Crossing and Selection of Dahlia (<i>Dahlia</i> Cav.) Lines with a Lower Degree of Petal Abscission

Dahlia (Dahlia Cav.) is an important ornamental plant used as cut flowers. Recently, we bred the “Eternity series” cultivars with long vase life to overcome the difficulty of long-distance transport due to their short vase life. However, dahlias, including the Eternity series, are ethylene-sensitive, inducing petal abscission within a short period. Therefore, cultivars with long vase life and low degree of abscission were crossed to examine the possibility of producing lines with both traits. The flower life of offspring after treatment with 10 μL·L−1 ethylene (time to ethylene response) was investigated in open-field cultivation during the summer–autumn of 2021. The degree of abscission was classified into three types according to the time to ethylene response and the occurrence of abscission: abscission within four days (high), abscission after four days (mid), and the absence of abscission during senescence (low). We selected 17 of the 105 lines with mid or low degrees of abscission. The degree of abscission of the selected lines was re-evaluated during greenhouse cultivation in the winter–spring of 2021–2022. Three lines (F182-10, F181-14, and F182-17) that showed no petal abscission in the winter–spring were selected. The drawing resistance force of the petals from lines F182-10 and F182-17 was maintained at 1.0 N even during the senescence stage (six days after harvest), which was related to their low degree of abscission. The degree of abscission of lines F182-10, F181-14, and F182-17 was stable during the re-evaluation in summer–autumn of 2023, and their times to ethylene response were 4.8, 5.8, and 4.6 days, respectively. Moreover, the vase lives of lines F182-10 and F182-17 were 5.8 and 5.6 days, respectively, while that of ‘Port Light Pair Beauty’ was 4.4 days. These results suggested that degree of abscission was inherited from ‘Port Light Pair Beauty’, and the vase life was improved after crossing with a cultivar with a long vase life. This is the first report about breeding dahlia with a low degree of abscission, and it indicates the possibility of producing lines with both long vase life and a low degree of abscission.