Reticulata Blanco Cv Research Articles

Comparative Transcriptome and sRNAome Analysis Suggest Coordinated Citrus Immune Responses against Huanglongbing Disease.

Citrus Huanglongbing (HLB), caused by the phloem-inhibiting bacterium Candidatus Liberibacter asiaticus (CLas), is the most devastating citrus disease, intimidating citrus production worldwide. Although commercially cultivated citrus cultivars are vulnerable to CLas infection, HLB-tolerant attributes have, however, been observed in certain citrus varieties, suggesting a possible pathway for identifying innate defense regulators that mitigate HLB. By adopting transcriptome and small RNAome analysis, the current study compares the responses of HLB-tolerant lemon (Citrus limon L.) with HLB-susceptible Shatangju mandarin (Citrus reticulata Blanco cv. Shatangju) against CLas infection. Transcriptome analysis revealed significant differences in gene expression between lemon and Shatangju. A total of 1751 and 3076 significantly differentially expressed genes were identified in Shatangju and lemon, respectively. Specifically, CLas infected lemon tissues demonstrated higher expressions of genes involved in antioxidant enzyme activity, protein phosphorylation, carbohydrate, cell wall, and lipid metabolism than Shatangju. Wet-lab experiments further validated these findings, demonstrating increased antioxidant enzyme activity in lemon: APX (35%), SOD (30%), and CAT (64%) than Shatangju. Conversely, Shatangju plants exhibited higher levels of oxidative stress markers like H2O2 (44.5%) and MDA content (65.2%), alongside pronounced ion leakage (11.85%), than lemon. Moreover, microscopic investigations revealed that CLas infected Shatangju phloem exhibits significantly more starch and callose accumulation than lemon. Furthermore, comparative sRNA profiles revealed the potential defensive regulators for HLB tolerance. In Shatangju, increased expression of csi-miR166 suppresses the expression of disease-resistant proteins, leading to inadequate defense against CLas. Conversely, reduced expression of csi-miR166 in lemon plants enables them to combat HLB by activating disease-resistance proteins. The above findings indicate that when infected with CLas, lemon exhibits stronger antioxidative activity and higher expression of disease-resistant genes, contributing to its enhanced tolerance to HLB. In contrast, Shatangju shows lower antioxidative activity, reduced expression of disease-resistant genes, significant ion leakage, and extensive callose deposition, possibly related to damage to plant cell structure and blockage of phloem sieve tubes, thereby promoting the development of HLB symptoms.

Investigation the differences in key taste-contributing substances between Shitougan(Citrus reticulata Blanco Cv. Manau Gan) and other citrus varieties

Investigation the differences in key taste-contributing substances between Shitougan(Citrus reticulata Blanco Cv. Manau Gan) and other citrus varieties

Mandarin orange (Citrus reticulata Blanco cv. Batu 55) ripeness parameters prediction using combined reflectance-fluorescence images and deep convolutional neural network (DCNN) regression model

This paper presents a novel approach for predicting the ripeness parameters of Mandarin oranges (Citrus reticulata Blanco cv. Batu 55) using a Deep Convolutional Neural Network (DCNN) regression model. The proposed method leverages the combined reflectance-fluorescence images of the fruit. The use of reflectance-fluorescence imaging enables the extraction of more features and information, which contributes to the accurate assessment of fruit ripeness. A comparison between the prediction model using a single Red-Green-Blue (RGB) image from both measurement modes and a combination image from both modes has been made. CNN regression model images with XSE_ResNet50 architecture to predict soluble solid content (SSC), acidity, firmness, and brix-acid ratio. Experimental results demonstrate that the fluorescence image (3 channels input) and the combined reflectance-fluorescence image (6 channels as input) accurately predict maturity parameters. The fluorescence image combined with DCNN performed well in predicting acidity and brix-acid ratio with R2 training/testing of 0.83/0.78 and 0.94/0.88 consecutively. For the SSC and firmness prediction, the reflectance-fluorescence (6 channels) images provide the best accuracy with R2 testing of 0.86/0.81 and 0.91/0.84. This accuracy is higher compared to the conventional image features-based model. Overall, these results show that reflectance-fluorescence images in a visible wavelength regime combined with the DCNN model could enhance the prediction accuracy of citrus maturity parameters.

Effect of the gellan-based edible coating enriched with oregano essential oil on the preservation of the ‘Tardivo di Ciaculli’ mandarin (Citrus reticulata Blanco cv. Tardivo di Ciaculli)

Mandarin, a globally recognized fruit esteemed for its nutritional content and bioactive compounds, as well as aromatic qualities, faces the critical challenge of post-harvest shelf life impacting its marketability and appeal to consumers. This study aims to assess the efficacy of edible coatings in preserving “Tardivo di Ciaculli” mandarin (Citrus reticulata Blanco cv. Tardivo di Ciaculli). Two distinct edible coating formulations, denoted as EC1(comprising gellan gum, glycerol, calcium chloride, and distilled water) and EC2 (comprising gellan gum, glycerol, calcium chloride, distilled water, and 2% oregano essential oil), were subjected to comparative analysis against control samples (CTR). In the experimental trial, mandarin fruits were immersed in the respective edible coating solutions for approximately 5 min and promptly stored at 6 ± 1°C. Qualitative, nutraceutical, microbiological, and sensory analyses were conducted throughout the cold storage period (7, 14, and 24 days at 6 ± 1°C) and during three distinct shelf-life phases (I shelf-life: 7 days at 6 ± 1°C plus 7 days at 15 ± 1°C; II shelf-life: 14 days at 6 ± 1°C plus 7 days at 15 ± 1°C; III shelf-life: 24 days at 6 ± 1°C plus 7 days at 15 ± 1°C). Chemical analysis of the oregano essential oil in EC2 revealed the presence of 27 compounds, with carvacrol being the predominant chemical, constituting 83.42% of the total oil. The findings indicate that the application of edible coatings effectively preserved the quality parameters of mandarin fruits, minimizing weight loss and water loss. Notably, the microbiological analysis, using a culture-dependent approach, demonstrated that EC2, incorporating oregano essential oil, exhibited the capability to diminish the viability of molds throughout the entire study duration, thereby extending the shelf life of mandarin fruits.

Extraction of high methoxyl pectin from unripe waste Ponkan mandarine (Citrus reticulata Blanco cv. Ponkan) with an eco-friendly solvent

The aqueous batch extraction of pectin from unripe Ponkan mandarin was evaluated for potential application in the food industry. A small central composite design with 4 variables (temperature, volume to mass ratio, pH, and mean particle size) and 3 levels was applied for pectin extraction optimization. Also, the kinetic of the pectin yield extraction was investigated at temperatures 70–90 °C, stirring rate of 100–700 rpm, ultrasound pretreatment system, and modeling using four mathematical models. The pectin extraction process was evaluated by yield of pectin and esterification degree. FTIR, TGA, and DTA were performed to evaluate the quality of pectin obtained. The small central composite design demonstrated that temperature and volume to mass ratio were significant variables, and the highest yield of pectin extraction was 11.62 % obtained at temperature and volume to molar ratio of 81.9 °C and 33.9 v/w %, respectively. Besides, the esterification degree showed higher than 70 % for all extraction conditions, suggesting high methoxyl pectin. The kinetics showed the stirring rate and the ultrasound pretreatment did not cause any significant alteration, while high temperatures proved to be beneficial to the rate and the yield of the pectin extraction. The best fit was provided by Fick's law, suggesting the extraction process is limited by internal mass transfer. FTIR showed the functional groups expected for pectin, and TGA and DTA indicated that the pectin obtained is proper for most food products, as only above 200 °C the pectin should degrade.

Development of Triploid Seedless Nagpur Mandarin (Citrus reticulata Blanco) through Endosperm Rescue

Nagpur mandarin is a popular table fruit across India and is exported to various countries. Only 1% of the total production is processed into various products. The development of seedless cultivars will boost agricultural incomes by enhancing the potential for export and processing. At present, only a couple of commercially seedless varieties are available, but these have yet to become popular. A research study was undertaken to quickly develop a high-quality seedless variety of Nagpur mandarin by combining the available technologies, viz., endosperm rescue, somatic embryogenesis, and mini-grafting, at CCRI, Nagpur. Complete plantlets of C. reticulata Blanco cv. Nagpur mandarin was successfully regenerated from hybrid endosperm tissue via somatic embryogenesis after attempting various permutations and combinations of media at various stages of regeneration, right from the primary callus to complete plantlet production. Maximum response (93.33%) and survival (91.67%) for primary callus induction were obtained in Murashige and Tucker (MT) + Malt Extract (ME) + Casein Hydrolysate (CH) (500 mg/L) +2,4-dichlorophenoxyacetic acid (2,4-D) (2 mg/L) medium. Maximum stimulation for embryogenesis and morphogenesis occurred in 2MT + CH (500 mg/L) + adenine sulfate (ad.s) (2 mg/L) + Benzyl Adenine (BA) (0.25 mg/L). The highest response (95.84%) for shoot differentiation occurred in MT + adenine sulphate (2 mg/L) + Gibberellic Acid (GA3) (1 mg/L) + BA (1 mg/L) (94.85%). The surviving plantlets were tested for ploidy status through flow Cytometry, chromosomal counting/cytogenetic technique, leaf morphology, stomatal characteristics, and the appearance of prominent thorns. In initial evaluation trials, the fruits of the triploid field-planted trees were found to be commercially seedless. These results demonstrated the recovery of stable triploids from the hybrid endosperm via somatic embryogenesis, which is the first of its kind in the field of Citrus triploid breeding in India.

Evaluation of Antioxidant Activity and Drug Delivery Potential of Cell-Derived Extracellular Vesicles from Citrus reticulata Blanco cv. 'Dahongpao'.

Plant extracellular vesicles (PEVs) have attracted increasing attention due to their rich composition, good antioxidant and anti-inflammatory activity, and ability to transport drugs. As a common fruit, citrus is an ideal material for extracting PEVs because of the diversity and abundance of bioactive substances in it. In our study, citrus-derived extracellular vesicles (CEVs) were extracted from red mandarin (Citrus reticulata Blanco cv. 'Dahongpao') and it was found that they contain high levels of lipids, proteins, and carbohydrates. The high levels of total phenols and total flavonoids suggest that CEVs have good chemical antioxidant properties. We also demonstrated through cell experiments that CEVs have significant antioxidant and anti-inflammatory effects. Furthermore, we found that CEVs have an encapsulation rate of 71.5 ± 0.19% and a high drug-carrying capacity of 4.96 ± 0.22% and can enhance antioxidant and anti-inflammatory activity when loaded with tangeretin. Our results show that CEVs contain abundant bioactive components, have low toxicity, exhibit good antioxidant and anti-inflammatory properties, and can serve as drug delivery agents. This study has important implications for utilizing citrus materials and developing natural anti-oxidative and anti-inflammatory biomaterials.

First Report of Fruit Rot Caused by Fusarium graminearum on Ponkan (Citrus reticulata Blanco cv. Ponkan) in China.

Ponkan (Citrus reticulata Blanco cv. Ponkan) is a Chinese citrus species with tasty fruit. In November 2021, an unknown postharvest disease of Ponkan fruit caused nearly 15% losses of 2000 fruits in Nanchang, Jiangxi Province (28.68° N, 115.85° E). The initial fruit's surface necrosis was brown (Xu et al. 2022) (Figure 1A). Disease spots spread to the entire fruit, white or grey hyphae appeared, and the fruit rotted. Twenty diseased fruits were surface-disinfested with 2% sodium hypochlorite and 75% ethanol, then rinsed with sterile distilled water to isolate the pathogen. Diseased tissue sections (5 × 3 mm) were incubated on potato dextrose agar (PDA) for 7 days at 25°C. Twelve of 15 monoconidial isolates have similar morphology. On PDA, the isolates produced copious white aerial mycelia. After 5-7 days on straw juice medium, two types of conidia appeared (Rice straw 60 g, Agar 20 g, distilled water 1000 mL) (Figure 1E-I). Macroconidia were abundant, falcate, slender, and slightly curved with 0-8 septa, mostly 4-5 septa (average 41.70 × 3.81 m, n=100) (Figure 1J). Microconidia were globose, oval, or piriform with 0-1 septa, 2.72 to 8.57 × 2.53 to 7.47 m (average 5.49 × 4.52 m, n=50) (Figure 1L), and chlamydospores were not observed. Conidial and colony morphology identified 12 monoconidial isolates as Fusarium graminearum (Fisher et al., 1982; Yulfo-Soto et al., 2021). Genomic DNA was extracted from three isolates using a DNA Extraction Kit (Yeasen, Shanghai, China). The ITS1/4 region combined with partial gene fragments of translation elongation factor-1 alpha (TEF-1α, primer TEF1/2, O'Donnell et al. 1998), RNA polymerase second largest subunit (RPB2, primer fRPB2-5F/7cR, Liu et al. 1999) and β-tubulin (β-tub, primer Bt2a/2b, Li et al. 2013) from the isolates were amplified and sequenced. The three tested isolates showed identical gene sequences. Sequences amplified from one representative isolate (PG16) have been submitted to GenBank. BLAST searches revealed that ITS (OM019317), TEF-1α (OM048103), RPB2 (ON364348), and β-tub (OM048104) had 99 to 100% identity compared with F. graminearum (MH591453.1, KX087136.1, MF662636.1, and MZ078952.1, respectively) in GenBank. The phylogenetic analysis combined ITS - TEF-1α - RPB2 (O'Donnell et al. 2015) concatenated sequences using MEGA7.0 (Mao et al. 2021) showed the isolate was clustered with the F. graminearum clade with 100% bootstrap support (Figure 2). The isolate PG16 was used for pathogenicity tests. Ponkan fruits were surface-disinfested with 75% ethanol and rinsed with sterile distilled water three times. Then, 30 punctured wound fruits (2-mm-diameter, 2-mm-depth) with a sterile needle and 30 unwounded fruits were inoculated with conidial suspension (10 µL, 3.0 × 105 conidia/mL). while the control fruits were inoculated with 10 µL sterile distilled water. All fruits were incubated at 25°C and 90% relative humidity. Two days later, all wounded fruits inoculated with conidial suspension showed disease spots, similar symptoms to the original rotten fruits (Figure 1D). Control and conidial-inoculated unwounded fruits were healthy (Figure 1B-C). The Pathogenicity test was repeated twice, and similar symptoms were observed. Morphologically and molecularly, the re-isolated fungus matched the inoculated isolate. First report of F. graminearum causing Ponkan fruit rot in China. As Ponkan is an important citrus crop with high economic value in China, identification of the causing agent, F. graminearum, for fruit rot allows the development of control measures to manage this disease.

Identification of Photosynthesis Characteristics and Chlorophyll Metabolism in Leaves of Citrus Cultivar (Harumi) with Varying Degrees of Chlorosis.

In autumn and spring, citrus leaves with a Ponkan (Citrus reticulata Blanco cv. Ponkan) genetic background (Harumi, Daya, etc.) are prone to abnormal physiological chlorosis. The effects of different degrees of chlorosis (normal, mild, moderate and severe) on photosynthesis and the chlorophyll metabolism of leaves of Citrus cultivar (Harumi) were studied via field experiment. Compared with severe chlorotic leaves, the results showed that chlorosis could break leaf metabolism balance, including reduced chlorophyll content, photosynthetic parameters, antioxidant enzyme activity and enzyme activity related to chlorophyll synthesis, increased catalase and decreased enzyme activity. In addition, the content of chlorophyll synthesis precursors showed an overall downward trend expected for uroporphyrinogen III. Furthermore, the relative expression of genes for chlorophyll synthesis (HEMA1, HEME2, HEMG1 and CHLH) was down-regulated to some extent and chlorophyll degradation (CAO, CLH, PPH, PAO and SGR) showed the opposite trend with increased chlorosis. Changes in degradation were more significant. In general, the chlorosis of Harumi leaves might be related to the blocked transformation of uroporphyrinogen III (Urogen III) to coproporphyrinogen III (Coprogen III), the weakening of antioxidant enzyme system activity, the weakening of chlorophyll synthesis and the enhancement in degradation.

Declined photosynthetic nitrogen use efficiency under ammonium nutrition is related to photosynthetic electron transport chain disruption in citrus plants

Nitrogen (N) is an essential nutrient for citrus growth and development. Previously, we identified citrus as an ammonium (as NH4+-N or AN) sensitive plant; however, the mechanism underlying the changes in photosynthetic physiology in response to AN stress remain unclear. ‘Lugan’ (Citrus reticulata Blanco cv. Ponkan) citrus seedlings were sand cultivated in the presence of two forms of N (AN and nitrate as NO3−-N or NN), and three N levels (1, 4 and 8 mmol L−1, as N1, N4 and N8). Biomass, leaf N concentration per unit leaf area (LNC), gas exchange, relative chlorophyll value (SPAD), photosynthetic N use efficiency (PNUE), chlorophyll a fluorescence, reactive oxygen metabolism, and non-structural carbohydrates (NSC) were determined. Compared with NN, AN significantly inhibited the growth of citrus seedlings, accompanied by a reduced net photosynthetic rate at N4 and N8, as well as LNC at N4, with a concomitant decline in PNUE. Leaf NSC, SPAD, light energy absorption and trapping were remarkably elevated by AN, which damaged the oxygen-evolving complex and increased the heat dissipation, resulting in disruption of the photosynthetic electron transport chain. Moreover, increased superoxide anion, H2O2, and malonaldehyde content, and downregulated superoxide dismutase, peroxidase, and catalase activities were also observed in citrus leaves under AN. However, the severity of these adverse effects of AN in citrus plants increased with N levels. Overall, these results indicate that AN supply reduces PNUE by disrupting the photosynthetic electron transport chain, which inhibits the growth of citrus seedlings.

Microemulsion of essential oils from citrus peels and leaves with anti-aging, whitening, and irritation reducing capacity

Although citrus essential oil is frequently used in cosmetics as fragrance, the biological activities related to skin benefits have been rarely investigated. This study aimed to investigate the anti-skin aging and anti-melanogenic effects of citrus oils and develop microemulsion system to reduce the irritation capacity of citrus oils. Oils from leaves and fruit peels of Citrus aurantifolia (Christm.) Swing and Citrus reticulata Blanco cv. Shogun were from hydro-distillation. Their chemical composition was analyzed using gas chromatography/mass spectrometry. Antioxidant activities were determined in terms of free radical scavenging activities, ferric reducing antioxidant power, and lipid peroxidation inhibition. Anti-aging and anti-melanogenic activities were investigated using related enzyme activity analysis. Oils with the most potent biological activities were selected for further incorporation into microemulsion. The irritation capacity of native and citrus microemulsion were investigated in human volunteers. Citrus oils comprised a range of chemicals, with limonene being a key component. All citrus oils demonstrated powerful antioxidative activities. C. reticulata dried peel oil significantly inhibited collagenase and tyrosinase activities, resulting in promising anti-aging and whitening properties. C. reticulata oil derived from dried peels (CR3) had a higher yield and more potent activity than the oils taken from fresh leaves and peels. Therefore, CR3 was developed into a microemulsion in which the internal droplet size was 266.5 ± 14.1 nm and the narrowest PDI of 0.396 ± 0.068. Microemulsion could significantly reduce the skin irritation property of CR3 in human volunteers. In conclusion, CR3 microemulsion was suggested as effective and safe for further cosmeceutical applications.

Impact of citrus species on the biological characteristics and life table parameters of Eutetranychus orientalis (Klein) (Acari: Tetranychidae)

Biological characteristics and life table parameters of Eutetranychus orientalis (Klein) were revealed on four different citrus species: grapefruit (Citrus paradisi Macf. cv. Star Ruby), lemon (C. limon (L.) Burm. f. cv. Meyer), mandarin (C. reticulata Blanco cv. Okitsu) and orange (C. sinensis L. cv. Washington Navel) under laboratory conditions. Results show that oviposition period, fecundity, and life table parameters varied significantly depending on the host plant species. Furthermore, host plant species had little effect on immature development, except for the teleiochrysalis and total developmental period, which was significantly shorter on lemon (13.77 days for females, 12.67 days for males). Total mean numbers of eggs laid by E. orientalis was 15.92 on mandarin and 29.78 on lemon. In addition, intrinsic rate of increase (rm), net reproductive rate (R0), finite rate of increase (λ) and doubling time (DT) are 0.12 day–1, 10.41 ♀/♀, 1.13 day–1 and 5.59 days for lemon, 0.17 day–1, 22.36 ♀/♀, 1.19 day–1 and 4.04 days for grapefruit, respectively. However, shortest and longest mean generation times (To) were obtained at 18.26 days on orange and 19.37 days on grapefruit. Our results demonstrate that intergeneric differences of Citrus should be considered when determining E. orientalis population abundance and dynamics in field conditions.

Effects of Foliar Spraying with Different Concentrations of Selenium Fertilizer on the Development, Nutrient Absorption, and Quality of Citrus Fruits

Selenium (Se) fertilizer has a good effect on many field crops, but there are few reports on the application of Se fertilizer on citrus. We investigated the effects of 0 mg/L (CK, water treatment), 50 mg/L, 100 mg/L, 150 mg/L, and 200 mg/L sodium selenite aqueous solutions on the growth, nutrition, and fruit quality of 15-year-old citrus unshiu (Citrus reticulata Blanco cv. Succosa). The results showed that a low concentration of Se fertilizer promoted the growth and development of the citrus plan, and a high concentration of Se fertilizer was found to slightly inhibit the growth and development of the plant. Among the different treatment groups, 150 mg/L selenium fertilizer showed have the best effect on these evaluated parameters. The results thus suggest that 150 mg/L of Se fertilizer promotes the formation of chlorophyll in the leaves of the test plant and increases the longitudinal and transverse diameter of the fruits and weight of single fruit, significantly enhancing the activity of antioxidant enzymes in the leaves, promoting the absorption of nutrients in the leaves, increasing the contents of total sugar and vitamin, and decreasing the acidity in the fruits and the pericarp thickness. It also promoted the accumulation of the total selenium content in the leaves and fruits and consequently improved the quality of the fruits. These results showed that appropriate concentration of Se treatment can improve the activity of antioxidant enzymes to enhance plant stress resistance, regulate the content of sugar and acid in fruits, and improve the quality of fruits.

Gum Arabic Edible Coating Reduces Postharvest Decay and Alleviates Nutritional Quality Deterioration of Ponkan Fruit During Cold Storage.

The storability recession during storage limits the postharvest storage life of Ponkan (Citrus reticulata Blanco cv. Ponkan) fruit and its nutritional value, which potentially lead to huge losses. To develop an effective technique to reduce Ponkan fruit postharvest decay and to maintain the nutritional quality, the preservation effect of 9, 12, and 15% postharvest gum arabic (GA) coatings on Ponkan fruit was investigated. The 12 and 15% GA coatings effectively reduced fruit decay as well as weight loss, retained higher total soluble solids (TSS) content, suppressed titratable acidity (TA) degradation, and postponed the rise in ripening index (RI). Moreover, the 12% GA-coated fruit exhibited a lower respiration rate, electrical conductivity, and malondialdehyde (MDA) accumulation than the uncoated (control) fruit. The 12% GA coating treatment decreased the loss of ascorbic acid (AsA), total phenols, and total flavonoids and maintained higher amounts of non-enzymatic antioxidants. Furthermore, the 12% GA coating treatment increased antioxidant enzymes' activities as well as delayed the reduction of total antioxidant capacity (TAC). These results suggest that, with the cold storage increasing time, the 12% GA-coated fruit exhibited better postharvest storability and higher nutritional quality than the control fruit. The GA coating treatment could be used as a commercial wax to improve postharvest storability, extend its storage life, and maintain the nutritional value of Ponkan fruit up to 120 days of cold storage.

Identification of Lasiodiplodia pseudotheobromae Causing Fruit Rot of Citrus in China

Considering the huge economic loss caused by postharvest diseases, the identification and prevention of citrus postharvest diseases is vital to the citrus industry. In 2018, 16 decayed citrus fruit from four citrus varieties—Satsuma mandarin (Citrus unshiu), Ponkan (Citrus reticulata Blanco cv. Ponkan), Nanfeng mandarin (Citrus reticulata cv. nanfengmiju), and Sugar orange (Citrus reticulata Blanco)—showing soft rot and sogginess on their surfaces and covered with white mycelia were collected from storage rooms in seven provinces. The pathogens were isolated and the pathogenicity of the isolates was tested. The fungal strains were identified as Lasiodiplodia pseudotheobromae based on their morphological characteristics and phylogenetic analyses using the internal transcribed spacer regions (ITS), translation elongation factor 1-α gene (TEF), and beta-tubulin (TUB) gene sequences. The strains could infect wounded citrus fruit and cause decay within two days post inoculation, but could not infect unwounded fruit. To our knowledge, this is the first report of citrus fruit decay caused by L. pseudotheobromae in China.

Expression of miRNAs and their target genes in roots of ‘Sanhu’ tangerine (Citrus reticulata blanco cv. ‘Sanhu’) in response to Candidatus Liberibacter asiaticus infection

MicroRNA (miRNA) profiles were studied in roots of ‘Sanhu’ tangerine plants with and without Candidatus Liberibacter asiaticus (CLas) infections by using solexa sequencing to investigate the possible involvement of miRNAs in the pathogenesis of Citrus Greening (Huanglongbing) disease. A total of 186 known miRNAs and 71 novel miRNAs were thus identified. Of them, 37 known and 18 novel miRNAs were significantly different in their expression patterns in roots of CLas-free and CLas-infected plants. CLas infection induced de novo expression of 6 known miRNAs and up-regulated the expression of 13 known miRNAs. It also prevented the expression of 11 known miRNAs and down-regulated the expression of 7 others. A total of 316 genes were predicted to be the targets of these differentially expressed miRNAs. Particularly, 34, 28, 21, and 20 genes were predicted to be the respective targets of cre-miR156a, cre-miR396b, cre-miR396g-5p, and cre-miRn70. The predicted putative target genes are known to be involved in stress response, plant growth and development, transcription, and metabolism. Quantitative analyses of the expression of several representative miRNAs and their target genes were generally in agreement with the predicted expression patterns (inverse proportion). Further research to unravel the interactions between these miRNAs and their target genes and determine the associated biological and pathological significance is recommended.

Ammonium nutrition inhibits plant growth and nitrogen uptake in citrus seedlings

Nitrogen (N) is an essential mineral nutrient for plant growth. Appropriate N fertilization may enhance the efficiency of N use and improve crop yield. However, the effects of N form and level on citrus plants are not well understood. We hypothesized that citrus plants are ammonium (as NH4+-N or AN) partial or insensitive based on the characteristics of preferential growth in the acidic red soil of southern China, where AN is the dominant N form in the soil. Citrus (Citrus reticulata Blanco cv. Ponkan) seedlings were cultivated in sand in the presence of three N levels (1, 4 and 8 mmol L−1) supplied in two N forms (AN; nitrate, as NO3--N or NN). Biomass, root morphology, leaf characteristics, N uptake, and assimilation were determined. Compared with NN treatment, plant growth characteristics, including biomass, growth rate, root and leaf characteristics were all markedly inhibited under AN conditions, resulting in malondialdehyde (MDA) accumulation throughout the plants, except the specific leaf area. Under AN conditions, higher N concentration and free amino acid (FAA) content were observed, while N accumulation, soluble protein content, and the activities of nitrate reductase (NR), glutamine synthetase (GS) and glutamate synthase (GOGAT) in root and leaf were reduced, except for GOGAT in root. Moreover, the trend in these changes was amplified by increasing N supply, and significant interactions between N form and level were also found. Taken together, our results demonstrate that citrus plants are highly ammonium sensitive, the findings provide a theoretical basis for the optimized N management in the high-quality production of citrus.

Rheological characterization of a pectin extracted from ponkan (Citrus reticulata blanco cv. ponkan) peel

The rheological properties of the optimized high-methoxyl pectin (PPOP), obtained from ponkan peel using nitric acid extraction (pH 1.6, 100 min, 36 ml/g liquid:solid ratio) were characterized. The flow behavior of aqueous and 0.1 M NaCl solutions at concentrations of 1%, 3% and 5% (w/w) was evaluated. The apparent viscosity of the solutions was directly related to the concentration. At the same concentrations and low shear rates the apparent viscosity values were close to those of a commercial citrus pectin. However, at higher shear rates, PPOP had a more shear thinning behavior. For both pectins, the presence of 0.1 M NaCl did not affect the apparent viscosity. The influence of pH, pectin and sucrose concentration on the gelling behavior of PPOP was investigated. Gelation occurred at pH < 3.5 and the strongest gel was obtained with 2.5% (w/w) pectin and 60% (w/w) sucrose at pH 2.5. The gel prepared under these conditions had viscoelastic behavior comparable to the gel prepared with a high-methoxyl commercial citrus pectin under the same conditions and displayed high thermal stability.

Comparative Metabolite Profiling of Four Citrus Peel Cultivars via Ultra-Performance Liquid Chromatography Coupled with Quadrupole-Time-of-Flight-Mass Spectrometry and Multivariate Data Analyses.

Citrus plants are one of the most economical fruit bearing trees grown worldwide for their medicinal use as well as for the flavor and food industry. This study attempts to characterize the metabolome difference in polyphenols of four Citrus species fruit peels; C. reticulata Blanco cv. Egyptian, C. sinensis (L.) Osbeck cv. Olinda Valencia, C. aurantiifolia Swingle cv. Mexican and C. paradisi Macfad. cv. Duncan via ultra-performance liquid chromatography coupled with quadrupole-time-of-flight-mass spectrometry platform. A total of 163 metabolites were characterized of which 28 were detected for the first time in Citrus cultivars including eight coumarin derivatives, three cinnamic acids conjugates, one polymethoxyflavone, 5 O-glycosides, 2 C-glycosides, three flavone-di-O-glucosides and six acetyl sugar derivatives of luteolin and kaempferol in addition to oxygenated and methylated fatty acids. Flavonoids amounted for the most abundant secondary metabolites class in the studied Citrus peels. The relative variability among these Citrus peels was estimated using clustering analysis with flavonoids accounting for cvs. segregation. Hierarchical clustering analysis revealed the chemical similarity of C. reticulata, C. sinensis and C. paradise peels and being distant them from that of C. aurantiifolia. To the best of our knowledge, this study provides the first report for metabolite compositional differences in these four Citrus peels.

The effects of transportation temperature on the decay rate and quality of postharvest Ponkan (Citrus reticulata Blanco) fruit in different storage periods

Ponkan (Citrus reticulata Blanco cv. Ponkan) is one of the widely grown and economically important citrus fruit species in China. Present study investigated the dynamic changes of Ponkan fruit’ storability in different storage period and under alternating temperature during the postharvest transportation and shelf life, aiming to find out an efficient and energy-saving transportation scheme for Ponkan fruit at different storage stage. The results showed that, the elongation of storage time and the higher transport temperature led to the increase of decay rate. The juice yield continued to decrease, without affecting by the transportation temperatures. The rind color turn yellow rapidly (with the citrus color index (CCI) increased from 3.61 to 9.25) during the first two months, and remained stable during the following period. The higher transportation temperature accelerated the rind color development. The total soluble solids (TSS) increased during the first month (from 11.21% to 13.25%), remained stable in the second and third months, and then decreased slightly in the fourth month, which was not evidently influenced by the transportation temperature. The titratable acidity (TA) showed a continuous decline which was accelerated by the high transportation temperature. The ethanol and aldehyde contents continue to increase and were not significantly affected by the transportation temperature. The total flavonoids content decreased during the transportation and shelf life of the newly harvested Ponkan fruit, while remained stable and was not significantly affected by the transportation temperature in the four months of storage. The alternating temperature of transportation affected the storability of Ponkan fruit at different storage periods. These finding provided a theoretical basis for the selection of transportation temperature from economic perspective.