Breeding of late-ripening Zuili variety Zuiguifei (Japanese plum)

Abstract: Zuiguifei (Prunus salicina L.) was bred by systematic breeding method from Zuili germplasm collections. Zuili is one of Japanese plums, and has a high prestige in Chinese plum industry as one of the very delicious plums with the longest cultivation history of more than 2500 years at Jiaxing city, Zhejiang province, China. Zuiguifei was firstly found from a farmer yard in July, 1997 at Nanhu District, Jiaxing City. When the fruit was ripening, Mr. Lu found it. And it was late- ripening and 20 years old, with a good fruiting trait and a nice quality, comparing with other Zuili cultivars. Its branches were collected and were grafted on rootstocks, coded as J-31 in the winter of 1997. J-31 has an elite taste for its rich juice, high soluble solids content and aromatic smell. Its pulp is easy melting and could be sucked for eating when it matures. This is coincident with one of the typical characteristics of Zuili after maturity. There is a deep purple red peel covering with dense grey-white dots when J-31 fruits ripen with yellow flesh and clinging stone. Its fruit is oblate, more symmetrical and slightly big. J-31 was named as Guifei, which was borrowed from one title of ancient Chinese emperor wives, in 2018. We conducted the first-round variety test with Tongxiangzuili as the control from 2016 to 2018. Tongxiangzuili is a more popular cultivar of Zuili and generally matures around mid-June. As Tongxiangzuili often has a low yield with unstable fruit set, the new varieties are required to be bred. Experiments have showed Guifei fruits generally ripen in early July or mid-July at Jiaxing City, sometimes in late June also. Guifei has a higher yield than Tongxiangzuili. Guifei could be regarded as a late-ripening Zuili vari-ety. Guifei was approved for a five- year field releasing by the Zhejiang Provincial Forestry Variety Committee with license No. ZHE-R-SV-PS-006-2019, and formally named as Zuiguifei in 2019. For getting a permanently field releasing approval for Zuiguifei, we carried out a new round variety test from 2021 to 2022 with Tongxiangzuili still serving as the control variety. Results showed that the whole fruit growth period of Zuiguifei was about 113 d from blooming to ripening. The variety test showed that the average yield of adult Zuiguifei trees was about 8.1 t·hm^-2 with 37.3% increasing than that of the control Tongxiangzuili. Its average soluble solids content was about 16.0% with up to more than 20.0%. Its peel was slightly sour and the titratable acid content in flesh with skin was 1.03% while the pulp was only about 0.72%. The Vc content of Zuiguif was 8.01 mg · 100 g- 1 flesh. Its mean fruit weight was 69.5 g. There was no significant difference in the content of total soluble solids between Zuiguifei and Tongxiangzuili. Based on experience, it is recommended that its yield may be controlled to about 9.0 t·hm-2 by thinning flowers and young fruits as higher yield probably decreases fruit quality. Zuiguifei is resistant to bacterial perforation and gummosis. As it is self-compatible, Zuiguifei could be grown solely. Its tree is slightly upright and requires pulling branches or other pruning measures to shape an opening tree. Organic manures should be considered as main fertilizer resource and N needs to be limited for fruiting trees. Zuiguifei has been introduced and tested in many places and showed good adaptation in southern provinces of Yangtze River, e.g. Zhejiang, Jiangxi, Guizhou, Sichuan, Chongqing, Shanghai, Jiangsu etc.