This was studied on the effect of chromosome doubling on induction to low temperature in order to obtain the informations for radish breeding with resistance to bolting. For the purpose of this, five varieties of cultured radish and their artificial autotetraploids were kept at 5℃ for 5, 10 and 15 days at development stage of embryo. Their plants were comparatively investigated, with the untreated, in bolting and flowering behavior at green house. The results obtained are summarized as follows:
1) The period from seeding to bolting and to flowering was highly variable among varieties and duration of seed vernalization, but it took more longer days in tetraploid than their original diploid varieties in any case. Varietal difference of period from seeding to bolting and to flowering between tetraploid and their original diploid in each variety was highest in unvernalized plot and was smaller with increasing the duration of seed vernalization. This phenomena were shown among the original diploid varieties and their tetraploids.
2) The period from bolting to flowering was also variable among varieties and duration of seed vernalization. And it took more longer days in tetraploids than in their original diploids and it showed that tetraploids are dull in induction of not only low temperature in developmental stage of embryo but also temperature and day-length after bolting. Varietal differences of period from bolting to flowering between tetraploids and their original diploids were not marked as in the period from seeding to bolting and to flowering.
3) In vernalized plots, the period from seeding to bolting and to flowering were generally reduced with increasing the duration of seed vernalization, but in unvernalized plots, the period from seeding to bolting and to flowering were longest and the period from bolting to flowering was the shortest than other vernalized plots. These phenomena were shown in both tetraploid and their original diploid in each variety.
4) Number of leaves bearing on plant at bolting stage were different among varieties and duration of seed vernalization, and tetraploids have higher number of leaves than its original diploids in each variety, but number of leaves bearing on plant at flowering stage were smaller in tetraploids with some exceptions. In both tetraploid and their original diploid varieties, number of leaves bearing on plant at bolting and flowering stage were the highest in unvernalized plots and it was decreased with increase the duration of seed vernalization, and these phenomena also were occurred in difference of number of leaves between tetraploid and original diploid in each variety.
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