Flower vase life is one of the most important traits for ornamental plants. The vase life of cut dahlia (Dahlia variabilis) flowers is very short, and genetic improvement of this trait is desirable. We started a breeding research program in 2014 to improve the vase life of dahlia flowers using conventional cross-breeding techniques. We found large significant differences in flower vase life among 24 dahlia cultivars: Nine cultivars had long vase life (e.g., 'Syukuhai', 'Rinka', and 'Micchan'); eight had normal vase life (e.g., 'Kamakura', 'Agitate', and 'Benifusya'); and seven had short vase life (e.g., 'Gin-Ei', 'Port Light Pair Beauty', and 'Yumesuiren'). We used 22 cultivars as initial breeding materials, repeatedly crossed them, and selected promising offspring with long vase life for three generations from 2014 to 2018. Two cycles of selection and crossing led to a 1.7-day increase in vase life (population mean) from the first to the third generation, clearly showing that this approach can extend the vase life of dahlia flowers. The mean vase life of 'Kamakura', a leading white dahlia cultivar in Japan, was 5.0–6.2 days in distilled water, 6.0–6.8 days in an isothiazolinic antibacterial agent CMIT/MIT solution (5-chloro-2-methyl-4-isothiazolin-3-one and 2-methyl-4-isothiazolin-3-one) and 6.0–7.6 days in a GLA solution (10 g·L−1 glucose, 0.5 ml·L−1 CMIT/MIT, and 50 mg·L−1 aluminum sulfate), whereas in six finally selected lines it was 6.2–12.0 days in distilled water, 6.6–10.2 days in CMIT/MIT solution, and 9.4–13.6 days in GLA solution (1.4–2.1 times that in 'Kamakura'). In particular, the selected second-generation line 606-46 showed a stably longer vase life than 'Kamakura'. 'Micchan', which has a long vase life, was a common progenitor used for breeding of parental lines in cross combinations with long vase life in the second generation and all cross combinations in the third generation. The final six selected lines with long vase life were all progeny of 'Micchan'. Our results strongly suggest that 'Micchan' has genes related to long flower vase life, and that the trait is heritable.
Carnation (Dianthus caryophyllus L.) is one of the main floricultural crops in Japan and worldwide. The vase life of cut ornamental flowers, including carnations, is important in determining their quality and consumers' preference. To improve the vase life of carnation flowers, my group started a breeding research program in 1992 using conventional cross-breeding techniques. We repeatedly crossed and selected promising offspring with long vase life for seven generations, from 1992 to 2008. In 2005, we developed two cultivars, 'Miracle Rouge' and 'Miracle Symphony', with genetically determined long vase lives of 17.7 to 20.7 days (3.2 to 3.6 times that of 'White Sim') under standard conditions (23°C, 70% RH, 12-h photoperiod). Line 532-6 showed an ultra-long vase life averaging 27.8 to 32.7 days (4.6 to 5.4 times that of 'White Sim'). We evaluated changes in ethylene sensitivity with flower senescence simply and accurately using a time-lapse video recorder. In 2010, we selected line 806-46b with both ultra-long vase life (27.1 days, 4.4 times that of 'White Sim') and ethylene resistance. Analyses using six cultivars and 123 selected lines from the 1st to the 7th generations revealed that the long vase life was strongly associated with a decrease in ethylene production.
Bacterial wilt (Pseudomonas caryophylli) is one of the most important and damaging disease of carnations (Dianthus caryophyllus) in Japan. It causes serious crop losses in carnations grown in the warm districts. However, breeding for resistance to this disease in carnation has been rarely carried out. Therefore, 277 carnation cultivars were screened for resistance to bacterial wilt by using the cut-root soaking method with an inoculum concentration of 107 cfu (colony-forming units)/ml. Two hundred seven cultivars (74.7%) were highly susceptible, whereas 3 cultivars, 'Wiko', 'Nocto', and 'Sandrosa' possessed adequate resistance.
We investigated ethylene production, ethylene biosynthesis genes, and senescence-related genes in flowers of a carnation (Dianthus caryophyllus L.) cultivar 'Miracle Symphony' (MS) and lines 006-13 and 62-2, which have a longer vase life than flowers of 'White Sim' (WS). WS flowers showed typical symptoms of senescence, but flowers of MS, 006-13, and 62-2 did not show symptoms of senescence, although they showed differences in vase life and ethylene production by day 15. The flowers of 006-13 and 62-2 produced small amounts of ethylene as a result of the low expression of two ethylene biosynthesis genes, DcACS1 and DcACO1; those of MS produced extremely low levels of ethylene. By day 15, the flowers of 006-13 and 62-2 showed increased expression of some senescence-related genes (DcCP1, DcbGal, DcGST1, and DcLip) that were upregulated by exogenous ethylene, indicating that a low level of ethylene production could induce the senescence of petals. In contrast to the upregulation of these senescence-related genes, the expression of DcCPIn, which was downregulated by exogenous ethylene decreased in petals of MS, 006-13, and 62-2 during flower senescence and was the same in all three lines at day 15. The results suggest that extended vase life depends on reduced levels of ethylene production, ethylene biosynthesis gene expression, and senescence-related gene expression.
The whole-genome sequence of carnation (Dianthus caryophyllus L.) cv. 'Francesco' was determined using a combination of different new-generation multiplex sequencing platforms. The total length of the non-redundant sequences was 568,887,315 bp, consisting of 45,088 scaffolds, which covered 91% of the 622 Mb carnation genome estimated by k-mer analysis. The N50 values of contigs and scaffolds were 16,644 bp and 60,737 bp, respectively, and the longest scaffold was 1,287,144 bp. The average GC content of the contig sequences was 36%. A total of 1050, 13, 92 and 143 genes for tRNAs, rRNAs, snoRNA and miRNA, respectively, were identified in the assembled genomic sequences. For protein-encoding genes, 43 266 complete and partial gene structures excluding those in transposable elements were deduced. Gene coverage was ∼ 98%, as deduced from the coverage of the core eukaryotic genes. Intensive characterization of the assigned carnation genes and comparison with those of other plant species revealed characteristic features of the carnation genome. The results of this study will serve as a valuable resource for fundamental and applied research of carnation, especially for breeding new carnation varieties. Further information on the genomic sequences is available at http://carnation.kazusa.or.jp.
The plant hormone ethylene plays an important role in the senescence process of carnation flowers. Recently, various genes that concern ethylene responses have been cloned from many sources of plants. Our main aim is to compare the sequences of ethylene receptor genes among carnations with different ethylene sensitivities. Four carnations, `White Sim' (ethylene sensitive control), `Chinera' (lower ethylene sensitivity), 64-13 and 64-54 were used. The carnations temporarily named as 64-13 and 64-54 are our breeding lines with less ethylene sensitivity, thus better flower retention. Total RNA was extracted using SDS-phenol method. Putative ethylene receptor genes were cloned by RT-PCR using degenerate primers that correspond to the highly conserved regions of ETR1 and ERS genes. Two kinds of DNA fragments, ≈1 kb in the length encoding putative ethylene receptor genes were cloned from all samples. An ERS-type gene was cloned that is identical to the gene, known as DC-ERS2 (Accession No. AF034770). Another was ETR1-type gene, which has not been reported in carnations yet. That was 91% identical to the ETR1 gene from melon or apple at the translated amino acid level. The deduced amino acid sequences of ERS-type genes among four samples were almost the same. However there were five mutations in `Chinera', one mutation in 64-13 and two mutations in 64-54, compared to `White Sim' at the translated amino acid level. As they located rather conserved regions of the gene, it is expected to affect the less ethylene sensitivity of the carnations.
