Self-incompatible MS-lines (MS-lines, their nuclei substituted with those of self-incompatible B-lines) and their counterpart B-lines with the same S-alleles were obtained in two radish cultivars, Seoulbommoo and Tokinashi, respectively. Using these lines, attempts were made, on the one hand, to clarify how the CO₂ treatment affected in breaking of self-incompatibility in the production of selfed seed in the MS-and B-lines, and, on the other, to estabilish the most effective system by combining the male sterility and self-incompatibility in the production of F₁ hybrid seeds between two cultivars. The results obtained were summarized as follows:
1. CO₂ treatment seemed to be effective in overcoming self-incompatibility in Joongkookcheongpi, Seoulmoo, and Seoulbommoo with short flowering time as well as in Tokinashi with longer flowering time.
2. In selfed-seed production by CO₂ treatment the ridge planting was more effective than the pot-planting.
3. The fluctuation of day and night temperatures in the vinyl-house were more effective in pod-setting, while constant high temperatures were not desirable for the breaking of self-incompatibility.
4. CO₂ treatment at 3% concentration for two hours was useful in multiplication of the MS-lines as in the case of self-incompatible lines.
5. Lower rates of occurrence of sib-seeds was observed when self-incompatible MS-lines and their counterpart S-allele maintainers were used.
6. 1.0∼4.9% occurrence of sib-seeds in MS-lines seemed to be caused by the delayed pollination in the old flowers.
7. By adopting planting system of arranging alternately self-incompatible MS-lines of one cultivar with maintainers of different cultivar using two kinds of MS-lines and their counterpart B-lines, production of F₁ hybrid seeds between two cultivars could be enhanced with reduced cost.
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