STUDIES ON SELF-INCOMPATIBILITY IN THE JAPANESE RADISH

Raphanus sativus var. macropodus (LÉV.) MAKINO

Abstract

This investigation was attempted in order to compare the effects of self-pollination with those of cross-pollination on the fertility of the Japanese radish. Three leading varieties Shogoin, Shiroagari, and Miyashige were used as material, and five different modes of pollination wereapplied, viz.:
(a) Flowers were merely bagged, but not pollinated artificially.
(b) Pollination within the same flower (self-pollination).
(c) Pollination between different flowers on the same individual (neighbor-pollination).
(d) Pollination between different individuals in the same variety. (cross-pollination).
(e) Pollnation under natural conditions as control (natural-pollination).
The results obtained are summarized as follows:
The cross-pollination (d) exhibited the highest percentage of fertility of all, and about 80-90 per cent. of the flowers treated produced normal pods. In three kinds of pollination within the same individual, (a), (b), and (c), they gave approximately similar results, and produced about 15-25 per cent. of normal pods. But the fertility of the (a) was somewhat lower than that of the other two. The fertility of the natural pollination (e) was about 70 per cent. The tendencies mentioned above were alsoobserved in the size of pods, the number and weight of seeds obtained.
It has often been advocated that in some self-incompatible plants the fertility of self-pollination is lower than that of neighbor-pollination.
The author attempted an experiment with the variety Shogoin to ascertain this fact, but no apparent difference existed between them. Consequently it may be said that the Japanese radish is a self-incompatible plant as already known, and that the different modes of pollination have no effect on fertility, when the pollen used is from the same individual.
In the groups in which the flowers were treated with pollen from the same individual, the individual variations in the grade of self-incompatibility exhibited a very wide range from complete self-compatibility to complete self-incompatibility. This suggests that there are some self-compatible individuals in the self-incompatible groups. The self-compatible individuals were selfed and tested for the fertility in subsequent generations. It seems probable that they do not breed true to self-compatibility, but segregate into two groups-self-compatible and -incompatibible. Only further studies can fully elucidate the exact nature of the phenomenon.