UNITED STATES DEPARTMENT
Agricultural Research Administration
Bureau of Plant Industry, Soils, and Agricultural Engineering
Div. Fruit & Vegetable Crops & Diseases Beltsville, Maryland.
REPETITIVE COLCHICINE TREATMENTS FOR INDUCING POLYPLOIDY IN PLANTS
Hamilton P. Traub
Principal Physiologist. February 26, 1951.
In addition to the usual four general methods of applying colchicine for inducing polyploidy in plants a fifth is here detailed. It consists of giving 4 or more repetitive 8-hour optimal colchicine treatments alternated with 16-hour recovery periods in water or a nutrient solution (see literature references at the end of the paper).
This method requires that the plants treated are in active growth during the treatment periods. Small seedlings of most plants, medium-sized herbaceous plants, and small root-grafts of such woody plant clones as the apple, give best results. The roots are washed free of all soil and several individuals are placed in a container that holds the colchicine solution which should cover the roots. The concentration of colchicine must be so regulated that the plant does not get a severe set-back when it is applied as indicated below. For small seedlings and herbaceous plants a 0.05% colchicine solution in water is generally strong enough, but for woody plants the strength may be increased to 0.1% or even higher in some cases.
The treatment periods are 8 hours in length—from 8 a.m. to 4 p.m. is apparently the most convenient time. The colchicine solution, which may be re-used, is then poured into another container through a funnel provided with a filter paper; the roots of the treated plants are washed in tap water, and the plants are allowed to remain in tap water, or a nutrient solution (Hoagland and Arnon, 1935) for a 16-hour period, from 4 p.m. to 8 a.m. the next morning. This procedure is repeated from 4 to 8 times, or more in rare cases, depending on the plant material. Four treatments are usually sufficient.
New colchicine solutions may be used for each treatment, but such a practice will prove to be very expensive. As an alternative, the solutions may be re-used over a fairly long period by adding water to make up for evaporation (determined by allowing an equal volume of solution with the same surface area to stand without plants for an equal time), but not for the moisture absorption by the plant, and filtering between changes to remove any accumulated debris. If the alternative method is followed, it should be realized that the amount of colchicine taken up by the plant is unknown at present. Thus the solution may remain approximately constant, or become concentrated or diluted with each re-use and addition of water, depending on whether the plant absorbs colchicine from the solution at a rate as great as, or greater or less than, that originally present. The optimum concentration in experiments with daylilies (Traub, 1951) has been indicated as 0.05%, but the mutagen is effective in the range of 0.025% to 0.1%, without too great injury to the plant at the higher concentration. Therefore, if the re-use program is not carried to the extreme it should give satisfactory results, as shown by the experiments of Traub (1951).
After treatment the plants are grown for at least two seasons in order to determine to what extent polyploidy has been induced. The procedure for determining the extent of polyploidy has been outlined in the mimeograph circular by Dermen and Emsweller (19149) which should be consulted. This paper also lists names and addresses of dealers who have colchicine for sale.
(See the mimeographed circular by Dermen and Emsweller (1949) for additional references.)