Submitted to: Propagation of Ornamental Plants
Publication Type: Peer reviewed journal
Publication Acceptance Date: 11/25/2010
Publication Date: 1/11/2011
Publication URL: www.ars.usda.gov/main/site_main.htm?modecode=53-06-20-00
Citation: Preece, J.E. 2011. Micropropagation in stationay liquid media. Propagation of Ornamental Plants. 10(4):183-187. Interpretive Summary: Clonal micropropagation typically employs shoot tip or nodal explants from which axillary shoots are induced to elongate. Alternately, one shoot grows and is subdivided into nodal segments, from which axillary shoots elongate to be further subdivided or rooted. To avoid somaclonal variation, adventitious shoot organogenesis and somatic embryogenesis are avoided and the focus is on production of axillary shoots and/or nodes. Shoot explants and proliferating and elongating shoots are cultured in vitro in a wide variety of vessels containing defined media that are usually gelled with agar and or gelcarin. Gelling of media is a method of providing support for the plant tissue so that it does not sink to the bottom of the vessel where conditions may be anaerobic leading to stress, poor growth, and death. The focus of this paper is the elimination of gelling agents and strategies for use of stationary liquid media without a filter paper or other support. On species where successful, time, labor, and money spent on gelling agents and solubilizing them by use of heat is eliminated (Savangikar et al. 2005). Dispensing media into vessels is safer and more comfortable to micropropagation laboratory workers because the liquid medium is not scalding hot because it is not heated. Additionally, media can be changed easily and quickly and cleaning of culture vessels is facilitated compared to when a gelling agent is used. In vitro growth can also be improved substantially if gelling agents, especially agar, are omitted from the medium. In some cases, labor in the transfer hood can be much more efficient if stationary liquid overlays are used on agar rather than traditional transfers to fresh medium.
Technical Abstract: Micropropagation of many species is reduced as agar concentration increases. Eliminating agar or other gelling agent completely can improve microshoot proliferation and growth. If established shoot cultures are placed in vitro into shallow layers of liquid media, most of the shoot masses will remain above the media where there is sufficient aeration. Not all species will grow normally on stationary liquid media and water soaking or hyperhydricity will result. Hyperhydricity can be overcome by use of temporary immersion bioreactors or by using agar solidified media. If agar is used, rather than transfer to new medium at approximately monthly intervals, liquid medium can be added as a thin layer to the top of the agar and good growth will result. For most species, it is not necessary to provide any additional support such as rafts, filter paper, sponges, glass wool, etc. if the shoot masses are sufficiently large when transferred to stationary liquid medium. Therefore, cultures can be established using a gelled media and once they have grown, they can be transferred into stationary liquid media, which will improve micropropagation efficiency.