Breeding report of a new spine grape cultivar Xiangci No. 4

Xiangci No. 4 is a new cultivar selected by the grape research team of Hunan Agricultural University from wild Vitis davidii Foex. resources found in Tongmu Town, Zhongfang County, Huaihua City, Hunan Province, and was registered as a new cultivar in 2020. Xiangci No. 4 exhibits the typical morphological characteristics of East Asian Vitis davidii Foex., with well-developed perfect flowers. Its branches and petioles bear conspicuous prickles, which are erect or slightly curved at the tip and measure 2-4 mm in length. Young leaves are bright reddish-brown and possess a distinct waxy layer on the adaxial surface. On the abaxial leaf surface, sparse pubescence is confined to the veins, which are otherwise glabrous. The first inflorescence typically emerges between the 3rd and 5th nodes, most frequently appearing at the 4th internode. Mature leaves are cordate, small, and exhibit a trilobed shape. The leaves are dark green, of moderate thickness, and possess a firm, rigid texture. The leaf margin serrations are predominantly bilateral and straight, occurring in low density. The petiole sinus is predominantly closed, ranging from semi- open to closed. Current- year shoots typically produce 1-3 inflorescences, with the occurrence of 2 inflorescences being the most common. The clusters of this cultivar are branched (shouldered), very loose, with thick skin and a prominent bloom (waxy coating). At the onset of veraison, the berry color is light purple, turning blue- black at physiological maturity. The average cluster weight is 222 g, and the average berry weight is 3.87 g. The berry shape index is 1.0. Each berry contains 3-4 seeds and the 100-seed weight is 3.59 g. The average soluble solid content ranges from 15.9% to 16.2%, and the average titratable acidity ranges from 0.18% to 0.26%. The fruit development period spans 128 days. Budbreak occurs consistently from late March to early April. Flowering takes place from late April to early May. Berry coloring begins in mid-to-late July, and the fruit ripens in early September, classifying it as a late-maturing variety. Xiangci No. 4 demonstrates exceptional potential for high yield. It typically begins bearing fruit the year after planting, achieving a yield of 500-750 kg per 666.7 m2 . By the third year, the yield can increase by an additional 250 kg per 666.7 m2 . Nodes 2 to 10 on the mother cane can produce fruitful shoots, with an average of 2 clusters per shoot. This cultivar exhibits strong drought resistance and adaptions to high-temperature and humid climatic conditions. It shows strong resistance to common grape diseases but is susceptible to downy mildew. While it possesses general strong pest resistance, there is a potential risk of invasion by root phylloxera. This variety demonstrates excellent adaptability during both spring and autumn planting in Hunan, Hubei, Anhui, Jiangxi, and most regions of South China.