Citrus is widely grown all over the world, and citrus fruits have long been recognized for their nutritional and medical value for human health. However, some local citrus varieties with potentially important value are still elusive. In the current study, we elucidated the biological characteristics, phylogenetic and phytochemical profiling, antioxidants and antioxidant activities of the two local citrus varieties, namely Zangju and Tuju. The physiological and phylogenetic analysis showed that Zangju fruit has the characteristics of wrinkled skin, higher acidity, and phylogenetically closest to sour mandarin Citrus sunki, whereas, Tuju is a kind of red orange with vermilion peel, small fruit and high sugar content, and closely clustered with Citrus erythrosa. The phytochemical analysis showed that many nutrition and antioxidant related differentially accumulated metabolites (DAMs) were detected in the peel and pulp of Zangju and Tuju fruits. Furthermore, it was found that the relative abundance of some key flavonoids and phenolic acids, such as tangeritin, sinensetin, diosmetin, nobiletin, and sinapic acid in the peel and pulp of Zangju and Tuju were higher than that in sour range Daidai and satsuma mandarin. Additionally, Zangju pulp and Tuju peel showed the strongest ferric reducing/antioxidant power (FRAP) activity, whereas, Tuju peel and pulp showed the strongest DPPH and ABTS free radical scavenging activities, respectively. Moreover, both the antioxidant activities of peel and pulp were significantly correlated with the contents of total phenols, total flavonoids or ascorbic acid. These results indicate that the two local citrus varieties have certain nutritional and medicinal value and potential beneficial effects on human health. Our findings will also provide an important theoretical basis for further conservation, development and medicinal utilization of Zangju and Tuju.

Satsuma mandarin (Citrus reticulata “Unshiu”) is a global cultivar with superior fruit characteristics and ranking among the top citrus cultivars in terms of production. It is also a key contributor to citrus breeding. However, the lack of high-quality genome makes the origin of Satsuma mandarin has long been a matter of debate. Here, we assembled a gap-free, high-quality genome of Satsuma mandarin. Meanwhile, we collected and sequenced 15 indigenous citrus varieties in Zhejiang Province, 12 Satsuma mandarins, 21 citrus hybrids related to Satsuma mandarin, 10 modern citrus varieties, and 7 other mandarins. Through high-resolution genome analysis, we inferred that Satsuma mandarin originated from a cross between C. reticulata “Ruju” × C. reticulata “Bendiguang” and proposed that Satsuma mandarin most probably originated in East area in Zhejiang Province of China, where the two parents-like cultivars are still found in a sympatric region to date. These results provide new insights into the origin model of Satsuma mandarin. The spread of mandarin is also discussed, which probably associated with the culture exchange and trade activities between Japan and China from Tang Dynasty and afterwards.

Protected cultivation is a cultivation practice that plays an important role in improving crop quality. Aroma is an important flavour that assesses the quality of yuzu. In this study, C. junos cv. ‘Kitou’ grown in open fields (CJKTF) and plastic greenhouses (CJKTP) were selected as the study material. Significant differences in aroma performance between CJKTF and CJKTP were found by the olfactory senses of the members of this research group and an electronic nose, with CJKTP having a stronger aroma. Regarding VOCs, GC-MS analyses revealed 13 VOCs up-regulated and 28 VOCs down-regulated in CJKTP compared to CJKTF. Transcriptome analysis revealed that 515 genes were up-regulated and 720 genes were down-regulated in CJKTP compared to CJKTF. The differential VOCs nerolidol and γ-cadinene, and the differential genes nerolidol synthase 1 (NES1), nerolidol synthase 1-like (NES1-like), and cadinene synthase (DCS), were in the sesquiterpene synthesis pathway and showed significant correlation. NES1, NES1-like, and DCS encode terpene synthases, which may be involved in the biosynthetic pathway of nerolidol and γ-cadinene. In conclusion, the use of plastic greenhouses for cultivation may improve the quality and aroma intensity of yuzu, as well as alter the expression of related genes, compared to field cultivation. These results suggest that protected cultivation is a suitable cultivation practice to enhance the aroma of yuzu.

Citrus cultivars are propagated asexually through methods such as layering, cutting, and grafting. Grafting plays a critical role in regulating citrus fruit quality by optimizing stock–scion combinations. This study evaluated the grafting compatibility of two interstocks with Cocktail grapefruits (Citrus paradisi Macf. cv. Cocktail) by analyzing physiological and volatile traits of the fruits. We used Changshanhuyou (Citrus paradisi cv. Changshanhuyou) and Ponkan (Citrus reticulata Blanco cv. Ponkan), which are traditional citrus varieties in Quzhou, Zhejiang Province, as interstocks. Our results showed that the grapefruit fruits grafted onto Changshanhuyou exhibited higher total soluble solids (12.3 °Brix) and a brighter, more uniform peel color. The acidity of fruits grafted onto Changshanhuyou was lower than that of fruits grafted onto Ponkan and similar to the fruits from the control group that were grafted directly onto trifoliate orange. In terms of volatile organic compounds (VOCs), 974 and 577 unique VOCs were identified in the peel and pulp, respectively. In the peel, 34 (26 upregulated and 8 downregulated) and 14 (13 upregulated and 1 downregulated) differentially accumulated VOCs were identified when comparing the trifoliate orange group with Changshanhuyou and Ponkan groups, respectively. The pulp exhibited greater VOC diversity, with 272 (24 upregulated and 248 downregulated) and 199 (4 upregulated and 195 downregulated) differentially accumulated VOCs detected for the same comparisons. In conclusion, compared with direct grafting onto trifoliate orange or on Ponkan as an interstock, grafting onto Changshanhuyou resulted in better fruit quality and distinct differences in flesh flavor. These findings suggest that Changshanhuyou is a more suitable interstock for Cocktail grapefruit (Citrus paradisi Macf. cv. Cocktail) cultivation.

To investigate the genetic variation underlying the phenotypic differences between Citrus reticulata ‘Bendizao’ and its seedling mutation cultivar Citrus reticulata ‘Dongjiang Bendizao’, we performed whole-genome resequencing of both cultivars using high-throughput sequencing technology, achieving sequencing depths of 22× and 36×, respectively. Compared to the reference genome, we identified 4,150,080 and 4,081,142 single nucleotide polymorphism (SNP) loci in ‘Bendizao’ and ‘Dongjiang Bendizao’, of which only 5.41% and 5.52% were located in exonic regions. Exonic SNPs with nonsynonymous mutations or termination alteration effects yielded 3088 candidate genes. In addition, 664,149 and 627,686 insertions/deletions (InDel) loci were detected in the two cultivars, with only 1.50% and 1.57% in exonic regions, leading to the identification of 1065 genes based on differential exonic InDel loci. Kyoto Encyclopedia of Genes and Genomes (KEGG) pathway enrichment analysis revealed that the genetic variations were predominantly enriched in pathways such as RNA polymerase, phenylpropanoid biosynthesis, and plant–pathogen interaction. qRT-PCR validation of the five selected differentially expressed genes confirmed that three of them were significantly upregulated in ‘Dongjiang Bendizao’ compared with ‘Bendizao’, with fold changes ranging from approximately 4 to 13. Future functional validation of key candidates, including members of the TPS21, E2.1.1.104, RPS2, and CNGC genes, will help elucidate their regulatory networks and facilitate stress-tolerance breeding. Collectively, this study provides insights into the genomic variation between the two cultivars and establishes a theoretical foundation for cultivar identification and genetic improvement of local citrus germplasm.