Tissue culture (TC) is a term for a form of high-tech plant cuttings. Instead of making a 3 inch long cutting of a plant stem and sticking it in potting soil or perlite to form one new plant, tissue culture involves taking a very small piece of a plant and turning it into thousands of new plants.

The difference between TC and regular cuttings is that this space age procedure must be done under totally sterile conditions. This makes it very costly since it requires laboratory type equipment and specialized techniques. Therefore, TC is generally used to multiply plants that are very difficult to propagate with other more low-tech methods. Or, it may be used to very rapidly reproduce high value plants where large numbers are in demand.

The TC Process - The following is a general description of the tissue culture process which may vary somewhat from lab to lab.
 

  • A part of the mother plant (called the explant) is placed in a sterilizing solution in order to kill any fungal spores that might be on its surface.
     

  • Using a cutting instrument such as a scalpel which has been sterilized in a flame, a very small piece of a root, leaf, stem or bud is cut from the sterile explant tissue.
     

  • This piece is placed in a test tube which contains a sterile mixture of organic matter called agar that is meant to act as nutrients. Also included with be one or more plant hormones to stimulate the process further. These mixtures can become quite exotic and each TC lab will develop its own favorite mix that works best for them.
     

  • The tubes are placed in a sterile, growing chamber with artificial light and climate control.

  • Eventually, the tiny cutting begins to multiply on the growing medium. It is then taken out, cut into even more pieces and returned to the sterile environment. This may be done several times as the tiny plantlets continue to multiply.
     

  • At the final stage in the laboratory, hormones are introduced to the system to encourage the development of roots.
     

  • Once root systems appear on the plants, they are then transferred into trays and moved to the greenhouse for growing on to saleable size.

Why Go to the Trouble and Expense?
  • Clone Productions - Since the resulting plants are actually all exact replicates of the original plant, TC is a way to maintain the precise characteristics of the original explant.
     

  • Difficult to Propagate Plants - TC may be a last resort option for some plants that do not easily propagate through standard cuttings, seeds, layering, grafting or other methods.
     

  • Fast Production - Plants reproduced through TC can be rapidly multiplied and made available for sale. This is especially useful for plants with high demand which can still maintain a decent price level. From a small piece of a plant, a good lab can turn out thousands of clones in a few short months.
     

  • Disease Free Plants - Because it is done under highly controlled, sterile conditions, TC may often be used to produce certified, disease resistant clones. By using specific techniques, virus infected plants may sometimes be propagated with the resulting clones being virus free.
     

  • Sports - Because a variety of growth hormones are routinely used in TC, there is a higher than usual likelihood that mutations or "sports" will be created. In species such as Hosta, many new cultivars have been discovered mixed in with the extremely large number of clones produced.

Why Not Use TC All the Time?
  • Expense - This is space age tech stuff and requires a high level of investment in equipment and highly trained staff. Therefore, it is not economically viable for every nursery. It is usually better to propagate a plant by some of the older, low-tech methods which do a good job at a much lower cost.
     

  • Sports - While this can be an advantage with certain species, it can also be a negative when too many sports occur. Also, with trees and shrubs, it may be years before the sporting (such as a change in fruit color) may be discovered. This factor is another cost consideration since plants must be inspected closely at all steps to assure quality.
     

  • Sanitation - The specter of fungal infections ruining an entire environmentally controlled room full of test tubes hangs heavily over the head of every TC lab. Extensive efforts must be made to take care in every step of the process to prevent contamination.

For more on tissue culture as it relates to hostas...

Note: We have provided some general information and observations on this topic aimed at the home gardener. Before you take any serious action in your landscape, check with your state's land grant university's Cooperative Extension Service for the most current, appropriate, localized recommendations.

 

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