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Concept: Rutaceae

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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

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Citrus bacterial canker is a disease that has severe economic impact on citrus industries worldwide and is caused by a few species and pathotypes of Xanthomonas. X. citri subsp. citri strain 306 (XccA306) is a type A (Asiatic) strain with a wide host range, whereas its variant X. citri subsp. citri strain Aw12879 (Xcaw12879, Wellington strain) is restricted to Mexican lime.

Concepts: Citrus, Taxonomic rank, Rutaceae, Persian lime

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Citrus limon L. (lemon, family: Rutaceae) is the third most popular edible fruit among the Citrus species. Our previous study has shown the significant antiplatelet activity of lemon extracts. The aim of the present study is to identify the features (retention time, m/z) associated with the antiplatelet activity of lemons by correlating a platelet aggregation assay with ultra-performance liquid chromatography single quadrupole mass spectrometry-based chemometrics analysis. The primary bioactivity-guided test results revealed that the butanol (BA) and ethyl acetate (EA) liquid-liquid extraction sections of the ethanol extract of lemons had significant inhibitory effects on platelet aggregation. Upon further separating the combined BA and EA sections with a silica column, four different active fractions were obtained, and their LC-MS data were collected. After modeling by two multivariate statistical techniques, namely, principal component analysis and orthogonal partial least squares discriminate analysis seven markers were predicted, identified, and tentatively classified as priority markers of bioactivity in lemons. Among them, the antiplatelet activity of four marker compounds, namely, oxypeucedanin hydrate, citric acid, diosmin, and limetin at concentrations lower than 300 μM was confirmed. Moreover, the specific mechanism of limetin interaction with the TP β receptor of thromboxane A2 and the effect of limetin on the PI3 K/Rap-1b signaling pathway through the βγ subunit of GPCR (i) in platelet aggregation were studied by differential proteomic analysis to illustrate the validity and persistence of these markers for application in lemon fruit platforms.

Concepts: Protein, Citrus, Analytical chemistry, Citric acid, Orange, Essential oil, Lemon, Rutaceae

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The Asian citrus psyllid (ACP), Diaphorina citri Kuwayama (Hemiptera: Psyllidae) is a devastating pest of Citrus spp. The aim of present study was to investigate the development and mortality of ACP on citrus (Citrus sinensis) (healthy and Huánglóngbìng- (HLB) diseased) and jasmine (Murraya paniculata) plants at various temperatures. Two new Isaria strains were collected from citrus orchards of Fuzhou (China), and HLB-diseased plants were verified by running PCR for 16S gene of Candidatus Liberibacter asiaticus (CLas). Development observations were recorded for egg, nymph and adult stages on all plants and three different temperatures (20, 25 and 30 °C) whereas mortality observations were recorded for the nymph (fifth instar) and adults on all plants at 25 °C. Field collected Isaria strains were belonged to previously reported Chinese strains under Maximum Parsimony (MP) and Maximum Likelihood methods, as well as, CLas isolates were belonged to previously reported Chinese isolates under MP and Neighbor-Joining methods. The fastest development and mortality was observed on HLB-diseased plants whereas longest time was taken by development and mortality completion on jasmine plants at all temperatures. The fastest developmental times of egg, nymph (first to fourth and fifth instar) and adult stages were ranged from 3.02 to 3.72 d, to 7.63-9.3 d, 5.35-5.65 d and 24.46-28.47 d on HLB-diseased plants at 30-20 °C, respectively. On the other hand, I. javanica caused the fastest mortality of nymphs and adults (32.21 ± 4.47% and 19.33 ± 4.51%) on HLB-diseased plants with the concentration of 1 × 108 conidia.mL-1 after 3 d and 7 d, respectively. It is concluded that there is a need for extensive molecular work to understand the extra-development and mortality of ACP on diseased plants, because, CLas bacterium can be supportive to uptake more sap from plant phloem.

Concepts: Developmental biology, China, Maximum likelihood, Fruit, Hemiptera, Adult development, Rutaceae, Murraya paniculata

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The present study aims towards fluoride remediation from synthetic water using steam-activated carbon of Aegle marmelos (bael shell/wood apple) (BAC) and Parthenium hysterophorus (PHAC) according to batch sorption techniques. The impact of different parametric conditions viz. initial fluoride concentration (4-12 mg/L), time (0-5 h), temperature (293.15-333.15 K), adsorbent dosage (4-14 g/L), pH (4-9), and RPM (150-350) were considered for both the adsorbents. Maximum defluoridation of 89% was achieved by BAC at a concentration of 10 mg/L, adsorbent dose 6 g/L, pH 5, temperature 313.15 K, agitation speed 250 rpm, and contact time 9 h, whereas PHAC attained maximum removal of 78% at an initial concentration of 8 mg/L, adsorbent dose 10 g/L, pH 4, temperature 313.15 K, and contact time 12 h. Instrumental analysis by SEM, EDX, and FTIR confirmed about the fluoride binding ability of the adsorbents. The Langmuir isotherm model provided the best fit (R2 = 0.9962 and 0.9945) to the removal process with maximum adsorptive uptake of 16.85 and 6.22 mg/g by BAC and PHAC respectively. The adsorption phenomenon was found to obey pseudo-second-order kinetics. The endothermic, spontaneous, and feasible nature of the sorption process was confirmed by the thermodynamic study. The total costs of 1 kg adsorbent preparation were calculated as 1.122 USD and 1.0615 USD which helped us in determining the economic feasibility of the adsorbents in large-scale applications. The growth of Chlorella sorokiniana BTA 9031 was also observed to be affected by the fluoride solution. Comparing the removal efficiencies of both the adsorbents, it can be concluded that BAC shell proved to be an efficient adsorbent over PHAC for fluoride elimination from aqueous solution. Graphical abstract Defluoridation of aqueous solution using biochar derived from Aegle marmelos shell and Parthenium hysterophorus.

Concepts: Concentration, Chemistry, Thermodynamics, Adsorption, Solutions, Aqueous solution, Rutaceae, Aurantioideae

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The Asian citrus psyllid (ACP) Diaphorina citri, vector of ‘Candidatus Liberibacter asiaticus’ (CLas), the putative causal agent of citrus Huanglongbing (HLB), is controlled by application of insecticides, which, although effective, has resulted in serious biological imbalances. New management tools are needed, and the technique known as ‘trap crop’ has been attracting attention. A potential plant for use as a trap crop in the management of the ACP is Murraya koenigii (curry leaf). However, for this plant to be used in the field, it needs to be attractive for the vector and must not harbor CLas. To verify the potential of curry leaf as trap crop for the management of HLB, we investigated the ability of D. citri to transmit CLas to M. koenigii, and to other test plants, including M. paniculata (orange jasmine) and ‘Valencia’ sweet-orange seedlings. For the tests, the insects were reared on a symptomatic CLas-infected plant and allowed to feed on the three test plant species. The overall maximum transmission rate for the citrus seedlings was 83.3%, and for orange jasmine was 33.3%. Successful transmission of CLas by ACP to the curry-leaf seedlings was not observed, and it was treated as immune to CLas. Supported by the previous results that M. koenigii is attractive for ACP, these results indicate that curry leaf is an excellent candidate for use as a trap crop, to improve the management of the insect vector and consequently of HLB.

Concepts: Insect, Fern, Orange, Plant morphology, Flowering plant, Rutaceae, Murraya, Curry Tree

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Zanthoxylum L. (prickly ash) is the only genus in the Citrus L. family (Rutaceae) with a pantropical distribution. We present the first detailed phylogenetic and biogeographic study of the genus and its close relatives in the proto-Rutaceae group. Our phylogenetic analyses based on two plastid and two nuclear markers show that the genus Toddalia Juss. is nested within Zanthoxylum, that earlier generic and intrageneric classifications need revision, and that the homochlamydeous flowers of the temperate species of Zanthoxylum are the result of a reduction from heterochlamydeous flowers. The biogeographic analyses reveal a Eurasian origin of Zanthoxylum in the Paleocene or Eocene with successive intercontinental or long-range migrations. Zanthoxylum likely crossed the North Atlantic Land Bridges to colonize the Americas in the Eocene, and migrated back to the Old World probably via the Bering Land Bridge in the Oligocene or Miocene. Zanthoxylum also colonized several Pacific Islands and the Hawaiian clade shows phylogenetic incongruence between the plastid and nuclear datasets, suggesting hybridization. The Hawaiian species are one of the rare examples of endemic Hawaiian lineages that are older than the current main islands.

Concepts: Biology, Species, United States, Pacific Ocean, Biogeography, Rutaceae, Beringia, Zanthoxylum

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Diaphorina citri is a vector of the bacterial causative agent of Huanglongbing (HLB = Citrus greening), a severe disease affecting citrus crops. As there is no known control for HLB, manipulating insect behaviour through deployment of semiochemicals offers a promising opportunity for protecting citrus crops. The behavioural responses of D. citri to plant volatiles, and the identity of these plant volatiles were investigated. Volatiles were collected from host plants Murraya paniculata, Citrus sinensis, C. reshni, C. limettioides, Poncirus trifoliata, and from non-host plants Psidium guajava, Mangifera indica, Anacardium occidentale. In behavioural assays, female D. citri spent more time in the arms containing volatiles from either M. paniculata or C. sinensis compared to the control arms. When D. citri was exposed to volatiles collected from A. occidentale, they preferred the control arm. Volatiles emitted from the other studied plants did not influence the foraging behaviour of D. citri. Chemical analyses of volatile extracts from C. sinensis, M. paniculata, and A. occidentale revealed the presence of the terpenoids (E)-4,8-dimethylnona-1,3,7-triene (DMNT) and (E,E)-4,8,12-trimethyltrideca-1,3,7,11-tetraene (TMTT) in higher amounts in A. occidentale. In further behavioural bioassays, female D. citri spent less time in arms containing a synthetic blend of DMNT and TMTT compared to the control arms. Female D. citri also spent less time in arms containing the synthetic blend in combination with volatile extracts from either M. paniculata or C. sinensis compared to the control arms. Results suggest that higher release of the two terpenoids by A. occidentale make this species unattractive to D. citri, and that the terpenoids could be used in reducing colonisation of citrus plants and therefore HLB infection.

Concepts: Citrus, Fruit, Cashew, Psidium guajava, Guava, Rutaceae, Anacardiaceae, Murraya paniculata

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Consumers are aware of diet causing health problems and therefore there is an increased demand for natural ingredients that are expected to be safe and health-promoting. Many of these compounds belong to the class of flavonoids and can be divided into these five groups: flavanones, flavones, flavonols, flavanols, isoflavones and anthocyanidins. Extracts from citrus fruits are usually used as functional ingredients for several products. The aim of this paper was to develop an UHPLC-UV-ESI-HRMS method to define the metabolite profile of different parts of citrus fruit, of a particular cultivar called ‘Ovale Calabrese’, and in its main by-products. The high resolution mass spectrometry analysis allowed the identification of 27 compounds belonging to the classes of flavonoids and terpenoids. The high contents of phytochemical compounds, reveal the potential use of the ‘Ovale Calabrese’ as a rich source of nutraceutical compounds.

Concepts: Nutrition, Mass spectrometry, Citrus, Fruit, Flavonoid, Orange, Grapefruit, Rutaceae

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Composition and changes in free volatiles have been extensively studied in citrus fruit such as mandarin. However, components of glycosidically bound volatiles and changes during fruit ripening have been rarely investigated. A total of 56 glycosidically-bound volatiles were identified in fruit peel at four ripening stages. The highest concentrations in glycosidically-bound volatiles were observed for methyl salicylate in ripening fruit. Concentration of total bound volatiles increased from color conversion stage at 150days after bloom (DAB), peaked at yellow stage (190DAB), followed by a decrease at orange stage (210DAB). Satsuma mandarin fruit at different ripening stages could be separated in a partial least squares-discriminant analysis (PLS-DA) plot using glycosidically bound volatiles as variables. In total 35 glycosidically bound volatiles were identified with variable importance in projection (VIP) score exceeding 1, which may be potential markers for separating fruit at different ripening stages.

Concepts: Citrus, Fruit, Orange, Tangerine, Rutaceae, Mandarin orange, Tangor, Satsuma