2023 年 92 巻 1 号 p. 22-29
The aim of this study was to select new pollinizers for Prunus spp. with high pollen germination rates at low temperatures and assess their effect on the fruit set of Japanese plum cultivars. In this study, we examined in vitro pollen germination in 17 plum cultivars and two Myrobalan plum lines (420-2-2 and 421-3-1) at eight temperatures (7.5°C, 10.0°C, 12.5°C, 15.0°C, 17.5°C, 20.5°C, 22.5°C, and 25.0°C). The extent of pollen germination was affected by the incubation temperature. The germination rates of most cultivars were highest between 20.0°C to 25.0°C and ≤ 20% between 7.5°C to 10.0°C. However, the two Myrobalan plum lines (420-2-2 and 421-3-1) showed higher germination rates than the other cultivars at 10.0°C with ≥ 25% germination. The high germination rate in Myrobalan 420-2-2 was further confirmed in experiments conducted by our group in 2020. Open field studies on the Japanese plum ‘Kiyo’ revealed that the fruit setting rate was 17.6% using Myrobalan 420-2-2 and only 9.9% in the control using ‘Hollywood’. The fruit setting rate of the Japanese plum ‘Taiyo’ was approximately 20% when pollinated with both the cultivars. However, both fruit setting rate and fruit quality did not differ significantly between ‘Kiyo’ and ‘Taiyo’ with either pollination treatment. The formation rates of perfect seeds in ‘Taiyo’ were 90% and 65% by pollination using Myrobalan 420-2-2 and ‘Hollywood’, respectively. However, pollination treatment using pollen from both cultivars did not show any variations in the early development of the ovary and ovule. S-genotyping in Myrobalan 420-2-2 was determined as S7S10; therefore, we assumed that Myrobalan could be cross-compatible with many other plum cultivars. In conclusion, we selected Myrobalan 420-2-2 as a new plum pollinizer as it can effectively pollinate Japanese plum and germinate at low temperatures with no adverse effect on fruit set and quality.
