Breeding of Cangdong 4: A high-quality, early-bearing and productive fresh-eating jujube cultivar

Cangdong 4 is a newly selected late-maturing fresh-eating jujube (Ziziphus jujuba Mill.) cultivar derived from a natural bud mutation of the traditional Dongzao variety. The mutant was discovered in 2007 in a century- old jujube tree in Zhangguangwang Village, Qingxian County, Hebei Province. A distinct scaffold branch on the tree displayed superior fruit characteristics including larger size, higher sweetness, and increased soluble solids. The branch was confirmed to be a stable bud mutation through three years of morphological comparison with standard Dongzao. From 2008 to 2010, systematic evaluation of fruit shape, shoot growth, leaf size, and floral characteristics confirmed the mutant’s phenotypic stability. In 2011, scions were grafted for propagation and field testing in the same region. Later trials (2015—2023) were conducted across multiple sites in Hebei Province, including Simazhuang, Baizhuang, and Baiya villages. Tests assessed regional adaptability by evaluating plant growth, fruit quality, yield potential, and stress resistance. DNA fingerprinting analysis using SSR markers confirmed genetic homology with Dongzao, confirming its origin as a somatic variant. The cultivar was officially registered as Cangdong 4 in 2024 by the Hebei Provincial Forest Variety Approval Committee (ID: Ji S-SV-ZJ-031-2024). Cangdong 4 trees are of medium vigor, with strong natural branching and fast crown formation, achieving fruit- bearing structure 1−2 years earlier than Dongzao. Shoots have wide branch angles (80°−90° ), rough bark with longitudinal striations, and sparse, degenerated thorns that abscise annually. Leaves are ovate, dark green, 6.01 cm long and 2.47 cm wide, with a length-towidth ratio of 2.43. Inflorescences are abundant, with 3-5 cymes per node and up to 13 flowers per cymose panicle. The flower diameter averages 5.4 mm. The fruit is nearly round, with a fruit shape index of 0.98, a depressed apex, and a medium-sized stalk cavity. The exocarp is thin, glossy, waxy, and devoid of fibrous remnants, while the flesh is yellowish-white, crisp, juicy, and residue-free, with a sweet flavor. Fruit weight averages 21.08 g (maximum 28.80 g). The fruit shows 30.72% soluble solids content (SSC), 307 mg·100 g-1 ascorbic acid, 9.04 kg· cm-2 firmness, and 97.6% edible portion. These attributes make it suitable for direct consumption, with a favorable sugar-acid balance appealing to consumers preferring high- sugar jujubes. In Cangzhou, Hebei (38° N, 116° E), the budbreak appears in midApril, flowers open in early June, and fruits mature from late September to mid-October, with a fruit development period of approximately 128 days. Terminal buds on annual shoots show a high germination rate (25.42%), with 3−4 fruiting spurs per shoot. Plants bear fruit in the second year and exhibit strong continuous fruiting ability. High-grafted trees achieved peak yields of 15.62 t·ha-1 . Cangdong 4 exhibits tolerance to low-temperature, drought and saline stress, and fruit-cracking resistance. It adapts well to loam, sandy, and clay soils in both plains and mountainous regions. The fruit demonstrates good postharvest handling properties, with extended shelf life under room and cold storage conditions, maintaining better flavor and firmness. The cultivar is ideal for promotion in jujube-appropriate areas across Hebei and adjacent regions, offering high yied potential, early formation, and excellent fresh-market value.