Breeding report of a new Chinese jujube cultivar Longpandongzao

Longpandongzao is a new fresh jujube cultivar selected from the superior line of Dongzao cultivar. A single plant mutation was discovered in the Dongzao cultivar orchard in Xuejiazhuang Village, Linyi County, Shanxi Province in 2008. After observation, its traits exhibited stable performance and then it was confirmed as a primary superior line in 2010. Scions of the superior line were collected for grafting and vegetative propagegation, with continuous monitoring for the traits stability. The results showed consistant expression of elite characteristics, leading to its selection as a secondary superior line in 2014. In 2015, pilot trials were initiated across diverse regions and climatic zones, and a fruit storage resistance test was conducted. Through long- term systematic multi- location observation and experiments, the superior traits of the cultivar displayed Distinctness, Uniformity and Stability. SSR molecular marker analysis identified it as a novel variant type, and it was subsequently confirmed as a superior selection line and officially named Longpandongzao. The tree is medium-sized with moderate vigor. Its secondary branches and bearing branches all exhibit a curved- growing habit. The number of newly sprouted branches are small and branch- forming ability (branching rate) is 15.6%. Primary shoots are reddish- brown with an internode length of 7.3 cm. Its thorns are fine and short, with underdeveloped structures. The lignification of bearing branches is relatively well-developed. It has an average length of 20.8 cm. The leaves are medium-sized and ovate-lanceolate. The leaf is flat with a petiole of 4.5 mm long, leaf length of 6.3 cm and leaf width of 5.9 cm. The flowers are night-opening with an average of 5.6 flowers per inflorescence and a diameter of 7.1 mm. The fruit is flat-round with the fruit shape index of 0.79, resembling a coiled peach, and has high ornamental value. Its surface is smooth and fruit peel is thin and brightly colored, with strong fragrance, delicate flesh, abundant juice, and a crisp, palatable taste. The fruit is large with an average single fruit weight of 23.50 g, and the maximum weight of 52.21 g. Its stone is small, flat, and short fusiform with an average weight of 0.87 g, the edible rate is 96.30%, and the kernel content is 33.0%. The content of soluble solids is 31.30%, the content of soluble sugar is 28.80%, the content of titratable acid is 0.28%, and the content of vitamin C is 3.331 mg · g- 1 . The cultivar exhibits strong fruiting capacity. The average fruit set on 2-3- year- old branches is 0.96, and on branches older than 3 years is 1.24. During the peak fruiting period, the yield per hectares ranges from 16 500 to 21 000 kg·hm-2 . The fruit setting is consistent, and the ripening is relatively uniform. In Yuncheng, Shanxi Province (115.972 384° E, 39.294 211° N), the fruiting period is approximately 129 d. Under the condition of open-field cultivation, it begins to sprout in early April and enters its peak flowering period from mid to late May, and fruits ripen with coloration in late September, classifying it as an extra-late-maturing cultivar. In greenhouses, maturity can be advanced by more than 15 d. In a normal year, the fruit cracking rate is 4.5% under open-field, while 1.0% under the condition of protected cultivation. The shelf life of its fruits is 10-15 d at the crisp ripening stage. They can be stored for 90 d in cold storage (storage conditions: temperature -2 ℃-1 ℃, and relative humidity above 95%). Multi-location trials in Yanhu District, Xia County, and Linyi County in Yuncheng District, as well as in Lüliang District have demonstrated characteristics of Longpandongzao, including curved branches, less new shoots, extra-late maturity, large fruit size, unique fruit shape, and excellent fresh-eating quality. It has strong adaptability and stress resistance, and storability. Therefore, it is suitable for promotion and cultivation in the south and west areas of Shanxi Province. Orchards should be choosed in the location with sufficient sunlight and deep soil layers. The optimal plant spacing is 1.5-2.0 m×3.0 m, with 110-148 trees per mu (0.067 hectares). Its trees should be trained into an open- center system. Winter pruning mainly involves removing woody branches; spring and summer management should focus on eradicating all new shoots. It should be irrigated once before sprouting, at the initial flowering stage, during fruit expansion and before soil freezing; and timely intertillage should be conducted to control weeds and preserve soil moisture. Some measures should be taken to control pests such as Apolygus lucorum, thrips and spider mites.