Abstract
In the present experiment, seed development was investigated in self-pollination of 4X Hyuganatsu and several cross combinations between 2X and 4X Hyuganatsu. In addition, possible methods to overcome self-incompatibility of 2X Hyuganatsu were examined, using pollen of 4X Hyuganatsu as a mentor or pioneer pollen. The results are summarized as follows.
1. Pollen of the 4X was not uniform in size and form as observed by scanning electron microscopy. Its in vitro germination was inferior to that of the 2X by 5%. The band patterns of glycoproteins from pollen and pistils of the 4X analyzed by isoelectric focusing electrophoresis were largely different from those of the 2X.
2. In almost all cases one well-developed seed was contained together with many large imperfectly developed seeds in the fruit of the 2X pollinated with the 4X and in the fruit of the self-pollinated 4X, although the fruit set was somewhat different between two pollinations. When the 4X was pollinated with pollen of the 2X, only one fruit was harvested, lacking a well-developed seed. The fruit set of the open-pollinated 4X tree was very low. A few fruits were harvested, containing about 3 well-developed seeds per fruit.
3. Three pollination methods were tried for overcoming the self-incompatibility of the 2X Hyuganatsu. When pollens of the 2X and 4X were pollinated on the left and right sides respectively, of stigmas of 2X Hyuganatsu (differential pollination), the most effective result was obtained on overcoming the self-incompatibility. One hour time-lag double pollination, where pollen of the 2X was used one hour after pollination by the 4X, showed the next best effectiveness. Pollination with mixed pollens of both ploidies was not effective at all.
