Crossings and Selections for Six Generations Based on Flower Vase Life to Create Lines with Ethylene Resistance or Ultra-long Vase Life in Carnations (Dianthus caryophyllus L.)

The vase life of cut flowers is one of the most important breeding targets in ornamentals; therefore, we started a research breeding program in 1992 to improve the vase life of carnation (Dianthus caryophyllus L.) flowers by means of conventional breeding techniques. Crossings and selections of six generations were effective to improve vase life. The mean vase life was 7.4 days for the initial parental generation derived from crossing six parental cultivars; in contrast, after six cycles of crossing and selection, it was improved to 15.9 days, resulting in a net increase of 8.5 days. Moreover, the significant increase of 0.9 days in mean vase life was observed from the fifth to sixth generations, indicating that the breeding progress of flower vase life was continuing in the sixth generation. We selected two ethylene-resistant lines (203-42S and 204-41S) in the fifth generation. The response time to 10 μL·L−1 ethylene was 23.0 h for line 203-42S and 34.2 h for 204-41S, whereas that of a control cultivar, ‘White Sim’ was 7.6 h. The mean vase life of the 18 selected sixth-generation lines ranged from 15.5 to 32.7 days (between 258% and 536% the value of ‘White Sim’). In particular, line 532-6 with an ultra-long vase life showed the longest vase life among all cultivars and lines; the mean vase life of line 532-6 was 32.7 days in 2007 and 27.8 days in 2008 (536% and 463% the value of ‘White Sim’, respectively) at 23°C and 70% RH under a 12-h photoperiod, without chemical treatment. Closer observation of petals during senescence showed that line 532-6 was characterized by a lack of brownish discoloration of petals, which was a senescence symptom of other selected lines with low ethylene production, when the flower lost its ornamental value.