Abstract
In the present experiment, some morphological and histological observations were made by means of both scanning electron and fluorescent microscopy concerning self-incompatibility in Hassaku, Citrus hassaku hort. ex Tanaka. Meanwhile, various treatments were tried in search of an effective method to overcome the self-incompatibility.
1. The pollen behavior on stigmas of self-pollinated mature flower buds was compared with that of buds cross-pollinated with Hyuganatsu, Citrus tamurana hort. ex Tanaka. Soon after cross-pollination, the stigma exudate began to co ver the pollen grains; 9 hours after pollination, the pollen grains were completely covered by the exudate. In contrast, self-pollinated pollen grains were not covered by the exudate so quickly as cross-pollinated grains, and individual grains were observed rather clearly on some parts of the stigma even 9 hours after pollination. Furthermore, the germination vigour in the case of self-pollination seemed to be a little weaker than that in the case of cross-pollination.
2. The amount of stigma exudate observed on immature flower buds, half the length of mature ones, was clearly less than that on mature flower buds which were to open the next day. Many papilla cells were clearly observed on the stigmas of immattre buds. When immatre flower buds were self-pollinated, and their stigmas were observed 24 hours after pollination, almost all the pollen grains were still cleary visible, because of the lesser secretion of stigma exudate. Germination vigour was also somewhat weaker than in the case of self-pollination on mature flower buds.
3. The pollen tube growth was observed after self-and cross-pollination on both mature flower buds and immature ones. In the case of mature flower buds, the pollen tubes of Hyuganatsu penetrated into the ovaries by the 5th day after pollination. However, almost all the pollen tubes of Hassaku were still in the stigma even 9 days after pollination. In the case of immature flower buds, the pollen tubes of Hyuganatsu grew rapidly into the styles; the number of the pollen tubes which had penetrated into ovaries by the 9th day after pollination was five times larger than that observed in the case of cross-pollination onto mature buds. On the other hand, all the pollen tubes of Hassaku had not reached the lower portion of thepeated e styles even 9 days after pollination.
4. Repated pollination of immature flower buds for 4 continuous days was found to be most effective for obtaining the self-fertilized seeds among all the treatments used.
