Abstract
Some Hydrangea macrophylla cultivars and interspecific H. macrophylla × H. serrata hybrids are self-incompatible, making it difficult to breed them for recessive characters. To overcome self-incompatibility, pollinating at different flowering stages and hot-water treatments of the inflorescences were conducted using ‘03NL3’, an interspecific H. macrophylla × H. serrata hybrid. Pollen tube growth was examined by fluorescence microscopy. At 3 days after pollination, the pollen tubes in flowers pollinated at 2 and 4 days after anthesis failed to reach the ovules. However, the pollen tubes were longer in styles pollinated 1 day before anthesis, and some had reached the ovules. For hot-water treatments, inflorescences were immersed in hot water (45°C) for 1–5 min before self-pollination. The 3- to 4-min treatments promoted pollen tube growth. Selfed ovules were obtained by bud pollination, hot-water treatment (45°C water for 4 min) of the inflorescences, and the combination of both treatments. Fertilized ovules were cultured in 1/2 MS medium and then grown in a greenhouse. At least half of these plants flowered within 2 years after self-pollination. The combination of bud pollination and hot-water treatment yielded the highest rate of selfed individuals.
