2022 Volume 21 Issue 4 Pages 401-412
A pollination method using pollen irradiated with gamma-rays (γ-rays) was applied to induce gynogenesis. For this study, the apple cultivars ‘Fuji’, ‘Jonathan’, and ‘Indo’ were used as seed parents. ‘Golden Delicious’ was used as a pollen parent. The pollen was irradiated with 500 Gy by γ-rays. After investigating the fruit set percentages and seed appearance of sampled fruits, we used SSR markers to elucidate the derivation of seedlings raised from the obtained seeds. The method was insufficient to obtain seedlings showing gynogenesis. However, irradiation might have induced embryonic development and abortion of most growing embryos and seeds by pollination with irradiated pollen. Most embryos degenerated about 50 days after pollination: the end of June. Therefore, embryos must be rescued before the timing of gynogenesis. Obtaining individuals showing gynogenesis using the irradiated pollen method requires fruit set first. For this experiment, ‘Indo’ was considered a suitable cultivar because of its high fruit set percentage. However, ‘Jonathan’ was judged as unsuitable due to its low fruit set percentage. Self-fertilized individuals were completely removed by emasculation. However, self-fertilized individuals numbered less than one out of 100 pollinated flowers. Therefore, increasing the number of flowers without emasculation must be more efficient than emasculating flowers because emasculation operations require much labor. Furthermore, after growing the seedlings, the derivation of the seeds should be investigated using the SSR marker. The results clarified that some pollen fertility was maintained after 500 Gy of γ-rays. However, individuals produced from irradiated pollen were very few. Such individuals numbered less than 5 out of 700 pollinated flowers. Therefore, 500 Gy of γ radiation may have been appropriate as the exposure dose. Future studies should clarify procedures of pollen tube growth, fertilization, embryogenesis, and abortion of embryo growth. Acquisition of individuals derived from gynogenesis by embryo culture is necessary.
