Horticultural Research (Japan)
Online ISSN : 1880-3571
Print ISSN : 1347-2658
ISSN-L : 1347-2658
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Breeding & Germplasm Resources
  • Satoshi Ohta, Yoshinobu Kono, Hideo Bessho, Keisuke Nonaka, Terutaka Y ...
    2021 Volume 20 Issue 2 Pages 131-142
    Published: 2021
    Released: June 30, 2021
    JOURNALS FREE ACCESS

    We have started to breed a new citrus variety suitable for processing to meet the recent consumer demand for processed fruits. To this end, it is a prerequisite to identify fruit traits suitable for processing. Questionnaire responses obtained from 18 processors indicated that fruit weight, yield rate, and seed number were particularly important for processing. Since the acceptable limits of these characters varied among the processing purposes, such as for jam and juice, we focused on the cut fruits involving a large volume for processing, to decide on a provisional selection criterion. A provisional criterion for the drip amount, considered as a problem for fruit processing so far, was also determined based on the questionnaire survey. Through this, we identified two fruit traits that were involved in the drip amount. Subsequently, we carried out interviews with three processors, and applied the provisional criterion for citrus breeding strains. Based on the results, selection criteria were confirmed as follows: In the primary selection stage, which has been examined mainly based on morphological surveys, citrus breeders should select strains with the following traits: ≧ 180 g for fruit weight, 3 ≦ for seed number, ‘little’ to ‘medium’ for juice amount, and ‘medium’ to ‘tough’ for pulp toughness. In the secondary selection stage, it was necessary for breeders to select candidates for commercial varieties based on additional evaluation, including the pulp ratio and drip amount, along with traits of ≧ 200 g for fruit weight, 3 ≦ for seed number, ≧ 80% for pulp percentage, and 1.60 g ≦ for drip amount (per 100 g of fruit).

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  • Ikuo Miyajima, Shiori Shibasato-Takami, Aina Ichikawa, Yuki Mizunoe
    2021 Volume 20 Issue 2 Pages 143-148
    Published: 2021
    Released: June 30, 2021
    JOURNALS FREE ACCESS

    Colchicine treatment of seeds of the South American rocoto pepper (Capsicum pubescens) was conducted to obtain self-compatible tetraploids, and their morphological characteristics and self-compatibility were investigated. In total, 38 tetraploids were obtained following colchicine treatment of the seeds of diploid rocoto pepper. The leaf width, petal length, and pollen grain diameter of tetraploids were significantly greater than those of diploids. Individuals exhibiting self-compatibility were identified in tetraploids, whereas no fruit setting was observed in self-pollinating diploids.

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  • Chieto Miyashita, Kosuke Kosakai
    2021 Volume 20 Issue 2 Pages 149-156
    Published: 2021
    Released: June 30, 2021
    JOURNALS FREE ACCESS

    We investigated the pollen quantity and morphology of 24 Bouvardia cultivars/lines and their germinability on different media, and evaluated the relationships between these characteristics and male fertility. First, the effects of various culture media and environmental conditions on the in vitro pollen germination of two species (B. ternifolia and B. longiflora) were examined. The conditions of 10% sucrose, 25°C, and 4h culture under light were selected as suitable for the germination of Bouvardia pollen. Second, the pollen characteristics, namely quantity, size, percentage of good quality pollen, and germinability, of 24 Bouvardia cultivars/lines (two B. ternifolia lines, two B. longiflora lines/cultivars, four 4x and eleven 8x hybrid cultivars, and three 8x and two 16x polyploid lines) were evaluated. The relationships between these pollen characteristics and male fertility were then analyzed. There was a strong positive correlation of male fertility with both pollen germination and the pollen tube length. These results suggest that the germinability of pollen significantly influences male fertility. Additionally, since the linear correlation between the pollen tube length and male fertility was strong, we consider that the pollen tube length could be applied as an index for evaluating male fertility in Bouvardia.

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Crop Production & Cropping Type
  • Sakura Hamasaki, Ittetsu Yamaga
    2021 Volume 20 Issue 2 Pages 157-162
    Published: 2021
    Released: June 30, 2021
    JOURNALS FREE ACCESS

    The β-cryptoxanthin content of satsuma mandarin fruit is altered by cultivation conditions or postharvest treatment. Previously, we reported that the β-cryptoxanthin content in the juice sacs and flavedo of satsuma mandarin was increased by mulching. This study, aiming to further clarify the conditions that raise β-cryptoxanthin levels, investigated the effect of a combination of mulching cultivation and pre-storage conditioning (20°C treatment or red LED irradiation) on the β-cryptoxanthin content in satsuma mandarin fruit after long-term storage. The β-cryptoxanthin content in the flavedo of ‘Aoshima unshiu’, harvested in early December, was increased by red LED irradiation at 20°C for 7 days. Moreover, the β-cryptoxanthin content in the juice sacs was maintained, and the content in the flavedo continued to increase in fruits that were stored for 4 months at 8°C and 85% relative humidity. In the fruits with combined mulching cultivation and red LED irradiation, the β-cryptoxanthin content of the flavedo was significantly higher than that of fruits cultivated without mulching and subjected to normal pre-storage conditioning. It is considered that, while mulching increased the β-cryptoxanthin content in the flavedo to some extent, the red LED irradiation increased it further; therefore, there was an additive effect of combination treatment. However, the difference caused by the red LED irradiation was not significant after long-term storage. In contrast, the β-cryptoxanthin content in the juice sacs and flavedo of fruit grown with mulching was maintained at a high level during long-term storage. These results indicate that mulching has the greatest effect on the β-cryptoxanthin content of fruit after long-term storage. In other words, the β-cryptoxanthin content of fruit at harvest is the most important factor governing the content of this substance after long-term storage.

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  • Ittetsu Yamaga, Yuji Emoto, Akihiro Nakamura, Masashi Furuya
    2021 Volume 20 Issue 2 Pages 163-170
    Published: 2021
    Released: June 30, 2021
    JOURNALS FREE ACCESS

    We investigated the growth and flower setting characteristics of young satsuma mandarin (Citrus unshiu Marc. ‘Aoshima unshu’) trees utilizing two scaffoldings to implement a branch training method that places buds at a high position along the rootstocks to obtain an early yield and stable fruit quality. Buds were placed on rootstocks at heights of 5 cm (normal) and 30 cm (budding height). The two-scaffold training treatment at normal height increased the number of leaves and canopy volume compared with treatment open center training. The number of flowers at budding height with the two-scaffold training treatment was increased at 1 year after planting; this treatment tends to increase the percentage of leafy flowers 2 and 3 years after planting. The number of vegetative shoots for the budding height with the two-scaffold training treatment was significantly lower compared with the normal height with the same training. On the other hand, the fruit diameter of plants that underwent the training treatment with the two scaffolds tended to be smaller than that of open center training. These results indicate that two-scaffold training for ‘Aoshima unshu’ facilitates fast initial growth, and slightly increases the percentage of leafy flowers at a budding height of 30 cm.

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  • Takayoshi Yano, Takafumi Kinoshita, Hiromichi Yamazaki, Kaori Nagasuga ...
    2021 Volume 20 Issue 2 Pages 171-177
    Published: 2021
    Released: June 30, 2021
    JOURNALS FREE ACCESS

    In order to stabilize strawberry production in summer and autumn in the Tohoku region of northern Japan, we investigated the effect of intermittent long-day treatment on flower induction and vegetative growth in everbearing strawberries. The results showed that the number of leaves on flowering branches tended to increase when 24-hour daylength treatment was performed every two weeks compared with continuous treatment. We found that ‘Natsuakari’ plants flowered continuously and developed leaves on branches appropriately under a 16 or 20-hour daylength after long chilling. On the other hand, we found that ‘Tochihitomi’ plants did not require long-day treatment for flowering after chilling. ‘Natsuakari’ plants exposed to two weeks of a 24-hour daylength followed by two weeks of natural daylength did not differ in flower number or yield from plants treated with a continuous 24-hour daylength.

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  • Takeshi Sawamura, Yoshikazu Kiriiwa, Takeshi Miyako, Atsushi Kano, Kat ...
    2021 Volume 20 Issue 2 Pages 179-187
    Published: 2021
    Released: June 30, 2021
    JOURNALS FREE ACCESS

    It is necessary to clarify leaf resistance when estimating the transpiration rate of tomato plants. We examined the effect of different conditions with different values of electric conductivity (EC) of the culture solution, cultivars, and media, on the leaf resistance and transpiration rate using a single truss tomato hydroponic system. We measured the real transpiration rate by investigating weight changes, calculated leaf resistance, and estimated the transpiration rate using leaf resistance and environmental factors. When tomato plants grew under different EC conditions, the total transpiration varied significantly and the transpiration rate decreased as the EC increased. The solution absorption and root bleeding rate under the EC8 condition were significantly lower than under EC1.35 in ‘Managua’ and ‘CF Momotaro York’. When tomato plants grew with D-tray, rock wool slab, and deep water culture under EC1.35 and EC8 conditions, there was no significant difference in root bleeding rates among media and that under EC8 was lower than EC1.35. The amount of transpiration was highest under EC 1.35 with deep water culture and lowest under EC 8 with rockwool slab. The leaf resistance affected EC of the culture solution, being different among cultivars. The leaf resistance was not changed among D-tray, rock wool slab, and deep water culture. The leaf resistance changed with time: it was high in the early morning and after 15:00 and low at noon. It was clarified that the leaf resistance was affected by different EC values of the culture solution and cultivars, and changed with time.

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Growth Regulation
  • Yuichiro Fujii, Kunihisa Morinaga, Takuya Murase, Rina Kishimoto, Maya ...
    2021 Volume 20 Issue 2 Pages 189-197
    Published: 2021
    Released: June 30, 2021
    JOURNALS FREE ACCESS

    The occurrence of reddish-pulp fruit was consistently lower in Niimi, Okayama (the north area) than in Okayama City (the south area) in 2013–2016 in field-grown ‘Shimizu-hakuto’ peach. A similar trend was observed in 2016 on comparison with peach trees grown in container boxes, which had been grown in the south area under the same conditions for several years and then transferred to the north area just before the onset of the 2016 growing season. The field temperature in the north area was lower than in the south area by 2°C during the peach fruit growing season in all experimental years. Especially, it was clearly shown that fruit in the south area encountered a higher air temperature (more than 25°C) compared with fruit in the north area during Stage 3 of fruit growth, in which fruit were covered with a fruit bag. These observations suggest that Reddish-pulp fruit disorder is stimulated by a high temperature during the fruit growing season. In order to control the temperature around fruit, a functional fruit bag coated with oxidized titanium, with high light reflecting performance, was developed. Fruit bagging by the functional bag during the growing season lowered the fruit surface temperature by 1.5°C and suppressed the development of Reddish-pulp fruit disorder. Fruit quality such as size, appearance, sugar and pH levels in juice, and harvesting time were not affected by the functional fruit bagging, compared with conventional bagging. The developed functional fruit bag provides a practical technique to control Reddish-pulp fruit disorder.

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  • Daisuke Yoshimura, Akihiko Sato, Daiki Ito, Hinako Nakamoto, Asami Oka ...
    2021 Volume 20 Issue 2 Pages 199-205
    Published: 2021
    Released: June 30, 2021
    JOURNALS FREE ACCESS

    This study was conducted to elucidate the mechanism of seedlessness in large-sized berry grapes induced by gibberellic acid (GA) treatment at the stage of full bloom to three days after full bloom. We selected ‘Kyoho’, ‘Pione’, ‘Honey Venus’, ‘Shine Muscat’, and ‘Fujiminori’ as large-sized grapes, and some clusters of these cultivars were treated with GA at the full-bloom stage, but some others were kept without GA treatment. Then, the percentages of seeded berries in a fruit cluster were investigated among GA-treated or GA-untreated clusters. As a result, ‘Kyoho’ and ‘Pione’ had seeded berries with low percentages even in GA-untreated clusters, whereas ‘Honey Venus’, ‘Shine Muscat’, and ‘Fujiminori’ had seeded berries with 60.3 to 71.6% in a cluster when GA was not applied. ‘Kyoho’ and ‘Pione’ may have a putative factor that prevents fertilization. In addition, GA treatment of ‘Honey Venus’, ‘Shine Muscat’, and ‘Fujiminori’ in the full-bloom stage induced seedlessness, even though the seeded percentage was cultivar-dependent with values from 40.8 to 0.0%. This shows that GA treatment prevents embryo development after fertilization among these cultivars. Furthermore, when gibberellin activities of florets before full bloom on some selected dates were evaluated with a bioassay in ‘Pione’, as a difficult fertilizable cultivar, and in ‘Honey Venus’, as an easy fertilizable cultivar, gibberellin activities of florets in ‘Pione’ were always higher than in ‘Honey Venus’. This may indicate that the inhibition of embryo sac formation led to difficult fertilizable properties of ‘Pione’ is induced with higher activities of gibberellin. Consequently, we could reveal two types of mechanism for seedlessness in large-sized berry grapes with GA treatment at full bloom. One type is caused by difficult fertilizable properties at flowering due to disturbance of the formation of the embryo sac, as shown in ‘Kyoho’ and ‘Pione’. In this type, GA only promotes fruit set of unfertilized berries. The other type is caused by inhibition of embryo development with GA after fertilization, as shown in ‘Honey Venus’, ‘Shine Muscat’, and ‘Fujiminori’.

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  • Akiko Ito, Daisuke Sakamoto, Toshihiko Sugiura, Takaya Moriguchi
    2021 Volume 20 Issue 2 Pages 207-215
    Published: 2021
    Released: June 30, 2021
    JOURNALS FREE ACCESS

    In order to develop a simple method to evaluate freezing tolerance of Japanese pear flower buds, we compared the total sugar concentration in xylem sap of shoots and the lethal temperature 50 (LT50 (°C)) of axillary flower buds on the shoots. We used shoots from the mature ‘Kosui’,‘Niitaka’, and/or ‘Nijisseiki’ trees grown in the following six orchards between December and February from 2011 till 2018: (i) the experimental orchard of the Institute of Fruit Tree and Tea Science, NARO (Tsukuba, Ibaraki, Japan), (ii) the experimental orchard of the Tottori Prefectural Agriculture and Forest Research Institute (Hokuei, Tottori, Japan), (iii) the experimental orchard of the Fukuoka Agricultural and Forestry Research Center (Chikushino, Fukuoka, Japan), (iv) the experimental orchard of the Kumamoto Prefectural Agricultural Experimental Station (Uki, Kumamoto, Japan), (v) a commercial orchard in Hikawa, Kumamoto Prefecture (Hikawa, Kumamoto, Japan) and (vi) the experimental orchard of Kagoshima Prefectural Institute of Agricultural Development (Satsumasendai, Kagoshima, Japan). There was a negative correlation for each cultivar between LT50 (°C) and corresponding sugar concentrations in the xylem sap (‘Kosui’: LT50 (°C) = –0.516A–0.417, ‘Niitaka’: LT50 (°C) = –0.342A–4.55, ‘Nijisseiki’: LT50 (°C) = –0.268A–9.84, where A means the total sugar concentration in xylem sap (mg·mL–1)). The calibration lines contain some outliers, and a part of them may relate to large changes in temperatures (atmosphere) encountered before sampling. Experiments using the ‘Kosui’ potted tree revealed that sugar concentrations in xylem sap responded within one or two days to the temperature transition whereas LT50 (°C) took more than 10 days, and these differences in responses may have caused these outliers. We also showed that the sugar concentrations in xylem sap were positively correlated with the index shown by refractometers like a portable Brix meter for measuring fruit quality. Thus, although there is a certain limitation on actual application, such as the requirement for a different calibration curve for each variety and the consideration of factors other than the sugar concentration to determine LT50 (°C), we suggest that regularly analyzing the xylem sap can help monitor vulnerability in freezing tolerance for certain orchards and/or years.

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Postharvest Physiology & Technology
  • Yuichi Matsumoto, Saori Maruta, Asuka Komaba, Keisuke Tsuge, Keiichi W ...
    2021 Volume 20 Issue 2 Pages 217-223
    Published: 2021
    Released: June 30, 2021
    JOURNALS FREE ACCESS

    The Jerusalem artichoke (Helianthus tuberosus L.) is a root vegetable rich in inulin, which has been reported to suppress elevated blood glucose levels. This study aimed to investigate changes in inulin and potassium contents of Jerusalem artichoke harvested in different periods. Furthermore, appropriate harvesting periods that result in tubers with high inulin and low potassium contents were determined. The results showed that the inulin content and its degree of polymerization gradually decreased from November to February, whereas the potassium content increased until December in the tubers. These results indicate that the optimal harvesting period for Jerusalem artichoke may be early November. Studies on the storage methods for tubers indicated that the increase in the potassium content observed in the field study can be suppressed under low-temperature storage. Therefore, we conclude that storage at low temperatures is effective for controlling the potassium content of tubers.

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Disease & Pest Management
  • Yuichi Matsumoto, Reiko Kojima
    2021 Volume 20 Issue 2 Pages 225-231
    Published: 2021
    Released: June 30, 2021
    JOURNALS FREE ACCESS

    The disease-controlling effect of Farm-A, a special liquid fertilizer composed of fermented hot water extract of sweetleaf (Stevia rebaudiana), was investigated. At 0.1 to 1% concentration, its effect against strawberry gray mold (Botrytis cinerea) and anthracnose (Colletotrichum gloeosporioides) was similar to that of dodecylbenzenesulphonic acid bisethylenediamine copper [II] salt (DBEDC) and propineb. The residual effect was prolonged compared with that of DBEDC. However, although DBEDC showed antibacterial activity against gray mold in culture medium, this activity was not observed with the fermented hot water extract of sweetleaf. As a result of treating whole cucumber seedlings in the two-leaf stage with the fermented hot water extract of sweetleaf, gray mold was controlled. Furthermore, even when the treatment was applied only to the first leaf, gray mold was controlled in the latter leaves that were not treated, and the expression level of the peroxidase gene increased in the first leaf. As a control effect was observed for multiple diseases, the residual effect was prolonged, a disease-controlling effect was observed even with local treatment, and it led to increased expression of related genes, it was considered that this effect of fermented hot water extract of sweetleaf on diseases is likely due to systemic acquired resistance.

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  • Yuichi Matsumoto, Syouta Uchida, Yuka Fukumoto, Saya Kanaya, Ayaka Hir ...
    2021 Volume 20 Issue 2 Pages 233-239
    Published: 2021
    Released: June 30, 2021
    JOURNALS FREE ACCESS

    Methods for suppressing southern blight of Jerusalem artichoke were examined. The growth of the pathogen in the medium and disease index of Jerusalem artichoke were both suppressed at pH 8 and above. Among fungicides registered for use on vegetables, sulfur agents suppressed growth of the pathogen in the medium. A suppressing effect was observed in the soil medium containing sulfur fertilizers. When Jerusalem artichokes were cultivated in soils containing sulfur fertilizers, the crops exhibited fewer symptoms. Additionally, mortality rates caused by southern blight during field cultivation were reduced with the application of sulfur fertilizers. On comparing disease resistance between two Jerusalem artichoke lines, Mitsuse conventional and Sunflower-potato, during field cultivation, the Sunflower-potato line exhibited lower mortality rates. These results suggest that sulfur fertilizers and the disease-resistant line, Sunflower-potato, may be used to suppress southern blight during cultivation. As sulfur fertilizers and resistant strains can be used in combination, an effect to suppress southern blight in Jerusalem artichokes might be expected.

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NEW TECHNOLOGY
  • Toshikazu Matsumoto, Hideki Nimiya, Akane Fujimoto, Tatsuki Kawakami, ...
    2021 Volume 20 Issue 2 Pages 241-246
    Published: 2021
    Released: June 30, 2021
    JOURNALS FREE ACCESS

    Polyethylene non‐woven fabric white reflective sheet treatments were applied to ‘Saijo’ persimmon to improve the coloration of fruits. Persimmon trees with modified leader type training were used in this study. The color chart (CC) value of curtain treatment was significantly increased compared with the control, and no significant difference was observed between curtain and mulch treatments. The sugar contents (°Brix) of fruit among the curtain treatment, mulch treatment, and control were not significantly different. No damage of fruits or twigs was observed in the curtain treatment, and no negative effect was observed in the shelf life of harvested fruits. White reflective sheet use with on-ground mulching has the disadvantage of the sheet becoming dirty during cultivation. On the other hand, curtain treatment using a white reflective sheet can be expected to prolong the useful life of the sheet as well as promote cost reduction. In this study, curtain treatment with white reflective sheet treatments improved the fruit skin color of persimmon.

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