Breeding report of a new late-ripening citrus cultivar Chunhongtangju

Chunhongtangju tangerine, a new late-ripening and fresh-eating citrus cultivar, was selected from the bud mutation of Shatangju (Citrus reticulata Blanco), a cultivar whose cultivated area is the largest in South China. It was initially selected in 2007 for its different mature period, and the further characteristic observation on the bud mutation variety was from 2008 to 2010. To evaluate its regional adaptability, the new bud mutation variety was tested respectively at three sites (including Qingyuan, Guangzhou and Zhaoqing in Guangdong province) over eight years from 2011 to 2019. Through years of investigation on its botanical/biological characteristics and fruit quality during the citrus bearing seasons, it showed a consistent genetic stability. It was selected as the excellent bud mutation variety of common Shatangju for promotion in 2019, and it was applied for and obtained the new plant varieties right in 2021. The trees of Chunhongtangju are moderately vigorous, with high bud break rate and branch development capability. Its fruit is oblate in shape, the longitudinal and transverse diameters of fruit is 42.15 mm and 50.66 mm, respectively, and the fruit shape index is 0.83, with an orange- red or smooth orange-colored peel. The average weight per fruit is 60.2 g with a pericarp thickness of 1.9 mm, and it is easy to peel off. The pulp is orange-colored and the texture is crispy, melting and fragrant. The soluble solids content is 15.6%, the titratable acid content is 0.29%, the ascorbic acid (Vitamin C) content is 15.0 mg per 100 mL fruit juice, and the edible rate is 77.9%. The first flowering date is in mid-March,the fruit development period is about 330 days and the fruit can be harvested in late February of the next year in Qingyuan area, Guangdong province. Under the same conditions, the average yield of four-yearold trees is approximately 2868 kg per 666.7 m2 , showing the high and stable yield characteristics as Shatangju. The SSR molecular markers were employed as a genetic classification approach to discriminate this new cultivar and the control Shatangju. The results showed that there were differences between two cultivars at the genetic level. There was no significant difference in drought and disease resistance between Chunhongtangju and Shatangju, but the cold stress resistance of new cultivar is higher than that of the control. The suitable growing area is in South China and similar planting areas of Shatangju.