The Horticulture Journal
Online ISSN : 2189-0110
Print ISSN : 2189-0102
ISSN-L : 2189-0102
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SPECIAL ISSUE: ORIGINAL ARTICLE
  • Shoko Hikosaka, Fumihiko Moriyama, Eiji Goto
    Type: Original Articles
    2021 Volume 90 Issue 4 Pages 357-364
    Published: 2021
    Released: October 23, 2021
    [Advance publication] Released: August 26, 2021
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    Supplementary material

    Sweet basil (Ocimum basilicum L.), one of the most widely consumed herbs globally, is used in raw or processed food, and for aromatic essential oils. We investigated the effects of photosynthetic photon flux density (PPFD; 150, 225, and 300 μmol·m−2·s−1, herein, referred to as P150, P225, and P300) and red to blue light ratios (R/B ratio) (R:B = 1:4, 1:1, and 4:1, herein, referred to as R/B 0.25, 1.0, and 4.0) with a 16 h light period on the leaf shape and concentrations of functional and aromatic compounds in basil. Total leaf dry weight and leaf mass per area increased with increasing PPFD and R/B ratio. Total leaf area tended to increase with increasing R/B ratio at the same PPFD. Although the highest growth was noted when R/B was 4.0 at P300, the leaves showed ruggedness and curling. β-Carotene concentration based on the leaf dry weight and leaf area at the fourth node increased with decreasing R/B ratio, regardless of PPFD. Concentrations of aromatic compounds (eugenol and linalool) based on dry weight were significantly higher at P150 than at other PPFDs and in treatments with greater amounts of red light. These results suggest that basil growth, appearance, and functional and aromatic compound concentrations can be adjusted as needed by manipulating the PPFD and R/B ratio, although R/B 4.0 at P300 caused malformed leaves.

ORIGINAL ARTICLES
  • Takashi Kawai, Tomoya Ichioka, Akari Ikeda, Tami Ohashi, Go Inohara, K ...
    Type: Original Articles
    2021 Volume 90 Issue 4 Pages 365-373
    Published: 2021
    Released: October 23, 2021
    [Advance publication] Released: July 13, 2021
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    Supplementary material

    Split pit in peach [Prunus persica (L.) Batsch] fruit is an internal disorder characterized by the splitting or fracture of the lignified endocarp known as the stone or pit. It is empirically known that split-pit peach fruit mature earlier than normal fruit on trees, thereby leading to frequent preharvest fruit drop in split-pit fruit. However, studies that accurately compare split-pit and normal fruit maturation and/or focus on the physiological mechanism underlying this difference in maturation are limited, partly due to the lack of an effective method to distinguish split-pit fruit from normal fruit on trees. Recently, we demonstrated that an acoustic vibration method could be effectively used for the nondestructive detection of split pit in unpicked peach fruit on trees. In this study, we applied this method to distinguish normal fruit from split-pit fruit and evaluate maturation on trees. Comparison of pairs of normal and split-pit fruit grown at a near-canopy position for three consecutive years (2018–2020) revealed that split-pit fruit matured earlier than normal fruit in most pairs. The average harvest date difference was approximately three days, at least under the experimental conditions in 2020. The amount of ethylene produced from seeds was significantly larger in immature split-pit fruit than immature normal fruit collected at fruit development stage from late June to early July, suggesting that the increased ethylene production from seeds during the fruit development stage is a possible cause of early maturation in split-pit fruit. From the results obtained, we discuss the effect of split pit on the maturation of peach fruit on trees in relation to practical cultivation management to reduce problems caused by split pit.

  • Yu Kinoshita, Ko Motoki, Munetaka Hosokawa
    Type: Original Articles
    2021 Volume 90 Issue 4 Pages 374-381
    Published: 2021
    Released: October 23, 2021
    [Advance publication] Released: June 05, 2021
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    Supplementary material

    A non-flowering natural cabbage mutant among the open-pollinated line ‘T15’ was found 42 years ago. The mutant was named ‘nfc’ (non-flowering cabbage) and has been propagated vegetatively by cuttings. ‘nfc’ hardly flowers during the spring season even after plenty of low-temperature periods. This study characterized the non-flowering trait of ‘nfc’ and assumed the mechanism. In the first experiment, we investigated the flowering characteristics of ‘T15’ and ‘nfc’ over three years. Throughout the 3-year cultivation period, all ‘T15’ plants flowered, while the flowering ratios of ‘nfc’ propagated by cuttings at the 1st, 2nd, and 3rd year were 0%, 32%, and 4%, respectively. In the last two years, other traits were also investigated in detail. The flowering dates of ‘nfc’ flowering plants were later than those of ‘T15’, and the average numbers of flowering shoots per flowering plant of ‘nfc’ were lower than those of ‘T15’. Moreover, the terminal bud of ‘nfc’ flowering plants continued to grow vegetatively, even when their lateral shoots flowered. In the second experiment, to verify the hypothesis that ‘nfc’ is a chimeric plant, we investigated protoplast-regenerated plants’ flowering characteristics from mesophyll protoplasts of ‘nfc’. We obtained colonies derived from different protoplasts of ‘nfc’ and regenerated plants from each colony (nfcPP lines). Suppose the ‘nfc’ is a chimeric plant, in that case, protoplast-regenerated plants’ flowering characteristics should be the same for each colony they derived. However, both flowering and non-flowering plants appeared in the same nfcPP lines derived from a single colony. From this, we concluded that ‘nfc’ is not a chimeric plant on flowering characteristics. These results indicate that ‘nfc’ is a mutant that maintains its flowering ability, but its flowering is strongly suppressed by some factors other than its structural characteristics.

  • Ruikun Chen, Kaede Takamura, Keita Sugiyama, Daisuke Kami, Koichiro Sh ...
    Type: Original Articles
    2021 Volume 90 Issue 4 Pages 382-392
    Published: 2021
    Released: October 23, 2021
    [Advance publication] Released: July 21, 2021
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    Supplementary material

    Genetic diversity analysis of worldwide Cucurbita genetic resources preserved in the Japanese Genebank can provide valuable information for breeding. In this study, 612 Cucurbita accessions of six species, including 40 accessions with no identification information, were genotyped with 30 SSR markers; 378 alleles were detected (12.6 alleles per marker; range, 4–24). By cluster analysis, the 40 unidentified and 53 likely misidentified accessions were (re)identified. The identification was verified by cluster analysis based on the sequence of the mitochondrial atp4ccmC region. After correction of the identification information, C. pepo accessions had the highest diversity indices among the species analyzed and thus showed potential as an ideal genetic resource for breeding. Among the three major species (C. moschata, C. maxima, and C. pepo), the diversity indices of accessions from Japan were lower than those of overseas accessions, indicating that the overseas accessions preserved in Japan are more genetically diverse and can be used as materials for the development of new cultivars. STRUCTURE and principal coordinate analyses of C. moschata revealed that several Japan accessions constituted an indispensable part of global crop genetic resources owing to their differences from overseas accessions. Commercial cultivars of C. maxima showed genetic similarity to each other in principal coordinate analysis, suggesting that they may have similar breeding properties. This study corrects some identification errors in the Genebank and could help improve the breeding of Cucurbita vegetables.

  • Hiroki Nakahara, Akihiro Maehara, Taro Mori, Naotaka Matsuzoe
    Type: Original Articles
    2021 Volume 90 Issue 4 Pages 393-400
    Published: 2021
    Released: October 23, 2021
    [Advance publication] Released: August 31, 2021
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    Ralstonia solanacearum causes bacterial wilt and undergoes spontaneous phenotypic conversion (PC) from its wild-type to an avirulent form. In previous studies, we reported that pre-inoculation of plants with PC mutants suppressed bacterial wilt and Verticillium wilt in eggplants. In addition, we previously revealed bacterial differences in the control effects in eggplant among PC mutants; 8107PC and 8103PC were selected as effective strains for controlling Verticillium wilt and bacterial wilt diseases, respectively. In this study, we investigated the biological control efficiencies of 8107PC inoculation among 19 eggplant cultivars, including 13 commercial cultivars and six rootstock cultivars, to select eggplant cultivars that stably prevent Verticillium wilt using PC mutants. Varietal differences in biological control were confirmed. Additionally, cultivars with a higher potential resistance to Verticillium wilt tended to be more suppressed by the PC mutant, suggesting that cultivar selection is important to achieve effective biocontrol. Furthermore, we found that the biocontrol with 8107PC against Verticillium wilt in grafted eggplant seedlings of Solanum melongena ‘Senryo nigo’ onto S. torvum ‘Tonashimu’ was the most effective rootstock cultivar against Verticillium wilt. The biocontrol was more effective than the non-grafted seedlings inoculated with the PC mutant and the grated seedlings not inoculated with the PC mutant. We also investigated biocontrol by the 8103PC inoculation against bacterial wilt using grafted seedlings (‘Senryo nigo’ as the scion) with ‘Tonashimu’ or S. melongena ‘Daitaro’ as rootstocks. Although ‘Daitaro’ had a low control effect against Verticillium wilt, the grafted seedlings showed a high control effect against bacterial wilt, regardless of the PC mutant inoculation. Conversely, seedlings grafted with ‘Tonashimu’ were vulnerable to bacterial wilt; however, inoculation with the PC mutant completely suppressed the disease. Therefore, this study demonstrated that bacterial wilt and Verticillium wilt could be effectively controlled by inoculation with PC mutants in seedlings grafted with ‘Tonashimu’. The combination of grafting and PC mutant inoculation is expected to be effective for the combined control of Verticillium wilt and bacterial wilt diseases in eggplants.

  • Ryota Arakawa, Hisae Fujimoto, Haruka Kameoka, Seiro Toriyama, Yoshihi ...
    Type: Original Articles
    2021 Volume 90 Issue 4 Pages 401-409
    Published: 2021
    Released: October 23, 2021
    [Advance publication] Released: August 31, 2021
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    Supplementary material

    Blossom-end rot (BER) in paprika (Capsicum annuum L.), as in tomato fruits, is a physiological disorder caused by calcium (Ca) deficiency in fruits. While studies have revealed that excessive nitrogen and potassium fertilization and high temperatures affect Ca transport to fruits and induce BER, few studies have investigated the effects of other elemental concentrations in paprika fruit and their association with BER occurrence. This study aimed to investigate the relationship between the changes in the elemental composition and incidence of BER in paprika fruits grown at different potassium nitrate (KNO3) concentrations and different temperature conditions. Paprika plants were grown in rockwool blocks in a greenhouse at 25°C and 30°C for approximately four months and irrigated with liquid fertilizer and three different concentrations (0, 27.9, and 74.4 mM) of KNO3 were added. Subsequently, the total fresh weights of ripe paprika fruits and the incidence of BER were measured, and the elemental compositions in the pericarp of the first and last sampled fruits were analyzed. The total fresh weights significantly decreased and the incidence of BER increased with increasing KNO3 concentrations and temperature. The profiles of 11 mineral elements in the pericarps of paprika fruits revealed a significant positive or negative correlation between not only the concentration of Ca, but also that of several other elements including boron (which crosslinks pectin in the cell wall like Ca) and the incidence of BER. These results suggest that Ca deficiency may not be the only cause of BER occurrence, and that several elements may also be involved. The insights from this study will contribute to help predict the incidence of BER and stabilize crop production by improving fertilizer application and environmental control.

  • R. M. S. M. B. Rathnayaka, Fumiya Kondo, Sudasinghe Sathya Prabandaka, ...
    Type: Original Articles
    2021 Volume 90 Issue 4 Pages 410-419
    Published: 2021
    Released: October 23, 2021
    [Advance publication] Released: September 17, 2021
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    The amounts of taste components, including those for pungency, in chili pepper fruit change depending on environmental factors. Our previous study revealed that the amount of capsaicinoid was significantly increased in chili pepper fruits that were cultivated under a drought stress condition. Therefore, the present experiment was conducted to determine the effect of drought stress on pungency and the expression levels of capsaicinoid biosynthesis genes in chili peppers. Japanese chili pepper cultivars ‘Shishito’ and ‘Sapporo’ were selected and cultivated in a greenhouse under a drought stress condition or an excess water supply condition. The fruits were used for morphological analysis, and the quantification of the capsaicinoid content in the placental septum was done using high performance liquid chromatography. Gene expression analysis was carried out using a quantitative reverse transcription polymerase chain reaction for 18 capsaicinoid biosynthesis genes. Based on the obtained gene expression patterns, we divided the 18 genes into three groups. The genes in group 1 (ACL, pAMT, Pun1, WRKY9, CaKR1, CaMYB31, FAT, and KAS I) showed higher gene expression levels in the drought stress condition than in the excess water supply condition in both cultivars at 20 DAF. The genes in group 2 (KAS III, BCKDH, ACS, BCAT, and 4CL) showed higher gene expression levels in the drought stress condition than in the excess water supply condition in only one of the cultivars at 20 DAF. The genes in group 3 (PAL, C3H, HCT, C4H, and COMT) did not show any significant differences in gene expression between the two treatments in either cultivar at all DAF. The genes in our experiment showed similar expression patterns in pungent parthenocarpic fruit and control fruit of ‘Shishito’ as in a previous study. Moreover, we found that the number of seeds tended to be lower in fruits cultivated under a drought stress condition, while capsaicinoid content was higher. It is possible that drought stress firstly affected the number of seeds in the fruits, and the decrease in the number of seeds subsequently caused changes in capsaicinoid biosynthesis.

  • Yu Gobara, Kyeong-Seong Cheon, Akira Nakatsuka, Nobuo Kobayashi
    Type: Original Articles
    2021 Volume 90 Issue 4 Pages 420-427
    Published: 2021
    Released: October 23, 2021
    [Advance publication] Released: September 17, 2021
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    There is a long-lasting flower trait with a temporal color change, known as “misome-shō”, in Japanese evergreen azalea. This trait has been found in several wild Japanese evergreen azalea species, such as Rhododendron kaempferi ‘Nikkō-misome’, R. macrosepalum ‘Kochō-zoroi’, R. indicum ‘Chōjyu-hō’, and R. × hannoense ‘Amagi-beni-chōjyu’. The corollas of long-lasting flower cultivars undergo a conversion of normal corollas to sepaloid corollas due to loss of function of the MADS-box B class gene, APETALA3 (AP3) homolog. Also, the long-lasting flower trait was shown to be recessive to normal flowers and controlled by a single gene. To develop a DNA marker for selection of the long-lasting flower phenotype, we carried out a multiplex-PCR approach to detect the ap3 mutant allele related to long-lasting flower traits, and investigated the flower phenotypes in crossed progenies of 23 cross combinations and 245 individuals. The normal flower phenotype individuals in the crossed progenies were homozygous for the normal allele or heterozygous for the normal allele and the ap3 mutant allele. On the other hand, the long-lasting flower phenotype individuals in the crossed progenies were homozygous for the ap3 mutant allele of long-lasting cultivars. These results support the idea that the long-lasting flower trait is caused by a mutation in the AP3 homolog, and it has been newly clarified that any combination of these mutant alleles in long-lasting flower cultivars has the long-lasting flower phenotype. In conclusion, our data indicate that efficient selection of individuals with long-lasting flowers will be possible by using selection DNA markers linked to the long-lasting flower trait.

  • Hayato Morimoto, Yuka Ando, Hiroaki Sugihara, Takako Narumi-Kawasaki, ...
    Type: Original Articles
    2021 Volume 90 Issue 4 Pages 428-449
    Published: 2021
    Released: October 23, 2021
    [Advance publication] Released: July 15, 2021
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    Supplementary material

    Current carnation cultivars have a wide range of flower colors, which is one of the important traits for the flower market. Since large numbers of commercial carnation cultivars bearing various flower colors and flower color patterns have been developed over the last few decades, a comprehensive understanding of the diversity of flower color characteristics has become difficult to achieve. In this study, 56 standard carnation cultivars and 54 spray carnation cultivars were collected and evaluated in terms of flower color and flower color pattern, two visual traits, and flower pigments. Visual flower color analysis indicated that the flower color pattern of the 110 cultivars could be categorized into five typical types and two minor types, and the five typical types were further classified into 16 sub-types. Additionally, flower colors of these carnations could be categorized into 15 hues. High-performance liquid chromatography (HPLC) analysis indicated that carnation flower color is basically determined by the combination of pelargonidin and cyanidin-based anthocyanins, chalcononaringenin 2'-O-glucoside and chlorophyll, giving cyanic, yellow and green color, respectively. Microscopic observation of the petal epidermis indicated that formation of anthocyanin aggregates in the vacuoles and cell shape affect color perceptions, either metallic or velvety, and this is involved in flower color diversification. A fundamental investigation of flower color characteristics will support further developments in flower-color breeding.

  • Sho Ohno, Mizuki Yokota, Haruka Yamada, Fumi Tatsuzawa, Motoaki Doi
    Type: Original Articles
    2021 Volume 90 Issue 4 Pages 450-459
    Published: 2021
    Released: October 23, 2021
    [Advance publication] Released: August 04, 2021
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    Supplementary material

    Yellow color in dahlia flowers is conferred from chalcones, butein and isoliquiritigenin. The color intensity of yellow dahlia cultivars is diverse, but a detailed study on this has not yet been performed. In this study, we first identified structures of flavonoids by nuclear magnetic resonance imaging in ray florets of the red-white bicolor ‘Shukuhai’, which contains chalcones, flavones and anthocyanins. Four anthocyanins, four flavone derivatives, five isoliquiritigenin derivatives and five butein derivatives were identified. Among the identified compounds, butein 4'-malonylsophoroside is considered to be the final product for butein derivatives and the presence of chalcone 4'-glucosyltransferase, chalcone 4'-glucoside glucosyltransferase, and chalcone 4'-glucoside malonyltransferase for isoliquiritigenin and butein modification was predicted. Also, the biosynthetic pathway of butein and isoliquiritigenin derivatives in dahlia with butein 4'-malonylsophoroside as the final product was predicted from the identified compounds. Next, we used nine yellow cultivars and lines with different color intensities and analyzed the correlation between the b* value, an indicator of yellow color, and level of chalcones. There was no difference in the presence or absence of major peaks among the cultivars and lines. Peak area per fresh weight measured by HPLC was high in butein 4'-malonylglucoside, butein 4'-sophoroside and isoliquiritigenin 4'-malonylglucoside, suggesting these three compounds were accumulated abundantly. Among the identified chalcones, the highest correlation coefficient was detected between the b* value and butein 4'-malonylglucoside (r = 0.86), butein 4'-sophoroside (r = 0.82) or isoliquiritigenin 4'-malonylglucoside (r = 0.76). These results suggest that these three chalcones confer yellow color in dahlia ray florets. The findings in this study will contribute not only to efforts at breeding new yellow dahlia cultivars, but also to molecular breeding of yellow flowers in other species by introducing the butein biosynthetic pathway.

  • Yang Yang, Shun Takenaga, Sho Ohno, Motoaki Doi
    Type: Original Articles
    2021 Volume 90 Issue 4 Pages 460-468
    Published: 2021
    Released: October 23, 2021
    [Advance publication] Released: June 05, 2021
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    Supplementary material

    Cut dahlia (Dahlia Cav.) flowers have recently become popular in Japan, but their marketability is limited by their poor vase life. During the postharvest period, the senescence of petals initiates from the outermost whorl and then proceeds into the inner petals. We found that the drawing resistances of petals in the dahlia ‘Kokuchou’, ‘Nesshou’, and ‘Saisetsu’ decreases with time because the petals gradually detach from the ovaries. A reduction in drawing resistance occurred prior to the end of vase life. Exogenous ethylene treatment of ‘Saisetsu’ cut inflorescences accelerated the decline of the petal drawing resistance and thus shortened the vase life. Ethylene production by individual florets in cut inflorescences began before or on the day of harvest. Simultaneously, abscission layers developed at the petal-ovary boundaries of the outermost florets. The florets without ovaries, which did not form the abscission layer, had a longer life than the florets with ovaries. Furthermore, we observed a marked rise in petal sugar contents in florets without ovaries compared to those with ovaries when maintained in 2% fructose. These results indicate that ethylene-promoted abscission layer development directs the course of petal senescence, which is characterized by wilting and discoloration due to a blocking of water flow and carbohydrates into the petals.

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