclusively, on the ability to regenerate whole plants from those cells, tissues, or organs into which ‘‘foreign’’ DNA has been inserted and expressed. Additionally, micro- propagation and other tissue-culture techniques, as well as new modalities in molecular biology, can allow for faster testing of new genotypes or field selections of plants. Brief History The science and art of plant tissue culture, and indeed of plant biotechnology, had its roots in the vision of the Austrian botanist Gottlieb Haberlandt (1854–1945) who visualized in 1902 the ability ‘‘to culture isolated vegetative cells from higher plants in simple nutrient solutions.’’ The first successful prolonged in vitro cultivation of plant tissues and organs—and their proliferation and differentiation—included, among others, tomato roots (1), tobacco, carrot calluses, and cambial tissues (2a,2b) shoot tips and meristems (3). Soon, an entire new arsenal of procedures and techniques for controlling plant regeneration and morphogenesis in Encyclopedia of Industrial Biotechnology: Bioprocess, Bioseparation, and Cell Technology, edited by Michael C. Flickinger Copyright  2010 John Wiley & Sons, Inc. culture became available to the scientific community. Some notable major discoveries included chemical and hormonal control of regeneration (4), basic and applied aspects of organogenesis and somatic embryogenesis (5), practical micropropagation and production of virus-free plants (6), haploid plants (7,8), culture and regeneration of protoplasts (9), production of secondary metabolites (10) and large-scale cell culture in bioreactors (11), to mention just a few milestones. This led, following many pioneering studies in dozens of laboratories around the world, to the first true breakthrough of plant biotechnology, namely, commercial micropropagation (12). In vitro mass production of clonal propagules of a small number of agriculturally important plants, primarily ornamentals, became practical in the early 1970s (13–15). Since then, the diversity of plant species that can be propagated in vitro has dramatically increased, and it is now practiced on a commercial scale worldwide, resulting in over 600 millions of plants annually, 60%–75 % of them being flowers and ornamental plants (16–20). Micropropagation is now an integral part of the plant propagation industry, complementing or replacing other methods of clonal vegetative propagation (cutting, grafting, division, and separation), or in some cases also propagation by seeds. The history, science, and practice of plant micropropaga- tion have been dealt with extensively in several books and reviews (14,19–33). Ongoing achievements in the in vitro culture of pollen, protoplasts, and cell suspensions, and their ability to regenerate whole plants, resulted in new disciplines of plant science: somatic cell genetics and metabolite produc- tion; somatic hybrids; production of haploid plants; selec- tion of variants and mutants; and improved generation of metabolites. All became available for the community of plant scientists and breeders, expanding the diversity and the agronomic and commercial value of plants. Objectives of Micropropagation and Related Applications 1. Large-scale clonal propagation where conventional vegetative propagation is not possible or practical; where there is a limited supply of stock plant mate- rial; or where the traditional vegetative propagation coefficient (rate) is very low 2. Initial rapid clonal propagation of new varieties (with offspring from sexual breeding and rare species selected from the wild) 3. Embryo rescue where seed and embryo germination is done in vitro to save otherwise nonviable sexual offspring 4. Recovery of pathogen-free propagation material 5. In vitro gene-banks for crop improvement 6. Breeding by somatic cell genetics (with haploid pro- duction from in vitro cultured pollen, somatic fusion of protoplasts or in vitro selection of somaclonal variation) 1