The Horticulture Journal
Online ISSN : 2189-0110
Print ISSN : 2189-0102
ISSN-L : 2189-0102
Advance online publication
Displaying 1-22 of 22 articles from this issue
  • Megumi Ogawa, Rihito Takisawa
    Article type: Original Articles
    Article ID: UTD-368
    Published: 2022
    Advance online publication: June 25, 2022
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    Artificially occurring parthenocarpy can be induced by exogenous application of plant hormones and is useful in the fruit production of many fruit crops and fruit trees. In cucumber (Cucumis sativus L.), a model species in the Cucurbitaceae family, the plant hormones auxin, gibberellin, cytokinin, and brassinosteroids are known to induce parthenocarpy. In tropical squash (Cucurbita moschata L.), synthetic auxins are known to induce parthenocarpy, but the effects of gibberellin, cytokinin, and brassinosteroids are still unknown. In addition, there are few published reports on the quality of parthenocarpic fruits induced by plant hormones in tropical squash, and the effects of these hormones remain largely unknown. In this study, we examined the effects of gibberellin, cytokinin, and brassinosteroids on the parthenocarpy of tropical squash and characterized the parthenocarpic fruits induced by the plant hormones. First, we evaluated fruit set and development in unpollinated fruits of ‘Kogiku’, a tropical squash cultivar, treated with gibberellic acid (GA3), a synthetic cytokinin-like substance, N-(2-chloro-4-pyridyl)-N′-phenylurea (CPPU), and brassinolide (BL). CPPU promoted parthenocarpy, but GA3 and BL did not, showing that cytokinin works as an important factor for parthenocarpy in tropical squash. Next, we investigated the quality of parthenocarpic fruits from ‘Kogiku’ induced by a synthetic auxin, 1-naphthylacetic acid (NAA), and CPPU. Total soluble solids and myo-inositol of NAA-treated parthenocarpic fruit were higher than those of pollinated fruits, whereas fructose of NAA-treated parthenocarpic fruit and fructose and glucose of CPPU-treated parthenocarpic fruits were significantly lower than those of pollinated fruits. These results showed that parthenocarpy of tropical squash induced by auxin and cytokinin had differing effects on fruit quality.

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  • Katsuhiko Inamoto, Kaori Nagasuga, Takayoshi Yano
    Article type: Original Articles
    Article ID: UTD-372
    Published: 2022
    Advance online publication: June 25, 2022
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    We investigated the effects of CO2 enrichment on photosynthesis, growth, and dry matter accumulation in the Oriental hybrid lily ‘Siberia’. The photosynthetic rate increased as the CO2 concentration was elevated compared to the ambient level. The increase in the photosynthetic rate was greater in the low concentration range and lower in the high concentration range. The relationship between the light intensity-photosynthetic rate and temperature-photosynthetic rate was investigated under different CO2 concentrations. The entire light-photosynthesis and temperature-photosynthesis curves moved toward a considerably higher photosynthetic rate when the CO2 concentration was increased from 380 ppm to 1000 ppm. In contrast, when the CO2 concentration was increased from 1000 ppm to 2000 ppm, the increase in the entire light-photosynthesis curve was small. The relationship between the CO2 concentration and the maximum temperature point of the photosynthetic rate was unclear. We also cultured ‘Siberia’ lily plants with and/or without CO2 enrichment (1500 ppm) altered before (the early stage) and after (the late stage) the visible flower bud stage. The CO2 enrichment increased dry weights dry weight/fresh weight ratios of whole plants, and individual parts at flowering, resulting in improved cut flower quality and enlargement of the mother bulb and daughter bulblets. The effective period of CO2 enrichment was after the visible flower bud stage. In cases where CO2 enrichment was effective for dry matter accumulation, the dry matter distribution ratios of the mother bulb and daughter bulblets to the whole plant were high, and those of the leaves, stem, and flower buds were low. The relative growth rate and net assimilation rate from planting to the flowering stage were increased with CO2 enrichment applied after the visible flower bud stage, indicating that the dry matter accumulation and photosynthesis were enhanced. Finally, the issues that need to be addressed for applying practical CO2 enrichment technology to various lilies are discussed.

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  • Saeko Konishi-Sugita, Kayo Sato, Etsuko Mori, Yuko Abe, Miho Hazebayas ...
    Article type: Original Articles
    Article ID: UTD-340
    Published: 2022
    Advance online publication: June 15, 2022
    JOURNAL OPEN ACCESS ADVANCE PUBLICATION
    Supplementary material

    The pathogenic bacterium Pseudomonas syrinage pv. actinidiae causes bacterial canker disease, which is the most damaging disease afflicting kiwifruit (Actinidia chinensis). The most prevalent strain is biovar 3 (Psa3), which is highly pathogenic. Therefore, Psa3-resistant varieties of kiwifruit are urgently needed. A previous study reported that Actinidia rufa, a wild Japanese species related to kiwifruit, is highly resistant to Psa3. Genome-wide DNA markers may be useful to locate the loci that confer Psa3 resistance. Therefore, in the present study, we used published kiwifruit genome sequence information to design 1,101 simple sequence repeat (SSR) markers covering the entire kiwifruit genome in silico. We next examined DNA polymorphisms in more than 1,000 polymerase chain reaction products for potential use as SSR markers among A. rufa Fuchu and A. chinensis FCM1, a pollen-providing parent Fuchu A. chinensis male 1, and other kiwifruit cultivars in order to develop Psa3 resistant kiwifruit cultivars. We finally obtained 351 polymorphic markers, in the entire kiwifruit genome, which can be applied to produce next-generation kiwifruit cultivars, including Psa3-resistant cultivars.

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  • Atsu Yamasaki, Junko Kaneyoshi, Michiharu Nakano, Akira Kitajima
    Article type: Original Articles
    Article ID: UTD-284
    Published: 2022
    Advance online publication: June 01, 2022
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    Mukaku Kishu–type seedlessness in citrus (Citrus L.) is characterized by the formation of small and edible seeds (type A seeds) with an immature seed coat and arrest of embryo development at an early stage. We investigated the effect of high temperature on embryo and seed development in the Mukaku Kishu–type seedless cultivar ‘Southern Yellow’ over a period of four years. In outdoor-grown trees, embryos at the zygote and proembryo stages were observed at 10 weeks after pollination (WAP), and embryo development was largely arrested at 18 WAP; as a result, only type A seeds formed. In glasshouse-grown trees, globular-stage embryos were observed at 10 WAP, and globular- to cotyledon-stage embryos developed by 18 WAP. The day temperature in the glasshouse was higher than outdoors. Seeds developed in the fruit of trees transferred into a glasshouse at 0–2, 0–4, or 2–4 WAP, but not 4–8 WAP. High temperature before flowering had no effect on seed development. We conclude that high temperature at 0–4 WAP releases the arrest of embryo development after 10 WAP in ‘Southern Yellow’.

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  • Hiroki Matsuo, Keiji Mine, Taro Sano, Hirotsugu Yoneda, Yosuke Yoshiok ...
    Article type: Original Articles
    Article ID: UTD-363
    Published: 2022
    Advance online publication: May 31, 2022
    JOURNAL OPEN ACCESS ADVANCE PUBLICATION

    Anthracnose, caused by the fungal pathogen Colletotrichum orbiculare, is one of the most severe diseases in watermelon (Citrullus lanatus) cultivation in Japan. Genetically conferred host resistance is the best way to control it. To develop new cultivars with high resistance, identification of promising sources of resistance is important. We focused on an old Japanese cultivar, ‘Tanso Teikosei’ (NR28), with high resistance, preserved at the Nara Prefecture Agricultural Research and Development Center, evaluated its resistance to diverse C. orbiculare strains distributed in Japan, and revealed the inheritance of its resistance. NR28 and two other accessions were resistant to the highly virulent MAFF 306737 strain. NR28 was also resistant to 16 other strains collected from various regions of Japan. Many strains caused severe symptoms and wilting in susceptible accessions, including the popular Japanese F1 cultivar WF01. CAPS marker analysis indicated that NR28 and the two other resistant accessions were homozygous for the resistance allele of Cla001017, previously reported as the gene responsible for resistance to US race 1. Susceptible accessions were homozygous for the susceptibility allele at Cla001017. Segregation analyses using F2 and BC1F1 lines derived from crosses between NR28 and a susceptible accession suggested that the dominant mutant allele of Cla001017 caused the high resistance of NR28. In contrast, NR28 and other resistant accessions homozygous for the resistance allele of Cla001017 were highly susceptible to two strains sampled in Iwate Prefecture. This suggests that these strains have overcome the Cla001017 resistance allele, as have strains of C. orbiculare classified as US race 2. NR28 and the two other resistant accessions are promising materials for breeding resistance in diverse C. orbiculare strains distributed in Japan that have similar pathogenicity to US race 1. The CAPS marker that we designed in this study offers efficient analysis for watermelon breeding.

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  • Tadahisa Higashide
    Article type: Invited Review
    Article ID: UTD-R019
    Published: 2022
    Advance online publication: May 31, 2022
    JOURNAL OPEN ACCESS ADVANCE PUBLICATION

    The fresh fruit yield of tomatoes (Solanum lycopersicum) is determined by yield components and related traits. In low-truss cultivation in Japan, light use efficiency in the same cultivar is not significantly affected by plant density or seedling stage at transplanting. Total dry-matter production equals light use efficiency × light intercepted by plants. Light interception is determined by leaf area index and the light extinction coefficient in the plant canopy. Light use efficiency is determined by leaf photosynthetic rate and light extinction coefficient. Light use efficiency is expressed as a function of daytime CO2 concentration. The high yield of modern tomato cultivars in the Netherlands is due to an increase in total dry matter production of plants, not to an increase in dry matter partitioning of fruits. An increase in the photosynthetic rate and a decrease in the light extinction coefficient may have increased light use efficiency among Dutch cultivars. Although modern Japanese cultivars have a high content of both water and soluble solids of fruits, yield has not increased. Since the yield of greenhouse tomatoes in Japan has increased little since the 1980s, Japanese researchers have attempted to improve the yield using current Japanese cultivars. Crop growth models can help management decisions on cultural practices, control of greenhouse climate, fertilization, and irrigation. Several models of tomato growth including TOMSIM and TOMGRO have been developed. A growth model based on the relationships among yield components and related traits has been developed to predict dry matter production and yield of greenhouse tomatoes. The model recommended a leaf area index with the highest dry matter production at a certain solar radiation. To improve yield of greenhouse tomatoes by using the model, a one-year experiment was carried out in a greenhouse. The annual yield of tomatoes with Brix at least 5° was at least 50 kg·m−2 for a popular Japanese cultivar, ‘CF Momotaro York’. For the near future, the growth models show promise for growers in helping yield improvement and crop management in greenhouses.

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  • Maria Suzuki, Kanae Masuda, Hideaki Asakuma, Kouki Takeshita, Kohei Ba ...
    Article type: Original Articles
    Article ID: UTD-323
    Published: 2022
    Advance online publication: May 25, 2022
    JOURNAL OPEN ACCESS ADVANCE PUBLICATION

    In contrast to the progress in the research on physiological disorders relating to shelf life in fruit crops, it has been difficult to non-destructively predict their occurrence. Recent high-tech instruments have gradually enabled non-destructive predictions for various disorders in some crops, while there are still issues in terms of efficiency and costs. Here, we propose application of a deep neural network (or simply deep learning) to simple RGB images to predict a severe fruit disorder in persimmon, rapid over-softening. With 1,080 RGB images of ‘Soshu’ persimmon fruits, three convolutional neural networks (CNN) were examined to predict rapid over-softened fruits with a binary classification and the date to fruit softening. All of the examined CNN models worked successfully for binary classification of the rapid over-softened fruits and the controls with > 80% accuracy using multiple criteria. Furthermore, the prediction values (or confidence) in the binary classification were correlated to the date to fruit softening. Although the features for classification by deep learning have been thought to be in a black box by conventional standards, recent feature visualization methods (or “explainable” deep learning) has allowed identification of the relevant regions in the original images. We applied Grad-CAM, Guided backpropagation, and layer-wise relevance propagation (LRP), to find early symptoms for CNNs classification of rapid over-softened fruits. The focus on the relevant regions tended to be on color unevenness on the surface of the fruit, especially in the peripheral regions. These results suggest that deep learning frameworks could potentially provide new insights into early physiological symptoms of which researchers are unaware.

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  • Ryo Norikoshi, Katsunori Kohata, Tomoko Niki, Kazuo Ichimura
    Article type: Original Articles
    Article ID: UTD-347
    Published: 2022
    Advance online publication: May 25, 2022
    JOURNAL OPEN ACCESS ADVANCE PUBLICATION
    Supplementary material

    Flower opening is associated with the expansion of petal cells. To understand the role played by soluble carbohydrates during cell expansion associated with petal growth, changes in soluble carbohydrate concentrations in petal limbs during flower opening in Phlox drummondii were investigated. The size of adaxial and abaxial epidermal cells in the petal limbs gradually increased during flower opening. 2-C-Methyl-d-erythritol (2-C-ME) was identified using 1H-NMR in P. drummondii petals. 2-C-ME was the most abundant carbohydrate in the petal limbs at five developmental stages, with the concentration of glucose the second highest, although the concentration of the latter was half of that of the 2-C-ME concentration in all five stages. The concentrations of 2-C-ME and glucose increased during flower opening. In contrast, inorganic ion concentrations did not increase during flower opening. The osmotic potential of petal limbs decreased considerably during the final stage of flower opening; this decrease could in part be attributed to the increasing 2-C-ME concentration. Transmission electron microscopic observations showed that the petal limb cells in open flowers were occupied primarily by the vacuole. The concentration of 2-C-ME in the vacuole was estimated to be 131 mM, which was much higher than the concentrations of the other carbohydrates. We conclude that the accumulation of 2-C-ME in the vacuole at a high concentration acts as an osmoticum, decreasing the osmotic potential of petal limbs and thereby increasing turgor pressure, which is thought to be involved in cell expansion of petal limbs during flower opening.

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  • Orawan Pimsorn, Somsak Kramchote, Patcharaporn Suwor
    Article type: Original Articles
    Article ID: UTD-359
    Published: 2022
    Advance online publication: May 25, 2022
    JOURNAL OPEN ACCESS ADVANCE PUBLICATION

    Lime (Citrus aurantiifolia var. Pan) fruits were coated with Aloe vera gel (AVG) at 0 (distilled water as control), 10, 20, 30, 40, and 50% concentration as a 5 min dip and stored at ambient temperature (29 ± 1°C, 74 ± 5% RH) for 16 days. AVG coating markedly slowed fruit yellowing based on color scores and CIE L*, a*, and b* values, resulting in an increase in shelf life of about four days longer than that of the control (10 days). It did not significantly affect other fruit responses; AVG-coated and uncoated fruit had comparable weight loss, juice content, total soluble solids (TSS), titratable acidity (TA), and vitamin C content. Thus, AVG coating improved shelf life of lime primarily through delayed yellowing without adverse effects on other physicochemical attributes.

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  • Masumi Yamagishi
    Article type: Original Articles
    Article ID: UTD-373
    Published: 2022
    Advance online publication: May 25, 2022
    JOURNAL OPEN ACCESS ADVANCE PUBLICATION
    Supplementary material

    The lily MYB12 gene, a positive regulator of anthocyanin biosynthesis, is targeted by microRNA828 (miR828). In bicolor tepals of Asiatic hybrid lilies with white lower halves and pigmented upper halves, accumulation levels of miR828 are higher in the lower halves than in the upper halves, and action of MYB12 is suppressed in the lower halves, resulting in bicolor tepal development. This is a newly identified mechanism of color pattern development in flowers. However, which wild species has donated the miR828-mediated bicolor tepal traits to these hybrid lilies is uncertain, and whether miR828-dependent pattern development occurs in species other than Lilium and is responsible for other types of color patterns is unknown. In this study, miR828 accumulation levels were compared between anthocyanin pigmented and unpigmented regions of flowers in lilies and other species. Lilium dauricum is among the parental wild species of Asiatic hybrid lilies. Lilium dauricum showed bicolor tepals, in which anthocyanins highly accumulated in the upper halves, and miR828 accumulation was more than 10 times higher in the lower halves than in the upper halves. Thus, the profile of miR828 accumulation was similar to that found in bicolor cultivars of Asiatic hybrid lilies. It is possible that the miR828-mediated bicolor tepal trait in Asiatic hybrid lilies is derived from L. dauricum. In L. cernuum var. album and an Oriental hybrid lily ‘Dizzy’, the suppression of MYB12 expression causes unpigmented tepals or tepal regions, but the unpigmented regions are spatially different from those in bicolor tepals of Asiatic hybrid lilies. MiR828 accumulation levels were similar between white and pink flowers of L. cernuum, and rather higher in pigmented regions than white regions of ‘Dizzy’ tepals, suggesting little involvement of miR828 in MYB12 expression suppression. MiR828 accumulation levels were evaluated in bicolor flowers of cherry sage, tulip, and Alstroemeria, but differences in miR828 accumulation were not detected between red and white petal/tepal regions, indicating that the mechanisms by which the bicolor flowers developed in these species are likely different from that occurring in Asiatic hybrid lilies and L. dauricum. Thus, the miR828/R2R3-MYB module is likely responsible for color only in lily flowers and only for the color pattern that consists of lower un-pigmented and upper pigmented regions.

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  • Yutaro Osako, Hisayo Yamane, Ryunhee Kim, Hisashi Miyagawa, Ryutaro Ta ...
    Article type: Original Articles
    Article ID: UTD-352
    Published: 2022
    Advance online publication: May 19, 2022
    JOURNAL OPEN ACCESS ADVANCE PUBLICATION
    Supplementary material

    Seed size affects the edible portion rate of lychee fruit and is therefore an important trait for fruit quality in lychee (Litchi chinensis). Lychee fruits can be classified into four categories in terms of seed properties: normal, small, aborted seed and seedless. ‘Salathiel’ is known to bear a relatively high rate of aborted-seeded (pseudo-parthenocarpy, stenospermocarpy) and seedless (parthenocarpy) fruit regardless of environmental and cultivation conditions. In other horticultural fruit crops, such as tomato, auxin metabolism and signaling is critical for parthenocarpy, although auxin metabolism has not been characterized in relation to (pseudo) parthenocarpy in lychee. The purpose of this study was to characterize the physiological and morphological properties of maternal reproductive organs in ‘Salathiel’ female flowers, with a specific focus on the associated auxin metabolism. Microscopic observations of the internal structures of the ‘Salathiel’ embryo revealed that ‘Salathiel’ reproductive organ differentiation is similar to that of normal-seeded cultivars. However, the obturator was significantly smaller in ‘Salathiel’ than in other normal-seeded cultivars, suggesting that specific developmental characteristics may exist in the maternal reproductive organs of ‘Salathiel’. Our investigation of indole acetic acid (IAA) contents revealed that IAA levels were significantly higher in ‘Salathiel’ than in other cultivars. Moreover, the IAA metabolite contents also differed significantly between ‘Salathiel’ and the normal-seeded and small-seeded cultivars. Specifically, N-3-hydroxy-2-oxindole-3-acetyl glutamic acid contents were significantly higher in ‘Salathiel’ than in ‘Yu Her Pau’ and ‘Hei Ye’. 3-hydroxy-2-oxindole-3-acetic acid was lower in ‘Yu Her Pau’ and ‘Salathiel’ than in ‘Hei Ye’, while indole-acetylaspartic acid was significantly lower in ‘Salathiel’ compared to ‘Hei Ye’. Expression analyses of the genes related to auxin biosynthesis, catabolism, transport, and signaling indicated that the IAA influx-related and efflux-related gene expression levels were respectively higher and lower in ‘Salathiel’ than in the other cultivars, which is consistent with the increased IAA accumulation in the ‘Salathiel’ ovary. The possible involvement of auxin metabolism in the aborted-seeded and seedless fruit production in ‘Salathiel’ is discussed herein.

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  • Hikaru Matsumoto, Yoshinori Ikoma
    Article type: Original Articles
    Article ID: UTD-364
    Published: 2022
    Advance online publication: May 19, 2022
    JOURNAL OPEN ACCESS ADVANCE PUBLICATION
    Supplementary material

    Combined treatment with gibberellin (GA) and prohydrojasmon (PDJ) is effective at reducing peel puffing in satsuma mandarin (Citrus unshiu Marc.). However, the effect of this treatment on volatiles remains unknown. In satsuma mandarin, dimethyl sulfide (DMS) is a key flavor compound. In this study, the effects of combined treatment with GA and PDJ on the content of volatiles, DMS, and S-methylmethionine (SMM), a precursor of DMS, in the juice sacs of satsuma mandarin were investigated. Mixtures of GA (1, 3.3, or 5 mg·L−1) and PDJ (25 or 50 mg·L−1) were applied to ‘Okitsu-wase’ and ‘Aoshima’ in mid-September. Gas chromatography-mass spectrometry analysis showed that among the volatiles, DMS content was reduced by the treatment, and was below the DMS odor threshold in several treatments. In ‘Okitsu-wase’, the DMS content in treated fruit was 1/3 to 1/17 of the control. In the treatment with GA and 50 mg·L−1 PDJ, a reduction in DMS content was observed until mid-November, irrespective of GA concentration, whereas in the treatment with 1 mg·L−1 GA and 25 mg·L−1 PDJ, the reduction was observed only until early November. In ‘Aoshima’, the DMS content was also reduced by the treatments, but in the treatment with 1 mg·L−1 GA and 50 mg·L−1 PDJ, the reduction was observed only until mid-November. Although the applied treatments delayed color development by approximately 1–2 weeks, this delay was not related to a reduction in DMS content. The effects on SMM and methionine content were small or negligible. As DMS has a strong odor, with trace amounts affecting fruit flavor, controlling DMS content is important. This study revealed that combined treatment with GA and PDJ reduced the accumulation of DMS in the juice sacs of satsuma mandarin fruits.

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  • Hiroko Hayama, Nobuhito Mitani, Takayoshi Yamane, Shinnosuke Kusaba
    Article type: Original Articles
    Article ID: UTD-348
    Published: 2022
    Advance online publication: April 15, 2022
    JOURNAL OPEN ACCESS ADVANCE PUBLICATION

    Vascular bundle browning (VBB) of the flesh tissue of the Japanese pear ‘Rinka’ was observed when the fruit was stored at 4°C. This symptom was not observed in mature fruit at harvest nor after storage at 25°C for one week following harvest; however, VBB frequently appeared when fruit was stored at 4°C. More than 50% of the fruit had the VBB symptom after storage at 4°C for one week. Further incidences and degrees of the symptoms were observed when the fruit was stored at 4°C for longer periods. No other cultivars have shown this kind of disorder induced by a short period of cold storage, indicating that VBB is a novel type of chilling injury (CI) in pears. The application of a 100 ppm ethephon (2-chloroethylphosphonic acid) solution at approximately 100 days after full flowering (DAF) significantly reduced the occurrence of VBB. Ethephon advances maturation and leads to an early harvest, causing a significant reduction in VBB, but ethephon-treated fruit harvested at the same harvest time as untreated fruit showed a reduced incidence of VBB. Treatment with 1-methylcyclopropene (1-MCP), an inhibitor of ethylene perception, increased the VBB development during cold storage and a subsequent storage period at 25°C. These results suggest that ethylene has a positive effect on alleviating the VBB development in the Japanese pear ‘Rinka’.

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  • Keita Tomiyoshi, Jun-ichiro Masuda, Sae Fujimori, Maiko Kurisaki, Misa ...
    Article type: Original Articles
    Article ID: UTD-350
    Published: 2022
    Advance online publication: April 15, 2022
    JOURNAL OPEN ACCESS ADVANCE PUBLICATION

    Characteristics and inheritance of rhizome coloration in the red rhizome lotus (Nelumbo nucifera) ‘Tomohiro’ were investigated to achieve stable production and breeding of red rhizome cultivars. Rhizome coloration proceeded from the basal internodes to distal ones during the growing stage, and coloration of enlarged distal rhizomes was completed in October. No individuals with both red and white rhizomes in one plant were found, and there were no rhizomes with a mottled pattern or an intermediate color between red and white. The coloration of the skin and flesh was synchronized in red rhizome plants. It was therefore estimated that the skin and flesh coloration of rhizomes was controlled by the same gene. Rhizomes of all selfed plants of ‘Tomohiro’ and white rhizome cultivars were red and white, respectively, and all F1 plants generated by crossing ‘Tomohiro’ and white rhizome cultivars were white. Rhizome color in F2 plants generated by self-pollination of F1 plants divided into white and red individuals with a 3:1 ratio. These results suggested that red rhizome coloration is governed by a single locus, designated RHIZOME COLOR (RHC), with dominant white (Rhc) and recessive red (rhc) coloration alleles.

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  • Kohei Mochida, Akira Nakatsuka, Tetsuya Kako, Nobuo Kobayashi
    Article type: Original Articles
    Article ID: UTD-366
    Published: 2022
    Advance online publication: April 15, 2022
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    Tree peony (Paeonia spp.) is a highly ornamental shrub originally from China. Its cultivars are classified into four groups: Chinese, Japanese, French, and American, based on morphological characteristics and geographic location. The French and American cultivars were developed by crossing the wild species P. lutea Delavay ex Franch. and P. delavayi Franch. with Japanese and Chinese cultivars. In this study, we evaluated phenetic relationships among major cultivar groups in the genus Paeonia L., using a dendrogram reconstructed from band pattern data for random amplified polymorphic DNA (RAPD) markers developed in a previous study. We also developed two sequence tagged site (STS) markers using RAPD markers specific to the French and American tree peony cultivar groups and an intersubgeneric hybrid. The former is an LuDeB marker able to detect the genetic relationship with P. lutea and P. delavayi, and the latter is an HPB marker able to identify the cpDNA of herbaceous peony in intersubgeneric hybrid cultivars between herbaceous and tree peony. The possession of bands obtained in this study also supported the breeding history of cultivar development in the genus Paeonia.

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  • Atsushi Matsumura, Shuji Sano, Yoshinori Ueda, Motoyoshi Yamasaki, Hay ...
    Article type: Original Articles
    Article ID: UTD-353
    Published: 2022
    Advance online publication: April 01, 2022
    JOURNAL OPEN ACCESS ADVANCE PUBLICATION

    Vegetable soybean, cultivated in the Nakakawachi region in Osaka Prefecture, is highly regarded as a special vegetable soybean in Japan. Understanding yield variability, and environmental factors that influence yield, are important for stably producing high quality vegetable soybeans. The objective of this study was to determine the respective effects of soil properties, including physicochemical and biological parameters, on agronomic traits of vegetable soybean cultivated under greenhouse conditions in the Nakakawachi region targeting 18 fields in the 2017 to 2018 season. Substantial differences in vegetable soybean yield were observed among fields, and the yield ranged from 299 to 968 kg/10 a. Regarding agronomic traits, pod production was significantly correlated with total node number, the number of branches and pods, while cultivation duration was also positively correlated with the market base pod yield. Although the nodule dry weight (DW) had no significant correlations with any agronomic traits among farmer’s fields, correlation analysis within each field frequently showed nodule DW had a positive correlation with vegetable soybean production. Regarding soil physicochemical factors, the factors influencing yield included total carbon, total nitrogen (N), and available N. Bacterial diversity in soil was evaluated at harvest of vegetable soybean in 2017. Principal coordinates analysis with 16S rRNA gene amplicon sequencing data showed fields could be divided into three groups. We assessed the correlation between vegetable soybean yield and the relative abundance of each bacterial family, resulting in significant correlations of some bacterial families with pod production. This study provides information on soil chemical factors that led to stable production of vegetable soybean cultivated in the Nakakawachi region.

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  • Masahiro Kamimori, Takeshi Isobe, Hiroshi Yakushiji
    Article type: Original Articles
    Article ID: UTD-358
    Published: 2022
    Advance online publication: April 01, 2022
    JOURNAL OPEN ACCESS ADVANCE PUBLICATION

    We aimed to determine the suitability of ‘Reikodai 1 go’ (BC1 from interspecific hybridization of Ficus carica L. and F. erecta Thunb.) as a ceratocystis canker disease-resistant rootstock for ‘Masui Dauphine’ fig. In this study, ‘Masui Dauphine’ was grafted onto ‘Reikodai 1 go’ and grown in 45 L pots under artificial soil infestation with Ceratocystis ficicola Kajitani et Masuya. Ceratocystis canker resistance, tree growth, and fruit production was assessed by comparing scion growth and fruit production in ‘Reikodai 1 go’-grafted and ‘Masui Dauphine’ own-rooted trees. No significant differences in the initial growth of the shoots (first year of planting) was observed between ‘Reikodai 1 go’-grafted and own-rooted trees. ‘Reikodai 1 go’-grafted trees demonstrated a tendency towards scion overgrowth. Soil inoculation with C. ficicola (nine times in three years; 2 L of suspension with 105 conidia/mL per pot) resulted in the death, or inhibited growth, of own-rooted trees. However, inoculated ‘Reikodai 1 go’-grafted trees revealed no growth inhibition and had growth similar to those of non-inoculated own-rooted and non-inoculated ‘Reikodai 1 go’-grafted trees. These results suggest that ‘Reikodai 1 go’-grafted trees were highly resistant to soil infestation with C. ficicola. No significant differences were observed between ‘Reikodai 1 go’-grafted trees with or without C. ficicola inoculation in terms of fruit production (considering fruit set, date of maturation, fruit length, width, fruit weight, estimated yield, skin color, and soluble solids content). When comparing fruit production of ‘Reikodai 1 go’-grafted and own-rooted trees, no differences were observed between the two in terms of fruit characteristics. Therefore, the use of ‘Reikodai 1 go’ as a rootstock is unlikely to cause considerable problems in the fruit production of ‘Masui Dauphine’ fig trees. Overall, shoot growth and fruit production of ‘Masui Dauphine’ grafted onto ‘Reikodai 1 go’ were not significantly different from those of the own-rooted trees. Therefore, it is expected that the introduction of ‘Reikodai 1 go’ rootstock for ‘Masui Dauphine’ production will be an effective approach for controlling ceratocystis canker.

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  • Takumi Arakawa, Shinji Kamio, Masahiko Yamada
    Article type: Original Articles
    Article ID: UTD-344
    Published: 2022
    Advance online publication: March 16, 2022
    JOURNAL OPEN ACCESS ADVANCE PUBLICATION

    Large nut weight (NW) is an important target in chestnut breeding. The present study was conducted at the Nakatsugawa branch of the Gifu Prefectural Research Institute for Agricultural Technology, an important chestnut breeding site in Japan. We estimated the environmental variance components for NW by using nine cultivars/selections with three single-tree replicates for six years. The number of nuts evaluated for each tree was mostly over 100 nuts, with an average of 440 nuts. Subsequently, the dataset of average NW values for each tree was log-transformed and analyzed by ANOVA. The effects of genotype, year, and the genotype × year interactions were highly significant, whereas the tree effect was negligible. The resulting environmental variance components for the log-transformed values were as follows: variance among years = 5.2 × 10−4, variance among trees within genotype = 0, variance associated with the genotype × year interactions = 7.6 × 10−4, and residual variance = 11.2 × 10−4. The results suggest that tree replication is not necessary to evaluate the genotypic value of cultivars/selections or offspring in breeding and that year effect adjustment and yearly repeated measurements can effectively reduce environmental variance. The NW of 27 cultivars/selections with potential as cross-parents was also estimated with no tree replications and via measurements repeated for three years; the results ranged from 10.7 to 47.4 g, with high broad-sense heritability (0.93) based on a three-year evaluation for the log-transformed data. Based on the environmental variance estimates, the cultivars/selections used in chestnut breeding with NW above 22.3 and 26.7 g should be selected by evaluating one tree for three years at 95% probability and selecting those having nuts of 25 and 30 g or more, respectively.

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  • Chitose Honsho, Ryuto Sakamoto, Shuji Ishimura, Takuya Tetsumura
    Article type: Original Articles
    Article ID: UTD-335
    Published: 2022
    Advance online publication: March 04, 2022
    JOURNAL OPEN ACCESS ADVANCE PUBLICATION
    Supplementary material

    This study was conducted to obtain insights into unreduced gamete formation in Citrus tamurana hort. ex Tanaka ‘Nishiuchi Konatsu’ and ‘Hyuganatsu’, inferred from unreduced pollen and egg cell genotype information. To establish a method for fine genotyping of tissues with higher ploidy levels (up to hexaploidy), we first identified heterozygous single-nucleotide polymorphism (SNP) markers (CiC4240-04 and CiC5327-03) with close genetic distance to centromeres of ‘Nishiuchi Konatsu’ and ‘Hyuganatsu’. Fluorescence intensity-based standard plots were generated using real-time qPCR to accurately genotype these SNP markers on a two-dimensional panel. Ten normal seeds were obtained from fertilization of unreduced gametes by self-pollination of ‘Nishiuchi Konatsu’ or ‘Hyuganatsu’ × ‘Nishiuchi Konatsu’ crosses. Inner seed coats with hexaploid endosperm tissues and tetraploid embryos were obtained from normal seeds, and their CiC4240-04 and CiC5327-03 genotypes were determined with standard plots using real-time qPCR. Genotypes of unreduced pollen and egg cells were uniquely determined from the genotype information of 6x endosperms and 4x embryos, and the unreduced gamete formation process was inferred. The results showed that unreduced pollen formation was almost entirely due to first division restitution (FDR); therefore, it was concluded that FDR was the dominant formation process for unreduced pollen in ‘Nishiuchi Konatsu’. In contrast, there was no dominant process for the formation of unreduced egg cells because both FDR and second division restitution occurred in almost the same number of individuals with unreduced egg cells.

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  • Yoshihiro Takemura, Keisuke Tochimoto, Takushi Yoshida, Mutsuki Kitamu ...
    Article type: Original Articles
    Article ID: UTD-339
    Published: 2022
    Advance online publication: March 04, 2022
    JOURNAL OPEN ACCESS ADVANCE PUBLICATION
    Supplementary material

    Low temperature negatively affects pollen germination in many species, but artificial pollination can help alleviate these negative effects. With ongoing environmental changes, it is important to select pollinizers with pollen that has superior germination properties at lower temperatures. To select candidate cultivars for a new Pyrus pollinizer for pollen with superior germination properties at low temperatures, in vitro pollen germination was studied in 129 Pyrus plants. The highest germination percentage for most Pyrus plants was observed at 25.0°C and was < 20% at 10.0°C. However, ‘Narayoshinokoboku’, ‘Imamuranatsu’, and ‘Tosanashi’ showed a higher germination rate than the other Pyrus plants at 10.0°C, and the germination percentage rates of three plants were > 30%. The fruit setting percentage of the cultivars ‘Kosui’, ‘Hosui’, and ‘Gold-Nijisseiki’ were > 85% by pollination using these three selected cultivars in an open field. In addition, S-genotyping in selected cultivars was determined as follows: ‘Tosanashi’ (S1S7), ‘Imamuranatsu’ (S1S12), and ‘Narayoshinokoboku’ (S1S9). From these results, we concluded that all three cultivars showed cross-compatibility in most pear cultivars of the four major Japanese pear cultivars. The percentage of flower bud formation in ‘Tosanashi’ was > 50%, and the amount of pollen from ‘Narayoshinokoboku’ was more than double the amount of ‘Chojuro’. By assessing the chilling requirement in selected cultivars, a safe area for growth for each cultivar was evaluated as all areas with the exception of the Kyushu and Shikoku regions, based on the ongoing progress of global warming (average daily temperature increase of 3.7°C). In conclusion, we selected ‘Narayoshinokoboku’ and ‘Tosanashi’ as new Pyrus pollinizers because they combine the advantages of low-temperature germinability and high pollen load.

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  • Yan Wang, Hao Wang, Jing Zhang, Zhen-Shan Liu, Qing Chen, Wen He, Shao ...
    Article type: Original Articles
    Article ID: UTD-331
    Published: 2022
    Advance online publication: March 02, 2022
    JOURNAL OPEN ACCESS ADVANCE PUBLICATION
    Supplementary material

    The Chinese cherry (Prunus pseudocerasus/Cerasus pseudocerasus), which is native to China, is an economically important tetraploid fruiting cherry species. Its industry has been greatly limited due to some general disadvantages in the fruits such as small fruit size, high acid content, and short shelf-life. As such, it is urgent to carry out cross breeding and genetic improvement of this species. Here, seven cross combinations were designed by selecting five genotype landraces of the Chinese cherry and one semi-wild resource as cross parents. The fruit-set percentage, germination rate of the hybrid seeds, and growth status of the F1 seedlings varied among different parental genotypes and cross combinations. Three or four S-genotypes were detected in six tetraploid parents, with a maximum of five different alleles between two parents. Both the pollen vigor of the male parent and the differential S-genotype between parents may contribute to the variation in fruit-set percentages, ranging from 0 to 28.55%. Significant differences in the F0 fruit traits were observed among different combinations, indicating potential metaxenia of the Chinese cherry. Appropriate pretreatments, including the removal of endocarps, soaking with 150 mg/L GA3 for 24 h, and chilling stratification for 7–10 days, could significantly increase the germination rate of the hybrid seeds. According to the overall performance, using (semi)-wild resources as one of the parents should be taken into consideration more in Chinese cherry breeding programs. On the basis of these findings, we further constructed a flow chart for successful intra-specific crossing and efficient cultivation of robust F1 seedlings. This study will provide important references for the selection of cross parents, establishment of a feasible breeding program, and cultivation of robust F1 progenies of the Chinese cherry.

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  • Ayako Katayama-Ikegami, Yuta Sugiyama, Takane Katayama, Akiko Sakamoto ...
    Article type: Original Articles
    Article ID: UTD-342
    Published: 2022
    Advance online publication: February 11, 2022
    JOURNAL OPEN ACCESS ADVANCE PUBLICATION

    Changes in anthocyanin and endogenous abscisic acid (ABA) contents in the berry skins of Vitis labruscana × V. vinifera cultivars, ‘Aki Queen’, and ‘Ruby Roman’ were investigated during the fruit development period. Color development of ‘Aki Queen’ berries mainly occurred within 20 days post véraison, while that of the ‘Ruby Roman’ was prolonged for about 40 days. In both cultivars, the ABA level in the berry skin started to increase a few days before véraison; however, ABA accumulation ceased approximately 10 days after véraison in ‘Aki Queen’, while it continued until the late stage of maturation in ‘Ruby Roman’. In addition, higher indole-3-acetate aspartate (IAA-Asp) and lower isopentenyladenine (iP) contents were observed in ‘Ruby Roman’ than in ‘Aki Queen’ at the late development stage. The expression analysis of genes involved in ABA metabolism revealed that V. vinifera 9-cis-epoxycarotenoid dioxygenase 3 (VviNCED3), which is assumed to play a major role in ABA biosynthesis, remained relatively higher in ‘Ruby Roman’ than in ‘Aki Queen’ after véraison. Considering that ABA plays a regulatory role in grape maturation, these results may indicate that the coloration of ‘Ruby Roman’ at the later stage of maturation is partly attributable to an increased ABA pool in berry skins.

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