Temporary immersion systems for efficient mass propagation of medicinal and aromatic plants

Plant production through in vitro propagation is nowadays a well-established industry. Micropropagation protocols are widely based on semi-solid nutrient media, despite their inherent limitations. Expensive gelling agents, large numbers of relatively small containers, limited nutrient diffusion, large culture areas, and extensive manual handling can result in an unacceptable cost-benefit ratio. This is especially the case when the market demand for a given plant species is moderate. The use of liquid nutrient media offers various advantages like reduced production costs, improved physiological status of propagules, easy renewal of medium, scale up to bioreactor size, and possibilities of automation. However, in most plant species continuous culture of the explants in liquid medium leads to hyperhydration and subsequent loss of the propagules. This can be overcome with temporary immersion systems (TIS)where the plant material is only periodically in contact with the medium. The present contribution deals with the in vitro propagation of selected medicinal and aromatic plants in a twin flask TIS. Individual optimization of immersion times mostly resulted in higher multiplication rates when compared to conventional systems using semi-solid media. The additional benefits like cheaper nutrient media, reduced labour costs better utilization of shelving areas make TIS attractive alternatives to currently used micropropagation techniques.