Crabapple is a general term for a class of plants with fruits that are less than 5 cm in diameter in the genus Malus, family of Rosaceae (Dirr 2010). It is one of the traditional famous flowers in China (Pang 2008). Western horticulturists have introduced a large number of Chinese wild crabapple resources, starting in the 18th century. Through long-term breeding and improvement, nearly a thousand ornamental crabapple varieties have been selected and bred (Zhou et al. 2018). Most varieties of crabapple have high ornamental value, with wide range of growth habits (columnar, fastigiate, upright, spreading, drooping, and weeping), a variety of flower colors (white, pink, red, and purple), and different fruit colors (yellow, green, orange, red, and purple) (International Union for the Protection of New Varieties of Plants 2003). In recent years, with the increasing emphasis on germplasm resources in China, an increasing number of excellent varieties have appeared in the market, including ‘Yanzhi Yu’, ‘Chahua Nv’, ‘Yun Xiangrong’, and ‘Yi Honglian’ (Fan et al. 2023; Lu et al. 2023; Sun et al. 2023; Zeng et al. 2022).
The book ‘Flowering Crabapples’ recorded more than 1200 crabapple varieties, some of which have weeping or spreading tree habits, such as ‘Louisa’, ‘Red Jade’, ‘Molten Lava’, and others (Fiala 1994). In addition, the flower color of crabapple is mostly pink or purple red, such as ‘Prairifire’, ‘Praire Rose’, ‘Cardinal’, and others (Fiala 1994). The proportion of double or semidouble varieties is less than 10% (Zhang et al. 2021), and there are no pure white semidouble cultivars with a spreading habit. In response to the cultivar void that has semidouble white flowers and a spreading habit, we introduce a new flowering crabapple cultivar named ‘Xijiang Yue’.
Origin
Malus ‘Xijiang Yue’ is a new cultivar of crabapple obtained by natural hybridization breeding. In Fall 2011, a mixture of seeds from nine ornamental crabapple varieties (M. ‘Cinzam’, M. ‘Donald Wyman’, M. ‘Hargozam’, M. ‘Indian Summer’, M. ‘Purple Prince’, M. ‘Red Jade’, M. ‘Qian Cengjin’, M. ‘Sutyzam’, and M. × zumi ‘Calocarpa’) were collected from Nanjing Forestry University (Nanjing, Jiangsu, China) and National Crabapple Germplasm Genetic Center (Yangzhou, Jiangsu, China) (Gou et al. 2017). The seeds were cleaned (soaked for 4 h in ≈40 °C water to soften the seedcoats) and stratified (placed in moist sand medium and stored outdoors in a brick pond at −5 to 10 °C for 1 month to break dormancy). In March of the next year (2012), the seedlings were sown on raised beds (width, 1.5 m; length, 50 m; depth 8.0 to 10.0 cm) in the field with sandy loam and watered once every 3 d. Sprouted seedlings were grown for 1 year in the seedbed and then transplanted into the field with a 10.0 cm × 10.0 cm spacing. We observed ornamental crabapple seedlings (F1 generation) for 3 consecutive years. A specific single plant (with a spreading habit, pink-white semidouble flowers) was selected. We named it ‘Xijiang Yue’, which in Chinese means “as bright as the moon reflected in the water.” After 2 years of continuous observation, it was found that the flower shape and flower color of this single plant were stable.
In Autumn 2014 through 2017, three generations of seedlings were propagated using Malus hupehensis as the rootstock through maternal bud grafting in the Germplasm Genetic Center. After 4 years of observation, a total of 50 seedlings survived, and all showed the same phenotypic characteristics, demonstrating the stability of ‘Xijiang Yue’. Additionally, all grafted seedlings of this variety grew vigorously in Yangzhou (lat. 32°42′N, long. 119°55′E). They had good adaptability to high temperatures of 37 to 40 °C, good resistance to common diseases and pests (aphids, apple rust pathogen, and spider mites), and showed good horticultural characteristics.
Description
The distinguishing characteristics of ‘Xijiang Yue’ are semidouble flowers with pure white petals and a spreading growth habit. Among existing crabapple germplasm with spreading or weeping habit, ‘Xijiang Yue’ most resembles ‘Red Jade’. The predominant fruit color of ‘Red Jade’ is medium red, and the predominant fruit color of ‘Xijiang Yue’ is green-yellow. The flower type of the two cultivars is single (‘Red Jade’) and semidouble (‘Xijiang Yue’). In addition, there are some slight differences in petal shape, flower diameter, leaf apex, and other characteristics between the two cultivars (Table 1).
Comparisons of phenotypic characteristics between M. ‘Red Jade’ and M. ‘Xijiang Yue’.
Habit.
‘Xijiang Yue’ has a spreading growth habit with brown branches. It reaches ≈1.8 m in height, with a 1.9 m spread at 3 years old (Table 1 and Fig. 1A).
Phenotypic characteristics of M. ‘Xijiang Yue’. (A) The growth habit at the full blossoming stage. (B) Flowering branch with flowers at full bloom. (C) The different flowering stage of ‘Xijiang Yue’: (a) large bud stage; (b) initial blossoming stage; and (c) full blossoming stage. (D) Annual branches and leaves. (E) Mature fruit morphology.
Citation: HortScience 59, 11; 10.21273/HORTSCI18031-24
Foliage.
New expanding leaves are green, the mature leaves are ovate and green (length: 6.2 to 7.8 cm; width: 3.3 to 3.9 cm; petiole length: 1.8 to 2.9 cm), with an acuminate apex, serrated margins and moderately glossy adaxial leaf surface (Fig. 1D). The color of fallen leaves is mainly yellow.
Flower.
The flowering time of ‘Xijiang Yue’ starts in early April and lasts for 10 d in Jiangsu Province, China (lat. 32°42′N, long. 119°55′E). The flower is semidouble, in an umbrella inflorescence with light-pink buds [Royal Horticultural Society (RHS)-61B] and green-red flower stalks. The corolla has a shallow cup. The petals have a circular shape, wavy posture, and prominent veins. The diameter of the petals after flattening is medium (3.4 to 4.0 cm), in which the color of inner side and outer side are both white (RHS-NN155D and N155B) in the RHS color charts (Table 1; Fig. 1B and C).
Fruit.
‘Xijiang Yue’ has few fruits. The fruit is small in size (1.8 to 2.9 cm in diameter), with an oblate shape. The fruiting calyx is deciduous, and the main color of the fruit is green-yellow (RHS-153B) (Fig. 1E). The fruit has a moderate luster, and it can persist until late October in Yangzhou, Jiangsu, China.
Propagation and Cultivation
‘Xijiang Yue’ is suitable for planting between the Yellow River Basin and the Yangtze River Basin (located in a subtropical monsoon climate with four distinct seasons). It grows well in full sun. In addition, it prefers sandy loam soil with deep soil layers, loose and fertile soil, and good drainage. It can survive the winter safely in the south of the Yangtze River under the condition of field planting. ‘Xijiang Yue’ is mainly propagated by bud grafting or branch grafting using M. hupehensis as the rootstock in autumn (August to September in Jiangsu). Rootstocks ranging from 0.5 to 2.5 cm in diameter are used for budding. When grafting, scions were cut from ripened branches and were inserted into a T-shape cut in the bark of the rootstock, then the rootstock and buds were bound together with plastic film to prevent water loss (Zhou et al. 2020). If the grafted buds turn light green after 7 d, it indicates successful grafting. The graft is allowed to be exposed to air until March of the following year by removing the budding tape.
Availability
‘Xijiang Yue’ is available through the Nanjing Forestry University and Yangzhou Crabapple Horticulture Limited Company (contact: Wangxiang Zhang; E-mail: malus2011@163.com).
References Cited
Dirr M. 2010. Manual of woody landscape plants (6th ed). Stipes Publishing, Champaign, IL, USA. https://doi.org/10.5860/choice.37-1547.
Fan JJ, Zhang WX, Cheng M, Zhang DL, Veil J, Zhou L, Zhou T, Cai JH. 2023. ‘Chahua Nv’ Flowering Crabapple. HortScience. 58(3):291–292. https://doi.org/10.21273/HORTSCI17031-22.
Fiala JL. 1994. Flowering crabapples: The genus Malus. Timber Press, Portland, OR, USA.
Gou L, Quan J, Jin X. 2017. The International Crabapple Register and Checklist. China Forestry Publishing House, Beijing, China.
International Union for the Protection of New Varieties of Plants. 2003. Guidelines for the conduct of tests for distinctness, uniformity and stability [ornamental apple (Malus Mill.)]. TG/192/1.
Lu XJ, Chen YX, Zhang WX, Zhang DL, Fan JJ, Zhou T, Sun TT. 2023. ‘Yun Xiangrong’ flowering crabapple. HortScience. 58(5):557–558. https://doi.org/10.21273/HORTSCI17080-23.
Pang SH. 2008. The study about crabapple garden planning (MA Thesis). Hebei Agricultural University, Baoding, Hebei, China. https://doi.org/10.7666/d.y1307137.
Royal Horticultural Society. 2007. Royal Horticultural Society Colour Chart (5th ed). RHS Media, Royal Horticultural Society, London, UK.
Sun TT, Chen YX, Zhang WX, Fan JJ, Zhou T, Fan YR. 2023. ‘Yanzhi Yu’ Crabapple. HortScience. 58(5):513–514. https://doi.org/10.21273/HORTSCI17126-23.
Zeng J, Zhou T, Zhang DL, Zhang WX. 2022. ‘Yi Honglian’ Flowering Crabapple. HortScience. 57(3):374–375. https://doi.org/10.21273/HORTSCI16386-21.
Zhang WX, Xu BJ, Chen YX, Zhang DL. 2021. ‘Luokeke Nushi’ crabapple. HortScience. 56(10):1289–1290. https://doi.org/10.21273/HORTSCI15989-21.
Zhou T, Sheng XC, Zhou DJ, Fan JJ, Zhao MM, Zhang WX, Cao FL. 2018. Advances in the classification of crabapple cultivars. Yuan Yi Xue Bao. 45(2):380–396. https://doi.org/10.16420/j.issn.0513-353x.2017-0140.
Zhou T, Jiang H, Zhang WX, Zhang DL, Fan JJ, Zhang QQ, Wang GB, Cao FL. 2020. ‘Zi Dieer’ Crabapple. HortScience. 55(2):272–274. https://doi.org/10.21273/HORTSCI14590-19.