Some orchid species are difficult to propagate due to a variety of reasons and a few of these may also be on the list of endangered plants. To overcome hurdles in propagation, such orchids are then raised through tissue culture; by this technique, new plants are grown from different parts of the orchids/plants using a semi-solid medium as growth medium that is supplemented with minerals, under clean and sterile conditions.
A technique of tissue culture called mericloning has gained a lot of popularity in recent times for mass producing orchids. Mericlones literally means meristem cloning and meristematic tissues (or actively growing tissues) like the shoot tips, buds etc are used from the donor plant. These tissues are then grown on a semi-solid medium supplemented with minerals, under clean and sterile conditions.
How to mericlone that favourite orchid
1. Mericloning is done using techniques used in tissue culture. Materials required are sterile glassware (flasks, jars or test tubes), autoclaving apparatus (pressure cooker can also serve the purpose), distilled water (for cleaning and preparing the medium), growth-medium (agar-agar or its alternatives and mineral supplements), clean excision and transfer tools etc. Live material from the orchid from which mericlones are to be produced.
2. Commercially available ready to use tissue culture media can be obtained from companies like Sigma, which supplies tissue culture media meant specifically for orchids, like Knudson C Modified Orchid Medium, different types of Phytamax media. Some orchid species grow better in a particular growth medium like Cattleya likes MS Medium. The mineral supplements that are added to the growth medium, are more or less same for all orchids (though you may find experts disagreeing here), depending what you want to grow. Hormones like ‘cytokinins’ (found in coconut water) produces shoots while roots are produced when ‘auxins’ (found in willow bark and aspirins) are added.
3. Remove the shoot tip, which is devoid of any leaves (however small) from the orchid donor plant with a clean and sterile blade or a surgical blade.
1. Clean and disinfect your hands with ethyl alcohol.
2. Preparing the glassware and growth medium: The glassware and tools need to be washed properly with detergent and then thoroughly washed with pure sterile water. Prepare the growth medium (if using a commercial product, read instructions). Add the solidifying agent (agar-agar) in the end, heating the solution will help dissolve the agar. 10 gms of agar-agar can be dissolved in one litre of water. Adjust the pH of the growth medium (to 5.7). Pour the medium into the glassware. The growth medium containing glassware has to be autoclaved for about 20 minutes. You can also use the microwave instead of autoclaving.
3. Disinfecting the tissue: Dipping the tissue (to be used for cloning) for 15 to 20 minutes in a disinfectant removes surface microbes. You can use a low concentration of Sodium hypochlorite (1%), ethyl alcohol (70%) or chlorox bleach (10%). Ethyl alcohol or ethanol can also be used to clean the live material. Clean the tissue with clean and pure water twice or thrice to remove the disinfectant from the tissue surface.
4. After the medium has cooled and solidified, the cleaned and disinfected tissue parts have to be placed inside the glassware, on the growth medium, in as clean and aseptic conditions as possible. Seal the glassware tightly.
5. Maintenance after inoculation: Keep the culture containing glassware at 25 ± 2°C temperature. When kept at lower temperatures, the growth is slower.
6. Regular inspection of the material is required and if required the growing mericlones should be transferred to the new medium. This should be done in the case of bacterial infection inside the glassware or the material inside has overgrown space inside.
Mericlones are grown in flasks for 10 to 12 months before they are removed for transplanting in the pots.