With respect to the root shape of the radish, MALINOWSKI (1916) previously indicated that the long is due to several partially dominant cumulative factors, which are absent from the recessive round shape. UPHOF (1924), however, found a unifactorial difference in all crosses where different root shapes were concerned. The F
1 was intermediate in shape, and an approximate 1:2:1 ratio was always obtained in the F
2. In order to make an accurate determination of this fact the present writer has attempted a similar experiment to those of the previous investigators with long and round varieties in the Japanese and Chinese radish.
Perhaps the most direct, accurate, and concise description of shape in radish roots is given by root index (Root index=length/width). In the investigation the root shape was determined by this index, and the, results obtained were examined by statistical methods.
The F
1 was distinctly more vigorous than either parental form, and the root shape was approximately intermediate, but nearer the round parent. In the F
2 a trimodal curve appeared. Accordingly, as UPHOF'S paper showed, it is fair to believe that the 1:2:1 ratio of round, intermediate, and long is obtained in the F
2. While in the F
2 the extracted long was more round than the long parent. It seems probable that in addition to the single major factor which causes the difference between round and long shape, there is another independent factor which affects root shape in the same general way but to a slighter degree. Consequently, it is concluded that the round shape of root is incomplete dominant over the long, the main difference being due to a single factor, a lthough another factor may produce minor effects.
View full abstract