The Orchid Seedbank Project
PO Box 7042
Chandler, AZ 85246

Sugar (sucrose) pre-treatment of seed to decrease contamination

Orchid seed is often contaminated with large numbers of bacteria  or fungi, some of which are highly resistant to chemical  sterilization. Since we can't assure seed is free of such potential  contaminants, we recommend the use of a sugar pre-soak to diminish  the chances of contamination. Its use is particularly recommended  with particularly valuable seed.

Sucrose pre-treatments are very simple; the concept behind it  involves soaking the seed in a solution of sugar, which encourages  encysted organisms to "come alive," making them more  susceptible to traditional chemical sterilization.

The sugar solution need not be very concentrated, although some  use a solution that is as strong as a 50/50 saturated sugar plus  water solution (i.e., half strength of a saturated solution of  sugar). I have used a weaker solution, in the following manner.

A small test tube (I use 7 ml "Vacutainer" tubes that  have never been used for holding blood products as they were  intended- I purchase them new, and wash and sterilize tubes and their  stoppers) is used to hold the seed; I dump in whatever quantity of  seed I am going to use (from 1 to 5 cubic mm or more), and then an  equivalent amount of sugar. Then I add distilled water- usually 1-3  ml, but never so much that the seed is lost or diluted too much. I  then swipe the bottom of the stopper across a bar of soap to add a  *tiny* amount of wetting agent, and then stopper the tube and gently  agitate it.

Agitation is performed several times (at least every 8 hours) for  16-24 hours. During this period of time, if the seed did not sink  before, it almost certainly will now. The tube may be incubated at  room temperature, or at 37 degrees C if this is convenient. After  pre-treatment, I open the tube and use a piece of Whatman filter  paper to remove the sugar solution by absorption. The seed is then  ready for chemical sterilization and sowing into flask.

 

[OSP] [Technical Data]

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The Orchid Seedbank Project
PO Box 7042
Chandler, AZ 85246