Takashi Onozaki’s research while affiliated with National Agriculture and Food Research Organization and other places

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.

Genetic improvement of flower vase life is an important breeding target for ornamental plants. As the vase life of cut dahlia (Dahlia variabilis) flowers is very short, we initiated a conventional crossbreeding research program in 2014 to improve it. We evaluated the vase life of dahlia seedlings during summer (from July to early September) to develop dahlias that grow and bloom under high temperatures and have excellent vase life for Japanese summer conditions. Crossing and selection over five generations greatly improved vase life. The mean vase life increased from 4.4 days in the 1st generation, derived from 22 parental cultivars, to 8.0 days in the 5th generation, a net increase of 3.6 days. Mean vase life increased significantly by 1.6 days from the 4th to the 5th generation, indicating continued improvement. The mean vase life of the 12 lines selected from the 3rd and 4th generations ranged between 6.0 and 15.9 days in distilled water and from 7.8 to 14.6 days in GLA solution (10 g·L⁻¹ glucose, 0.5 mL·L⁻¹ CMIT/MIT [isothiazolinone derivatives], and 50 mg·L⁻¹ aluminum sulfate). Vase life was further extended by 0.5 to 4.0 days using 6-benzylaminopurine (BA) sprays compared to GLA alone. In particular, the 4th-generation line 003-15 vase life was 13.8 to 15.9 days (2.5× that of ‘Kamakura’, a leading white dahlia cultivar in Japan) in distilled water, 12.0 to 14.6 days (1.8× to 2.2×) in GLA, and 13.9 to 15.3 days (1.7× to 1.9×) in GLA+BA in winter and spring. Cut flowers of line 003-15 harvested under high temperatures in July–August and at 28°C with GLA treatment also had long vase life. The pedigree of line 003-15 suggests that genes related to long vase life derived from ‘Micchan’ (with a long vase life) may have accumulated or duplicated in line 003-15. Finally, four selected lines, including 003-15, had high ethylene sensitivity, as 10 μL·L⁻¹ ethylene treatment caused petal abscission in 2.0 to 2.8 days.

Cut dahlia flowers have a short vase life of 3–7 days, and some cultivars exhibit petal abscission, even inside of cardboard boxes during transport. This petal abscission is induced by ethylene in many cases. In the present study, we investigated the role of ethylene in dahlia flower senescence by comparing the responses to ethylene, ethylene inhibitors, and ethylene production among cultivars. Exogenous ethylene significantly accelerated petal abscission in seven cultivars and petal wilting in other five cultivars out of 12 cultivars. Whole florets and detached receptacles (with bracts) produced different amounts of ethylene; ethylene production was higher in ‘Carnelian’ and ‘Port Light Pair Beauty’ than ‘Heavenly Peace’ and ‘Purple Stone’. Onset of senescence was delayed in detached petals compared with attached petals, suggesting that petal abscission was induced by ethylene produced by ovary and receptacles. The ethylene action inhibitor 1-methylcyclopropene inhibited petal abscission and delayed petal wilting in eight cultivars. Moreover, the silver thiosulfate complex delayed petal wilting of ‘Carnelian’. Together, our findings suggested that ethylene plays a role in senescence of cut dahlia flowers and ethylene inhibitors can extend their vase life.

Fusarium root rot of lisianthus (Eustoma grandiflorum) caused by Fusarium solani is one of the most important and damaging lisianthus diseases. It occurs commonly in Japan and worldwide and causes serious crop losses. However, little effort has been made to breed lisianthus for resistance to this disease. We initiated a breeding program for resistance to F. solani in 2014. Twenty-nine lisianthus cultivars (E. grandiflorum) and one inbred line of Eustoma exaltatum were evaluated for resistance to two isolates (MAFF712388 and MAFF712411) of F. solani, as a first step toward the breeding of resistant cultivars. Seedlings were inoculated following injury by needle, then grown using hydroponic equipment—an efficient and reliable method for evaluating resistance. We found large differences in resistance among the 29 cultivars and the one inbred line tested. ‘Papillon Pink Flash’ was highly resistant to both isolates and showed no disease symptoms in a total of four tests. Furthermore, E. exaltatum Ohkawa No. 1 was highly resistant to isolate MAFF712388, showing no disease symptoms, and resistant to isolate MAFF712411. On the other hand, ‘Mink’, ‘Nagisa A’, ‘Nagisa B’, and ‘Vulcan Marine’ were stably susceptible with 70% to 100% of plants of these four cultivars wilting in all tests. MAFF712411 had greater pathogenicity than MAFF712388, but it is not clear whether the two isolates belong to different races.

This book summarizes recent advances in carnation genome research for large-scale transcriptome analysis, the draft genome sequence, DNA markers and genome mapping, flower color, mutations, flower opening, vase life, interspecific hybridization, fragrance. The carnation is one of the most important ornamental flowers in the world, along with the chrysanthemum and the rose. The genus Dianthus is a member of the Caryophyllaceae and includes more than 300 species of annuals and evergreen perennials. Modern carnation cultivars are the product of highly complex hybridization, owing to their long history of breeding. The carnation genome was first sequenced in ornamentals by a Japanese research team in 2013. The carnation has been genetically improved over the years, and there are various types of flower colors, shapes, patterns, and sizes. In this book, the molecular mechanism of flower color development and the transposable elements responsible for this diversity are studied in detail. In addition, it presents breeding and physiological research for improving flower vase life, one of the most important traits in ornamentals, based on a model of ethylene susceptible flowers. To improve selection efficiency, genomic analysis tools including DNA markers and genetic linkage maps are also highlighted. In closing, the book discusses mutation breeding technologies such as ion-beam irradiation and genetically modified carnations.

Flowering time is one of the most important traits in carnation (Dianthus caryophyllus L.) breeding because it decides the yearly yield. Two previously developed mapping populations were used to determine the number and effect of quantitative trait loci (QTLs) for flowering time. Flowering time showed large phenotypic segregation in two F2 populations and in different years. Despite the different populations and different years, one major common QTL for flowering time was detected in linkage group 10 with the effect explaining from 18.2%–22.5% of the overall phenotypic variance. We developed a DNA marker, qD1Flw1-sc43-4, that was located close to the detected QTL for flowering time. We could distinguish the flowering time and categorize the genotypes of an F1 population derived from a cross between late flowering ‘Light Pink Barbara’ and early flowering ‘Kaneainou 1 go’ using the qD1Flw1-sc43-4 marker. Our results suggest that flowering time in carnation involves several genetic factors. In this study, we identified one of the major factors for flowering time and developed a DNA marker that was tightly linked to the major QTL.

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.