‘Luo Xue’: A New Hydrangea Cultivar

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Qunlu Liu School of Design, Shanghai Jiao Tong University, Shanghai 200240, China

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Jun Qin Shanghai Chen Shan Botanical Garden, Shanghai 201602, China; Shanghai Engineering Research Center of Urban Tree Ecology and Applications, Shanghai 200020, China

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Shuai Qiu Hangzhou Landscaping Incorporated Company Hangzhou 310020, China

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Kai Gao Hangzhou Landscaping Incorporated Company Hangzhou 310020, China

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Yonghong Hu Shanghai Chen Shan Botanical Garden, Shanghai 201602, China

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Xianquan Zhang Shanghai Chen Shan Botanical Garden, Shanghai 201602, China

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Kang Ye Shanghai Chen Shan Botanical Garden, Shanghai 201602, China

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Jun Yang Shanghai Chen Shan Botanical Garden, Shanghai 201602, China

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Hydrangea is an evergreen or deciduous shrub or woody vine of the genus Hydrangea Linn. in the Saxifragaceae family. The plants in this genus have large inflorescences, a lengthy florescence, and high ornamental value (US Department of Agriculture-National Agricultural Statistics Service 2014). The Hydrangea cultivars primarily derived from H. macrophylla, H. paniculata, H. arborescens, and H. quercifolia (Khaing et al. 2016). Among these species, H. macrophylla stands out as the most diverse, boasting an impressive collection of more than 1000 cultivars (Wu and Alexander 2019). The cultivars of H. macrophylla exhibit two types of variations in flower morphology; one is a semispherical or nearly entirely spherical clusters of showy sterile flowers possessing visually striking sepals, commonly known as “mop-heads”; another is flat clusters of inconspicuous and diminutive fertile flowers surrounded by a ring of more prominent sterile flowers, named as “lacecaps.” The cultivars can be applicated in both ground and potted planting, as well as in the production of fresh cut flowers, dried flowers, and pressed flowers (Cerbah et al. 2001). Nevertheless, H. macrophylla cultivars are sensitive to high temperature (Lu et al. 2022) and prone to disease, such as rust, powdery mildew, leaf spot, root rot, and botrytis blight (Park et al. 2012).

H. chinensis is a native species in China and Japan, distributes in Anhui Province, Hunan Province, Jiangxi Province, Guangxi Zhuang Autonomous Region, and Taiwan Province in China. Its height is up to 2 m according to the Flora of China. Foliar disease incidence appeared reduced on H. chinensis compared with H. macrophylla, as observed in the nursery. On the leaves of H. macrophylla, there were many necroses caused by disease in Autumn 2017 (Fig. 1A); however, the necrosis was much less on the leaves of H. chinensis in the same year (Fig. 1B).

Fig. 1.
Fig. 1.

Leaves of H. macrophylla (A) and H. chinensis (B) in autumn.

Citation: HortScience 59, 5; 10.21273/HORTSCI17692-24

To enhance the stress tolerance of hydrangea cultivars, crossbreeding has been performed between H. macrophylla and H. chinensis. As a result, a novel cultivar known as Luo Xue was successfully produced, with tolerance to high temperatures and foliar disease (Fig. 2B) and a significant increase in inflorescence stem rigidity.

Fig. 2.
Fig. 2.

‘Luo Xue’ seedlings in flowering season (A) and its leaves in autumn (B).

Citation: HortScience 59, 5; 10.21273/HORTSCI17692-24

Origin

The female parent of ‘Luo Xue’ is H. macrophylla ‘Magical jade’, which has mophead inflorescences. The primary color of the sterile sepals is green and white, and eventually turns to pink. H. chinensis, the male parent, has Lacecap inflorescences and white sterile sepals (Fig. 3).

In 2014, seedlings of H. chinensis were collected from Tianmu Mountain located in Zhejiang Province, China, and subsequently propagated by cutting and cultivated in the Qingshan Lake nursery of Hangzhou Landscape Incorporated Company. From May to Jun 2017, artificial pollination was carried out between H. macrophylla ‘Magical jade’ and H. chinensis. The fruits were harvested and aseptically sowed in Murashige and Skoog medium over the period of Sep–Oct 2017. Subsequently, the seedlings were transplanted into trays and cultivated within a greenhouse in Dec 2017. The plants were transferred to 1-gallon containers in Apr 2018 and subsequently cultured in the shady greenhouse. The hybrid progeny began to bloom in May 2019. Subsequently, individual plants exhibiting lace cap inflorescences, sterile flower sepals color ranging from green to white, and hard inflorescence stems were chosen for further evaluation. Three generations of cuttings were carried out in the spring, autumn and winter of 2019. In the meantime, the plants were continuously observed and compared to confirm that the ornamental traits were stable and uniform.

Description

‘Luo Xue’ exhibits several characteristics that are in the intermediate transitional state between its parents. The shape of sterile sepals of ‘Luo Xue’ is more like that of H. chinensis. Nevertheless, sterile sepals of ‘Luo Xue’ has serrations at the edge. Green color (RHS-142C) on the sterile sepals of ‘Luo Xue’ is apparent, which is a trait of ‘Magical jade’. The lenticels on the stem of H. chinensis are not distinct, whereas lenticels can be observed on stem of ‘Luo Xue’ but much less than those on ‘Magical jade’ and with lighter color (Fig. 3).

Fig. 3.
Fig. 3.

The inflorescence, floret, and branch of ‘Luo Xue’ and its parents. (a) Inflorescence of ‘Magic Jade’; (b) floret of ‘Magic Jade’; (c) branch of ‘Magic Jade’; (d) inflorescence of H. chinensis; (e) floret of H. chinensis; (f) branch of H. chinensis; (g) inflorescence of ‘Luo Xue’; (h) floret of ‘Luo Xue’; and (i) branch of ‘Luo Xue’.

Citation: HortScience 59, 5; 10.21273/HORTSCI17692-24

Habit

‘Luo Xue’ is a deciduous upright shrub; the height of 2-year-old potted seedlings is ∼0.55 to 0.69 m tall (Fig. 2A). Its current-year branches are green, hairy, and cylindrical, with medium number of lenticels which are red. Its internode length is ∼7.8 to 14.3 cm. There is no anthocyanin coloring at the stem nodes (Fig. 3).

Foliage

The dimensions of the leaves range from 7.8 to 14.3 cm in length and 5.2 to 5.9 cm in width. They are unlobed and have a narrow oval form, with a long tip and a wedge-shaped base. The serration depth is moderate, and the serration density is dense. The leaves exhibit a medium green color and possess a strong glossiness on the upper surface. They also display a strong vesicularity and are devoid of hair. Additionally, the petioles do not exhibit any anthocyanin coloration (Fig. 2).

Flower

‘Luo Xue’ has lacecap type of inflorescences, ∼4.5 to 5.0 cm in height and 10.9 to 13.5 cm in diameter. Fertile flowers are moderately conspicuous, surrounded with a single whorl of sterile flowers. The sepals of sterile flowers are arranged in one whorl, consisting of three or four expanded ovate pieces. These sepals are ∼3.9 to 4.0 cm in width, flat in shape. They exhibit a moderate overlap and feature moderate notches along the edges. The sterile flowers’ sepals are white (RHS-NN155B), dispersed with a bright yellow-green color (RHS-142C). The fertile flowers in the center of the inflorescences have light purple-pink (RHS-68D) petals (Fig. 3). ‘Luo Xue’ blooms in early May and lasts to late June in Hangzhou, Zhejiang Province, China.

Cultivation

‘Luo Xue’ can be planted alone or in patches, but it should not be planted too densely. Partial shade is considered to be the optimal condition.

The recommended time frame for planting is from mid- to late October until late November, with daily management practices commencing after the planting process. It is imperative to implement measures to inhibit the growth of weeds.

After germination in spring, excess sprouts at the base of the plant should be removed, and it is recommended to cut off remaining inflorescences after flowering.

In the south of China, there is sufficient rain in spring, and generally no additional watering is needed. However, during the plum rains period, it is important to ensure unobstructed drainage and no standing water in the fields. In the middle and lower reaches of the Yangtze River, proper watering is required during the continuous high temperature and drought period in July.

The decomposed organic fertilizer can be used as base fertilizer applying to the soil. Fertilization is advisable during sprouting and before the onset of flowering. Additionally, it is recommended to apply topdressing once after the blooming period.

To mitigate the occurrence of pests and diseases, it is recommended to conduct spraying insecticide or germicide every 15 d during April and July. In autumn, it is advisable to prune the branches, remove the accumulated debris.

Recommendation

The cultivation environment of ‘Luo Xue’ requires semishade, good drainage, fertile and loose soil, and no frost damage after the branches sprout in spring. Thus, it can be planted in the middle and lower reaches of the Yangtze River and the south of China. According to the minimum temperature of the above area in China, ‘Luo Xue’ is hardy to US Department of Agriculture plant hardiness zone 5 to 9.

Availability

A patent has been applied for ‘Luo Xue’ by Shanghai Chenshan botanical garden and Hangzhou Landscaping Incorporated Company (application no. 20210913). This cultivar is available through Shanghai Chenshan botanical garden and Hangzhou Landscaping Incorporated Company.

References Cited

  • Cerbah M, Mortreau E, Brown SC, Siljak-Yakovlev S, Bertrand H, Lambert C. 2001. Genome size variation relationships in the genus Hydrangea. Theor Appl Genet. 103:4551.

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  • Khaing MT, Jung HJ, Han TH. 2016. Trend of hydrangea cultivar development. Trends Agric Life Sci. 53:6368.

  • Lu AX, Ling R, Cheng SY, Zhai JW, Zheng ZX, Wu SS. 2022. Physiological and biochemical responses of eight Hydrangea cultivars to high temperature stress. Chin J Trop Crops. 43(4):816828.

    • Search Google Scholar
    • Export Citation
  • Park MJ, Cho SE, Park JH, Lee SK, Shin HD. 2012. First report of powdery mildew caused by Oidium hortensiae on mophead hydrangea in Korea. Plant Dis. 96(7):1072.

    • Search Google Scholar
    • Export Citation
  • US Department of Agriculture-National Agricultural Statistics Service. 2016. 2014 census of horticulture specialties.

  • Wu X, Alexander LW. 2019. Genetic diversity and population structure analysis of bigleaf hydrangea using genotyping-by-sequencing. J Am Soc Hortic Sci. 144(4):257263.

    • Search Google Scholar
    • Export Citation
  • Fig. 1.

    Leaves of H. macrophylla (A) and H. chinensis (B) in autumn.

  • Fig. 2.

    ‘Luo Xue’ seedlings in flowering season (A) and its leaves in autumn (B).

  • Fig. 3.

    The inflorescence, floret, and branch of ‘Luo Xue’ and its parents. (a) Inflorescence of ‘Magic Jade’; (b) floret of ‘Magic Jade’; (c) branch of ‘Magic Jade’; (d) inflorescence of H. chinensis; (e) floret of H. chinensis; (f) branch of H. chinensis; (g) inflorescence of ‘Luo Xue’; (h) floret of ‘Luo Xue’; and (i) branch of ‘Luo Xue’.

  • Cerbah M, Mortreau E, Brown SC, Siljak-Yakovlev S, Bertrand H, Lambert C. 2001. Genome size variation relationships in the genus Hydrangea. Theor Appl Genet. 103:4551.

    • Search Google Scholar
    • Export Citation
  • Khaing MT, Jung HJ, Han TH. 2016. Trend of hydrangea cultivar development. Trends Agric Life Sci. 53:6368.

  • Lu AX, Ling R, Cheng SY, Zhai JW, Zheng ZX, Wu SS. 2022. Physiological and biochemical responses of eight Hydrangea cultivars to high temperature stress. Chin J Trop Crops. 43(4):816828.

    • Search Google Scholar
    • Export Citation
  • Park MJ, Cho SE, Park JH, Lee SK, Shin HD. 2012. First report of powdery mildew caused by Oidium hortensiae on mophead hydrangea in Korea. Plant Dis. 96(7):1072.

    • Search Google Scholar
    • Export Citation
  • US Department of Agriculture-National Agricultural Statistics Service. 2016. 2014 census of horticulture specialties.

  • Wu X, Alexander LW. 2019. Genetic diversity and population structure analysis of bigleaf hydrangea using genotyping-by-sequencing. J Am Soc Hortic Sci. 144(4):257263.

    • Search Google Scholar
    • Export Citation
Qunlu Liu School of Design, Shanghai Jiao Tong University, Shanghai 200240, China

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Jun Qin Shanghai Chen Shan Botanical Garden, Shanghai 201602, China; Shanghai Engineering Research Center of Urban Tree Ecology and Applications, Shanghai 200020, China

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Shuai Qiu Hangzhou Landscaping Incorporated Company Hangzhou 310020, China

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Kai Gao Hangzhou Landscaping Incorporated Company Hangzhou 310020, China

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Yonghong Hu Shanghai Chen Shan Botanical Garden, Shanghai 201602, China

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Xianquan Zhang Shanghai Chen Shan Botanical Garden, Shanghai 201602, China

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Kang Ye Shanghai Chen Shan Botanical Garden, Shanghai 201602, China

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Jun Yang Shanghai Chen Shan Botanical Garden, Shanghai 201602, China

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Contributor Notes

This project was funded by Science and Technology Research Project of Shanghai Greening and City Appearance Administration in 2021 and 2023 (G212410 and G232406), and the Shanghai Agriculture Applied Technology Development Program, China (Grant No. T20210101).

Q.L. and J.Q. are the corresponding authors. E-mail: Liuql@sjtu.edu.cn or qinjun03@126.com.

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  • Fig. 1.

    Leaves of H. macrophylla (A) and H. chinensis (B) in autumn.

  • Fig. 2.

    ‘Luo Xue’ seedlings in flowering season (A) and its leaves in autumn (B).

  • Fig. 3.

    The inflorescence, floret, and branch of ‘Luo Xue’ and its parents. (a) Inflorescence of ‘Magic Jade’; (b) floret of ‘Magic Jade’; (c) branch of ‘Magic Jade’; (d) inflorescence of H. chinensis; (e) floret of H. chinensis; (f) branch of H. chinensis; (g) inflorescence of ‘Luo Xue’; (h) floret of ‘Luo Xue’; and (i) branch of ‘Luo Xue’.

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