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• Aluminum (Al) affected the contents of N-containing compounds in Citrus. • Al affected the activities of N metabolism–related enzymes in Citrus. • Al differentially affected N metabolism between Citrus sinensis and C. grandis. • Increased leaf GOGAT might be an index of Al–tolerance in Citrus plants. Citrus are mostly planted in tropical/subtropical acidic soil areas, and are susceptible to aluminum (Al) toxicity, which affects tree growth and fruit quality. However, the effects of Al stress on the nitrogen (N) metabolism in different Al-tolerant Citrus varieties, and whether N metabolism is related to Al-tolerance in different Citrus varieties, were remained unveiled. In the current study, Al-tolerant "Xuegan" (Citrus sinensis) and Al-sensitive "Sour pummelo" (C. grandis), were irrigated with different nutrient solutions with or without Al. Al decreased the dry weights (DW) of leaves, stems and roots, as well as the N content, the N accumulation, total soluble proteins (TSPs) and total free amino acids (TFAAs) of different tissues of C. grandis , but it increased the ratio of root DW to shoot DW. In contrast, Al did not change the parameters mentioned above, except for decreasing the content and accumulation of N in C. sinensis roots. Al did not change the content of NO 3 – in different position leaves and roots, but decreased the content of NH 4 + in C. grandis. Al decreased the content of NO 3 – in different position leaves and roots, but except for the lower leaf, Al did not change that of NH 4 + in C. sinensis. Although Al affected the activities and gene expression levels of N metabolism–related enzymes in the leaves and roots of these two Citrus species, the effects of Al on these parameters were more pronounced in C. grandis than in C. sinensis. Results from correlation analysis (CoA) and principal components analysis (PCA) indicated that the increased root DW/shoot DW and NO 3 --N content in the roots and middle/upper leaves might be the related indicators of Al toxicity, whereas the enhanced activity of leaf GOGAT might be related to the Al–tolerance in Citrus plants. In conclusion, this study preliminarily revealed that the impact of Al on N metabolism and the response of N metabolism–related indicators to Al stress in Citrus , providing scientific reference for high-yield and high-quality cultivation of Citrus grown in acidic soil areas. [Display omitted] [ABSTRACT FROM AUTHOR]

• Root traits such as root diameter, root number, root length differ among rootstocks. • The seasonal change of fine roots in Trifoliate differs from the other 3 rootstocks. • Citrus fine roots distributed 28–68 cm and −45∼−20 cm horizontally and vertically. • Fine roots' spatial distribution differs among rootstocks in different seasons. Understanding fine roots' spatial distribution and dynamics in citrus can enable proper site and time of fertilizing to improve the nutrient uptake efficiency below the root zone, reduce agricultural non-point source pollution and improve the performances. However, the seasonal changes and spatial distribution of citrus fine roots remain unclear. Here we investigated the dynamical changes and spatial distribution of fine roots in four rootstocks by 30° angle tube instillation and monthly capturing within a year with minirhizotrons. The results indicated that in the whole investigation, root diameter of Trifoliate (Poncirus trifoliata) was smallest, while root diameter and root number of Carrizo (Citrus sinensis × P. trifoliata) was biggest. In winter under water scarcity condition, root diameter, root length and root surface area of Trifoliate changed rapidly, then moderately in other seasons. However, the change pattern of Trifoliate differed obviously from that of the other three rootstocks. Fine roots of Trifoliate distributed nearest to the trunk and deepest belowground, while that of Rusk (C. sinensis × P. trifoliata) and Xiangcheng (C. junos) distributed the longest distance and the shallowest depth, respectively. Root length of Trifoliate and Rusk distributed mainly in depth of -45∼-30 cm, that of Xiangcheng distributed mostly in depth of -30∼-15 cm. However, root length of Carrizo distributed mostly in different depths in varied seasons. This research not only uncovered the differences in root traits and their changes of different rootstocks, which indicates the differences root phenology and probably contribute the differences in performances, but also revealed their root space distribution, which is very essential for citrus precise cultivation. [ABSTRACT FROM AUTHOR]

• Methylparaben (MP) efficiently inhibits the growth of P. digitatum in vitro. • MP undermines the cell wall and plasma membrane of P. digitatum. • MP destroys the mitochondria and vacuolates cytoplasmic matrix of P. digitatum. • MP disturbs the redox level and induces the antioxidant system of P. digitatum. Parabens are one of the "generally regarded as safe" salts since its lower toxicity for the environment and human health. The curative activities of methylparaben (MP) had been detected previously by applying them into coating films in some fruits. In this study, we investigated the antifungal activities and putative mechanisms of MP against Penicillium digitatum , which causes the destructive citrus green mold disease during postharvest period. The results indicated that MP inhibited the P. digitatum hyphal growth in vitro at a minimum inhibitory/fungicidal concentration of 0.40 and 0.60 g L−1, respectively. The conidial germination rates were also distinctly restrained. Under scanning and transmission electron microscopies, the treated hyphae were slender and shrunken, had defects in developing conidiophores, and exhibited apoptotic mitochondria and vacuolated cytoplasmic matrix. Meanwhile, MP damaged the plasma membrane to accelerate the intracellular substances leaking out, and induced the activity of chitinase to degrade cell wall. The MP-treated hyphae showed activated the antioxidant enzymes, superoxide dismutase and peroxidase, and stimulated the content of antioxidant glutathione. MP alleviated the disease prevalence of inoculated citrus in the fruit decay test, but did not display good preservative effect in storage experiment. Collectively, our findings basically elucidate the underlying physiological antifungal mechanism of MP against P. digitatum. [ABSTRACT FROM AUTHOR]

• HC1 is a vital binding site for Al in citrus root CW compared with pectin. • Boron regulates CW compounds via changing enzymes network to alleviate Al toxicity. • Boron supply reduced Al toxicity by decreasing Al accumulated in HC1 and pectin. Based on the soil acidification situation in citrus plantation of southern China and even worldwide, it's essential to explore improved methods for resistant aluminum (Al) toxicity in plant. Trifoliate (Poncirus trifoliate (L) Raf.) is the most common rootstock in China. The ambition of this research was to illustrate the influence of boron (B) on Al bound in cell wall (CW) and the mechanism in trifoliate seedlings. Healthy seedlings were exposed to 0 or 300 µM AlCl 3 ·6H 2 O with 10 µM B (H 3 BO 3 , control) and 50 µM B, respectively. The results displayed that Al accumulated in roots and root tips during Al exposure. However, Al content in root rips was reduced under B sufficient that reflected by lower morin fluorescence intensity compared to B10-treated roots. More specifically, B addition abates the Al content in root CW, manifested in lower Al content in pectin and hemicellulose 1 (HC1), with HC1 being more prominent. Moreover, B addition inhibited the pectin methyl-esterase (PME) activity to reduce pectin content, while increasing the xyloglucan endotransglucosylase (XET) and xyloglucan endotransglucosylase-hydrolase (XEH) activity. Thereby HC1 content was decreased, ultimately suppressing the bound site of Al in pectin and HC1, and diminished Al content in CW with B supply. Collectively, our results illustrate that B supply was attributed to the mitigation effect of B on Al toxicity by induced devaluation of Al accumulation in CW, which was associated with the reduction of binding Al with pectin and HC1 by regulating compounds of CW through adjusting CW enzymes (PME, XET, and XEH). [ABSTRACT FROM AUTHOR]

• Drought reduced mycorrhizal colonization, mycelium length, and GRSP levels. • AMF boosted fructose, glucose, arabinose, fucose, and inositol under drought. • AMF reduced sucrose while up-regulated PtAI, PtNI , and PtSPS under drought. • AMF increased trehalose under drought, along with up-regulated PtTPS1 and down-regulated PtTRE1–5. Arbuscular mycorrhizal (AM) fungi have been demonstrated to enhance drought tolerance in host plants, whereas the underlying mechanisms, especially those involving sucrose and trehalose metabolism, remain unexplained. The study was to investigate the impact of inoculation with the AM fungus Funneliformis mosseae on mycorrhizal formation, root sugar fractions levels, and the relative expression of genes involved in the metabolism of sucrose and trehalose in trifoliate orange (Poncirus trifoliata) plants exposed to drought stress. Drought treatment reduced mycorrhizal colonization in roots and mycelium length in soils, resulting in lower concentrations in glomalin-related soil proteins in inoculated plants. However, inoculated plants presented significantly higher biomass production, root: shoot ratio, root morphological variables (length, area, and volume), as well as leaf gas exchange variables under drought treatment compared with uninoculated plants. In addition, a total of seven monosaccharides and three disaccharides were identified in the roots. The fungal treatment significantly increased root d -fructose, glucose, d -arabinose, l -fucose, and inositol levels under drought treatment, whereas sucrose levels were reduced, accompanied by up-regulated expression of PtAI, PtNI , and PtSPS genes. AM fungal inoculation significantly raised trehalose levels only under drought conditions, which was associated with the up-regulation of PtTPS1 expression and the down-regulation of PtTRE1–5 expression. In summary, AM fungi regulated the trehalose synthesis and sucrose cleavage in roots of trifoliate orange in response to soil drought, thus providing the benefits of drought tolerance in mycorrhizal plants. [ABSTRACT FROM AUTHOR]

• Pectin/pectinase is closely related to mandarin peelability. • Transcriptome profiling in mandarin peel during fruit maturation is revealed. • There are 78 genes encoding pectinase in mandarin peel. • Three PL genes are highlighted as regulators for citrus peelability. Peelability is an important fruit quality trait of citrus. Pectinase is a group of heterozygous enzymes that function in pectin degradation, which is implicated in fruit ripening and softening. Previously we established a method to quantify citrus peelability through two mechanical indexes (peel-pulp adherence and peel resistance of penetration), and exhibited the genetic diversity of peelability in mandarins (Citrus reticulata Blanco). With this method, the present study first confirmed that Clementine is an easy-peeling mandarin in comparison with Fremont, and both showed increasingly easy peeling as the fruits matured. A range of measurements for the two mandarins at three maturation stages demonstrated that peelability had negative correlation with pectin contents but positive with pectinase activity. Subsequently, RNA sequencing was performed for comparative transcriptomic profiling of the two varieties at three maturation stages. We identified 12322 differentially expressed genes (DEGs) in total. Through comparative time-course analysis, the gene expression patterns were displayed with 12 clusters each in albedo and flavedo. Some cell wall-related gene ontology terms were over-represented in albedo and flavedo Cluster6. We mined 153 genes encoding pectinase (pectin methylesterase, polygalacturonase, pectin lyase (PL), beta-galactanase, pectin acetylesterase and alpha-arabinofuranosidase) in silica from Clementine genome, and 78 of them were significantly expressed in the peel of Clementine or Fremont, whereas 62/60 belonged to the DEGs in albedo/flavedo. In weighted correlation network analysis, six/five out of eight/nine modules in albedo/flavedo had eigengene values that were significantly correlated with the two mechanical indexes, pectin contents and pectinase activity, and six/eight pectinase genes were present in the co-expression networks. Based on the results of multi-approach bioinformatics analysis, three PL genes (Ciclev10004783m.g, Ciclev10020423m.g and Ciclev10031429m.g) were highlighted as potential regulators for peelability. This study provides clues for understanding the molecular basis of the regulation of citrus peelability, and proposes pectinase as a target for peelability-oriented breeding of citrus. [ABSTRACT FROM AUTHOR]

• Regional weather variations significantly impact the quality of citrus. • A digital replica of Valencia orange growth process quantifies this weather impact. • Our models predict citrus fruit quality at harvest with about 5 % error. • Warmer regions produce larger and less acidic oranges compared to coastal areas. • Fruit temperature gradients vary across regions, affecting quality upon harvest. The quality of citrus fruit is influenced by various growing conditions, including weather. However, the impact of weather differences between growing regions on citrus quality at harvest is not well understood. This study employs a mechanistic-driven digital replica of the growth process of a Valencia orange from fruit set until harvest to quantify this impact. Measured daily temperature, humidity, rainfall, solar radiation, and wind speed data from various orange growing regions of South Africa, including Citrusdal, Nelspruit, Letsitele, and Sundays River Valley (SRV), inform and drive this digital model. The results suggest that the differences in weather conditions between growing regions significantly affect fruit diameter (FD), fruit weight (FW), rind thickness (RT), rind weight (RW), total soluble solids (TSS), titratable acidity (TA), and °Brix/acid ratio of oranges at harvest. The differences between growing regions led to variations of up to threefold for FD, twofold for FW, RT, RW, TSS, °Brix/acid ratio and up to fourfold for TA upon harvest. Particularly, oranges produced from warmer Letsitele and Nelspruit regions are found to be larger, sweeter and less acidic compared to those from coastal SRV upon harvest. The study also reveals the impact of the fruit growth process on the temperature gradient within the fruit, which varies across growing regions. The maximal temperature difference between the fruit core and surface during the growth process ranges from 4 °C to ∼7 °C. These variations in fruit temperature gradient could lead to variations in temperature-driven quality decay of fruit from different climatic regions at the start of their postharvest journey. These findings provide valuable insights for the citrus industry, aiding to optimize practices, harvest planning, and postharvest logistics. The output of this digital twin will help identify areas needing extra precooling to extend postharvest shelf life and minimize quality decay. Real-world use allows growers to schedule harvests based on regional weather conditions. [Display omitted] [ABSTRACT FROM AUTHOR]

• Infestation of citrus rootstocks by T. semipenetrans resulted in significant decrease in plant growth and biochemical changes. • Seven tested citrus rootstocks showed different levels of resistance to infestation by T. semipenetrans. • Carrizo citrange showed high resistance to infestation and reproduction of T. semipenetrans , while Sour Orange, Australian sour orange, and Volkameriana proved to be the most sensitive. • Sensitive rootstocks tend to accumulate more reactive oxygen species, are more susceptible to oxidative stress, and exhibit increased antioxidant metabolic activity in response to attack by this plant-parasitic nematode. • Carrizo citrange could be proposed as a resistant citrus rootstock for the sustainable control of the most threatening citrus nematode, T. semipenetrans. Tylenchulus semipenetrans , the causal agent of the 'citrus slow decline', is considered to be the most devastating nematode pest of citrus, causing considerable crop losses throughout the world. The management of this citrus nematode represents a significant challenge due to its wide host range and its adaptability to various environmental conditions. Nematicides application is the most prevalent control approach, however, their use often is associated with increased production costs and major risks to consumer health and the environment. The objective of this study is to contribute to the development of an alternative and effective method to control this plant-parasite. It intends to evaluate the resistance of the seven commonly used citrus rootstocks in Morocco based on their agronomic, physiological, and biochemical behavior in response to inoculation with T. semipenetrans. Results indicated that T. semipenetrans exhibited a strong reproductive capacity on Sour Orange, Australian sour orange, and volkameriana, showing higher root and soil infestation rates, with respectively 466.3, 250.5, and 273.3 females/10 g of root, and 1062.2, 1030.7, and 1053.2 females per 100 g of soil, compared to the other rootstocks varieties. These rootstocks allowed highest T. semipenetrans reproduction rates in both rhizospheric soil (> 3) and root (> 0.68), they also showed the highest infestation rate with more than 3 nematodes per cm of root. Moreover, these rootstocks showed significant biochemical alterations including a sharp increase in the activity of antioxidant enzymes, catalase (CAT), peroxidase (PO), polyphenol-oxidase (PPO), and in proline and malondialdehyde (MDA) accumulation compared to the control and other tested rootstocks. In contrast, T. semipenetrans reproduced poorly (with less than 135 females/10 g of root), less infested the roots (less than 0.33 females/cm of root), and induced slight biochemical modifications in Carrizo citrange. Thus, Carrizo citrange endowed with high resistance to T. semipenetrans could serve as a suitable rootstock to control this citrus devastating nematode. [ABSTRACT FROM AUTHOR]

• Reflectance and fluorescence images of citrus cv Batu 55 have been acquired • Ripeness related parameters i.e. brix, acidity, firmness have been obtained • Pre-trained DCNN model have been trained using single and stacked images • Prediction model based on combination images show higher accuracy 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. [ABSTRACT FROM AUTHOR]

• β-Citraurin was present in peel of all twelve red-peeled citrus cultivars. • β-Citraurin contributed to redness more than other or total colored carotenoids. • Expression of PSY1 and CCD4b1 were unlinked to carotenoid content among cultivars. Peel color in citrus is largely genetically controlled. Red peel is favored by customers and is important, therefore, for fruit external quality. In order to understand the factors affecting distribution of carotenoids and color intensity of red-peeled citrus, we compared carotenoid accumulation and gene expression in the peel of twelve fully ripe red-peeled citrus cultivars with different genetic backgrounds. The results showed that β-citraurin, a red C 30 carotenoid, was the second or third most abundant colored carotenoid in the peel of all twelve red-peeled citrus, ranging from 9.4 % to 26.7 % of total carotenoids. Statistical analysis of carotenoid composition and content showed that of the main carotenoids β-citraurin had the highest correlation with red appearance of cultivars. In addition, β-cryptoxanthin, which accounted for 3.6 % to 16.4 % of the total carotenoids, were also significantly positively correlated with citrus color index (CCI). The expression of two key genes, phytoene synthase 1 (PSY1) and carotenoid cleavage dioxygenase 4b1 (CCD4b1), differed among cultivars with a range of 3.5- and 48.8-fold, respectively. Surprisingly, accumulation of total carotenoids and β-citraurin was not correlated with the expression of PSY1 and CCD4b1 , respectively, implying that diverse factors influence high carotenoid accumulation in red-peeled citrus. [ABSTRACT FROM AUTHOR]

• A total of 27 different genes between precocious trifoliate orange and its wild-type trifoliate orange were identified. • PtCCHC and PtMBD6 genes related to flowering of citrus were screened and identified. • The expression levels of PtCCHC and PtMBD6 in different citrus species and developmental stages were detected by qRT-PCR. • The function of the PtCCHC was analyzed, and overexpression of PtCCHC in Arabidopsis led to early flowering. • Overexpression of PtMBD6 in Arabidopsis resulted in late flowering phenotype, and silencing PtMBD6 in citrus reduced the expression of PtFT. Flowering is a pivotal developmental event for fruit trees. Most of knowledge about the molecular regulatory mechanisms of flowering regulation comes from studies in model plants. However, knowledge on the regulation of the floral transition from vegetative growth in perennial fruit species is limited. Citrus is an evergreen perennial fruit tree genus with a complex genetic background. In this study, a total of 27 genes with sequence differences between precocious trifoliate orange and wild-type trifoliate orange were identified based on data from a previous study. qRT-PCR result showed that two candidate genes, PtCCHC and PtMBD6 , were differentially expressed between precocious trifoliate orange and wild-type. Moreover, PtCCHC was highly expressed, whereas PtMBD was expressed low at the early flowering stage in precocious trifoliate orange. Overexpression of PtCCHC in Arabidopsis resulted in early flowering and overexpression of PtMBD6 in Arabidopsis resulted in late flowering. We also found that silencing PtMBD6 can reduce the expression of PtFT in Citrus lemon. This study will provide valuable insights for future studies in citrus flowering. [ABSTRACT FROM AUTHOR]

• In Huanglongbing (HLB)-affected sweet orange trees. • The interactive biotic (C Las) and abiotic (osmotic) stresses exist simultaneously. • GA 3 improves carbohydrate translocation by reducing starch and callose deposition. • GA 3 helps to alleviate osmotic stress by increasing leaf relative water content. • GA 3 could be used as a potent grove management strategy to improve tree productivity. Huanglongbing (HLB; citrus greening disease) is presumably caused by the bacterium Candidatus Liberibacter (C Las). Here, we present evidence in terms of physiological, carbohydrate, transcriptome, phytohormones, and key enzyme activities behind the beneficial effect of gibberellic acid (GA 3) in mitigating biotic (C Las-infection) and abiotic (osmotic) stresses in HLB-affected 'Valencia' sweet orange. For two consecutive years, non-fruiting leaves of untreated control tress accumulated ≈ 8 % higher fructose whereas fruiting leaves accumulated ≈ 10 % higher fructose and glucose compared to GA 3 treated trees. Control trees also had higher starch (≈ 25 %) and callose (≈ 15 %) content than GA 3 trees, which are indicators for osmotic stress, and C Las-induced plasmodesmata closure resulting in anemic growth. In non-fruiting leaves of control trees, higher auxins and salicylic acid, and lower jasmonic acid content were found compared to GA 3 trees. In fruiting leaves, higher abscisic acid was found in control trees than GA 3 trees, suggesting water deficient conditions. In February, non-fruiting leaves of control versus GA 3 , differentially expressed genes (DEGs) related to response to stress, defense response, and carbohydrate metabolic process were upregulated, and those with stomatal movement and gibberellic acid mediated signaling pathway were downregulated. DEGs encoding sucrose synthase (provide UDP-glucose for callose synthesis) and invertase (sucrose to hexose conversion) were upregulated in control compared to GA 3 trees, indicating a higher capacity to import assimilates thus attracting water as well as callose accumulation. Furthermore, osmotic stress induced key markers including DEGs encoding lactate dehydrogenase and hexokinase, and the acyl-CoA-binding protein transcription factor family were upregulated in control compared to GA 3 trees, with a concomitant of higher enzymatic activity of alcohol dehydrogenase in control trees. Altogether, control trees indicate a higher carbohydrate tradeoff on defenses against biotic (C Las), and abiotic (osmotic) stresses than on growth. GA 3 improves vegetative growth as indicated by greater leaf weight and area, stem length, leaf relative water content thus improving photosynthetic activity as well as gas exchange potential in leaves. Thus facilitating, and better carbohydrate translocation within the tree body leading to better fruit retention on tree and productivity in HLB-affected sweet orange. [ABSTRACT FROM AUTHOR]

• Juice sacs are less responsive to HWT than epicarps of two tangors. • HWT elicited a notable rise of volatile content during conservation of 'W-Murcott'. • 'W-Murcott' had low ability to retain organic acids content during the storage. • More carbon is diverted to alternative fates than ethanol production in 'Murcott'. • Glycolytic ATP-saving enzymes appear to be more active in 'W-Murcott'. Citrus is highly susceptible to damage from cold temperatures, and conditioning procedures are commonly used to protect the fruit, and maintain its sensory qualities and external appearance. This study investigates the response of two tangor cultivars, 'Murcott' and 'W-Murcott,' to hot water conditioning treatment (HWT, 50 °C for 3 min) during the postharvest period (storage at 5 °C). The study analysed the internal quality parameters, metabolic profiles, and the activities of enzyme related to carbohydrate metabolism in tangor. The results indicate that there were no significant changes in soluble solids or titratable acidity after cold storage. 'Murcott' tangors experienced less weight loss compared to 'W-Murcott'. Additionally, in this variety the treatment led to an increase in ethanol concentrations, which is often associated with undesirable flavours. It could be observed that 'Murcott' undergoes significant carbon diversification to cellular destinations other than fermentation in the peel. These traits are further enhanced by heat treatment. Furthermore, this variety demonstrates a greater ability to preserve specific carbohydrate pool during the postharvest. 'W-Murcott' appears to be under more stressful postharvest conditions than 'Murcott'. This is indicated by the increased activity of ATP-saving enzymes (PPi-PFK, PEPC) and a lower ability to retain the level of relevant organic acids at the conclusion of the postharvest and shelf-life periods. These differences can mostly be attributed to varietal factors. Although 'Murcott' exhibited improved positive features due to HWT, the opposite trend was observed for 'W-Murcott'. In conclusion, although these two cultivars share a close genetic relationship, they respond differently to heat treatment. [Display omitted] [ABSTRACT FROM AUTHOR]

• Purified EE-GRSP solid was added into soil to analyze GRSP function. • EE-GRSP/DE-GRSP increased with EE-GRSP addition but decreased with the time. • EE-GRSP addition elevated SOC and the fraction of WSA at 0.25‒4 mm size. • High addition of EE-GRSP increased soil NH 4 N, Olsen-P, and available K levels. • A direct evidence regarding EE-GRSP function was provided. Glomalin-related soil protein (GRSP) is a glycoprotein metabolite produced by arbuscular mycorrhizal fungi. Although GRSP has favorable effects on soil, there is a lack of causal evidence to support these claims. In this study, different amounts of purified easily extractable GRSP (EE-GRSP) solid (0.25‒1 g/kg) were mixed with soil and buried under the canopy of field Lane late navel orange trees in 0.45-μm nylon mesh bags. The impacts of EE-GRSP addition on soil traits, including endogenous GRSP levels, soil fertility, and the distribution and stability of soil water-stable aggregate (WSA) were studied. At 7 and 15 months of EE-GRSP addition, the levels of easily extractable, difficultly extractable, and total GRSP increased to varying extents with the increase of EE-GRSP addition but decreasing over time. The addition of EE-GRSP also led to an increase in the fraction of WSA at the size of 0.25‒4 mm, and the effect was more pronounced with higher amounts of EE-GRSP addition, resulting in a significant improvement in WSA stability (24.7 % to 91.3 % at 7 months and 36.2 % to 121.4 % at 15 months). Furthermore, high amounts (1 and 2 g/kg) of EE-GRSP significantly increased the levels of available K, NH 4 N, and Olsen-P in the soil. Soil organic carbon levels also showed a tendency to increase with increasing EE-GRSP addition, with increases ranging from 66.0 % to 246.0 % at 7 months and 14.5 % to 402.4 % at 15 months. Overall, this work provides the first evidence that adding EE-GRSP to soil can enhance soil fertility and aggregate stability in the citrus orchard. [ABSTRACT FROM AUTHOR]

• Significant differences in fruit quality between citrus grafted on Trifoliate orange and Ziyang xiangcheng. • Citrus grafted on Ziyang xiangcheng has higher nitrogen utilization efficiency. • The difference in nitrogen absorption and utilization between two types of rootstock affects fruit quality. Excessive amounts of nitrogen are frequently applied in citrus production in China, and different rootstocks affect the absorption of nutrients and fruit quality of citrus. This study used 15N tracing technology and 3-year-old Jinqiu Shatangju tangerine (Citrus reticulata ' Jinqiu Shatangju ' , abbr. JST) grafted on two rootstocks of trifoliate orange (Poncirus trifoliata [L.] Raf., abbr. TO) and Ziyang Xiangcheng (Citrus junos Sieb. ex Tanaka, abbr. ZYXC) as the plant materials. Conventional urea and urea labeled with 15N were applied. The results showed that the total content of nitrogen in all the organs of JST grafted on ZYXC was higher than that of the TO. The two types of rootstocks had a significant impact on fruit quality, and the total soluble solids and titratable acid of the fruit significantly negatively correlated with the total nitrogen content in multiple organs. During fruit maturation, there was a relatively consistent distribution of Ndff (nitrogen derived from fertilizer) in various organs of the JST grafted on both types of rootstocks. There were significantly higher amounts of Ndff in various organs of the JST grafted on ZYXC than on TO. There was a significantly higher ratio of nitrogen supplied to the fruit of JST grafted on ZYXC than that of TO, while the opposite was found in the leaves. This indicated that ZYXC absorbed and utilized more nitrogen fertilizer than TO, and this could be the reason for the difference in fruit quality between the two rootstocks of JST. [Display omitted] [ABSTRACT FROM AUTHOR]

• 'Licheng' is a nonapomictic citrus variety native to China. • Trees producing polyembryonic seeds were found in a garden of 'Licheng'. • Autotetraploids were selected from plants developed from polyembryonic seeds. • A low sequencing depth region were found on chromosome 4 of 'Licheng'. • CitRWP gene is located in the low sequencing depth region. Tetraploid plays major roles in the polyploid breeding and production of citrus plants. Autotetraploids of nonapomictic citrus varieties are desirable in citrus polyploid breeding due to their high frequencies of hybrid polyploid production, certain genotypes and some predictable phenotypes. However, it is difficult to obtain autotetraploids of nonapomictic citrus varieties. In the present study, the nonapomictic sweet orange variety 'Licheng', which is native to China, was used as the main material. A 'Licheng' tree, LCOYC-04, that produced polyembryonic seeds at a frequency of 34.96±2.88 % was selected. Plants that grew from self-pollinated polyembryonic seeds of LCOYC-04 were investigated by flow cytometry. Four tetraploids were selected from 550 plants and identified according to chromosome observation. Exonic single-nucleotide polymorphism (SNP) locus genotyping based on genome resequencing showed that 22.18 %-70.49 % of heterozygous loci in the genome of LCOYC-04 were homozygous in the genomes of plants grown from self-pollinated monoembryonic seeds. The proportions of homozygous loci were 2.07 %-2.45 % in the 4 selected tetraploids. These values were close to those in 7 asexual 'Licheng' relatives (1.97 %-2.71 %). Therefore, the 4 tetraploids were confirmed to be autotetraploids of LCOYC-04. Genome sequencing revealed a region of low sequencing depth (approximately 855 kb) on chromosome 4 of all 'Licheng' trees. The CitRWP gene, which is responsible for the occurrence of nucellar embryos in citrus plants, was located in the low sequencing depth region. It was confirmed by quantitative PCR that one of two allelic CitRWP gene was defective in genome of 'Licheng'. The current study indicates that it is possible to induce nonapomictic citrus to mutate into facultatively apomictic citrus through chromosome segment deletion, and provides a reference for excavating autotetraploids which produce polyembryonic and monoembryonic seeds. [ABSTRACT FROM AUTHOR]

• Application of melatonin and interstocks preserved fruit quality during cold storage. • Shelf life of treated 'Kiyomi Tangor' fruit extended up to 90 days in cold storage. • Melatonin and interstocks activated antioxidant activity, delaying fruit senescence. • Combined application preserved fruit texture, color, sugar and vitamin c level. Fruit quality can be improved using rootstocks and melatonin (MT) after harvest. However, the effects of the combined use of interstocks and MT on citrus fruit storage quality and physiological senescence are unknown. Hence, this study aimed to assess how MT treatment affects the organoleptic quality and antioxidant system of Kiyomi Tangor fruit obtained from trees growing on rootstocks with and without interstocks during the cold storage period. All treatments reduced fruit weight loss while increasing firmness, soluble sugars, total soluble solids, titratable acids, and skin color as compared with those of the control, indicating that MT and rootstocks slowed the deterioration of fruit quality during cold storage. Furthermore, the combined use of interstocks and MT prevented electrolyte leakage and malondialdehyde from accumulating, suggesting the potential hindrance of reactive oxygen species (ROS) generation and oxidative harm. This can be attributed to the improved efficacy of superoxide dismutase, catalase, peroxidase, and ascorbate peroxidase in removing ROS. Although both MT and rootstocks can improve the quality of Kiyomi Tangor fruit after harvest, the combination of MT and interstocks provided the highest quality during cold storage. [ABSTRACT FROM AUTHOR]

• Alley cropping during winter/spring reduce mandarin water stress by 26.9 %. • Alley cropping during summer increase mandarin water stress by 60 to 144 %. • Both diversifications require more water than monoculture to alley crops irrigation. • Yield was not reduced by diversified cropping systems effect. • RDI during stage II of fruit growth over SDI-irrigated trees reduced yield by 30 %. The diversified cropping systems has several environmental benefits, but there is no certainty about their effect on the water status of trees, especially in areas with permanent low availability of irrigation water. Therefore, our objective was to evaluate the effect of the establishment of diversified cropping systems in a traditional monoculture (MC) of adult mandarin trees on its water status and yield under sustained deficit irrigation (SDI) and regulated deficit irrigation (RDI). Six treatments were tested during three consecutive seasons: (i) a mandarin monoculture under SDI (MC-SDI), with permanent bare alleys and irrigated at ∼70 % ET c during the entire season (actual amount of irrigation water available in the area); (ii) a diversified mandarin crop (D1-SDI), irrigated as MC-SDI, with a rotation of fava bean and barley/vetch in the alleys; and (iii) a second diversified mandarin crop (D2-SDI), irrigated as MC-SDI, with a seasonal rotation of fava bean, purslane and cowpea. Additionally, three RDI treatments were evaluated, denoted as (iv) MC-RDI, (v) D1-RDI and (vi) D2-RDI, irrigated as MC-SDI, except during the stage II of fruit growth, when it was reduced by 50 % with an irrigation threshold of a solar midday stem water potential of ∼ –1.5 MPa. The mandarin yield was not affected by the effect of diversified cropping systems, but the RDI reduced it on average by 30.1 % with respect to SDI. The alley cropping of fava bean and barley/vetch during winter and spring under sustained deficit irrigation conditions reduced the water stress intensity of mandarin trees by 26.9 % over the entire season, while cultivation of purslane or cowpea during summer increased it by 60–144 %. Both diversifications required a greater amount of water than the monoculture, in these terms an additional reduction in the irrigation of mandarin trees, as in the RDI treatment, allowed to solve this additional water requirement, but promoted an increase in the water stress intensity of the trees, which may affect their productivity in the mid and long-term. [Display omitted] [ABSTRACT FROM AUTHOR]

• The phylogenetic relationships, evolution, and transcriptome of the CclKNOX gene family in citrus clementina were systematically analyzed. • Genetic transformation and transcriptome date revealed the role of CclKNOX3 in citrus shoot development. • CclKNOX5 could interacts with CclKNOX3, and regulated the expression of WUS. • CclKNOX4 could binds to the TGAC cis-element of CclKNOX3 and CclKNOX5 promoters to regulated their expression. KNOTTED1-LIKE HOMEOBOX (KNOX) genes are a relatively conserved gene family in plants, and have important regulatory functions in the morphological development of plants. In this study, a total of 9 KNOX proteins were found from citrus and divided into two classes, Class I and Class II. Subsequently, their gene structures, protein characteristics and sequence features were analyzed. Spatial expression analysis showed that most of the genes exhibited a constitutive expression pattern in different tissues of Citrus clementina. Interestingly, the expression pattern of CclKNOX3 was different from other Class I members, as it was mainly expressed in stems, lateral buds and shoot tips. Overexpression of CclKNOX3 led to strong differentiation of shoot apical meristem and curled leaves in transgenic tobacco and lemon. In addition, CclKNOX3 was found to interact with CclKNOX5, localized in the nucleus and have transcriptional inhibitory activity. Further transgenic analysis found that 35S:CclKNOX5 transgenic tobacco showed similar phenotype with 35S:CclKNOX3. Furthermore, yeast one hybrid and luciferase assay confirmed that CclKNOX3 and CclKNOX5 were regulated by CclKNOX4. This study expands our knowledge about the citrus KNOX family and provides valuable informations for future studies on shoot developmental regulation. [ABSTRACT FROM AUTHOR]

• Mandarino Cleopatra and Citrange Carrizo rootstocks produce more palatable mandarins. • Mandarino Cleopatra and Citrange Carrizo rootstocks produce juicier mandarins. • The rootstock does not significantly affect the amino acid concentrations in mandarins. • Citrus macrophylla rootstock producers' mandarins with higher fructose concentrations. Rootstock's can affect the characteristics and quality of citrus fruit. Knowing which rootstocks produce better quality fruit is very important in late mandarin varieties, due to their high economic value. The objective of this study is to know the effects on yield and the main morphological, biochemical and sensory properties of the late mandarin variety 'Afourer' when cultivated on three different rootstocks [ Citrus macrophylla Wester (CM), Mandarino Cleopatra (MC) and Citrange Carrizo (CC)]. The morphological properties (weight and dimensions) and colorimetric characteristics (external and internal fruit color) were analyzed. The main biochemical characteristics, including total antioxidant activity analyzed by ABTS and DPPH methods, organic acids and sugars determined by HPLC, and juice metabolomics by 1H-NMR, were also investigated. In addition, the juice quality was assessed by a sensory panel. The CC rootstock produced up to 77 kg of fruit/tree more than MC. Fruits cultivated on MC and CC had significantly larger dimensions, a greater orange coloration and up to 17 % more juice than fruits cultivated on CM. In terms of biochemical properties, there were no significant differences in most of the properties analyzed among the three rootstocks, highlighting only that the CM rootstock induced 13 % more fructose in the fruits than the rest of the rootstocks. Fruits cultivated on the CC and MC rootstocks had a better taste when evaluated by sensory analysis than those cultivated on the CM rootstock. [ABSTRACT FROM AUTHOR]

• Aboveground biomass in citrus trees is determined by tree age rather than N fertilizer application. • Accumulated temperature drives the growth and development of citrus trees in the field. • Stem diameter indicators can predict the growth trend of citrus tree. • Integrative view of N fertilizer management in citrus orchards. Tree growth is influenced by both, the availability of nutrients in the soil and temperature. However, how the interaction of nitrogen (N) fertilization and accumulated temperature (≥10 °C) determines the growth of evergreen citrus trees is still unknown. To characterize this interaction, we studied the biomass distribution of young citrus trees in a four-year field experiment (2018–2021, Chongqing city, China) and used the results to build an allometric growth model. Based on a completely randomized block design (Two-way ANOVA and Duncan´s test), three N levels were established, namely, N0 (no N fertilizer), N1 (80 % of the farmer's usual fertilization), and N2 (farmer's usual fertilization). Our results indicate that excessive N fertilizer application increases the inorganic N content in deep soil, whereas the aboveground biomass distribution was largely dependent on tree age, but independent of N fertilization. An allometric growth model of citrus aboveground biomass was established at different N levels and provided a realistic quantitative relationship between accumulated temperature and growth. It indicates that canopy volume (power function), stem diameter (linear function) and total aboveground biomass (exponential function) are highly positively correlated with accumulated temperature, rather than N fertilization. Since the canopy volume and total aboveground biomass are also significantly positively correlated with stem diameter, this parameter seems to be suitable for estimating the biomass of young citrus trees in the field. Further research is required to characterize the relationship between growth of citrus trees and other environmental factors. [ABSTRACT FROM AUTHOR]

• Oligonucleotide (oligo) sequences are highly conserved within the genomes of the citrus family. • It was effective to employ eight oligo pools (OPs) for visualizing specific chromosome regions and nine chromosome painting probes (CPPs) for identifying whole chromosomes in citrus plants. • A simple method for identifying hybrid Citrus microcarpa was developed. • Molecular cytogenetic maps of C. microcarpa, Citrus aurantiifolia , and Citrus limon were constructed. Based on these maps, three molecular cytogenetic ID cards were generated for the three Citrus species. Citrus microcarpa is one of the most popular species for flavoring and industrialized juice production, making it an increasingly important economic crop. At present, C. microcarpa has been mistakenly regarded as a type of lemon in China. The lack of a simple identification method for hybrid C. microcarpa is the major obstacle limiting its comprehensive recognition and utilization. In this study, firstly nine pairs of chromosomes were marked by eight oligo pools (OPs) in C. microcarpa, C. aurantiifolia , and C. limon , which showed that oligonucleotide (oligo) sequences are highly conserved within the genomes of the citrus family, suggesting that eight OPs and nine chromosome painting probes (CPPs) can be used as universal probes for the identification of each chromosome in citrus plants. Then we developed a method for the identification of C. microcarpa by using fluorescence in situ hybridization (FISH) mapping and Chromoycin A3 (CMA) staining. Moreover, we constructed the molecular cytogenetic maps containing the physical positions of eight OPs, 45S rDNA, 5S rDNA, CL, CMA banding and fragile sites in C. microcarpa, C. aurantiifolia , and C. limon , which visualize the significant differences among the three Citrus species. Combining the highly different morphological and cytological characteristics of C. microcarpa with C. aurantiifolia and C. limon , it is clear that C. microcarpa is a Citrus hybrid species, not a lemon species. Overall, this study provides a better understanding of C. microcarpa from the molecular cytogenetic perspective. [ABSTRACT FROM AUTHOR]

• Various genetic transformation methods are important for citrus genetic breeding. • A simple, rapid and efficient root transformation technique is established in a variety of citrus varieties. • Protein interactions and FT gene signal transduction are investigated using root transformation method. • Overexpression of CjCAD promoted lignin accumulation in transgenic citrus roots. Although several methods of citrus genetic transformation have been studied and published, it is still necessary to further improve the efficiency of genetic transformation and increase the varieties used for citrus genetic transformation. Here, we report a simple, rapid and efficient root transformation technique for citrus to facilitate gene function studies. We found that infestation of Agrobacterium rhizogenes into citrus seedlings of five different species could produce stable transgenic roots in a short period after comparing and optimizing the selection of citrus species, bacterium concentration, cutting time and infection method. PCR and fluorescence observations showed a positive root transformation efficiency of approximately 13%-36% in the five tested citrus species. To demonstrate the utility of this method in the functional verification of citrus genes, a bimolecular fluorescence complementation (BiFC) assay was used to prove the interaction between CrCIPK6/9 and CrCBL5/6 in Citrus reticulata. Additionally, the PCR results showed that CrFT-RFP was transferred from the transgenic positive root to the stem in Citrus reticulata. Finally, overexpression of CjCAD from Citrus junos promoted lignin accumulation in transgenic citrus roots. This method could not only be used to study genes in roots but also various genes involved in plant growth and development. Taken together, we demonstrated that this method allows fast study of gene function in a wide range of citrus species, which would facilitate the understanding of novel genes in citrus. [ABSTRACT FROM AUTHOR]

• 15 genotypes of F. hindsii were utilized to select the optimal genotypes for transformation. • The T0 generation produced highly chimeric transgenic plants. • the editing types of T1 generation more complex, which may be due to apomixis in citrus. • CRISPR/Cas9 vector was improved by using the endogenous U6 promoter in F. hindsii. The CRISPR/Cas9 editing system is presently regarded as one of the most efficient tools for genome editing and has been implemented in perennial fruit crops. However, the characteristics of transgenic plants and their subsequent generation have rarely been reported in fruit trees. In this study, 15 distinct preserved germplasm resources of Hongkong kumquat (Fortunella hindsii) were utilized to selecting suitable genotypes for genetic transformation. The shoot regeneration efficiency, seed number per fruit, and epicotyl diameter displaid a moderate positive correlation with transformation efficiency, with correlation coefficients of 0.6267, 0.5429, and 0.5388, respectively. The transcription factor RKD family gene FhRWP was knocked out in kumquat, resulting in the production of seven T0 and 34 T1 plants. Editing efficiency of T0 generation ranged from 1.62% to 68.11%, with a significant difference in editing activity among cases. Up to 23 editing types were detected in a single positive transformant, demonstrating that the high degree of citrus editing chimerism. Not all of T1 lines exhibited an increase in editing efficiency relative to T0. The descendants of T0-A2/A3 were all negative, while the other group of T1 lines showed both higher chimera and editing efficiencies of up to 92% than the others. Finally, the CRISPR/Cas9 vector was improved by using the endogenous U6 promoter in F. hindsii. This study provides novel insights into the application of the CRISPR/Cas9 system in asexual plants and serves as a reference for gene function verification in citrus and other species. [ABSTRACT FROM AUTHOR]

• The liquid fermentation compound (LFC) was prepared with CHC and probiotics. • LFC strongly inhibited the growth of P. digitatum in vitro. • The postharvest quality of citrus fruit was improved by treating with LFC. • The disease incidence and severity of green molds in citrus fruit was reduced by treating with LFC. • LFC can act as an efficient natural antistaling agent for citrus fruit. In this study, we produced a novel liquid fermentation compound (LFC) from the co-fermentation of probiotics and Chinese herbs and assessed its benefits on the postharvest storage quality of citrus fruit. Harvested fruit were treated with sterile water (Control), probiotic suspensions (PS), a combination of Chinese herbs (CHC) or LFC for 5 min and then stored at 20 °C and 85–90% RH for 42 d. The results of in vitro tests showed that LFC strongly inhibited the growth of P. digitatum. Storage trials showed that PS, CHC and LFC treated fruits had lower weight loss and higher vitamin C and total soluble solid contents at day 42 after treatment. However, there were no significant differences in firmness among all groups. Only LFC-treatment significantly delayed the loss of titratable acidity content at day 21 after treatment. Interestingly, decay incidence in LFC treated-fruit was also significantly lower than both CHC- and PS-treated fruit (P < 0.05). PAL and PPO activity in LFC-treated fruit were significantly higher than other groups at days 4 and 6, respectively, after incubation (P < 0.05). After incubation with green mold for 8 d, the disease index of fruit treated with PS, CHC, or LFC was 50, 58.3 and 33.3%, respectively, whereas complete decay was observed in water-treated fruit. A significant reduction of lesion diameters, was recorded for LFC-treated fruit, as compared to other treatments. Based on these results, LFC can be considered as a novel, efficient and natural antistaling agent for citrus fruit. [ABSTRACT FROM AUTHOR]

• Different citrus scion/rootstock combinations respond differently to infection with CLas. • Sensitivity of the cultivar in the scion position has a larger influence on disease progression. • Gene expression response is different in leaves and roots. • Genes associated with starch metabolism respond in an opposite fashion in roots and leaves. The devastating citrus disease Huanglongbing (HLB), associated with bacterial pathogens of the genus Candidatus Liberibacter, has spread across many citrus production areas worldwide causing devastating economic losses. In Florida, infection rates in most commercial citrus orchards approach 100 percent by the time trees are 3–4 years old. Most scion cultivars are highly susceptible to Ca. Liberibacter asiaticus (CLas), the pathogen prevalent in Florida, but significant tolerance has been identified within the species Poncirus trifoliata (trifoliate orange) and some of its hybrids that are commonly used as rootstocks. In this study we investigated the relative influence of rootstock and scion in citrus plants composed of susceptible and tolerant cultivars in both the scion and the rootstock position on HLB disease progression and expression of stress and disease-related genes. Experiments were conducted in the greenhouse using the susceptible cultivars 'Valencia' orange (Citrus sinensis) and 'Cleopatra' mandarin (C. reticulata), and the tolerant trifoliate hybrid cultivars 'US-802' (C. grandis × P. trifoliata), 'US-897' (C. reticulata × P. trifoliata), and 'US-942' (C. reticulata × P. trifoliata). Plants were either mock-inoculated or graft-inoculated with CLas. The incidence of CLas infection at 6 and 12 months after inoculation and the severity of the disease was different among scion/rootstock combinations. Typically, trees with a tolerant cultivar in the scion position contained a lower number of bacteria and were less damaged by infection than trees with a susceptible cultivar in the scion position, regardless of rootstock. Previous observations of significant influence from rootstock on field tree tolerance to CLas may be partially the result of differential rootstock ability to tolerate other stresses, or respond favourably to therapeutic treatments, under the weakened condition caused by the infection. Differential expression of defense-related and other genes found largest fold-differences between non-infected and infected plants when a susceptible cultivar was in the scion position. Fewer genes responded in roots than in leaves, and genes associated with starch metabolism responded strongly and in an opposite direction when comparing roots and leaves, probably indicative of carbon depletion occurring in roots of infected plants. [ABSTRACT FROM AUTHOR]

• Sixty-six accessions of 'true citrus fruit trees' group were used in this study. • Conserved group I intron (PQRS) sequence motifs were detected in Citrus genus. • The secondary structure of the common P8 stem–loop region was predicted. • Our result shows that trn L UAA intron can be a good barcode for 'true citrus'group. Cytoplasmic chloroplast DNAs was explored to establish phylogenetic relationships among 'True citrus' group and elucidate its molecular evolution. Conserved group I intron (PQRS) sequence motifs were detected in Citrus genus and showed differences of nucleotide variation between elements and some species. The P8 stem-loop region was the only variable region in trn L intron of Citrus species. The deletion of 6 bp has been detected between sites (40–45) in the partial alignment of P8 stem-loop resulted in a change in conformation of the secondary structures in the ancestral species and other derived species and this could be explained by the evolution and speciation of this genus. The consistency index (CI=1) and the retention index (RI=1) values suggest that the changes are mostly apomorphic despite the absence of homoplasy (HI=0). The phylogenetic tree confirms and shows a branching of C. limon , C. sinensis , C. paradisi , C. tangelo and C. aurantium in a monophyletic clade. This result so far to C. reticulata ruled out the maternal contribution of mandarin gene pool in the elaboration of these secondary Citrus species. The Maximum Likelihood tree indicated that the genus Citrus is quite distant from the related genera Poncirus, Microcitrus, Eremocitrus and Fortunella except only Fortunella margarita species. Here new insight is given about mechanism involving in the evolution of the trn L intron in 'True Citrus'. From the study it appears that an explicit rejection of the null hypothesis and a scenario of a demography history and recent expansion of 'True Citrus' genotypes seem to be retained that may be an important factor influencing the power of genetic diversity in 'True Citrus'. [ABSTRACT FROM AUTHOR]

• Scion root pruning decreased the N but increased the C level in mandarin leaves. • Scion root pruning recovered the numbers of flowers and fruits. • Scion root pruning enhanced fruit diameter and length. • Scion root pruning positively affected soluble solids content but not titratable acidity. Intensive scion rooting in 'Shiranuhi' mandarin [(Citrus unshiu × C. sinensis) × C. reticulata ] trees contributed to reduced flowering, yield, and fruit quality at commercial mandarin orchards. To elucidate the effect of a cultural technique on controlling the loss of fruit quality and yield, mandarin trees were grouped into three treatments as follows: no scion root (without scion roots), scion root intact, and scion root pruning in thirteen-year-old 'Shiranuhi' mandarin trees. Scion root pruning reduced leaf nitrogen (N) and enhanced leaf carbon (C), thereby increasing the leaf C/N ratio in scion root pruned trees, than those with intact scion roots. Physiological responses of flowering and fruiting were significantly enhanced by pruning scion roots in mandarin trees. Fruit size, fruit fresh weight, and soluble solids content (SSC) were considerably greater in scion root pruned trees than those with intact scion roots. Furthermore, pruning scion roots increased total fruit yield than that in mandarin trees with intact scion roots. Overall, the results indicated that scion root pruning should contribute to minimizing cultural problems, such as low yield and poor fruit quality, which have been caused by scion rooting in 'Shiranuhi' mandarin orchards. [ABSTRACT FROM AUTHOR]

Highlights • Four 2x × 4x crosses were conducted using three diploid seedy cultivars as seed parents. • High germination rate and shoot regeneration was achieved via an optimized embryo rescue approach. • Numerous triploid and tetraploid progenies were obtained as determined by flow cytometry analysis. • Hybrid nature of the selected triploids and two different origins of the selected tetraploids were confirmed. Abstract Seedlessness is a primary breeding objective for citrus fresh fruit market, and triploids have been proven to have great value to produce seedless fruits. In this study, aiming to produce triploid plants for developing some seedless cultivars, four 2x × 4x interploid crosses were conducted using three elite but seedy cultivars as seed parents and one newly flowered doubled diploid and two allotetraploid somatic hybrids as pollen parents. As a result, a total of 1454 developed and 3409 undeveloped seeds from 341 fruits were obtained. Using an optimized embryo rescue approach, 669 developed and 1301 undeveloped seeds germinated in vitro, with an average germination rate as 52.5% for the crosses using 'Nadorcott' tangor and 'Bendizao' tangerine (polyembryonic) as seed parents and 31.0% for the crosses using 'Orah' mandarin (monoembryonic) as seed parent. Then by shoot and root induction, totally 1354 plantlets were regenerated, among which 401 and 54 plants were proved to be triploids and tetraploids by flow cytometry (FCM) analysis and chromosome counting. Hybrid nature of the selected triploid progenies, as well as two different origins (doubled diploid and hybrid origins) for the selected tetraploid progenies was further confirmed by single nucleotide polymorphism (SNP) markers. [ABSTRACT FROM AUTHOR]

Highlights • Evidence that negative influence of treated waste water (TWW) is mainly salinity. • Secondarily treated waste water's organic load has a marginal influence. • Root zone aeration facilitates ion selectivity and improves plant performance. • X639 was less sensitive to TWW than Volkameriana in these conditions. • Aeration enhanced K transport from the roots to leaves. Abstract The effects of root zone aeration and irrigation water quality (WQ) were studied in two rootstocks with contrasting tolerances to abiotic stress. We hypothesized that the main influence of TWW is that of its salinity (especially Na and K and their ratios), that the organic load and its BOD have a marginal influence and that aeration facilitates selectivity of roots and/or leaves and therefore improves plant performance. The factorial experiment included root zone aeration, fresh water (FW), TWW, and fresh water with a salt concentration similar to TWW (FW + NaCl). One year old unworked rootstocks of sensitive Citrus volkameriana (Volka) and tolerant X639 (Cleopatra mandarin X Poncirus trifoliata) were treated for 4 months, followed by 2 months of recovery. Measurements included ionic and water relations, photosynthetic parameters, growth, morphology, tissue specific membrane properties, and sugar and starch contents. Volka was highly sensitive to WQ and aeration while X639 was influenced much less. During the first two months aeration increased Volka leaf photosynthesis and gas exchange by 15%, water and potassium (K) uptake by 20%, carbon storage by 15% and biomass by 20%; which compensated for the negative effects of poor WQ. Changes in distribution of K and Na ions hint at the mechanisms for the aeration influence on tolerance to poor WQ. Results indicate that aeration enhanced K transport from the roots to leaves and reduced Na concentrations in the roots of the sensitive rootstock. These, as well as changes in the wide range of leaf and root parameters measured, are discussed with relation to their implications for our understanding of plant response and tolerance to low WQ in poorly drained soils. [ABSTRACT FROM AUTHOR]

Highlights • A green, blue, grey and white water footprints have been estimated for citrus at the provincial level. • The impacts of climatic and non-climatic factors have been evaluated on the variability of citrus water footprint components. • Water footprint increases when the crop yield decreases. • The water footprint depends on the non-climatic factors rather than the climatic factors. Abstract Citrus is one of the most important crops on the world and the southern part of Iran has a huge field for citrus. Exporting these products to farmers is very important economically. Shortage of water resources is the main challenge for citrus gardens. Therefore, water resources management of citrus is essential in these regions. The purpose of this paper is calculation of water footprint components of citrus production in Hormozgan province. Then, it evaluated the impacts of climatic and non-climatic factors on the variability of citrus water footprint during 2002-2016. The total water footprint of citrus was 6.69 m3 kg−1 with sharing of 2%, 16% and 82% for the green, blue and white + grey, respectively. Also the results showed crop yield is the most important factor on temporal variation of citrus water footprint. The trend of blue, grey and white water footprints is significantly increasing in 2002-2016. This research provides practical approaches for managers and policy-makers in the agriculture area for managing the water footprint and helps to optimize the water consumption and cultivation of citrus at regional scales. [ABSTRACT FROM AUTHOR]

Highlights • Soil properties were enhanced by organic cultivation. • Integrated management resulted in higher yield but smaller fruits. • Sugars and organic acids did not differ between the organic and integrated system. • Antioxidant capacity was higher in integrated produced fruits. • Principal component analysis clearly distinguished the two management systems. Abstract Two mandarin orchards old trees, the first cultivated as organic farm and the second adapting integrated farming approach were assessed, regarding soil properties, plant nutrition and fruit quality attributes. Organic cultivation enhanced some of the soil properties, mainly by increasing the levels of exchangeable potassium, magnesium and phosphorus, while potassium, magnesium and zinc were also higher in the leaves of organically cultivated trees. Yield was higher under integrated cultivation, with fruits of lower diameter and length. Peel color was advanced under organic cultivation, which induced higher maturity index and total soluble solids in the juice. The individual carbohydrates and organic acids assessed did not differ between the two cultivation systems, while fruits produced under integrated system exhibited higher hesperidin content and higher antioxidant capacity than the organic ones. The principal component analysis resulted in a clear distinction between the two systems, based mainly on the yield, peel and flesh participation in the whole fruit and leaf potassium and sodium concentrations. Overall, the two systems did not differ considerably, but their few significant differences were enough to be clearly distinguished. The integrated produced fruits with higher antioxidant capacity, justified the aspect that organically produced food cannot be "a priori" characterized as better than the integrated one. On the other hand the superiority of organic food can be surely based on the low or zero pesticide residues and on preserving environmental and economic sustainability. [ABSTRACT FROM AUTHOR]

Highlights • A method of sequence-related amplified polymorphism is used to detect scion roots. • The method employs sequence-characterized amplified region markers. • The method can be used by identify early scion rooting in Citrus cultivars. Abstract Recently, scion rooting at the grafted region of Poncirus trifoliata rootstocks has been found to decrease fruit setting and quality. Under cultivation conditions, the identification of scion-rooted Shiranuhi mandarin hybrid [(Citrus unshiu Marcov. × C. sinensis Osbeck) × C. reticulata Blanco] trees is difficult. Therefore, we aimed to develop a novel method for rapid and accurate identification of scion roots based on sequence-related amplified polymorphism (SRAP) in combination with a sequence-characterized amplified region (SCAR) marker. The genomic DNA was extracted from the normal rootstocks of P. trifoliata and scion roots of Shiranuhi. The sequence of amplified DNA fragments from scion root samples was analyzed using SRAP F4 and R15 primer combination, and was used to construct nine combinations of SCAR primers. Five markers (P1, P2, P3, P4, and P6) were obtained, of which SCAR-P3 presented the best results. We also efficiently screened the scion roots in Kiyomi and Settokka. These SCAR markers accurately identified scion rooting in Shiranuhi mandarin hybrid and other citrus cultivars, thus allowing the implementation of improved cultivation techniques to ensure normal fruit setting. The proposed method can also be applied to control the damage caused by scion rooting in other Citrus cultivars. [ABSTRACT FROM AUTHOR]

Graphical abstract Highlights • The fruit detachment method conditioned the abscission pattern. • The fruit detachment force was different according to abscission zone. • The breakage type AZ-C predominated in natural fall and the snap method. • The breakage type AZ-A predominated for the canopy shaker and pull test methods. • Canopy shaker and snap methods showed similar percentage of detached fruit with calyx. Abstract Fruit detachment can occur due to natural causes or be mechanically performed by a combination of mechanical stresses that cause tissue breakage in the plant. Forced abscission should not coincide with natural abscission zones (AZ). Abscission zones are very important in citrus harvesting both in terms of the destination market and of the possible damage caused to the tree or fruit. The objective of this study is to determine the abscission pattern of sweet oranges with a canopy shaker and compare it with other detachment systems. Five plots of Valencia oranges were tested during the 2017 and 2018 harvesting seasons, using a commercial tractor-drawn canopy shaker. The diameter, weight and breakage type were evaluated in the cases of natural fall, snap method, mechanical harvesting with canopy shaker, and pull test. Breakage type AZ-C predominated in natural fall (89.0%) and the snap method (79.5%). Similarly, AZ-A predominated for the canopy shaker (58.8%) and pull test (45.3%). Mechanical action on the fruit produced peel tear by breaking the flavedo, which reached highest frequency in the snap method (7.6%). Peel tear breakage required a mean fruit detachment force value of 99.3 N, higher than the average abscission values for AZ-C (88.7 N) and AZ-A (66.6 N). The fruit that remained on the tree after canopy shaker harvesting showed lower mean values of fruit detachment force (16.3%) than the pre-harvest fruit. The frequency of fruit with calyx with the canopy shaker and snap methods was similar, with a mean value of 36%. [ABSTRACT FROM AUTHOR]

Graphical abstract Highlights • Parentages of triploid citrus cultivars 'Yellow Bell' and 'Tahiti lime' were examined. • Tri-allelic SSR marker genotypes were used to identify unknown parents of triploid. • SNP genotypes of chloroplast genomes confirmed the triploids' parental combinations. • DNA marker analysis identified 'Summer Fresh' as the pollen donor of 'Yellow Bell'. • Tri-allelic genotype analysis also confirmed the parentage of triploid 'Tahiti lime'. Abstract Triploid breeding is an effective way to obtain seedless hybrids. In addition to artificial breeding, some triploid cultivars occur naturally in the genus Citrus. 'Yellow Bell', a new lemon cultivar recently patented in Japan was selected from the small seed of an open-pollinated 'Villafranca' fruit. Therefore, it has an unknown pollen parent. To characterize the pollen parent of 'Yellow Bell', possible parental cultivars were genotyped using simple sequence repeat markers, and then the parental relationships were estimated by establishing the inheritance of tri-allelic marker genotypes. As a result, the pollen-donating parent of 'Yellow Bell' was determined to be 'Summer Fresh', which was growing 40 m from the maternal tree in the same orchard. The parentage of 'Tahiti lime', a lime cultivar having a long cultivation history, was evaluated in a similar manner and it was confirmed that 'Mexican lime' and a true lemon cultivar were the parents. [ABSTRACT FROM AUTHOR]

Highlights • A + D formulation inhibited different growth stages of Phytophthora citrophthora. • A + D applied on postharvest lemons exhibited BR preventive activity. • A + D lacked brown rot curative activity on postharvest lemons. • Field A + D application prevented BR on fruit harvested and inoculated up to 21 d after. Abstract Brown Rot (BR), caused by Phytophthora spp., is a citrus postharvest disease. In Argentina, world leader in lemon production, BR management is based on cultural practices and chemical control using inorganic salts of limited efficacy. Commercial formulations containing ametoctradin plus dimethomorph (A + D) and ametoctradin plus methiran (A + M) have been recommended against Phytophthora infestans in potato crops; however, their use on citrus is unexplored. The aim of this work was to evaluate the effectiveness of A + D and A + M to inhibit a Phytophthora citrophthora local isolate and to control BR in lemons by pre- and postharvest applications. A + D affected zoospore structure and motility, and inhibited mycelial growth and sporangia formation more efficiently than A + M. In applications on postharvest lemons, A + D presented BR preventive activity (90% incidence reduction), while it lacked curative action. A field treatment with A + D reduced 50% of BR incidence in lemons harvested and inoculated up to 21 d post-application. Our results encourage the incorporation of the commercial A + D formulation into the management strategies to reduce or avoid citrus BR. [ABSTRACT FROM AUTHOR]

Highlights • The highest graft success percentage and highest concentration of micro-mineral were observed in Tahiti and Deperse scions on Volkamer rootstock. • IAC, Tahitian lime, Persian lime, and Deperse lime genotypes on Volkamer lemon rootstock were the best combination, respectively. • In the non-infected areas to WBDL, Mexican lime rootstock with Tahitian lime scion is recommended. Abstract This study was conducted in order to examine the effect of different rootstocks on vegetative growth and mineral elements' content in scion of different Persian lime genotypes. For this purpose, this study was arranged as factorial in randomized complete block design with two factors including rootstock (Bakraei, Mexican lime, Volkamer lemon and Sour orange) and scion (IAC, Tahiti lime, Deperse lime and Persian lime) during 2014-2017. T-budding method was used for grafting and some parameters such as graft success percentage, scion length and diameter growth and amount of mineral elements in the leaf of the studied scions were measured. According to our results, the highest graft success percentage and rate was observed in Tahiti and Deperse lime scions on Volkamer lemon rootstock; the highest length and diameter of scion was observed in IAC scion on Volkamer lemon rootstock. The highest lengthwise and diameter growth velocity index of the scion was observed for IAC scion on Volkamer lemon rootstock as well as for Tahiti lime on Mexican lime and Volkamer lemon rootstocks while the lowest rate was related to IAC and Persian lime scions, on Bakraei and Sour orange rootstock respectively s. The highest fresh and dry weight of scions was related to IAC and Tahiti lime scions on Volkamer lemon rootstock. The highest and lowest nitrogen levels were observed in Deperse lime and Persian lime scions, on Bakraei rootstock respectively. The highest concentration of iron, zinc and manganese was obtained from the scion of Deperse lime on Volkamer lemon rootstock and the lowest concentration of sodium was obtained from the scions on Volkamer lemon rootstock. According to the results of this investigation studying on the interaction between rootstock and scion regarding the total vegetative traits and mineral elements, Volkamer lemon rootstock is introduced as one of the best scion compounds with scions of IAC, Tahiti lime, Persian lime and Deperse lime, respectively. In areas which are non-infected to Witches Broom Disease of Lime, Mexican lime rootstock with Tahiti lime scion is recommended. [ABSTRACT FROM AUTHOR]

Highlights • The morphological characteristics and reproductive potential of three autotetraploid kumquats were examined. • Tetraploid kumquats had the typical morphological characteristics of tetraploid Citrus plants. • The fruits of these tetraploid kumquats showed desirable traits for kumquats such as thicker pericarp and higher SSC. • When tetraploids were crossed with diploid kumquats, triploid progenies were obtained. Abstract Three Fortunella (kumquat) species, the Meiwa kumquat (F. crassifolia Swingle), the Round kumquat [ F. japonica (Thunb.) Swingle] and the Changshou kumquat (F. obovata hort. ex Tanaka), showing tetraploid, which had been induced by treating the seeds with colchicine, were examined for origin and horticultural characteristics (e. g. morphology of leaves, flowers, pollen and fruits). Additionally, these tetraploid kumquats were crossed to produce triploid kumquats. All of the tetraploids were confirmed to be derived from the nucellar embryo of each original kumquat by examining their chromosomal composition with chromomycin A 3 staining. All of the tetraploid kumquats had the typical morphological characteristics of tetraploid Citrus plants, such as round and thick leaves, and large flowers and pollen grains. On the other hand, the fruits of these tetraploid plants showed desirable traits for kumquats such as thicker pericarp and higher soluble solids content. Furthermore, when these tetraploids were crossed with some diploid cultivars, triploid progenies were obtained from almost all of the cross combinations. [ABSTRACT FROM AUTHOR]

Highlights • Physiological and biochemistry parameters were studied in citrus rootstock genotypes under B excess in the irrigation water. • The rootstocks used were Forner Alcaide nº5 and its two progenitors the genotypes citrange Carrizo and mandarin Cleopatra. • Forner Alcaide nº 5 was more B-excess tolerant than citrange Carrizo but not than mandarin Cleopatra. • Leaf B concentration and its toxicity determines the contrasting responses among citrus rootstock genotypes. Abstract Citrus rootstocks, (i.e. Carrizo citrange, Cleopatra mandarin, and Forner-Alcaide nº5) influence the agronomical and physiological behavior of citrus trees under unfavorable environmental conditions. Citrus are very sensitive to boron (B) toxicity. However, when good-quality water is scarce, growers must use water treatment and desalination plant water for irrigation, which may have a B concentration that is above the threshold recommended for citrus trees (0.5 mg L−1). There is little information on the relative tolerance of citrus rootstocks to an excess of B, and the physiological and biochemical mechanisms involved. In this work, the morphological, physiological, biochemical and nutritional responses of three citrus rootstock plants, Carrizo citrange (Citrus sinensis (L.) Osb. × Poncirus trifoliata (L.) Raf.), Cleopatra mandarin (Citrus reshni Hort. ex Tan.) and Forner-Alcaide nº 5 (Cleopatra mandarin × Poncirus trifoliata (L.) Raf.), under different concentrations of B in the irrigation water (0.25, 5 and 10 mg L−1), grown in containers in a greenhouse, were studied. The results showed that Carrizo citrange was very sensitive to B toxicity, as the plants had the most reduced vegetative growth, the greatest concentration of B in their leaves, stem and roots, a greater concentration of malondialdehyde in leaves, and a lesser net assimilation of CO 2. The other two genotypes did not show differences in the accumulation of B in their tissues. Nevertheless, Cleopatra mandarin showed a greater tolerance, as its photosynthetic system was less affected by B toxicity, probably due to its potent antioxidant system, which is based on a high activity of catalase, which restricts the accumulation of malondialdehyde in its leaves. Forner-Alcaide nº 5 had an intermediate tolerance, similar to Cleopatra mandarin than to Carrizo citrange, as per the accumulation of B in its leaves. Forner-Alcaide nº 5 was the only genotype whose root was not affected by B toxicity. [ABSTRACT FROM AUTHOR]

Highlights • CIELAB color coordinates and concentration of total carotenoids, chlorophyll, β-cryptoxanthin, and lutein were measured in the skin of lemon fruits. • Measurements were performed in the September-January period in three consecutive years in Fino 49 fruits of trees located in two experimental orchards. • Color coordinates a*, b*, L* and H were highly correlated with all pigments measured except for β-cryptoxanthin. • Pigment changes showed chlorophyll and lutein degradation and an increase of β-cryptoxanthin concentration, which was the pigment of the yellow color. Abstract In the present work, the coordinates L*, a* and b* from the CIELAB color space, as well as the chlorophyll, total carotenoids and the content of the carotenoids Lutein and β-cryptoxanthin were measured in the skin of fruits from the Fino 49 lemon during its development, with the aim of understanding the relationship that exists between the color changes of the fruit's skin (color coordinates) and the pigment content. Also, the understanding of the relative importance of the contents of lutein and β-cryptoxanthin with respect to the total content of carotenoids was sought. The period of study lasted three years; from September 2015 to January 2016, from September 2016 to January 2017, and from September 2017 to January 2018, the periods that comprised the color changes of the lemon fruit until its harvest. The fruits were measured every two weeks in the experimental plot of the IMIDA (Murcian Institute of Agricultural and Food Research and Development) located at La Alberca (Murcia, Spain) and in the experimental orchards from the CEBAS-CSIC, located in Santomera (Murcia). During the experiment, the color and chlorophyll, Lutein and β-cryptoxanthin concentrations were measured. The results showed that there was a good correlation between the color coordinates and the pigments responsible for the lemon's skin color: all the color pigments were correlated with the a*, b* color coordinates and the Hue angle index. Throughout the fruit's maturation, a degradation of the chlorophylls was observed, as well as an increase of β-cryptoxanthin, which is responsible for the green and yellow color of the fruits, respectively. Lutein, which was found in high concentrations, decreased with time, but did not contribute to the fruit's color. [ABSTRACT FROM AUTHOR]

Highlights • ' Red Rough' lemon favor greater yield to sweet oranges on tropical hardsetting soils. • 'Valencia Tuxpan' show lower tolerance to drought on tropical hardsetting soils. • In drier years 'Red Rough' lemon favors higher yield on tropical hardsetting soils. • 'Santa Cruz' Rangpur lime favor high-quality fruits on tropical hardsetting soils. • 'Sunki Tropical' and VKL x RPL-010 are as productive as 'Santa Cruz' Rangpur lime. Abstract Naturally occurring subsoil horizon restricting root development and a narrow genetic base of scion-rootstock combinations make the citriculture in Brazilian Northeast prone to biotic and abiotic stresses. The diversification of citrus orchards through the introduction of new scion-rootstocks combinations is an important strategy to reduce the risks associated with these constraints. Three experiments aiming at identifying appropriate scion-rootstock combinations for enhancing genetic diversification in citrus orchards under rainfed conditions in tropical hardsetting soils were established in Sergipe state in 2008. In each one, a different sweet orange ('Sincora', 'Valencia Tuxpan' and 'Pineapple') was grafted on six rootstocks ('Santa Cruz' Rangpur lime, 'Red Rough' lemon, 'Orlando' tangelo, 'Sunki Tropical' mandarin, HTR–051 and VKLxRPL–010 hybrids). After eight years the experiments were evaluated for plant development, yield performance and fruit quality. In general, all sweet oranges grafted on 'Red Rough' lemon showed great development and cumulative yield as does with 'Santa Cruz' Rangpur lime, with the later showing better fruit quality as an advantage. Inversely, HTR-051 hybrid displayed low yields despite high yield efficiency, for this rootstock induces dwarfism. 'Sunki Tropical' mandarin brought high yields of medium quality fruits, while the VKLxRPL-010 hybrid induced productive precocity, especially for 'Sincora' sweet oranges. Based upon these results, all tested scions grafted on 'Red Rough' lemon and 'Santa Cruz' Rangpur lime, followed by 'Sunki Tropical' mandarin are indicated for genetic diversification of groves, when planted at conventional density. On the other hand, the hybrid HTR-051 seems to have great potential for high density orchards, since it shows high yield efficiency and good quality of fruit. [ABSTRACT FROM AUTHOR]

Metaphase chromosomes of five Korean landrace citrus were analyzed to understand the phylogenetic relationship among them and to compare these characteristics with those of other Citrus species including previously reported six Korean landrace mandarins at a cytogenetic level using CMA banding patterns and rDNA loci. The CMA banding patterns of the five Korean landrace citrus were 1 A+2B+2C+6D+7E in dongjeongkyul ( C. erythrosa ), 3B+1C+7D+5E+2 F in hongkyul ( C. tachibana ), 2 A+1B+3C+4D+8E in sadoogam ( C. pseudogulgul ), 1 A+3B+1C+7D+6E in dangyooza ( C. grandis ), 1 A+1B+1C+9D+6E in jigak ( C. aurantium ). All types of chromosome bands were present in all accessions except in hongkyul, in which type A chromosome was absent but two of type F chromosomes were observed. The numbers of type A, B, and C chromosomes were lower in all accessions. In contrast, the type D and E chromosomes were remarkably constant and predominantly observed in all accession. The distributions of 5S and 45S rDNA loci by FISH were heterogeneous among them. All accessions possessed one 5S rDNA locus except for hongkyul, which displayed two 5S rDNA loci. And they always co-localized with 45S rDNA locus. All 45S rDNA loci were homotopic to CMA-positive regions. Every type A and B chromosomes possessed one 45S rDNA locus in the proximal region of the chromosomes. There was no type C and E chromosome with rDNA observed. Hierarchical cluster analysis and UPGMA phenogram based on CMA banding pattern combined with 5S and 45S rDNA loci of 11 Korean landrace citrus showed the strong karyotype dissimilarity in the invested taxa. [ABSTRACT FROM AUTHOR]

For the first time, efficiency of the carnauba wax-nanoclay emulsions in preserving postharvest quality of ‘Valencia’ fruit was evaluated upon simulated storage and marketing. The different coatings containing nanoclay (i.e., 0.0, 0.5 and 1.0 w%) applied on orange and their performance were compared with uncoated fruit and two different commercial waxes. In general, the presence of nanoclay in the carnauba wax formulation greatly enhanced fruit sensory acceptability, nutritional quality and effectively prevented fruit weight loss during storage. Moreover, according to several statistical analyses such as cluster analysis, PCoA and Heat map-based surveys, the carnauba wax-nanoclay emulsions possessed similar behaviors with the maximum efficiency and placed accordingly in the same cluster, while the other four treatments were lonely occupied the next positions. Such nano-formulations could propose as a promising and cost-effective alternative avenue for commercial fruit waxes, towards sustainable postharvest management in retarding respiration rates and weight loss alongside preserving sensory and nutritional quality of fruits. [ABSTRACT FROM AUTHOR]

• Fe (Arg) application increased proline and carbohydrate content by 16.40% and 13.21% and decreased the phenol and MDA content by 10.68% and 30.12%. • Enzyme activities such as peroxidase (POD), catalase (CAT), and super oxidase dismutase (SOD) were highest at pH 8.2 and salinity 120 mM and 0.2% Fe (Arg). • The highest expression of NAC36 and ERF109 genes were recorded at the co-treatments of pH 8.2, 60 mM NaCl and 0.2% Fe(Arg). • The highest photosynthesis rate, chlorophyll, and carotenoids, were obtained at pH 6.5, the salinity of 0 mM and 0.2% Fe (Arg) which increased by 3.70%, 22.44%, and 5.26%. In agricultural production systems, iron (II)-amino acid chelate is the latest novel compounds that enhance plant tolerance against soil stress. Salinity-alkaline stress can be considered one of the most critical threats to crops. This study was conducted to investigate the impact of iron(II)–amino acid chelate on some biochemical characteristics and genes expression of Sour Oranges under salinity and alkaline stress. The studied factors comprised two levels of pH (6.5 and 8.2), three levels of salinity (0, 60, and 120 mM NaCl), and three levels of Iron(II)–Arginine Chelate (0, 0.1, and 0.2%) in three replications. The results revealed that the highest photosynthesis rate was obtained at pH 6.5, the salinity of 0 mM and 0.2% Fe (Arg). Furthermore, Fe (Arg) application increased proline and carbohydrate content by 16.40% and 13.21% and decreased the phenol and MDA content by 10.68% and 30.12%, respectively, rather than the control. Enzyme activities such as peroxidase (POD), catalase (CAT), and super oxidase dismutase (SOD) were highest at pH 8.2, salinity 120 mM, and 0.2% Fe (Arg). Also, WRKY46 and MYB308 genes were highly expressed at pH 6.5, 120 mM NaCl and 0% Fe (Arg) and pH 8.2, 120 mM NaCl and 0.1% Fe(Arg) respectively. Moreover, the highest expression of NAC36 and ERF109 genes were recorded at the co-treatments of pH 8.2, 60 mM NaCl and 0.2% Fe(Arg), and pH 8.2 with no salinity stress and Fe(Arg) application, respectively. Therefore, Fe(Arg) foliar application partially alleviates the adverse effects of salinity and alkaline stress in Sour Orange. [ABSTRACT FROM AUTHOR]

• The supply of b improved trifoliate seedlings growth by activating antioxidant system. • B supplementation increased the nutrients of zn and Fe, which in turn act on provoked the antioxidant enzymes. • Different pathways to resisted the damage of H + toxicity in root and leaf. Boron (B) deficiency and H +toxicity are two prominent factors that severly restrict trifoliate seedlings growth in acid soil. Exogenous B can support to mitigate the harm of H +toxicity, however, research on the protective mechanism and the impact of physiological processes in citrus is limited. To fill the above gaps, the current study was performed on trifoliate rootstock using two pH levels (pH 4 and pH 6) and various B treatments (B0, B1, B2, B3, B4) to identify how B confers tolerance to H + toxicity in trifoliate rootstock. Our results illustrate that H +toxicity suppressed plant growth, specifically the root elongation (27.22%). Boron capitalized the positive effect on plant growth as soon as it is applied to culture medium. The supply of B increased the activity of antioxidant enzymes and the content of antioxidant substances in root of trifoliate seedlings under H + toxicity to scavenging the massively accumulated reactive oxygen species (ROS), reducing the malondialdehyde (MDA) content (12.07%-53.45%) and promoting root development. Meanwhile, the higher levels of osmolytes after B supply in root were better for maintaining water in cell and resisting H + toxicity. Furthermore, B supplementation improved nutrients content including macro and microelements in root, especially the elements constituting superoxide dismutase (SOD), which in turn activated the antioxidant enzymes system. In conclusion, the ameliorative effects of B to H +toxicity in trifoliate seedlings was based on B homeostasis, improved antioxidant defense system, and then nutrient content. These findings provide a new insight into the regulation of H +toxicity tolerance of citrus by B fertilizer application in acid soils. [ABSTRACT FROM AUTHOR]

• Hypoxia stress increased PA-synthesizing enzymes' activity. • Rich-16-6 rootstock was more receptive to root application of SiNP than foliar. • SiNP improved rootstocks' ability to mitigate oxidative damage. Polyamines (PAs) have a variety of roles in plant environment interactions and stress responses, which control the tolerance induction of plants under hypoxic stress. Citrus plants are sensitive to waterlogging conditions because it frequently causes root zone hypoxia (RZH) and severe abiotic stress to their growth. Therefore, the present study investigated whether silicon (SiO 2) could improve hypoxia tolerance by modulating the activity of PAs biosynthesizing enzymes and, in turn, variation in different PAs profiles involved in critical metabolic processes. Three commercially used citrus rootstocks (Carrizo citrange, Rubidoux, and Rich16-6) were subjected to flooding environments (with and without oxygen) with different treatments in both the presence and absence of SiNP (silicon nanoparticles) through roots and foliar application. Hypoxia stress increased PA-synthesizing enzymes' activity and PAs' formation in plant leaves and roots. Under hypoxia stress, exogenous SiNP raised the concentration of endogenous silicon (SiO 2) and a large concentration of polyamines (PAs) by regulating PA biosynthesis. In the response to SiNP, it was also observed that an increase in plant biomass (leaf, stem, and root tissues) resulted in an overall improvement in plant growth. Rich-16-6 rootstock was found to be more receptive to root application of SiNP than foliar application in contrast to Rubidoux and Carrizo citrange plants, indicating genotype variability of citrus rootstocks in silicon uptake. Our findings demonstrate that the accumulation of silicon-induced polyamine enhanced growth and reduced reactive oxygen species (ROS) that might help to reduce oxidative damage in citrus rootstocks under hypoxic stress, providing an optimal strategy for stress tolerance. This study enhances the impact of nanoparticles on fruit crop production, significantly relieving pressure, and is a potential platform for future research. [Display omitted] [ABSTRACT FROM AUTHOR]

• Multi-omic approach (proteomics and transcriptomics) were used to identify nodes that can help in explaining these differences and ultimately contribute to the understanding of the midrib and root in response to the CLas early invasion. • A new grafting method, leaf-disk grafting, was uesd in this study. • We observed that lignin synthesis, secondary metabolites, and detoxification pathway played the important roles in response to the CLas early invasion. • Cell wall related genes were upregulated and most hormone metabolism were suppressed, respectively, during CLas early invasion. Citrus Huanglongbing (HLB), caused by Candidatus Liberibacter asiaticus (C Las), is the most destructive disease of citrus plant. HLB can harm almost all citrus varieties and no cure is currently available. Our previous study reported that Wanjincheng orange (Citrus sinensis Osbeck) leaf and root exhibit significant difference in response to CLas infection using leaf-disk grafting. In this study, we used a multiomic approach (proteomics and transcriptomics) to identify nodes that can help in explaining these differences and ultimately contribute to the understanding of the response of midrib and root in the early invasion of C Las. The results of comparative transcriptomic analysis displayed that 2,782 differentially expressed genes (DEGs) were upregulated and 2,807 were downregulated. Meanwhile, the results of comparative proteomic analysis displayed that 226 and 182 differentially expressed proteins (DEPs) were up- and downregulated by C Las, respectively. Transcriptomic and proteomic association analyses revealed 2 downregulated and 6 upregulated genes in midrib and root. The analysis of DEGs and DEPs revealed that secondary metabolites, and detoxification pathways played important roles in response to the early invasion of C Las. Moreover, nitrogen metabolism in midrib and root was influenced by C Las. This study revealed the transcriptomic and proteomic differences between midrib and root in Wanjincheng orange during early invasion of C Las and provided some potential genes and proteins for breeding HLB-tolerant citrus in future. [ABSTRACT FROM AUTHOR]

• Autotetraploid of citrus junos shows higher salt tolerance than the corresponding diploid. • Transcriptomes of diploid and autotetraploid differ greatly under salt stress. • Plant chitin signaling is the key pathway responding to salt stress in autotetraploid citrus junos. Polyploidization is a widespread phenomenon in flowering plants, and it often enhances abiotic stress tolerance. However, the related molecular mechanism remains largely unknown, especially for perennial woody plants. Here, we found that autotetraploid citrus (Citrus junos Sieb. ex Tanaka) had greater salt tolerance than their diploid progenitors. Transcriptome analysis identified a large number of differentially expressed genes (DEGs) between autotetraploid and diploid roots under salt stress. GO analysis showed that chitin response-related genes were enriched in roots of autotetraploid. Consistently, the autotetraploids exhibited higher chitinases activity than the diploids under salt stress. The top five transcription factor (TF) families with the largest number of TFs were bHLH, ERF, MYB, NAC, and WRKY in autotetraploids and diploids, and 25 TFs were higher expressed in autotetraploids than in diploids under salt stress. Our results revealed that salt stress induced the activation of chitin pathway, thus reducing in ROS accumulation, eventually enhancing salt tolerance of autotetraploid citrus. Our research provides the theoretical basis for citrus breeding aiming at abiotic stress tolerance enhancement. [ABSTRACT FROM AUTHOR]

• The CND-r² indices were effective in establishing the nutritional status of citrus varieties;. • The CND methodology established the critical level of adequate nutrients in leaves;. • Establishment of the real need for fertilizer application in citrus orchards;. • Multi-nutrient associations more effective in expressing the limitation of citrus productivity. Critical levels (CL) and sufficiency ranges (SR) of nutrients in citrus leaves for fruit production for fresh market consumption may help in defining the real need for fertilizer application in orchards, such as those located in tropical and subtropical soils, which have low natural fertility. The study aimed to establish and compare the nutritional patterns obtained by the Composition Nutritional Diagnosis method (CND) in citrus grown for consumption for fresh, in a subtropical climate and then generate CL and SR in leaves. A database was used with fruit production and leaf nutrient contents obtained in the 2016/17, 2017/18, 2019/20 and 2020/21 harvests in non-irrigated commercial orange and tangerine orchards. The multivariate CND calculation method was used. The CND method was effective in diagnosing the nutritional status of citrus, regarding the concentration of the nutrients N, P, K, Ca, Mg, S, Cu, Fe, Mn, Zn and B in deficient, adequate and excessive concentrations. The CL calculated were 18, 1.2, 9.0, 25, 2.8 and 3.0 g kg−1 of N, P, K, Ca, Mg and S, respectively, and 117, 45, 97, 66 and 19 mg kg−1 of B, Cu, Fe, Mn and Zn, respectively. The existing recommendation in the regional recommendation guide for citrus may be overestimating the need for application of the micronutrients. The SRs established from the CND index are different from those obtained in other countries and regions. Multi-nutrient associations were more effective than single nutrient analysis in expressing that limitation of a particular element can reduce citrus productivity. The adoption of the nutritional standards for macronutrients obtained may allow the rational use of fertilizers in citrus orchards, with an improvement in the nutritional balance of the plants, which will consequently have greater yields. [ABSTRACT FROM AUTHOR]

During the last decade, the worldwide market for fresh citrus fruits, mainly those that are seedless with easy-peeling and nice orange-colored skin, greatly increased. The elaboration of organoleptic quality is strongly defined by genetic and environmental components and their interaction. While several mandarin breeding programs have been developed worldwide, very few focus on the issues of tropical areas, and few data are available for citrus germplasm evaluation in a tropical environment. To optimize the mandarin production system, research related to the exploration of existing citrus germplasm, the expansion of the genetic base of orchards and the evaluation of the agronomic potential of new genotypes must be conducted. The objective of this study was to characterize and evaluate 25 mandarin varieties from typical Brazilian tropical citrus germplasm according to genetic, morphological and physicochemical traits over two consecutive years. Simple correlation coefficient analysis showed significant positive and negative correlations among characteristics (e.g., fruit diameter and total soluble solids). Principal component analysis showed that fruit diameter, fruit weight, total soluble solids, total titratable acidity, fruit surface texture and adherence of albedo to pulp were the variables that most contributed to phenotypic variability. Genetic diversity analysis grouped accessions in four main clusters corresponding to traditional edible Chinese mandarins, Mediterranean mandarins, tangelos and tango hybrids and nonedible mandarins. A multiple factorial analysis showed that phenotypic diversity was associated with genetic diversity mainly for taste, shape and color traits. The results of this study will be used for the conservation of the indigenous germplasm, identification of varieties with valuable traits related to fruit quality and subsequent exploitation in citrus breeding programs. [ABSTRACT FROM AUTHOR]