Yellow-horn (Xanthoceras sorbifolium Bunge) is a rare woody oil plant mainly distributed in China, with nutritious seeds that contain a high oil content in the seed kernels (Xie and Zhang, 2018). It is suitable for both biodiesel production and high-grade edible oil (Liu et al., 2017). Because it is mainly distributed in northern China, it has been referred to as “northern oil tea” (Chang et al., 2019). The State Forestry Administration has listed yellow-horn as the main tree species for the construction of biomass diesel raw material base. At the same time, its large number of flowers, rich flower type, and long flowering period make it an ideal tree for landscaping (Yang et al., 2021).
In recent years, the cultivation of yellow-horn has received extensive attention in China (Ao et al., 2012). Great progress has been made in breeding new and improved varieties. The new varieties reported so far are both ornamental and high-yielding. Most 10-year-old trees can produce more than 1500 kg/ha with intensive field management. ‘Yan Zi’ is a new variety of yellow-horn bred by the team headed by Y.A. It has a short inflorescence axis, dense inflorescences, and a small range of coloration at the base of the petals, which is deep purple. The cultivar is characterized by beautiful flowers, along with its fruit production. The new variety is highly adaptable, showing tolerance to cold and drought as well as barren and saline environments. It can be widely planted in northern China.
Origin
In 2016, a scientific research group found the mother tree of ‘Yan Zi’ with outstanding flower characteristics in a seeding forest of yellow-horn in Dongying City, Shandong Province. The team subsequently conducted a regional trial for variety selection and breeding. The rootstocks of ‘Yan Zi’ were 1-year old yellow-horn; the scions were branches of the native mother tree. The second generation was propagated by bud grafting in July of the following year with scions from the first generation of grafted plants. The survival rate of both generations was more than 95%. To date, multiple generations have been bred. The grafted seedlings have all flowered. In addition, after 4 years of observation, the characteristics of all grafted asexual single plants were consistent with the native parent tree. The genetic traits were stable. The novel cultivar retained the highly desired traits of the parent tree. It is suitable for cultivation as an ornamental cultivar because of the high ornamental value of the flowers (Fig. 1).
The flowers of yellow-horn novel cultivar Yan Zi.
Citation: HortScience 57, 3; 10.21273/HORTSCI16410-21
Description
Tree.
‘Yan Zi’ can grow as a deciduous shrub or tree, with a height of 2 to 5 m.
Leaves.
Odd-pinnate and lanceolate, with leaves spreading. The young leaves are yellow-green whereas mature leaves are green. Leaf expansion stage begins in early May, at the same time as flowering.
Flowers.
The inflorescence are numerous and cylindrical, with short terminal and lateral inflorescence axes that are green and a purplish red. The upper part of the petal is white throughout the flowering period, but the color of the lower part of the petal changes with the flowering period. The lower part of the petal is yellow at the first flowering, light purple-red at full flowering, and dark purple at the final flowering. The area of the lower, dark-purple part of the petals is very small (≈5 mm), making the whole flower looks almost white, which is the outstanding characteristic of ‘Yan Zi’. The pedicel is short and not hairy. The petals are obovate-lanceolate and are separated from each other, whereas the upper part of the petal is unvalved and is rolled longitudinally and slightly ruffled. Early bloom of the cultivar begins in early May. ‘Yan Zi’ enters the full flowering stage in mid-May. Florescence lasts for ≈20 d.
Fruit and seeds.
The fruit are rounded, ≈6 cm in transverse diameter, and ≈6.2 cm in longitudinal diameter, with three carpels. The fruit can be harvested in early August. The seeds are black and spherical, and the number of seeds per fruit is ≈12.
‘Yan Zi’ grows best on deep, moist, fertile, well-aerated, neutral to slightly alkaline soils, and grows poorly on low wetlands. It is a deep-rooted species with strong sprouting ability. It is suitable for promoting planting in China from the west to Xinjiang, the northeast to Liaoning, the north to Inner Mongolia, and the south to Henan. It grows normally in areas with an average annual temperature of 3 to 18 °C and an average annual precipitation of 550 to 600 mm.
By using the bud or branch grafting method, graft propagation is usually carried out in the spring and summer. The scions should be grafted onto 1-year old yellow-horn seedlings. Branch grafting and T-shaped bud grafting are carried out in spring and summer, respectively. Vigorous branches with plump buds are selected as scions. The scions of branch grafting are collected during dormancy. The scions for bud grafting should be new shoots and should be collected when used. After grafting, the tillers derived from the rootstocks should be cut after they sprout to ensure the growth of scions. The recommended spacing for large, grafted plants is 2 × 2 m in the early stages. In addition, ‘Yan Zi’ should be transplanted and spaced wider gradually as the tree ages. Large seedlings need to be transplanted in winter or early spring to be able to transplant without injury to the root system. Fertilizer is applied three times a year: 20 d before flowering, 10 d after flowering, and during the fruit expansion period. Watering is suggested to be carried out after fertilization. At the same time, more attention should be given during the rainy season to ensure timely drainage to help prevent the roots from rotting. Pruning should be carried out according to the crown shape requirement of ornamental tree species. The emphasis of pruning is to thin out the dense branches, overlapping branches, cross branches, weak branches, diseased branches, and branches with insect infestation. At the same time, attention should be given to the prevention and control of common diseases of yellow-horn, such as root knot nematodes and stem rot.
Availability
A small number of samples of ‘Yan Zi’ are available commercially from Beijing Forestry University. Requests for scions for research purposes may be addressed to Yan Ao (e-mail: aoyan316@163.com).
Literature Cited
Ao, Y., Duan, J., Yu, H.Y., Jiang, C.Y. & Ma, L.Y. 2012 Research progress on Xanthoceras sorbifolia Bunge J. China Agr. Univ. 17 197 203 https://doi.org/CNKI:SUN:NYDX.0.2012-06-026
Chang, Z.J., Li, H. & Bu, L.F. 2019 Quality comparison of cold pressed and hot pressed Xanthoceras sorbifolia Bunge seed oils China Oils and Fats 44 121 123 https://doi.org/CNKI:SUN:ZYZZ.0.2019-10-026
Liu, Y.L., Huang, Z.D., Ao, Y., Li, W. & Zhang, Z.X. 2017 Transcriptome analysis of yellow horn (Xanthoceras sorbifolia Bunge): A potential oil-rich seed tree for biodiesel in China PLoS One https://doi.org/10.1371/journal.pone.0074441
Xie, Z.Y. & Zhang, W.H. 2018 Effects of drought and rewatering on growth and photosynthetic physioecological characteristics of Xanthoceras sorbifolia J. Appl. Ecol. 29 1759 1767 https://doi.org/10.13287/j.1001-9332.201806.007
Yang, F., Han, S.S., Nan, Y., Chen, X.J., Sun, Y.B., Liu, S.C. & Ma, B.P. 2021 Progress in research and development of Xanthoceras sorbifolia China J. Chinese Materia Medica 46 4334 4343 https://doi.org/10.19540/j.cnki.cjcmm.20210524.603
