Studies on the Self-and Cross-Incompatibility in Sweet Potato. : Preliminary IV

Abstract

Some self-incompatible plants can be made to bear self-fertilized seeds when their flowers are pollinated in the bud stage. Such phenomenon is called "pseudo-fertility" and is explained on the basis that the special substance that inhibits the pollen germination is not yet produced when the flowers are premature. Sweet potato varieties are commonly known to be self-incompatible as well as cross-incompatible in certain matings, so there still remains much room for further investigation concerning the subject. If pseudo-fertility is easily induced in sweet potato, the breeding work of this crop may become more advantageous for obtaining seeds in voluntary matings. Desiring to throw some light on this line of experiment, the anthor had carried on a series of experiments in regard to chances and causes of this phenomenon since 1939 at Konosu Farm of the Imperial Agricultural Experiment Station. The varieties used for material, and methods of artificial inducement of blooming, pollination operations, measurements of pollen germination and pollen tube growth, etc., are the same as discribed in the previous paper (T0GARI and KAWAHARA: 1942). The following summary may be made from the results of these experiments: 1. There were no flower bearing self-fertilized seed in the bud-Pollination at 5 p.m. on the day before blooming. Similar observations were made in both compatible and incompatible matings when the young buds were pollinated with viable pollen (Tab. 1) The results indicate the difficulty to induce pseud-fertility by the application of prmnature pollination in sweet potato. In order to elucidate the mechanism of such phenomenon of failure in inducing pseudo-fertility, it is necessary to study pollen bebaviors. 2. Viable pollen failed to germinate in both compatible and incompatible pollinations one or two days before blooming (Tab. 2). Therefore, it may be concluded that the pollen receptivity, i. e., the ability to make pollen germinate on the stigma, does not yet arise at this time in the buds. It is thus necessary to study the stage when the pollen receptivity occurs. 3. Unopened buds in the course of development were pollinated with viable pollen at fourth hour intervals from 4 p.m. the day before blooming to the day of blooming. The compatible pollen was found to germinate for the first time in the pollination at 0 a.m. on the day of blooming (Tab. 3, 4). Consequently, it is not till several hours before blooming that the pollen receptivity occurs in stigma. 4. In incompatible matings, the germination when failure of pollen is always observed with exception of 0.2 percent germination when pollinated at 4 a.m. (Tab. 3, 4). These results lead the author to conclude that the peculiarity of prematnre pistil to compatibility and incompatibility with the occurence of pollen receptivity of stigma, is not different from the completed stage. 5. Since pollen cannot germinate until the pollen receptivity occurs in stigma and that the young stigma with the pollen receptivity behaves similar to the matured one in regard to compatibility and incompatibility, pseudo-fertility in sweet potato may be presumed to be presumed to be hardly induced by means of the bud-pollination. 6. The pistil behavior in question as well as the pollen receptivity mentioned above was found to arise when the ovary was removed two days before blooming (Fig. 1, Tab. 5, 6). From these observations, following presumption may be made: The function causing compatibility or incompatibility is either already generated in the stigma two days before blooming or arise independently of the ovary. In these respects, there is something peculiar about sweet potato that makes it distinguishable from Petunia in which pseudo-fertility mechanism was elucidated by Dr. YASUDA.