Ornamental crabapple is a multipurpose woody plant of the Malus in the Rosaceae’s family, which is an attractive small tree or shrub with beautiful flowers, colorful fruits, and various tree habits (Rong et al. 2022). Ornamental crabapple is recognized as one of the “four unique spring flowers,” together with peony, plum, and orchid (Xu et al. 2021). In the 18th century, crabapples from China were introduced to Europe and America and hybridized with native crabapple cultivars (Fan et al. 2023; Fiala 1994). Previous studies have recorded more than 1200 genotypes of crabapple germplasm (Fiala 1994), most of them with white, pink, and red flowers. There were few transitional color flowers under subtropical monsoon climatic conditions, in which the flower color changed from dark to light or from one color to another slowly.
At present, nearly a thousand crabapple germplasms have been cultivated through long-term breeding and selection (Dirr 2010; Jiang et al. 2020), including many white and pink flowering crabapples with single petals such as M. ‘Dai Long’ (Yin et al. 2021) and M. ‘Hong Yi’ (Zhang et al. 2021). And some double flowering cultivars including M. ‘Yangzhi Yu’ (Jiang et al. 2020) and M. ‘Zi Dieer’ (Zhou et al. 2020). However, there still are some limitations on the selection of diverse flowering crabapple cultivars with transitional color flowers. The phenotypic variation of ornamental crabapple, including size, color, structure, and function, is an important basis for germplasm innovation, which affects its economic and ornamental value to a large extent (Zhou et al. 2019). The cultivation of different flowering crabapples with transitional colors is of profound significance to enrich the color and landscape structure in cultivars.
Origin
Malus ‘Yanyu Jiangnan’ is a new outstanding cultivar of ornamental crabapple, which was selected from open-pollinated progenies of M. ‘Purple Prince’. In Autumn 2011, a batch of seeds was collected from the National Crabapple Germplasm Genetic Center in Yangzhou City (lat. 32°42′N, long. 119°55′E) and sown in a seedbed in Spring 2012. A single specific plant was selected by observing from 2012 to 2015, which had large number of flowers and earlier flowering time. The flower was small in diameter (2.5–2.9 cm), with a shallow-cup shape, and the petals were transparent and light purple (RHS-75C; Royal Horticultural Society 2007). The individuals showed stable traits by observation for 2 years (2015–16), and three generations of grafted seedlings were propagated with the rootstock of M. hupehensis from 2014 to 2017.
In Spring 2017, some of the grafted seedlings began the initial flowering period. Each individual had vigorous growth and showed strong adaptability to high temperatures of 37 to 40 °C and cold temperature of 4 to 6 °C in Yangzhou during the observation period (2017–19). In 2019, the National Forestry and Grassland Administration approved it as a new cultivar and formally named ‘Yanyu Jiangnan’ after an on-the-spot expert examination.
Description
The specificity of M. ‘Yanyu Jiangnan’ is the unique transitional flower color and tree habit. According to the consistency and specificity of different cultivars, the most similar cultivar was determined as M. ‘Royal Raindrop’. There are significant differences between M. ‘Yanyu Jiangnan’ and M. ‘Royal Raindrop’ in tree habit, flower shape, and leaf traits including glossiness, length, width, shape, and anthocyanin coloration (Table 1). Distinctive characteristics of M. ‘Yanyu Jiangnan’ are as follows.
Comparisons of Malus ‘Yanyu Jiangnan’ and Malus ‘Royal Raindrop’.
Habit.
The tree had strong vigor and an upright, open form of gray-red (RHS-178A) branches (Royal Horticultural Society 2007) (Fig. 1A). It reaches ≈3.8 m in height, with a 1.4-m spread at 6 years old (Table 1).
Phenotypic characteristics of ‘Yanyu Jiangnan’. (A) The tree habit at the beginning of flowering stage. (B) Full bloom flowers. (C) The bloom stages of inflorescence in ‘Yanyu Jiangnan’: (a) initial color stage, (b) balloon stage, (c) initial blossoming stage, (d) full blossoming stage, (e) final blossoming stage, and (f) front view of blooming flower. (D) Leaves. (E) Mature fruits: (a) front view of infructescence, (b) back view of infructescence, (c) polar view of fruits, and (d) fruit pulp.
Citation: HortScience 58, 5; 10.21273/HORTSCI17124-23
Phenotypic characteristics of ‘Yanyu Jiangnan’. (A) The tree habit at the beginning of flowering stage. (B) Full bloom flowers. (C) The bloom stages of inflorescence in ‘Yanyu Jiangnan’: (a) initial color stage, (b) balloon stage, (c) initial blossoming stage, (d) full blossoming stage, (e) final blossoming stage, and (f) front view of blooming flower. (D) Leaves. (E) Mature fruits: (a) front view of infructescence, (b) back view of infructescence, (c) polar view of fruits, and (d) fruit pulp.
Citation: HortScience 58, 5; 10.21273/HORTSCI17124-23
Phenotypic characteristics of ‘Yanyu Jiangnan’. (A) The tree habit at the beginning of flowering stage. (B) Full bloom flowers. (C) The bloom stages of inflorescence in ‘Yanyu Jiangnan’: (a) initial color stage, (b) balloon stage, (c) initial blossoming stage, (d) full blossoming stage, (e) final blossoming stage, and (f) front view of blooming flower. (D) Leaves. (E) Mature fruits: (a) front view of infructescence, (b) back view of infructescence, (c) polar view of fruits, and (d) fruit pulp.
Citation: HortScience 58, 5; 10.21273/HORTSCI17124-23
Flower.
The flowers had a shallow cup pattern with a single ovate petal and prominent venation. The inflorescence type was umbellate and the flower bud was purple with a small flattened diameter (2.5–2.9 cm) (Fig. 1B and C). The front edge of the petal is red-purple (RHS-64B), the center color is red-purple (RHS-65C), the base color is white (RHS-65D), and the back color is red-purple (RHS-70B; Royal Horticultural Society 2007) (Fig. 1C). The initial flowering period is early, around April first, and lasts for 8 to 10 d in Xiannv town, Yangzhou City (lat. 32°42′N, long. 119°55′E).
Foliage.
The spreading leaves are red-green (RHS-139A) with short length (4.6–5.3 cm) (Royal Horticultural Society 2007), medium width (3.0–3.4 cm), and a medium ratio of length to width (≈1.5) (Table 1). The leaf margin is serrate and the petiole is short (1.1–1.5 cm). The leaf is a green and glossy surface with moderate anthocyanin coloring (RHS-139A; Royal Horticultural Society 2007) (Fig. 1D).
Fruit.
M. ‘Yanyu Jiangnan’ sets a large amount of fruit. The fruits are spherical with a long stalk (2.6–3.9 cm) and sometimes with calyx. The fruit diameter (1.1–1.2 cm) is small with a faintly lustrous exocarp and without powder. The main fruit color is dark-red (RHS-46B), the flesh color is orange-red (RHS-34C; Royal Horticultural Society 2007) (Fig. 1E), and the fruit period lasts from July to October.
Cultivation
Malus ‘Yanyu Jiangnan’ is suitable to be planted between the Yellow River basin (lat. 32°10′N to 41°50′N, long. 95°53′E to 119°05′E) and Yangtze River basin (lat. 24°30′N to 35°45′N, long. 90°33′E to 122°25′E), China (USDA Hardiness Zones 5–9; Agricultural Research Service, U.S. Department of Agriculture 2012). ‘Yanyu Jiangnan’ performs best in full sun and fertile sandy soils with good drainage. It also can be planted in partial sun or partial shade areas. ‘Yanyu Jiangnan’ is suitable for both single-tree residential plantings and naturalized landscapes. It was propagated using M. hupehensis as a rootstock. Scion buds were collected from current year’s healthy hardwood branches and grafted during the fall season (August to September in Yangzhou). The buds were wrapped with plastic film to prevent water loss. The plastic film can be removed after 30 d (Zhou et al. 2020). Compared with M. ‘Royal Raindrop’, ‘Yanyu Jiangnan’ has relatively stronger resistance to drought and cold. The grafted individuals showed no insect or disease problems over 5 years.
Availability
Malus ‘Yanyu Jiangnan’ is available through Nanjing Forestry University and Yangzhou Crabapple Horticulture Limited Company (Contact: Wangxiang Zhang; E-mail: malus2011@163.com).
References Cited
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