A new early-ripening citrus cultivar Renxuanzaogan

Abstract: Gonggan is a local characteristic mandarin variety in Guangdong with a cultivation history of over 1100 years and a total cultivation area of approximately 26 667 m² . Breeding early maturing citrus varieties can solve the problem of inconsistent market quality caused by early harvest of citrus, and also avoid excessive concentration of market periods. In September 2017, Renxuanzaogan was found in an orchard where Gonggan was cultivated, in Renhua County, Shaoguan city by the Fruit Research Institute of the Guangdong Academy of Agricultural Sciences, Shaoguan University, Shaoguan Agricultural Science and Technology Extension Center, and Renhua County Agricultural and Rural Development Service Center. After three consecutive years of observation on biological characteristics, it was proved that its maturity period was one month earlier than the control Gonggan, with significant and stable differences existing. The certificate of Plant New Variety Rights was issued by the Ministry of Agriculture and Rural Affairs in 2023 (CNA20201005931). As is similar to the control variety Gonggan, this variety is susceptible to citrus huanglongbing and citrus brown spot disease. The tree posture of Renxuanzaogan is open. The spring shoots have short spines, with a length of 0.10 cm. The leaf blade is broadly lanceolate, with wavy edges, leaf shape index of 2.07, petiole length of 0.85 cm, and narrow winged leaves. The flower is white with 5 petals, 1.32 cm in length and 0.59 cm in width, and 13-16 filaments, partially united. The anthers are light yellow, and the style is arched, higher than the stamens. The fruit is nearly spherical, with a single fruit weight of 78.07 g and a fruit shape index of 0.84. The fruit sur-face is glossy, with flat oil cells. The fruit skin is yellow orange, with a thickness of 0.15 cm, which is easy to peel off. The core is semi-plump, and the segments are semi-lunar and neat. The segment membrane is thin and easy to separate, and the juice sacs are compact and spindle-shaped. The flesh color is uniform, with a medium orange color. The fruit edible rate is 73.86%, the fruit juice content is 48.89%, the soluble solids content is 14.0%, the total acid content is 0.52%, the total sugar content is 112 g·kg-1 , and the vitamin C content is 356 mg · L- 1 . The number of seeds per fruit is 3-10, with wedge- shaped seeds, white cotyledons, and multiple embryos. There is a significant difference in the genome between Renxuanzaogan and the control of Gonggan. Compared with the genome of Clementine, Renxuanzaogan was identified as 2 874 326 SNPs and 588 506 InDels, while Gonggan was identified as 2 726 005 SNPs and 579 333 InDels. The differences in SNPs and InDels between Renxuanzaogan and Gonggan were 881 840 and 172 838, respectively, accounting for 32.35% and 29.83% of the total SNPs and InDels identified in Gonggan. This variety is suitable for cultivation in Gonggan cultivation areas with an annual average temperature of over 20 ℃ in Guangdong and Guangxi. Seedling breeding can use rootstocks such as trifoliate orange (Poncirus trifoliata Raf.), Suanju (Citrus reticulata Blanco), and Xiangcheng (C. junos). Planting disease-free container seedlings in new orchards can accelerate the formation of high-yield tree shapes. It is very important to prevent and control citrus huanglongbing. It is necessary to control the transmission of pests, such as citrus psyllid, whitefly and aphid during the shoot emergence period in spring, summer and autumn. When the temperature is between 20 ℃ and 28 ℃, the prevention and control of citrus brown spot disease is priority during the shoot emergence period in the rainy season.