Horticultural Research (Japan)
Online ISSN : 1880-3571
Print ISSN : 1347-2658
ISSN-L : 1347-2658
Volume 19 , Issue 4
Showing 1-11 articles out of 11 articles from the selected issue
REPORTS
Breeding & Germplasm Resources
  • Naoya Hamabe, Akiko Baba, Minori Maeda, Hiroyuki Katsuoka, Motohiro Ta ...
    2020 Volume 19 Issue 4 Pages 331-337
    Published: 2020
    Released: December 31, 2020
    JOURNALS FREE ACCESS

    ‘Koyama New Summer’ is a bud mutation of ‘Hyuganatsu’ (Citrus tamurana hort. ex Tanaka), which has highly parthenocarpic traits compared with ‘Hyuganatsu’. We investigated fruit setting and quality of ‘Koyama New Summer’ and ‘Hyuganatsu’ that had been covered with cheesecloth during the flowering period. The number of ‘Koyama New Summer’ fruits harvested per area occupied by tree crowns was larger than that for ‘Hyuganatsu’. It was considered that the factor determining the larger number of fruits in ‘Koyama New Summer’ was the fact that there were more leafless fruits than in ‘Hyuganatsu’. It was considered that ‘Koyama New Summer’ is capable of achieving sufficient fruit setting through parthenocarpic traits alone. In addition, the pulp ratio per fruit of ‘Koyama New Summer’ was larger than that of ‘Hyuganatsu’, and in the case of peeling by hand, its edible portion is larger than ‘Hyuganatsu’. Using decision tree analysis to clarify factors determining the high fruit quality (defined as fruits with a large diameter, high Brix, and low acidity), the results showed that height above the ground should be >142.5 cm, the fruiting mother shoot length should be >12.25 cm, and the number of leaves on the fruit-bearing shoot should be >0.5. The results indicate the importance of maintaining an optimal sunlight environment and strong tree vigor for producing high-quality fruits of ‘Koyama New Summer’.

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  • Tetsuya Kako, Kohei Mochida, Akira Nakatsuka, Nobuo Kobayashi
    2020 Volume 19 Issue 4 Pages 339-347
    Published: 2020
    Released: December 31, 2020
    JOURNALS FREE ACCESS

    The natural habitats of Veronica ornata Monjuschko (Plantaginaceae), an endangered perennial plant endemic to Japan, were investigated on the Oki Islands of Japan. Seedlings obtained from wild plants were characterized as ornamental plant resources. The morphological diversity of the plant form, flower characteristics, and flowering periods were observed in this species distributed in various environmental habitats on the Oki Islands. The varietal characteristics of this species make them applicable wide-ranging utilization for pot and cut flowers and bedding plants materials. Besides the predominant purplish-blue flower color, white and purple flower plants were found, and they are considered potential breeding resources to develop new flower color varieties. It was also suggested that flowering plants could be produced that bloom for long periods by combining varied flowering periods. The regional genetic resource, V. ornata, is proposed as a new ornamental plant native to Japan. Breeding new cultivars and development of a production system based on their characteristics comprise the next step.

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Propagation & Transplant Production
  • Yoshitaka Nakamura, Tetsushi Tanaka, Masahiro Kasuya, Katsutoshi Taki, ...
    2020 Volume 19 Issue 4 Pages 349-354
    Published: 2020
    Released: December 31, 2020
    JOURNALS FREE ACCESS

    We investigated the effects of temperature on aerial and seed tuber sprouting and plumule and radicle elongation of Japanese yam (Dioscorea japonica Thunb.) ‘Inabu-2 gou’. Sprouting of aerial tubers cultured at 30°C was the earliest within 3 days after the start of culture. At this temperature, the sprouting rate of aerial tubers on the 7th day after culturing was also the highest, at 76%, and the final sprouting rate reached over 80%. Although the initial sprouting rates of seed tubers cultured at 20°C and 35°C were the same, the sprouting rates on the 7th and final days in the cultures were higher at 25°C and 30°C. It was considered that the optimal temperature range for the sprouting of aerial and seed tubers in this study was about 30°C and 25–30°C, respectively. The lengths of plumules and radicles of aerial tubers were the longest at 30°C. The heavier the aerial tuber, the longer the plumule and radicle. The lengths of the plumule of seed tubers were also the longest at 30°C; however, the length of radicles was the longest at 25°C and 30°C. No clear effects of the initial size of aerial tubers on the number of sprouted buds were observed. According to the results of the above experiments, we concluded that the optimal temperature for early growth of aerial and seed tubers was about 30°C and 25–30°C, respectively.

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Soil Management, Fertilization & Irrigation
  • Yuka Nakano, Jun Kuriyama, Megumu Takahashi, Yosuke Yanai, Hidekazu Sa ...
    2020 Volume 19 Issue 4 Pages 355-364
    Published: 2020
    Released: December 31, 2020
    JOURNALS FREE ACCESS

    We examined the effect of drainage and irrigation by the Farm-Oriented Enhancing Aquatic System (FOEAS) on yield of summer-sown winter-harvest broccoli over three cultivations. Irrigation treatments were non-irrigation, once at transplanting, and twice at transplanting and the middle stage. Regarding the effect of drainage, constructing FOEAS reduced the drop in the oxygen concentration of soil during rainfall. As for cv. Grand-dome, the percentage of hollow stems was lower in the plot with FOEAS than that in the plot without FOEAS in the dry year. On the other hand, cv. Bellstar plants had a larger weight and width of the head in the plot without FOEAS than those in the plot with FOEAS in the dry year. Concerning the effects of irrigation, cv. Grand-dome in the twice-irrigated plot showed a lower percentage of hollow-stems than that in the plot without irrigation in the dry year. Comparing cv. Bellstar heads in the twice-irrigated plots with those in the plot without irrigation, the width was 7% larger in the dry year, and the weight was 10% larger in the early-rainy and middle-dry year. These results suggest that irrigation and drainage controlled by FOEAS promote stable production of broccoli.

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Crop Production & Cropping Type
  • Satoru Murakami, Suguru Yamane, Nozomi Hashimoto, Yuji Araki
    2020 Volume 19 Issue 4 Pages 365-372
    Published: 2020
    Released: December 31, 2020
    JOURNALS FREE ACCESS

    Artificial pollination using electrostatic techniques is predicted to reduce pollen consumption and increase the amount of pollen adhesion. In this study, we conducted detailed experiments on artificial pollination of Japanese pear and kiwifruit using electrostatic pollen-dusting machines. Dusted Japanese pear and kiwifruit pollen using electrostatic pollen-dusting machines maintained high germinating rates. From visual observations, the amount of pollen increased when using electrostatic pollen-dusting machines; however, the amount of sprayed pollen was reduced by approximately 50%. Electrostatically pollinated kiwifruit and Japanese pear did not show lower fruit weight, sugar content, or acid, compared with practice pollination. Thus, electrostatic pollination did not influence fruit quality. The most adequate pollen dilution was 20-times in Japanese pear and 40-times in kiwifruit. In Japanese pear, the increase in the quantify of pollen adhesion using the electrostatic pollen-dusting machine and 20-times pollen dilution was similar to that of the 10-times pollen mating machine and 500-times liquid pollination, but it was slightly inferior in comparison with that of the 10-times bonten. Our findings indicate that electrostatic pollen dusting machines are capable of reducing pollen usage by improving the adhesion strength of pollen and lowering the sprayed pollen dilution.

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  • Tomoaki Toya, Takeshi Suzuki, Yoshiharu Fujii
    2020 Volume 19 Issue 4 Pages 373-379
    Published: 2020
    Released: December 31, 2020
    JOURNALS FREE ACCESS

    It is not clear whether the remaining roots of the previous tree are the cause of soil sickness syndrome in Japanese pear. In this study, we investigated the gradual changes in soil sickness risk in soil mixed with pear roots, and the effects on the growth of the annual nursery of pear planted in soil mixed with roots. First, we prepared a mixed plot of fresh or dried pear roots in non-pear soil and used the rhizosphere soil assay method to assess the soil sickness risk. As the result, regardless of the dry conditions of the pear roots, the inhibition rate of soil did not change, suggesting the growth inhibitory substances were not released in the roots decomposition process. Next, we mixed dry roots in non-pear soil in a plot and planted the annual nursery of pear. As the result, the growth of the trees in the mixed pear roots was similar to that in the non-mixed soil, and it did not show the growth suppression noted in the continuous cropping soil. Therefore it was clarified that mixed roots in soil did not cause soil sickness syndrome in Japanese pear. Furthermore, after planting the annual nursery of pear in non-pear soil, when having measured gradually by the rhizosphere soil assay method, the soil inhibition rate increased with the growth of trees. This suggested that the accumulation of growth inhibitory substances in soil occured during the process of tree growth.

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  • Satomi Tanimoto, Housei Hadano, Kuninori Matsunaga, Satoru Motoki
    2020 Volume 19 Issue 4 Pages 381-389
    Published: 2020
    Released: December 31, 2020
    JOURNALS FREE ACCESS

    To increase the yield performance and profitability of mini carrots, it is necessary to determine the most appropriate planting density. In the present study, a morphological survey of commercially-available mini carrots was conducted for eighteen months across Japan (Study 1) and a reference value for the upper limit of the morphological characteristics for growing and harvesting mini carrots was obtained. A study to compare and examine the characteristics (yield, shapes/sizes, and carotene/sugar contents) of mini carrots planted and grown under different conditions was also conducted; the periods of time required for harvest were 70 (conventional), 90, and 110 days and the planting density was 3 (conventional), 6, and 9 rows, i.e., 125,000, 250,000, 375,000 plants・10 a–1, respectively (Study 2). The mean weight of the underground part and β-carotene/sugar contents of mini carrots planted in 3 rows and harvested after 110 days were significantly larger and higher, respectively. However, there were no significant differences in the weight of the underground part when mini carrots were planted and harvested under other conditions. When carrots were planted in 6 rows, the characteristics of mini carrots, suggested by the results of Study 1, were maintained until 110 days. The longer the period of time required for harvest, the greater the yield and β-carotene/sugar contents. In conclusion, most measured data in terms of yield, shape, and qualities were not affected by the planting density in the case of customized harvesting after 70 days. When the harvesting period was delayed to 90 or 110 days, dense planting in 6 and 9 rows was appropriate to increase yield and qualities without changing the standard shape.

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  • Keita Takahashi, Tomoo Maeda, Hiromi Ikeura, Tasuku Kurauchi, Daniel Z ...
    2020 Volume 19 Issue 4 Pages 391-398
    Published: 2020
    Released: December 31, 2020
    JOURNALS FREE ACCESS

    In Japan, carrot cultivars are generally classified into western and oriental varieties. Recently, new intermediate cultivars were obtained by crossbreeding between these two types of cultivars. In the present study, the growth of these cultivars was also investigated to evaluate their suitability for cultivation in Aomori Prefecture, a cold region of Japan. We also determined the levels of sugars, as indicators of the eating quality, and carotenoids, as functional components, and volatile compounds, in western carrot (cv. Oranje), oriental (cv. Shinbeni-kintoki), and intermediate (cv. Kyoukurenai) cultivars. As a result, there was no significant difference in the growth of aerial parts in the three cultivars. However, the root shape in ‘Kyoukurenai’ was intermediate between western and oriental cultivars. There was no significant difference in the total content of sugars among these cultivars. However, ‘Shinbeni-kintoki’ had a smaller content of fructose but larger content of sucrose. The levels of carotenoids were significantly lower in ‘Kyoukurenai’ than in the other cultivars. In terms of the carotenoid composition, 93.4% of total carotenoids was occupied by β- and α-carotene in ‘Orange’ and 80.9% by lycopene in ‘Shinbeni-kintoki’; however, the ratio of β- and α-carotene/lycopene was almost even in ‘Kyoukurenai’. We found that the types of volatile compounds present in these cultivars were almost the same; however, the level of each compound was different. The compounds considered strongly related to the carrot-specific flavor were found to be high in ‘Shinbeni-kintoki’ and low in ‘Kyoukurenai’. On the contrary, ‘Orange’ was found to have high levels, hence a strong flavor, of sabinene and p-cymene, which are considered as “fresh green”. Based on these results, we could confirm the levels of sugars and carotenoids, as well as cultivar growth in cold regions, and could also advance knowledge on the aroma components contained in the three selected varieties.

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  • Satoshi Mizushima
    2020 Volume 19 Issue 4 Pages 399-405
    Published: 2020
    Released: December 31, 2020
    JOURNALS FREE ACCESS

    The effects of light quality on the growth of watercress were investigated using red light-emitting diodes (LED) and white LED as light sources in the growth chambers. Under conditions of only red LED light irradiation, watercress grew spindly with a markedly decreased fresh weight and stem elongation. Under conditions of only white LED light irradiation, the main stem elongation of watercress was inhibited. Optimal growth could be achieved under the light conditions, whose ratio of red to white LEDs was 50 : 50 based on the photosynthetic photon flux density. This condition increased the fresh weight and satisfied the delivery basis with a more than 10-cm stem length. It also improved almost all the measured values as compared with those of fluorescent light. Therefore, it is desirable to combine red and white LED in watercress cultivation to optimize vegetative growth.

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  • Kazuki Tsuge, Kazuma Yanagisawa, Satoru Motoki
    2020 Volume 19 Issue 4 Pages 407-415
    Published: 2020
    Released: December 31, 2020
    JOURNALS FREE ACCESS

    Allium victorialis L. subsp. platyphyllum Hulten is a perennial plant that can be found between Hokkaido and Nara Prefecture in Honshu, Japan. Although strains of A. victorialis near Hokkaido have been characterized, the morphological features of strains that span the rest of its range in Japan are unknown. Bulbs of 22 strains of A. victorialis were obtained from the Saku Branch of the Nagano Vegetable and Ornamental Crops Experiment Station (Komoro City, Nagano Prefecture). These bulbs had been continuously cultivated at the station and originated from throughout the plant’s range within Japan with emphasis on strains from the eastern region of Honshu. The collected strains were then cultivated in an open field in Komoro City of Nagano Prefecture. Fourteen morphological traits were evaluated once each year for three years (2015–2017) starting at bulb planting in order to account for seasonal variation and identify differences among the strains. Differences in the survey year and strain affected the morphological traits of A. victorialis. The survey year was more influential on several traits that were evaluated than strain based on two-way analysis of variance; some traits were shared among all strains. By comparing the average values of all the strains among the survey years, the leaf part was determined to increase over the three years. Based on principal component analysis, several strains collected from Nagano Prefecture did not group together, which indicates that the morphological traits of strains from Nagano Prefecture were highly diverse.

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NEW CULTIVAR
  • Katsuhiro Shinya, Tomonori Akiyama, Hidehito Amemiya, Yu Takekoshi, Ak ...
    2020 Volume 19 Issue 4 Pages 417-422
    Published: 2020
    Released: December 31, 2020
    JOURNALS FREE ACCESS

    ‘Kaitouka17’ was bred with the target of cultivating a variety to replace the early-ripening variety ‘Hikawahakuho’ in Yamanashi Prefecture. The beginning of harvest for ‘Kaitouka17’ is almost identical to that of ‘Hikawahakuho’. The fruit weight is 298 g, which is high for an early-ripening variety. The flesh was a weak tendency to split. The skin color pattern is solid flush, and it readily colors uniformly. The flesh firmness was 2.4 kg on the first day of harvest and decreased with the passage of days. In 2016, it was 2.0 kg after 16 days of first harvesting, and in 2017, it was 1.9 kg after 18 days of first harvesting. The flesh firmness of the auxin-treated fruits after harvest was 0.4 kg 9 days after treatment, and the amount of ethylene produced increased rapidly 1 day after treatment. However, DNA markers revealed that ‘Kaitouka17’ was a stony hard peach. Thus, this study showed that ‘Kaitouka17’ had moderately soft flesh in spite of having the stony hard flesh allele. ‘Kaitouka17’ is expected to be widely used as a substitute for ‘Hikawahakuho’ and later-ripening varieties.

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