Abstract
Two C. japonica trees exhibiting male sterility were found in Niigata Prefecture, Japan. These trees exhibited not only male sterility but also female sterility, because their seeds did not germinate. Both trees were pollinated normally in the pollen dispersal season in April. There were initially no differences in ovules between sterile and normal trees. However, differences appeared in the ovules from May to June. The female gametophytes underwent repeated nuclear fission, and a free nucleus was formed in the seeds of normal trees. However, a free nucleus was not formed in the female gametophyte, and there was adhesion during the free nucleus stage in the two sterile trees. Archegonia did not develop, and the gametophytes degenerated. Moreover, all seeds from the two sterile trees were unviable. The degeneration in the female gametophytes of the two sterile trees was similar. As no free nucleus formed in the two sterile trees, the cause of female sterility is believed to be abnormalities in meiosis in the megaspore mother cell, resulting in failure to form a normal female gametophyte.
