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.
Agricultural Research Service, U.S. Department of Agriculture 2012 USDA plant hardiness zone map Agricultural Research Service, U.S. Department of Agriculture USA
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