61 Application of Bioreactor System for Mass Propagation of Horticultural Plants K.Y. Paek 1 • D. Chakrabarty 1,2* 1 Research Center for the Development of Advanced Horticultural Technology; Chungbuk National University, Cheong-ju 361-763, Korea 2 Floriculture Section, National Botanical Research Institute, Lucknow, India Corresponding author: * debasis1972@rediffmail.com Keywords: Bioreactor, balloon type bubble bioreactor, micropropagation, organogenesis, somatic embryogenesis ABSTRACT Conventional micropropagation technique is a typically labor-intensive means of producing elite clones. High production costs generally limit the commercial use of micropropagation. Bioreactor technology offers various advantages due to possibilities of automation, saving labor and reducing production costs by providing optimum growth conditions to achieve both maximum yield and high quality of propagules, or to keep the production costs as low as possible by integrating automated facilities and simple low cost devices. The use of bioreactor technology is starting to be commercialized and the results suggest the practical applicability of this technique in plant propagation. Here we attempted to focus on the development of cost-effective methods for commercial micropropagation of several important horticultural plants using a bioreactor system and also to identify the problems related to large-scale plant micropropagation. 1. INTRODUCTION Efficient commercial micropropagation depends on rapid and extensive proliferation along with the use of large-scale cultures for the multiplication phase. Mechanization and automation of the micropropagation process can greatly contribute to overcoming the limitation imposed by existing conventional labor-intensive methods. Automation of micropropagation in bioreactors has been advanced by several authors as a possible way of reducing costs of micropropagation (Preil 1991, Sharma 1992, Takayama and Akita 1994, Christie et al. 1995, Leathers et al. 1995, Son et al. 1999, Ibaraki and Kurata 2001, Chakrabarty and Paek 2001, Paek and Chakrabarty 2003, Paek et al. 2005, Ziv 2005). Bioreactors containing liquid media are used for large-scale growth of various tissues. The use of bioreactors for micropropagation was first reported in 1981 for begonia propagation (Takayama and Misawa 1981). Since then it has proved applicable to many species through the use of shoots, bulbs, microtubers, corms and somatic embryos (Paek et al. 2005). Information on the use of bioreactors as a system for plant propagation through the organogenic or embryogenic pathway is presently being applied to several ornamental and some vegetable and fruit crop plants (Table 1). Paek and Chakrabarty (2003) and Paek et al. (2005), reviewed different reactor configurations for plant cell suspensions, plant tissue and organ cultures. The relative advantages and selection criteria for various reactor configurations were discussed for specific process applications. Those bioreactors are fundamentally classified by agitation methods and vessel construction into: a) mechanically agitated (stirred tank bioreactor, rotating drum bioreactor, spin filter bioreactor), or b) pneumatically agitated and non-agitated bioreactors (simple aeration bioreactor, bubble column bioreactor, air-lift bioreactor, balloon type bubble bioreactor-BTBB). Mechanically agitated bioreactors depend on a variety of impeller designs but still it has several limitations such as high power consumption, high shear and problems with sealing and stability of shafts in tall bioreactors. Aeration, mixing, and circulation in bubble column or airlift bioreactors is provided by air entering the vessel through a sparger; as the air bubbles rise, they lift the plant biomass and generate efficient mixing in the liquid phase. In recent years, large-scale cultivation of plant cells, embryos, or organs has made use of airlift or bubble column bioreactors and, to a lesser extent, of mechanically stirred tank bioreactors, due to the former lower shearing force properties. The disadvantages of air-lift and bubble column bioreactors are foaming induced by large volumes of air, and growth of cells in the head space. The phenomenon of foaming and cell growth on the wall of vessel is due to the diameter of the vessel and the top of the vessel is the same (Paek et al. 2001). To overcome this problem we designed a bioreactor that has a larger top section diameter and/or a balloon type bioreactor (BTBB; Figs. 1A-E). Usually micropropagation can be achieved mainly in two different ways: a) shoot proliferation via shoot meristems or axillary buds or b) by somatic embryogenesis. The technique, however, is still costly due to intensive hand manipulation of the various culture phases and is not used commercially for all plant species. In this chapter we summarise the problems related to large-scale plant propagation using a bioreactor system within the context of the most recent developments in application of bioreactors for large-scale propagation of horticultural plants.