Long-term Preservation of Japanese Pear (<i>Pyrus pyrifolia</i> (Burm. f.) Nakai) Pollen

The long-term preservation of pollen is imperative for the conservation of genetic resources and cross-breeding. In the present study, we demonstrated that preserved pollen of the Japanese pear (Pyrus pyrifolia (Burm. f.) Nakai) retains viability for a minimum of 50 years. In 1973, fresh pollen from ‘Chojuro’ was collected and immediately subjected to freeze-drying for 15 minutes at pressures ranging from 3.3 to 13 Pa. The pollen was then sealed in ampules under a vacuum and preserved at −20°C for 40 years followed by −30°C for 10 years. In 2013 and 2023, the viability of this pollen was investigated. The rate of pollen germination showed no significant differences between the preserved and fresh pollen. In 2013, flowers of ‘Kosui’ and ‘Niitaka’ were pollinated with pollen preserved for 40 years as well as fresh pollen. The growth of the pollen tubes in the pistils of preserved pollen was normal. Pollination with preserved pollen resulted in 77.1 and 86.7% fruit set, yielding 3.2 and 8.3 perfect seeds per fruit in ‘Kosui’ and ‘Niitaka’, respectively. In 2023, the fruit set and perfect seeds per fruit of ‘Kosui’ pollinated with 50-year-preserved pollen were 66.7% and 3.5, respectively. There were no significant differences between preserved and fresh either year for either trait. The results of the present study demonstrate that the viability of pear pollen can be sustained for a minimum of 50 years when preserved in a freeze-dried state at temperatures ranging from −20 to −30°C.