Ornamental crabapples or flowering crabapples of the genus Malus in the Rosaceae family are woody plants from the temperate zone cultivated mainly for their luscious display of flowers in spring as well as attractive fruit in autumn and winter (Fiala, 1994; Huang et al., 2020; Lu et al., 2016). The diversity of growing habits and tree shapes available also contribute to their immense popularity in North American suburban garden landscapes. In China, ornamental crabapple trees are a representation of one’s financial prowess and social standing, and “symbolize everything good in Chinese painting, poetry, and the garden arts” (Guo et al., 2019).
The breeding of Chinese ornamental crabapple started in 2002 and is carried out primarily by hybridizing cultivars imported from North America and Europe. After a decade of concerted breeding efforts, several highly economically valuable ornamental crabapples were introduced to the Chinese market. These include M. ‘Yangzhi Yu’ (Jiang et al., 2020), M. ‘Zi Dieer’ (Zhou et al., 2020), M. ‘Fenghong Nichang’ (Fan et al., 2019), M. ‘Fen Balei’ (Zhou et al., 2019), M. ‘Hongxia’ (Shi et al., 2019), and M. ‘Meizhen Haitang’ (Zhang et al., 2018b).
In the past decade, extensive research and fieldwork in ornamental crabapple cultivation and breeding have extended their leaf colors from green to a broad spectrum of red and purple hues (He et al., 2017; Zhang et al., 2018a; Zheng et al., 2008), further adding to their appeal.
The new yellow-leaf crabapple cultivar, Malus spectabilis ‘Duojiao’, was derived from a natural mutant of the species M. spectabilis ‘Riversii’, and its attractive foliage distinguishes it from other crabapple cultivars. New, unfolded leaves are initially reddish-yellow, then gradually lighten to an attractive yellow with strong leaf surface glossiness. Young leaves turn from yellow to yellowish green, with irregular green patching along their central veins, finally maturing into dark green. These foliage characteristics were found to be stable and consistent during a 4-year observation period.
Yellow-leaf mutants are well-documented in many other plant species (Li et al., 2015; Lu et al., 2017; Lyu et al., 2017). However, despite the abundance of crabapple cultivars with attractive foliage colors, no cultivar before the discovery of ‘Duojiao’ was reported to have yellow leaves, making this an important milestone in the research and breeding programs of color-foliage crabapples. ‘Duojiao’ is a rare, deciduous yellow-leaf cultivar ideal for the study of plant photosynthesis, chlorophyll metabolism, and chloroplast development. The genetic mechanism of the leaf coloration in ‘Duojiao’, and the interplay between the photoperiod and the circadian clock in colored leaves of plants are still being explored (Johansson and Staiger, 2015). The results are expected to provide a technical reference to improve directional breeding of ornamental crabapples as well as other colored-leaf plants. In addition, the study of this unique cultivar will make significant contributions to the landscape plantings of ornamental crabapples.
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