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Concept: Mandarin orange


Cultivated citrus are selections from, or hybrids of, wild progenitor species whose identities and contributions to citrus domestication remain controversial. Here we sequence and compare citrus genomes-a high-quality reference haploid clementine genome and mandarin, pummelo, sweet-orange and sour-orange genomes-and show that cultivated types derive from two progenitor species. Although cultivated pummelos represent selections from one progenitor species, Citrus maxima, cultivated mandarins are introgressions of C. maxima into the ancestral mandarin species Citrus reticulata. The most widely cultivated citrus, sweet orange, is the offspring of previously admixed individuals, but sour orange is an F1 hybrid of pure C. maxima and C. reticulata parents, thus implying that wild mandarins were part of the early breeding germplasm. A Chinese wild ‘mandarin’ diverges substantially from C. reticulata, thus suggesting the possibility of other unrecognized wild citrus species. Understanding citrus phylogeny through genome analysis clarifies taxonomic relationships and facilitates sequence-directed genetic improvement.

Concepts: Citrus, Orange, Grapefruit, Tangerine, Rutaceae, Pomelo, Mandarin orange, Clementine


Mandarin orange (MO) is an important fruit crop of tropical and subtropical regions of the world. A total of 217 morphologically distinct rhizobacteria from MO orchards in 3 states of northeastern India were isolated and analyzed for 4 plant-growth-promoting (PGP) attributes: nitrogen fixation, production of indole acetic acid like substances, solubilization of phosphate, and ability to antagonize pathogenic fungi. Isolates were ranked based on in-vitro-assayed PGP attributes, and 10 superior isolates were selected to test their effect on seedling emergence and seedling growth in a completely randomized pot experiment. These 10 isolates increased seedling emergence over a noninoculated control within 45 days after sowing. Five isolates, namely RCE1, RCE2, RCE3, RCE5, and RCE7, significantly increased shoot length, shoot dry biomass, and root dry biomass of 120-day-old seedlings over the noninoculated control. The beneficial effects of 4 selected strains, namely Enterobacter hormaechei RCE-1, Enterobacter asburiae RCE-2, Enterobacter ludwigii RCE-5, and Klebsiella pneumoniae RCE-7, on growth of the seedlings were visible up to 1 year after their transfer to 8 kg capacity pots. These strains were superior both in terms of in-vitro-assayed PGP attributes and of their beneficial effect in low phosphorus soil and, thus, may be promising bioinoculants for promoting early emergence and growth of MO seedlings.

Concepts: Ethanol, Citrus, Orange, Tangerine, Rutaceae, Mandarin orange, Clementine, Tangor


Numerous coating strategies are available to control the surface properties and confer new properties to substrates for applications in energy, environment, biosystems, etc., but most have the intrinsic limitations in the practical setting: (1) highly specific interactions between coating materials and target surfaces are required for stable and durable coating; (2) the coating of bulk substrates, such as fruits, is time-consuming or is not achievable in the conventional solution-based coating. In this respect, material-independent and rapid coating strategies are highly demanded. We demonstrate spray-assisted nanocoating of supramolecular metal-organic complexes of tannic acid and ferric ions. The spray coating developed is material-independent and extremely rapid (<5 sec), allowing for coating of commodity goods, such as shoe insoles and fruits, in the controlled fashion. For example, the spray-coated mandarin oranges and strawberries show significantly prolonged post-harvest shelf-life, suggesting practical potential in edible coating of perishable produce.

Concepts: Citrus, Complex, Complexity, Surface, Orange, Differential geometry, Specific properties, Mandarin orange


Although studies have quantified bacterial transfer between hands and various materials, cross-contamination between the surface of fresh citrus fruit and the edible portions during hand peeling has not been reported. This study quantifies transfer of Salmonella to the edible portion of citrus fruit from a contaminated peel during hand peeling. Citrus fruits used for this study were Citrus sinensis (sweet orange) cultivars ‘Valencia’ and ‘Navel’, Citrus unshiu (Satsuma mandarins), Citrus reticulata × Citrus paradisi (‘Minneola’ tangelo or ‘Honeybell’), and C. paradisi (grapefruit) cultivar ‘Marsh’. An avirulent Salmonella Typhimurium LT2 (ATCC 700720) resistant to rifampin was used for all experiments. The inoculum containing approximately 9 log CFU/mL (50 μL) was spot inoculated onto the equator, stem, or styler of each fruit and allowed to dry for 24 h. Six volunteers put on single-use latex gloves and peeled inoculated fruit. Peel, edible fruit portion, and gloves were collected and enumerated separately. Three replicates of the study were performed in which each volunteer peeled two inoculated fruit of each variety (n = 36 fruit per variety). Cross-contamination from contaminated surface of citrus fruits to edible portion or gloved hands during peeling was affected by inoculation sites. Average Salmonella transfer to the edible portion ranged from 0.16% (Valencia inoculated at the equator) to 5.41% (navel inoculated at the stem). Average Salmonella transfer to gloved hands ranged from 0.41% (grapefruit inoculated at the stem) to 8.97% (navel inoculated at the stem). Most Salmonella remained on the peel of citrus fruits. The average level of Salmonella remaining on the peel ranged from 5.37% (Minneola inoculated at the equator) to 66.3% (Satsuma inoculated at the styler). When grapefruit was inoculated, the Salmonella that remained on the peel showed a bimodal pattern in which some individuals left almost all Salmonella on the peel, while others left substantially less.

Concepts: Citrus, Fruit, Orange, Grapefruit, Rutaceae, Pomelo, Tangelo, Mandarin orange


Most indigenous citrus varieties are assumed to be natural hybrids, but their parentage has so far been determined in only a few cases because of their wide genetic diversity and the low transferability of DNA markers. Here we infer the parentage of indigenous citrus varieties using simple sequence repeat and indel markers developed from various citrus genome sequence resources. Parentage tests with 122 known hybrids using the selected DNA markers certify their transferability among those hybrids. Identity tests confirm that most variant strains are selected mutants, but we find four types of kunenbo (Citrus nobilis) and three types of tachibana (Citrus tachibana) for which we suggest different origins. Structure analysis with DNA markers that are in Hardy-Weinberg equilibrium deduce three basic taxa coinciding with the current understanding of citrus ancestors. Genotyping analysis of 101 indigenous citrus varieties with 123 selected DNA markers infers the parentages of 22 indigenous citrus varieties including Satsuma, Temple, and iyo, and single parents of 45 indigenous citrus varieties, including kunenbo, C. ichangensis, and Ichang lemon by allele-sharing and parentage tests. Genotyping analysis of chloroplast and mitochondrial genomes using 11 DNA markers classifies their cytoplasmic genotypes into 18 categories and deduces the combination of seed and pollen parents. Likelihood ratio analysis verifies the inferred parentages with significant scores. The reconstructed genealogy identifies 12 types of varieties consisting of Kishu, kunenbo, yuzu, koji, sour orange, dancy, kobeni mikan, sweet orange, tachibana, Cleopatra, willowleaf mandarin, and pummelo, which have played pivotal roles in the occurrence of these indigenous varieties. The inferred parentage of the indigenous varieties confirms their hybrid origins, as found by recent studies.

Concepts: DNA, Gene, Genetics, Virus, Citrus, Population genetics, Orange, Mandarin orange


Male sterility derived from Satsuma mandarin (Citrus unshiu) has been used in Japanese citrus breeding programs to obtain seedless cultivars, which is a desirable trait for consumers. Male sterility has often been evaluated by anther development or pollen fertility; however, the inheritance and heritability of male sterility derived from Satsuma is poorly understood. In this study, we investigated the mode of inheritance and broad-sense heritability of male sterility derived from Satsuma. Initially, we evaluated the total number of pollen grains per anther and apparent pollen fertility, as indicated by lactophenol blue staining, in 15 citrus cultivars and selections to understand the male sterility of Satsuma. The results indicated that male sterility was primarily caused by decreased number of pollen grains per anther in progeny of Satsuma. We also evaluated these traits in three F1 populations (hyuganatsu × ‘Okitsu No. 56’, ‘Okitsu No. 46’ × ‘Okitsu No. 56’ and ‘Okitsu No. 46’ × ‘Kara’), of which the parents are derived from Satsuma. Individuals in these populations showed strong segregation for number of pollen grains per anther. The apparent fertility of pollen also showed segregation but was almost constant at 70%-90%. The estimated broad-sense heritability for the number of pollen grains per anther was as high as 0.898 in the ‘Okitsu No. 46’ × ‘Okitsu No. 56’ and ‘Okitsu No. 46’ × ‘Kara’ populations. These results indicated that the number of pollen grains per anther primarily determined male sterility among progeny of Satsuma, and this trait was inherited by the progeny. Development of DNA markers closely linked to male sterility using the F1 populations of ‘Okitsu No. 46’ × ‘Okitsu No. 56’ and ‘Okitsu No. 46’ × ‘Kara’ is expected to contribute to the breeding of novel seedless citrus cultivars.

Concepts: Citrus, Pollen, Tangerine, Mandarin orange, Satsuma, Fruits originating in Asia, Japanese fruit


Three essential oils (EOs) were isolated from the peel of citrus fruits Citrus reticulata L., Citrus reticulata chinase Blanco and Citrus sinensis (L.) Osbeck (Family: Rutaceae) and evaluated against Culex pipiens L.1758 (Family: Culicidae). Chemical composition indicated that the EOs were rich in essential phytochemicals including hydrocarbons, monoterpenes and sesquiterpenes. These constituents revealed some variability among the oils displaying interesting chemotypes limonene (35-51%), 1R-α-pinene (1.04-2.5%), γ-terpinene (0.46-5.65%) and sabinene (0.51-5.42%). The toxicity proved that C. sinensis oil had more effect than C. reticulata chinase and C. reticulata oils against larvae (LC50 = 15.35, 16.11 and 32.84 mg/L, respectively). However, C. reticulate was the most active as fumigant against adults (LC50 2.74 μL/L air). The in vivo effect on acetylcholine esterase (AChE), carboxyl esterase (CbE), acid phosphatase (ACP), alkaline phosphatase (ALP), adenosine triphosphatase (ATPase) and glutathione-S-transferase (GST) were also demonstrated. To the best of our knowledge, this is the first report about the chemical composition and mosquitocidal activity of C. reticulata chinase essential oils. Conclusively, the tested essential oils could be used as eco-friendly alternatives in mosquitoes control programme.

Concepts: Citrus, Fruit, Orange, Essential oil, Tangerine, Lemon, Rutaceae, Mandarin orange


Mandarin (C. reticulata), citron (C. medica) and pummelo (C. maxima) are important species of the genus Citrus and parents of the interspecific hybrids that constitute the most familiar commercial varieties of citrus: sweet orange, sour orange, clementine, lemon, lime and grapefruit. Citron produces anthocyanins in its young leaves and flowers, as do species in genera closely related to Citrus, but mandarins do not and pummelo varieties that produce anthocyanins have not been reported. We investigated the activity of the Ruby gene, which encodes a MYB transcription factor controlling anthocyanin biosynthesis, in different accessions of a range of Citrus species and in domesticated cultivars. A white mutant of lemon lacks functional alleles of Ruby, demonstrating that Ruby plays an essential role in anthocyanin production in Citrus. Almost all the natural variation in pigmentation by anthocyanins in Citrus species can be explained by differences in activity of the Ruby gene, caused by point mutations, deletions and insertions of transposable elements. Comparison of the allelic constitution of Ruby in different species and cultivars also helps to clarify many of the taxonomic relationships in different species of Citrus, confirms the derivation of commercial varieties during domestication, elucidates the relationships within the subgenus Papeda and allows a new genetic classification of mandarins.

Concepts: Gene, Evolution, Citrus, Orange, Grapefruit, Citron, Rutaceae, Mandarin orange


Citrus fruits are thought to have inhibitory effects on oxidative stress, thereby attenuating the onset and progression of cancer and cardiovascular disease; however, there are few reports assessing their effect on vascular remodeling. Here, we investigated the effect of drinking the juice of two different citrus fruits on vascular neointima formation using a cuff-induced vascular injury mouse model. Male C57BL6 mice were divided into five groups as follows: 1) Control (water) ©, 2) 10% Citrus unshiu (CU) juice (CU10), 3) 40% CU juice (CU40), 4) 10% Citrus iyo (CI) juice (CI10), and 5) 40% CI juice (CI40). After drinking them for 2 weeks from 8 weeks of age, cuff injury was induced by polyethylene cuff placement around the femoral artery. Neointima formation was significantly attenuated in CU40, CI10 and CI40 compared with C; however, no remarkable preventive effect was observed in CU10. The increases in levels of various inflammatory markers including cytokines such as monocyte chemotactic protein-1, interleukin-6 (IL-6), IL-1β, and tumor necrosis factor-α in response to vascular injury did not differ significantly between C, CU10 and CI10. The increases in cell proliferation and superoxide anion production were markedly attenuated in CI10, but not in CU10 compared with C. The increase in phosphorylated ERK expression was markedly attenuated both in CU10 and CI10 without significant difference between CU10 and CI10. Accumulation of immune cells did not differ between CU10 and CI10. These results indicate that drinking citrus fruit juice attenuates vascular remodeling partly via a reduction of oxidative stress. Interestingly, the preventive efficacy on neointima formation was stronger in CI than in CU at least in part due to more prominent inhibitory effects on oxidative stress by CI.

Concepts: Immune system, Inflammation, Citrus, Fruit, Orange, Grapefruit, Juice vesicles, Mandarin orange


The freshness of citrus fruits commonly available in the market was non-destructively assessed by Raman spectroscopy. Intact clementine, mandarin and tangerine species were characterised concerning their carotenoids skin Raman signalling in a time course from the moment they were acquired as fresh stock, supplying the market, to the physical degradation, when they were no longer attractive to consumers. The freshness was found to strongly correlate to the peel Raman signal collected from the same area of the intact fruits in a time course of a maximum of 20days. We have shown that the intensity of the carotenoid Raman signal is indeed a good indicator of fruit freshness and introduced a Raman coefficient of freshness (CFresh), whose time course is linearly decreasing, with different slope for different citrus groups. Additionally, we demonstrated that the freshness assessment could be achieved using a portable Raman instrument. The results could have a strong impact for consumer satisfaction and the food industry.

Concepts: Citrus, English-language films, Fruit, Orange, Grapefruit, Tangerine, Mandarin orange, Clementine