Studies on Artificial Polyploid Plants VI

On the Different Growth of the Diploid and Tetraploid Radish in the Winter Season

Abstract

Tetrap oid plants of a radish variety“Minowase”were obtained by treating young seedlings with 0.2% aqueous solution of colchicine. Second generation progenies were grown for the seeds in the following year (1941). The fertility of the tetraploids is much reduced; i. e. the tetraploids set 2.91 seeds per capsule while the diploids set 5.14 seeds.
This radish is usually cultivated in the summer. In the present work, however, the cultivation of the tetraploids and their controls was made in the cold climate during a period from October 10th to March 4-5th in 1941-1942. The percentage of seed germination in the field was found to be higher in the tetraploids (92% germination in 1260 seeds sown) than that of the diploids (79% germination' in 720 seeds sown). Very distinct differences in some characters are visible in these polyploid varieties. It is readily recognized in the rosette stage that the diploids show the prostrate type with leaves which lie on the surface of the soil, while the tetraploids are of the erect type whose leaves spring up almost vertically or at a varying angle with the horizon. The tetraploids are also characterzied by a more intense green colour as compared with the diploids. Furthermore, the tetraploids indicate the gigas form in many plant characters as given in the following table.
It is very noteworthy that the tetraploids show marked superiority in development of plants, especially of tap roots (Fig. 3). The average weight of the tap roots amounts to 295g in the tetraploids as compared with 57g in the diploids whose growth is seriously checked in the winter season. This difference in the development is doubtless due to the increasement of winter hardiness by chromosome doubling.