Pear pollen selection using higher germination properties at low temperatures and the effect on the fruit set and quality of Japanese pear cultivars

To determine the lowest temperature possible for pollen germination in pear, in vitro pollen germination was studied in 7 wild pear species and 16 pear cultivars at six temperatures (7.5, 10.0, 12.5, 15.0, 17.5, and 20.0 °C) over two years. The extent of pollen germination was affected by the incubation temperature. Most cultivars did not germinate at a temperature below 12.5 °C; however, the cultivar Pyrus communis L. showed a higher percentage of germination than the other cultivars at 7.5 °C. The percentage of germination for La France and Le Lectier pears was >50% at 10.0 °C. We investigated the effects of cross pollination between the cultivars P. communis L. and 'Chojuro' and the Japanese pear cultivars 'Gold-Nijisseiki' and 'Hosui' pertaining to fruit set and quality at a low temperature (10.0 °C). The bearing rate of the cultivars 'Gold-Nijisseiki' and 'Hosui' depended on the type of pollen used for pollination. Pollination with European pear pollen resulted in a higher bearing rate (50%) in these cultivars. In contrast, the bearing rate of the cultivar 'Chojuro' was <20%. Fruit quality and number of seeds per fruit (seed yield) in the cultivars 'Gold-Nijisseiki' and 'Hosui' were not affected by the type of cultivar used for pollination. Methods involving the use European pear pollen combined the advantages of higher germinability and higher monocarpic under low temperature condition.