Breeding report of a new fragrant-flavored and firm-fleshed plum cultivar Guoxin

Guoxin plum is a new variety of late-maturing, highly fragrant, and high-quality plum with firm flesh, bred by Liaoning Institute of Pomology. This cultivar was selected via artificial hybridization, employing the Chinese-originated variety Longyuanqiuli as the female parent and the introduced variety Australia No. 14 as the male parent. Artificial hybridization was conducted in 2005, and seeds were sown in 2006. The plants began to bear fruit in 2010, and the elite line numbered 06- 17- 07 showed excellent performance. In 2011, it was grafted into the National Germplasm Repository of Plums and Apricots. In 2012, it was propagated on a large scale using the seedlings of Prunus tomentosa as the rootstock. Regional trials were carried out in multiple areas of Liaoning province in 2013. From 2014 to 2018, observation and identification for five successive years showed that its traits were stable and excellent. It was applied for in May 2019 and obtained the Plant Variety Rights certificate (CNA20191002278) in June 2021. The fruit is flat to round, with an average single fruit weight of 115.8 g and a maximum weight of 137.9 g. The fruit apex is flat, and the pedicel cavity is deep and narrow. The suture line is shallow, the flesh is symmetrical with good uniformity. The fruit skin has a yellow-green base color that turned purplish-black upon ripening, and it is not easy to peel off. The flesh is yellow, with a red color near the skin, firm and crisp, with a rich flavor and high quality. The soluble solid content is 20.7%, soluble sugar content is 9.0%, titratable acidity is 1.6%, vitamin C content is 6.0 mg · 100 g-1 , and firmness without peel is 4.3 kg · cm-2 . It exhibited semi-detached nucleus, obovate nucleus, rough nuclear surface. In Xiaoshipeng area of Gaizhou, Liaoning, this variety sprouts in early April and blooms in late April, with a flowering period of approximately 7 days. The fruits begin to color in early August and mature in early September, with a fruit development period of about 127 days. The leaves fall at the end of October, and the vegetative growth period is about 200 days. In the initial fruiting stage, the fruits are mainly borne on medium and long fruit branches, while in the full fruiting stage, the fruits are mainly borne on short fruit branches and flower cluster- like fruit branches. The sprouting rate is 93.6%, and the branching ability is strong. It has good early fruitfulness. The grafted seedlings can form flower buds in the year of planting, bear fruit in the second year, and the acre-yield can reach 1600 kg in the sixth year, with continuous high yield and no alternate bearing phenomenon. The natural fruit setting rate is 17.5%, and the self-pollination fruit setting rate is 0.3%. Pollenizer trees such as Longyuanmi and Guomei need to be configured. It has been cultivated in Liaoning, Beijing, Hebei, Shanxi, Shandong, Shaanxi, Gansu, Henan, Chongqing, Ningxia, Qinghai, and southern Xinjiang, and has shown good performance. It has strong cold and drought resistance. No obvious frost damage, bacterial shot hole disease, or gummosis was found in five years of field observation. In the survey of two- year- old grafted seedlings, the frost damage index was 27 (strong), the gummosis disease index was 31 (moderately resistant), and the bacterial shot hole disease index was 33.6 (moderately resistant). It can be stored at room temperature for 10-15 days. It can be planted to the north of Heilongjiang in solar greenhouses. For open-field cultivation, it is suitable for areas south of Shenyang, Liaoning, and regions with similar climates.