Cultivation Process

In May 2018, the unique flower color of X. sorbifolium was noted by researchers at a plantation in Chaoyang City, Liaoning Province. The 1-year-old X. sorbifolium seedlings were used as rootstocks and the branches of the mother tree were collected for the first-generation grafting in July 2018. Branch grafting was used to propagate. The planting density was 2 × 2 m. The second-generation grafting was performed in 2019. The grafted plants showed high yield and resistance to cold, drought, and barrenness. They showed little susceptibility to insect pests. Observations over several years indicated that the flower characters of the grafted plants were stable and consistent with that of the mother tree. Different from other cultivars, the petals of Yan Xue are mostly white. In Sept. 2021, this novel cultivar was named Yan Xue and authorized by the State Forestry and Grass Administration.

Plant Morphological Characteristics

The cultivar is a deciduous shrub or small tree, and the shape of the tree is round. The bark has strip cracking that is gray–brown (L* = 32, a* = 6, b* = 31; L*, a*, and b* represent a color space defined by the International Commission on Illumination). The branchlets are brown (L* = 37, a* =  0, b* = 17) and stout, with terminal and lateral buds with imbricate bud scales. The current-year branches are green (L* = 91, a* =  −12, b* =  45) (Fig. 1). The leaves are odd-pinnate compound with dark green (L* =  35, a* = −17, b* = 34) on the leaf surface and gray–white (L* = 82, a* = −16, b* = 0) on the leaf undersurface. The leaf edges are serrated and microcurly; they taper at the top and have a wedge shape at the base (Fig. 1). The leaves sprout in early April and fall in mid-October. The cultivar has two types of flowers. The male flower has functional stamens and a completely abortive vestigial gynoecium, and the female flower has unfunctional stamens and a fertile gynoecium. Inflorescences of female flowers are terminal, and male flowers are axillary. The lengths of terminal and lateral inflorescences are similar and the inflorescence axis is green (L* = 86, a* =  −22, b* =  29). The pedicels are glabrous and ≈2 to 3 cm long.

Plant (A) and leaf (B) morphology of ‘Yan Xue’.

Citation: HortScience 57, 10; 10.21273/HORTSCI16657-22

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Plant (A) and leaf (B) morphology of ‘Yan Xue’.

Citation: HortScience 57, 10; 10.21273/HORTSCI16657-22

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Plant (A) and leaf (B) morphology of ‘Yan Xue’.

Citation: HortScience 57, 10; 10.21273/HORTSCI16657-22

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The flowers of ‘Yan Xue’ are single and the petals are broad ovate (Fig. 2). There are five petals, one pistil, and eight stamens. During the initial flowering stage, the petal base is yellow (L* = 95, a* =  −5, b* = 45). The colored area is small and most of the petal is white (L* = 98, a* = 0, b* = 0). During the full flowering stage, the petal base is light red (L* = 55, a* = 37, b* = 20) and the other parts of the petal are white. The petals are crinkly and the flowers are fragrant. The average length and width of the petals are ≈1.7 cm and 0.7 cm, respectively. The large number of flowers gives ‘Yan Xue’ high ornamental value. The commercial cultivar most similar to the new cultivar Yan Xue is the cultivar Senmiao jinfenguan (Supplemental Fig. S1). A comparison between the two cultivars is reported in Table 1. The flowers sprout before or at the same time as the leaves. In Chaoyang City, flowering occurs at the beginning of May, and the blooming period lasts ≈20 d.

Flowers of ‘Yan Xue’ during the early flowering stage (A) and full flowering stage (B).

Citation: HortScience 57, 10; 10.21273/HORTSCI16657-22

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Flowers of ‘Yan Xue’ during the early flowering stage (A) and full flowering stage (B).

Citation: HortScience 57, 10; 10.21273/HORTSCI16657-22

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Flowers of ‘Yan Xue’ during the early flowering stage (A) and full flowering stage (B).

Citation: HortScience 57, 10; 10.21273/HORTSCI16657-22

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Table 1.

Main characteristics of ‘Yan Xue’ compared with ‘Senmiao jinfenguan’.

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The cultivar starts fruiting in the second year after planting. The capsule subglobose is ≈5 to 8 cm in diameter, with green pericarp. The pericarp apex is dehiscent at maturity. The oblate, black, shiny seeds are ≈1.5 cm in diameter. There are ≈9 to 15 seeds per fruit. They mature in early August in Chaoyang City. The harvesting time is early August in Chaoyang City.

Cultivation Techniques

‘Yan Xue’ has strong adaptation ability. The natural distribution of ‘Yan Xue’ occurs in temperate continental climates, with a horizontal distribution of 32° to 46°N and 100° to 127°E (Cai et al., 2017). The climatic characteristics of these areas are cold winter, hot summer, long hours of sunshine, and low annual rainfall. The annual average temperature ranges from 3 to 18 °C, and the annual average rainfall ranges from 43 to 969 mm. The vertical distribution of X. sorbifolium occurs at an elevation of 300 to 1200 m. The distribution includes rocky mountains, hills, and shallow mountain plateau areas. It is a sun-loving plant species, but it can survive in the shade. It has strong salt, alkali, cold, and drought resistance capabilities. It is not resistant to waterlogging and wind, and it should not be planted in low-lying areas with poor drainage (Zhang, 2019).

For the grafting of this cultivar, 1- to 2-year-old X. sorbifolium seedlings with a ground diameter of more than 0.8 cm can be used as rootstock. The 1-year-old strong branches in the middle and upper parts of the mother plant should be selected as scions. The scions should be untied in time after surviving. The sprout tillers of rootstock should be removed to ensure the growth of scions. Furthermore, cutting is suitable for the propagation of ‘Yan Xue’.

Fertilizer, water management, and pest control need to be strengthened (Wang et al., 2020). After the grafted plants germinate, they should be watered according to the soil conditions. Generally, the plants should be watered at the early flowering stage, at the fruit rapid growth stage, after fruit harvest, and before the soil freezes. The soil should be loosened regularly to maintain ventilation and improve the soil water-holding capacity. Combined with soil loosening, weeds should be removed to avoid competition for water and fertilizer with grafted plants. Regarding the soil conditions, ‘Yan Xue’ is not very demanding. Sufficient base fertilizer should be applied in autumn, nitrogen fertilizer should be applied before flowering, and phosphorus fertilizer should be applied during fruit expansion. Young trees should be pruned to expand the crown of the trees. After planting in spring, three to four main branches with an open angle should be retained, and the branches below them should be removed. During the second year after planting, lateral branches on the main branch should be chosen. Lateral branches should be 30 to 40 cm away from the trunk. The other branches should be cut back. The branches should be kept 5 to 10 cm long to cultivate a fruiting branch group. When the plant enters the fruit-bearing period, more attention should be focused on the cultivation and regeneration of the fruit-bearing branch groups. For overmature trees, old and weak branches should be removed. Overlapping branches, dense branches, and competitive branches should be cut. The cultivar shows some susceptibility to root rot, aphids, and other pests. Root rot is caused by the high moisture content of the soil for a long period. The water should be drained over time after rain. Aphids can be controlled by 70% imidacloprid powder in 2000-times liquid spray (Chen et al., 2021; Li, 2021).

Availability

The new cultivar ‘Yan Xue’ is commercially available from Beijing Forestry University. Requests for scions for research purposes may be addressed to Yan Ao (e-mail: aoyan316@163.com).