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‘Zhongshi No. 1’: A New Cultivar of Xanthoceras sorbifolium with All-female-flowers Trait

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Xi Wang State Key Laboratory of Tree Genetics and Breeding, Research Institute of Forestry, Chinese Academy of Forestry, Beijing 100091, China

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Huihui Xu State Key Laboratory of Tree Genetics and Breeding, Research Institute of Forestry, Chinese Academy of Forestry, Beijing 100091, China

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Xiaojuan Liu State Key Laboratory of Tree Genetics and Breeding, Research Institute of Forestry, Chinese Academy of Forestry, Beijing 100091, China

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Yingchao Li State Key Laboratory of Tree Genetics and Breeding, Research Institute of Forestry, Chinese Academy of Forestry, Beijing 100091, China

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Haiyan Yu State Key Laboratory of Tree Genetics and Breeding, Research Institute of Forestry, Chinese Academy of Forestry, Beijing 100091, China

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Quanxin Bi State Key Laboratory of Tree Genetics and Breeding, Research Institute of Forestry, Chinese Academy of Forestry, Beijing 100091, China

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Libing Wang State Key Laboratory of Tree Genetics and Breeding, Research Institute of Forestry, Chinese Academy of Forestry, Beijing 100091, China

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Yellowhorn (Xanthoceras sorbifolium) is a woody oil tree belonging to the family Sapindaceae and the monotypic genus Xanthoceras that mainly grows in northern China (Bi et al., 2019). It is highly resistant to arid and salty environments, has wide applications to ecology, is edible, and has medicinal and ornamental value. The kernel contains up to 54.8% oil, composed of 19 fatty acids. Nervonic acid accounts for 3.8% of the fatty acids in the kernel of yellowhorn; this fatty acid is essential for human health and is rarely present in other plants (Liang et al., 2021). In addition, yellowhorn seed oil is considered an ideal raw material for potential biodiesel use in China, as it is environmentally friendly and renewable (Lang et al., 2020; Yu et al., 2017).

Among angiosperms, 89%∼90% of species are hermaphroditic with their flowers possessing both stamens and pistils, 6%∼7% are dioecious with only female or male flowers on a single plant, and 5% are monoecious bearing separate flowers of each sex on the same plant (Barrett and Hough 2012; Renner and Ricklefs 1995). Yellowhorn is monoecious, with racemes that produce functional female flowers (stamens aborted) on the terminal inflorescence and functional male flowers (gynoecium aborted) on the lateral inflorescence. Rarely, the lateral inflorescence can produce functional female flowers. If there are such female flowers, they are only on the first apical lateral inflorescence and there are fewer than 2% female flowers. There are also male flowers on the terminal inflorescence. Generally, the middle of the terminal inflorescence produces the female flowers, and the upper and lower parts produce the male flowers (Fig. 1A). There are few fruits on the lateral branches because only female flowers develop fruit and the number of staminate flowers greatly exceeds that of pistillate flowers. Therefore, it is also called the plant of “a thousand flowers with one fruit” (Zhang et al., 2018). Recently, some new yellowhorn cultivars have been released (Yang 2019), but the inflorescence fertility still is a huge challenge for the breeding of this species. After many years of selective breeding, we bred a new cultivar named Zhongshi No. 1 (‘中石1号’), of which terminal and lateral inflorescence can form female flowers and produce many fruits (Figs. 1D and 2). The high inflorescence fertility increases the yield of yellowhorn and promotes the enthusiasm of farmers for yellowhorn cultivation, which improves the local environment and farmers’ economic levels. It will also provide genetic resources for yellowhorn sex determination research.

Fig. 1.
Fig. 1.

(A) Normal yellowhorn, red arrows point to terminal inflorescence with fewer female flowers, blue arrows point to lateral inflorescence with male flowers, bar = 5 cm. (B–F) New Xanthoceras sorbifolium cultivar Zhongshi No.1: (B) red arrows point to terminal inflorescence with all female flowers, blue arrows point to lateral inflorescence with all female flowers, bar = 5 cm. (C) Structure of the female flower. The upper right corner shows filament and the uncracked anther, bar = 1 mm. (D) Lateral fruits, as shown by red arrows, bar = 10 cm. (E) Leaves front, bar = 3 cm, (F) leaves back, bar = 3 cm.

Citation: HortScience 58, 1; 10.21273/HORTSCI16922-22

Fig. 2.
Fig. 2.

A typically grafted ‘Zhongshi No.1’ in Jing Bian of Shaanxi Province.

Citation: HortScience 58, 1; 10.21273/HORTSCI16922-22

Origin

Normally, yellowhorn has many male flowers and few female flowers, the surface of new shoots is glabrous or hairy, and the backs of its leaves are green. Zhongshi No. 1 is a new cultivar in which lateral female flowers form fruit, and it can be considered a female plant. In 2007, a batch of seeds selected from Tongliao, Inner Mongolia, was sown in Heituozi, Zhangwu County, Liaoning Province, and planted to field in the following year. In 2013, one yellowhorn plant was found to have all female flowers in a field investigation, with many fruits on the lateral inflorescence; the backs of its leaves were gray-white, the shoots were hairy, and the fruits were round. In Jun 2014, five plants were grafted by budding and observed for 6 years, after which scions were collected from each plant. The next year, 30 plants were grafted by budding. Following grafting propagation, there was no obvious difference between the cloned individuals, and the morphological and growth characteristics were consistent. The cloned progeny of different ages had the same morphological and growth characteristics as the mother plant after multiple instances of grafting propagation, and the trait inheritance was stable (Fig. 1B; Supplemental Fig. 1). In Dec 2020, a new plant variety certificate was issued by the State Forestry and Grassland Administration (20200432), and it was named ‘Zhongshi No. 1’.

Description

Tree.

‘Zhongshi No. 1’ is a deciduous shrub or tree, with an open form, medium main branch density, a straight stem, and a succulent roots. The current-year branch is purple-red, and the new shoots are hairy.

Foliage.

The leaflets are obovate and hairy, and less waxy on the front, and off-white on the back, and the leaves spread before flowering (Fig. 1E and F).

Flowers.

‘Zhongshi No. 1’ is a raceme; the bud normally starts to swell (budbreak) and sprout in mid-April, and the bud scales are brown and hairy. The inflorescence form and start to elongate; all contain terminal and lateral developed functional female flowers and have fertile pistils with a hairy ovary and nondehiscent anthers. The color of the basal part of the petals changes sequentially to yellow, orange, and purple-red with flowering time, and the petals have white margins (Fig. 1B and C). The flowering period lasts for ∼15 d.

Fruits and seeds.

Side branches bear many small round fruits, which have transverse and longitudinal diameters of ∼50.04 × 49.91 mm, mainly with three carpels. The seeds in each fruit are 16 to 22 in number, ∼11.3 × 13.9 mm (transverse × longitudinal diameter) in size, and average 0.83 g in weight. On drying fresh seeds, the seedcoat usually turns from bright black to dark brown with no dehiscence.

Cultivation Techniques

Suitable areas.

‘Zhongshi No. 1’ is grown widely in northern China. It is a light-loving and semishade-tolerant species, suitable for planting on sunny slopes. It has strong adaptability to climatic conditions and can overwinter safely at ∼–40 °C. Suitable areas are mountains, hills, or sandy land with loess parent material, whereas low wetlands with poor drainage, heavily saline-alkali land, or rocky mountains are not suitable. The soil layer should exceed 50 cm and the slope ≤25°. The planting row spacing should be 2 to 3 m, and the planting hole generally measures 60 × 80 cm.

Graft propagation.

It is mainly propagated by bud or bark grafting from April to May each year. It is recommended that rootstocks with robust growth and no pests or diseases be selected from seedlings ≥2 years old with a ground diameter of 1∼5 cm.

Summer pruning.

Summer pruning mainly involves pruning, topping, removing buds, wiping buds, and twisting branches.

Nutrient management.

The roots are fleshy and not resistant to waterlogging. Fertilizing and water management should be done mid-to-early October, with 30 to 45 t/hm2 of miscellaneous fertilizer and 0.5 to 1.5 kg/plant of compound fertilizer. Top-dressing is done three times a year: before germination, after flowering, and during fruit expansion. Irrigation should be done at the same time as fertilization, and drainage is necessary in the rainy season. It is important to prevent and control chlorosis, sooty blotch, psyllidae, and other pests and diseases.

Availability

Some seeds of ‘Zhongshi No. 1’ are available from Quanxin Bi (Research Fellow, e-mail: biquanxin@caf.ac.cn) at the Research Institute of Forestry, Chinese Academy of Forestry. This work was financially supported by the Central Public-Interest Scientific Institution Basal Research Fund (CAFYBB2019ZY004).

References Cited

  • Barrett, S.C.H. & Hough, J. 2012 Sexual dimorphism in flowering plants J. Expt. Bot. 64 1 67 82 https://doi.org/10.1093/jxb/ers308

  • Bi, Q.-X., Zhao, Y., Cui, Y.-F. & Wang, L.-B. 2019 Genome survey sequencing and genetic background characterization of yellow horn based on next-generation sequencing Mol. Biol. Rep 46 4 4303 4312 https://doi.org/10.1007/s11033-019-04884-7

    • Search Google Scholar
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  • Lang, Y.-H., Sun, Y., Feng, Y.-J., Qi, Z., Yu, M. & Song, K. 2020 Recent progress in the molecular investigations of yellow horn (Xanthoceras sorbifolia Bunge) Bot. Rev. 86 136 148 https://doi.org/10.1007/s12229-020-09224-0

    • Search Google Scholar
    • Export Citation
  • Liang, Q., Fang, H.-C., Liu, J.-N., Zhang, B.-H., Bao, Y., Hou, W.-R. & Yang, K.-Q. 2021 Analysis of the nutritional components in the kernels of yellowhorn (Xanthoceras sorbifolium Bunge) accessions J. Food Compos. Anal. 100 103925 https://doi.org/10.1016/j.jfca.2021.103925

    • Search Google Scholar
    • Export Citation
  • Renner, S.S. & Ricklefs, R.E. 1995 Dioecy and its correlates in the flowering plants Amer. J. Bot. 82 596 606 https://doi.org/10.1002/j.1537-2197.1995.tb11504.x

    • Search Google Scholar
    • Export Citation
  • Yu, H.-Y., Fan, S.-Q., Bi, Q.-X., Wang, S.-X., Hu, X.-Y., Chen, M.-Y. & Wang, L.-B. 2017 Seed morphology, oil content and fatty acid composition variability assessment in yellow horn (Xanthoceras sorbifolium Bunge) germplasm for optimum biodiesel production Ind. Crops Prod. 97 425 430 https://doi.org/10.1016/j.indcrop.2016.12.054

    • Search Google Scholar
    • Export Citation
  • Yang, Y. 2019 Current situation and prospect of breeding research of Xanthoceras sorbifolium. Forest Eco. Sci. 34 4 363 368 https://doi.org/10.13320/j.cnki.hjfor.2019.0057

    • Search Google Scholar
    • Export Citation
  • Zhang, N., Ao, Y., Su, S.-C., Liu, J.-F., Huang, Y.-Y., Liu, J.-F. & Zhang, X.-J. 2018 Analysis of morphological and anatomical features and meteorological factors during the sex differentiation in Xanthoceras sorbifolium Bunge Xibei Zhiwu Xuebao 38 10 1846 1857 https://doi.org/10.7606/j.issn.1000-4025.2018.10.1846

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Supplemental Fig. 1.
Supplemental Fig. 1.

(AD) The flowers of ‘Zhongshi No.1’ in 2015 and 2016. Red circles surround the terminal inflorescence, blue circles surround the lateral inflorescence. (EF) The fruits of ‘Zhongshi No. 1’. Red arrows point to the lateral fruits.

Citation: HortScience 58, 1; 10.21273/HORTSCI16922-22

  • Fig. 1.

    (A) Normal yellowhorn, red arrows point to terminal inflorescence with fewer female flowers, blue arrows point to lateral inflorescence with male flowers, bar = 5 cm. (B–F) New Xanthoceras sorbifolium cultivar Zhongshi No.1: (B) red arrows point to terminal inflorescence with all female flowers, blue arrows point to lateral inflorescence with all female flowers, bar = 5 cm. (C) Structure of the female flower. The upper right corner shows filament and the uncracked anther, bar = 1 mm. (D) Lateral fruits, as shown by red arrows, bar = 10 cm. (E) Leaves front, bar = 3 cm, (F) leaves back, bar = 3 cm.

  • Fig. 2.

    A typically grafted ‘Zhongshi No.1’ in Jing Bian of Shaanxi Province.

  • Supplemental Fig. 1.

    (AD) The flowers of ‘Zhongshi No.1’ in 2015 and 2016. Red circles surround the terminal inflorescence, blue circles surround the lateral inflorescence. (EF) The fruits of ‘Zhongshi No. 1’. Red arrows point to the lateral fruits.

  • Barrett, S.C.H. & Hough, J. 2012 Sexual dimorphism in flowering plants J. Expt. Bot. 64 1 67 82 https://doi.org/10.1093/jxb/ers308

  • Bi, Q.-X., Zhao, Y., Cui, Y.-F. & Wang, L.-B. 2019 Genome survey sequencing and genetic background characterization of yellow horn based on next-generation sequencing Mol. Biol. Rep 46 4 4303 4312 https://doi.org/10.1007/s11033-019-04884-7

    • Search Google Scholar
    • Export Citation
  • Lang, Y.-H., Sun, Y., Feng, Y.-J., Qi, Z., Yu, M. & Song, K. 2020 Recent progress in the molecular investigations of yellow horn (Xanthoceras sorbifolia Bunge) Bot. Rev. 86 136 148 https://doi.org/10.1007/s12229-020-09224-0

    • Search Google Scholar
    • Export Citation
  • Liang, Q., Fang, H.-C., Liu, J.-N., Zhang, B.-H., Bao, Y., Hou, W.-R. & Yang, K.-Q. 2021 Analysis of the nutritional components in the kernels of yellowhorn (Xanthoceras sorbifolium Bunge) accessions J. Food Compos. Anal. 100 103925 https://doi.org/10.1016/j.jfca.2021.103925

    • Search Google Scholar
    • Export Citation
  • Renner, S.S. & Ricklefs, R.E. 1995 Dioecy and its correlates in the flowering plants Amer. J. Bot. 82 596 606 https://doi.org/10.1002/j.1537-2197.1995.tb11504.x

    • Search Google Scholar
    • Export Citation
  • Yu, H.-Y., Fan, S.-Q., Bi, Q.-X., Wang, S.-X., Hu, X.-Y., Chen, M.-Y. & Wang, L.-B. 2017 Seed morphology, oil content and fatty acid composition variability assessment in yellow horn (Xanthoceras sorbifolium Bunge) germplasm for optimum biodiesel production Ind. Crops Prod. 97 425 430 https://doi.org/10.1016/j.indcrop.2016.12.054

    • Search Google Scholar
    • Export Citation
  • Yang, Y. 2019 Current situation and prospect of breeding research of Xanthoceras sorbifolium. Forest Eco. Sci. 34 4 363 368 https://doi.org/10.13320/j.cnki.hjfor.2019.0057

    • Search Google Scholar
    • Export Citation
  • Zhang, N., Ao, Y., Su, S.-C., Liu, J.-F., Huang, Y.-Y., Liu, J.-F. & Zhang, X.-J. 2018 Analysis of morphological and anatomical features and meteorological factors during the sex differentiation in Xanthoceras sorbifolium Bunge Xibei Zhiwu Xuebao 38 10 1846 1857 https://doi.org/10.7606/j.issn.1000-4025.2018.10.1846

    • Search Google Scholar
    • Export Citation
Xi Wang State Key Laboratory of Tree Genetics and Breeding, Research Institute of Forestry, Chinese Academy of Forestry, Beijing 100091, China

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Huihui Xu State Key Laboratory of Tree Genetics and Breeding, Research Institute of Forestry, Chinese Academy of Forestry, Beijing 100091, China

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Xiaojuan Liu State Key Laboratory of Tree Genetics and Breeding, Research Institute of Forestry, Chinese Academy of Forestry, Beijing 100091, China

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Yingchao Li State Key Laboratory of Tree Genetics and Breeding, Research Institute of Forestry, Chinese Academy of Forestry, Beijing 100091, China

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Haiyan Yu State Key Laboratory of Tree Genetics and Breeding, Research Institute of Forestry, Chinese Academy of Forestry, Beijing 100091, China

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Quanxin Bi State Key Laboratory of Tree Genetics and Breeding, Research Institute of Forestry, Chinese Academy of Forestry, Beijing 100091, China

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Libing Wang State Key Laboratory of Tree Genetics and Breeding, Research Institute of Forestry, Chinese Academy of Forestry, Beijing 100091, China

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Contributor Notes

Q.B. is the corresponding author. E-mail: biquanxin@caf.ac.cn.

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