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The origin and dispersal of cultivated and wild mandarin and related citrus are poorly understood. Here, comparative genome analysis of 69 new east Asian genomes and other mainland Asian citrus reveals a previously unrecognized wild sexual species native to the Ryukyu Islands: C. ryukyuensis sp. nov. The taxonomic complexity of east Asian mandarins then collapses to a satisfying simplicity, accounting for tachibana, shiikuwasha, and other traditional Ryukyuan mandarin types as homoploid hybrid species formed by combining C. ryukyuensis with various mainland mandarins. These hybrid species reproduce clonally by apomictic seed, a trait shared with oranges, grapefruits, lemons and many cultivated mandarins. We trace the origin of apomixis alleles in citrus to mangshanyeju wild mandarins, which played a central role in citrus domestication via adaptive wild introgression. Our results provide a coherent biogeographic framework for understanding the diversity and domestication of mandarin-type citrus through speciation, admixture, and rapid diffusion of apomictic reproduction.

Shiikuwasha, a citrus fruit native to Okinawa, Japan, has various cultivation lines with distinct free volatile and non-volatile components. However, the glycosylated volatiles, which are sources of hidden aromas, remain unknown. This study aimed to characterize the chemical profiles of free and glycosidically bound volatile as well as non-volatile components in the mature fruits of six Shiikuwasha cultivation lines: Ishikunibu, Izumi kugani-like, Kaachi, Kohama, Nakamoto seedless, and Ogimi kugani. Free volatiles were analyzed using solid-phase microextraction–gas chromatography–mass spectrometry. Glycosides were collected via solid-phase extraction and hydrolyzed with β-glucosidase, and the released volatiles were measured. Additionally, the non-volatile components were determined using non-targeted proton nuclear magnetic resonance analysis. Total free and bound volatiles ranged from 457 to 8401 µg/L and from 104 to 548 µg/L, respectively, and the predominant free volatiles found were limonene, γ-terpinene, and p-cymene. Twenty volatiles were released from glycosides, including predominant 1-hexanol and benzyl alcohol, with Kaachi and Ogimi kugani showing higher concentrations. Principal component analysis (PCA) revealed that taste-related compounds like sucrose, citrate, and malate influenced line differentiation. The PCA of the combined data of free and bound volatile and non-volatile components showed flavor component variances across all lines. These findings provide valuable insights into the chemical profiles of Shiikuwasha fruits for fresh consumption and food and beverage processing. [ABSTRACT FROM AUTHOR]

Citrus depressa Hayata is a citrus cultivar grown in Japan and Taiwan. To assess the differences in genetic characteristics and volatile organic components (VOCs) in the leaves and edible parts of the fruits of 23 C. depressa accessions from different geographic origins, the tissues were analyzed using cleaved amplified polymorphic sequence markers and gas chromatography-mass spectrometry. A phylogenetic cluster analysis demonstrated that Kagoshima accessions had a close genetic relationship with one another, with Okinawan "Izumi kugani-like" being the most distinct accession. The predominant volatiles in the leaves were γ-terpinene, p-cymene, limonene, and linalool. Multivariate analysis and volcano plots revealed distinct volatiles in the leaves of each cultivation region: piperitone and citronellal (Kagoshima); 5,9,9-trimethyl-spiro[3.5]non-5-en-1-one (Okinawa); and hexanal (Taiwan). Furthermore, the edible parts of Taiwanese fruits contained abundant amounts of monoterpenes, including linalool and 1,8-cineole. In contrast, Kagoshima and Okinawa accessions were rich in aldehydes and esters, respectively. In conclusion, the genetic and volatile profiles of 23 C. depressa accessions of different origins could be distinguished, and multivariate analysis suggested that C. depressa contains diverse VOCs depending on where it is cultivated. These findings demonstrate the exclusivity of C. depressa resources in each region, which could assist farmers and agro-industries in promoting food products derived from C. depressa fruits. [ABSTRACT FROM AUTHOR]

Featured Application: This study assessed the physicochemical traits, total carotenoids, metabolites, and volatile profiles of Okinawan shiikuwasha and calamansi. The physicochemical characteristics and flavor components unique to shiikuwasha and calamansi fruits provide valuable insights for food processing. The discovery of the distinct characteristics of the two citrus cultivars may be beneficial to producers and consumers, thereby supporting local agro-industries. Shiikuwasha (Citrus depressa Hayata) and calamansi (C. microcarpa Bunge) are distinct citrus species with a strong sour taste that grow naturally in Okinawa, Japan. The present study aimed to characterize the physicochemical traits, total carotenoid content, and taste/nutrient-related metabolite and volatile organic compound (VOC) profiles of the mature fruits from three shiikuwasha cultivation lines ("Izumi kugani", "Izumi kugani-like", and "Ogimi kugani") and calamansi. The shiikuwasha lines had higher ratios of soluble solids/titratable acidity but a lower total carotenoid content than calamansi. There were positive statistical correlations between total carotenoids with red, yellow, and orange indices (a*, b*, and a*/b* color spaces, respectively). Principal component analysis (PCA) revealed that shiikuwasha had higher sucrose and choline contents, while calamansi was richer in sourness-related metabolites such as citrate and malate. PCA plots displayed differences in the VOCs between the two citrus cultivars, wherein volatile accumulation was much richer in juices prepared from the whole fruits than in juices from the edible flesh parts. The plots also showed that monoterpenes and sesquiterpenes differentiated the VOC profiles of shiikuwasha and calamansi. This study reveals differences in the flavor components of the two citrus cultivars and highlights the potential uses of each in local and regional agro-business. [ABSTRACT FROM AUTHOR]