JARS v63n1 - Revisiting Polyploids

Revisiting Polyploids
Dr. Mark Konrad
Sewickley, Pennsylvania

Rhododendron 'Epoch' [colchicine treated seed of white-flowered R. minus Carolinianum Group] is a tetraploid that was created by August Kerr whom I consider an authority on the subject matter. He published at least four articles in the Journal American Rhododendron Society . Weldon Delp created what I believe is a second tetraploid of the Carolinianum Group. He germinated the seeds directly on meadow saffron (fall crocus), so I was told.

Colchicine is an anti-mitotic agent which has gained wide use as an experimental drug in the study of cell division and function.

Mitosis can be arrested in metaphase (chromosomes are arranged on equator of spindle) with the use of colchicine. Too high a concentration may completely prevent cells from entering mitosis with death being the result. The proper concentration and exposure allows for recombination of the chromosomes, hopefully with successful polyploidy.

As a matter of interest, colchicine has been used for hundreds of years in the treatment of gouty arthritis with the first description dating back to 1763. Its anti-inflammatory property is relatively selective for this condition. Kerr warned about the toxicity of this drug.

August Kehr with his many articles had focused attention on its use with the genus Rhododendron . His last insightful article, "Polyploids in Rhododendron Breeding" appeared in the fall issue of the ARS journal, Vol. 50, No. 4, 1996, p. 215. Further improvements were noted.

With this method he used 0.1% colchicine solution to which he added a small amount of demethyl chloride (commonly called DMSO) and a small amount of detergent. He misted the seedlings with this solution twice daily for at least 7-10 days.

With my method on blueberries, I use 0.6 mg colchicine tablets which are purchased from a pharmacy with the use of a prescription. The colchicine tablets are placed in a closed container and a small amount of water is added to soften the tablets.

As the seeds germinate they are transferred to the tablets with the use of a toothpick. They are left under fluorescent lighting for 24 hours at which time they are again transferred with the use of a toothpick to a medium and allowed to grow on under fluorescent lighting.

For years I have been working with blueberry seeds in an attempt to induce polyploid plants. The method may have application for rhododendron seeds as well.

Kerr stated in his 1973 article that medical colchicine tablets should not be used. However, I feel it is worth a try to simplify the method.

It is too early to tell whether I have been successful, but I'm encouraged by the results so far.

Literature cited:
Kerr, August. 1966. Breeding for a purpose, Journ. Amer. Rhod. Soc . 20:3.
Kerr, August. 1971. A tetraploid, R. carolinianum , Journ. Amer. Rhod. Soc . 25:1.
Kerr, August. 1973. Questions and answers, Journ. Amer. Rhod. Soc . 27:1.
Kerr, August. 1996. Polyploids in rhododendron breeding, Journ. Amer. Rhod. Soc . 50:4.

Dr. Konrad is a member of the Great Lakes Chapter.