Diallel Analysis of Root Shape in Japanese Radish ‘Sakurajima daikon’

Abstract

The root shape, as well as the very big root, of Japanese radish ‘Sakurajima daikon’ is an important trait different from those of other cultivars. We clarified the mode of inheritance of the root shape in ‘Sakurajima daikon’ for effective breeding. We conducted a half-diallel analysis using 8 × 8 half-diallel crosses among its inbred lines with different root shapes. We measured the root length and root diameter as factors which represent the root shape. The root shape was analyzed using the image analysis software “SHAPE” based on Fourier descriptors. The 1st principal component (PC1) mostly showed the ratio of the root diameter to root length, and the 2nd principal component (PC2) mostly showed the degree of the root top width and root bottom roundness. The root length showed a high broad-sense heritability, a high narrow-sense heritability, and incomplete dominance. The root diameter and PC1 showed a high broad-sense heritability and a low narrow-sense heritability. The inheritance of the root diameter showed overdominance, that of PC1 showed overdominance to complete dominance, and that of PC2 showed overdominance. A lower broad-sense and narrow-sense heritability compared to other traits indicates that PC2 tends to be easily influenced by enviromental factors. Dominant genes for the root length, root diameter, PC1, and PC2 had effects to elongate the root length, enlarge the root diameter, increase the ratio of the root diameter to root length, and increase tapering of the root bottom, respectively. These findings indicate that the F₁ hybrid is effective for breeding typical ‘Sakurajima daikon’ with a round root, and that it is neccesary to accumulate dominant genes concerning the root diameter and PC1 to either parental lines, and also to accumulate recessive genes concerning a round root bottom to both parental lines.