Further studies on the behavior of incompatible pollen in the Japanese radish

Abstract

1. In Shôgoin, a variety of the Japanese radish, the activity of incompatible pollen on stigmas after bud-pollination was more rapid than that of compatible pollen after crossing of open flowers (table 1, 2, 3 and 4). The fact that immature stigma was more receptive than mature one indicates that in the Japanese radish pollen is inhibited to some extent on the mature stigma even though it is compatible. The result is fully in accord with that of the broccoli by SEARS (1937). 2. Table 5 gives the percentage of pollen ger-mination after self-pollination in variety Minowase. The germination of pollen was decreased. No emptied pollen grains which had exhausted their contents into their tubes were found on the stig-mas. Pollen-tubes usually ceased to develop, when they were about as long as the diameter of a pollen grain. Nearly all of the tubes failed to penetrate the stigma. Some tubes bended or coiled around the papillae. 3. Minotetra-Daikon (4x=36) is a tetraploid variety induced by colchicine method. The beha-vior of pollen after self-pollination in Minotetra-Daikon was similar to that of Minowase (table 6). Consequently, it seems that Minotetra-Daikon is also self-incompatible. 4. The results of cross-pollination in variety Minowase (2x×2x) are shown in table 7. The percentage of pollen germination was large. Numerous emptied pollen grains were found on the stigmas. The tissue of the style was penetrated freely by pollen-tubes. The longest tubes could be found in the ovary in about 6 or 8 hours after pollination. 5. Both cross-compatible and-incompatible combinations were found in the cross-pollination of variety Minotetra-Daikon (4x×4x). The pollen and tube behavior of the cross-compatible mating was similar to that of cross-pollinition in variety Minowase. On the other hand, the pollen be-havior of cross-incompatible mating closely resem-bled that of the self-pollination (table 8). 6. The following results were obtained in the combination between Minowase and Minotetra-Dai-kon (_??_2x×_??_4x). The percentage of pollen germination was large. Many emptied pollen grains were found on the stigmas. However, the longest tubes failed to penetrate the ovary in about 24 hours after pollination (table 9). It seems probable that the tube growth of 2x pollen is slower than that of x pollen. 7. In the combination between Minotetra-Dai-kon and Minowase (_??_4x×_??_2x), the percentage of pollen germination was large as shown in table 10. However, there were individual differences in the percentage of emptied pollen grains and in the length of the longest tubes. Previously NISHIYAMA (1949) reported that in the combination between Minowase and Minotetra-Dai-kon (_??_2x×_??_4x), the development of many cap-sules was found to be normal. When matured, however, most of the seeds were empty and shrivelled, and no viable seeds were obtained. In the reciprocal crossing (_??_4x×_??_2x), the development of capsules produced was weak, and the majority of seeds obtained were small, but filled and viable. These small and plump seeds were determined to be triploid. Cytological studies of the failure of seed development in these crossings will be reserved for the future.