Sugar is crucial for fruit flavor and nutrition, directly influencing the sensory perception and acceptance of consumers. Fruit sugar accumulation primarily depends on sugar metabolism and transport; however, the molecular regulatory mechanisms in citrus have not been fully elucidated. Physiological and metabolic analyses were performed on the 'Ehime 30' and 'Harumi' hybrid population, which exhibited stable transgressive levels of total soluble solids (TSS) and sucrose. High- (#13, #107) and low- (#237, #290) TSS and sucrose fruits were selected for transcriptional analyses. The results showed that CitERF36 exhibited significantly higher expression in high-TSS and sucrose fruits. Moreover, in this population, a significant positive correlation was observed between CitERF36 expression and both TSS and sucrose content. Localized to the nucleus, CitERF36 showed markedly higher expression in fruit than in other organs during development. In CitERF36-overexpressing tomato fruits, sucrose content was significantly elevated, whereas silencing CitERF36 in citrus led to a notable reduction. Through DNA affinity purification-sequencing analysis, Y1H, electrophoretic mobility shift assay, and dual-luciferase assays, CitERF36 was shown to activate CitSUT2 expression and repress CitvINV3 expression. The CitSUT2 locus, encoding CitSUT2.1 and CitSUT2.2 in mandarin, exhibited proton-coupled sucrose transport activity in Xenopus laevis oocytes and mediated sucrose accumulation in genetically transformed tomato and citrus. Additionally, CitvINV3, localized to the vacuole, showed the highest invertase activity at pH 5 in yeast complementation assays and facilitated the conversion of sucrose to hexose using transformation in citrus. These findings reveal a novel regulatory mechanism influencing fruit sucrose transport and metabolism, providing a theoretical basis for enhancing citrus fruit quality.

Gene editing technology continues to advance, and the range of available editing tools is steadily expanding. Recently, several compact and ultracompact systems have been developed, gaining considerable attention because their components can be efficiently packaged into viral vectors. To identify compact tools suitable for efficient genome editing in citrus, Casπ, CoCas9, along with their respective single guide RNAs, were synthesized, and CRISPR/Casπ and CRISPR/CoCas9 constructs were designed to assess their editing efficiency in ‘Wanjincheng’ orange (Citrus sinensis Osbeck). The Casπ was able to mediate genome editing in the citrus genome, although with low efficiency. In comparison, CoCas9 showed a transformation efficiency three times higher than that of the widely used SpCas9. Moreover, while the gene editing efficiency of CoCas9 was comparable to that of SpCas9, the significantly elevated transformation efficiency resulted in a significantly higher overall editing efficiency for CoCas9 relative to SpCas9. Mutation profiles generated by CoCas9 and SpCas9 were highly similar, and both nucleases displayed comparable target specificity at three potential off-target sites. These results indicate that Casπ is not suitable for application in citrus genome editing, whereas CoCas9 represents a promising alternative to SpCas9 for efficient and precise genome modification in citrus.

Bitterness is regarded as one of the crucial characteristics influencing citrus fruit flavor and post-harvest processing. The novel citrus cultivar ‘Yangguang No.1’ (YG) exhibits a relatively reduced level of bitterness, particularly in the peel, compared to its parent (‘Chunxiang’, CX). In this study, integrated metabolomic and transcriptomic analyses were employed to investigate the disparities in bitterness between YG and CX. Metabolomic profiling, conducted using a widely targeted ultra-performance liquid chromatography-electrospray ionization-tandem mass spectrometry (UPLC-ESI-MS/MS) approachd, revealed that flavonoid compounds associated with bitterness, particularly nobiletin and tangeretin, accumulated at significantly lower levels in YG. Transcriptome analysis indicated that differentially expressed genes in YG relative to CX were markedly enriched in metabolic pathways including phenylpropanoid biosynthesis and flavonoid biosynthesis. Weighted gene co-expression network analysis (WGCNA) revealed that the expression of CitF3’H, CitF3’H-like and CitOMT2/3/5/10/11/12 was closely correlated with the accumulation of bitter flavonoids. Functional validation showed that overexpression of CitF3’H-like in YG peel resulted in increased nobiletin content, whereas virus-induced gene silencing (VIGS) of CitF3’H-like in CX seedlings led to a significant reduction in nobiletin levels. These findings demonstrated that CitF3’H-like played a functional role in the biosynthesis of nobiletin in citrus. Collectively, this study identifies CitF3’H-like as a key candidate gene involved in the accumulation of bitter compound, and provides valuable insights for breeding citrus varieties suitable for post-harvest processing through reduced bitterness.

From 2018 to 2021,carry out on-tree storage on Orah mandarin for four consecutive years.Fruit quality was collected and analyzed monthly from January to June,and temperature,rainfall,fruit dropping,fruit puffiness and sac granulation were investigated. The results showed that the rising temperatures in the spring caused the peel color to change from red to yellow and that the fruit continued to grow during the on-tree storage period. In mid-June,the single fruit weight,transverse diameter and longitudinal diameter increased by 29.2%–40.4%,7.6%–9.8% and 7.5%–11.5%,respectively,compared with the fruit in January. The content of total soluble solids were the higher in February–March（13.03%–15.97%）but decreased in April when the new shoots grew and flowered. This value then increased from May and by mid-June,it had exceeded the levels previously measured in February–March.The hundred-point test system of pulp crisp property was above 80,and the highest score was in March.The rate of fruit that was edible and suitable to be used as juice did not change significantly. However,the hardness of both the peel and pulp and the contents of titratable acidity and vitamin C decreased by 21.3%–23.9%,15.8%–45.1%,28.4%–53.2% and 27.2%–45.4%,respectively,during the on-tree storage period in mid-June compared with those in January. Spraying fungicide can effectively control the fruit drop caused by fungal infections,and storing approximately half of the fruit on the trees had no significant effect on the yield of following year. Orah mandarin stored on-tree to mid-June was of high quality,which renders them suitable to fill the void of high-quality citrus fruit for sale in summer.

为阐明不同发光二极管(LED)光质对金秋砂糖橘生长发育和光合特性的影响,以金秋砂糖橘容器苗为试验材料,设置LED红光(R)、蓝光(B)、红蓝复合光(RB11、RB21、RB41、RB81)共6种光质处理,并以LED白光(W)为对照组.处理2个月后研究新梢茎叶形态、生物量、光合色素含量和光合特征参数变化,并对相关指标进行主成分分析.结果表明:红光显著促进新梢茎长、叶片数、叶面积和生物量,抑制茎粗和叶厚,而蓝光的作用与红光相反;低比例红光显著促进新梢茎长、茎粗、叶片数、叶面积和生物量,但随着红光比例的增加呈显著降低趋势,其中,RB11处理的茎长、茎粗、叶片数和叶面积分别是对照组的1.97倍(P<0.05)、1.14倍(P>0.05)、2.05倍(P<0.05)、1.84倍(P<0.05),新梢鲜重和干重,以及叶鲜重、茎鲜重、叶干重和茎干重分别是对照组的1.68倍(P<0.05)、1.88倍(P<0.05)、1.46倍(P>0.05)、3.00倍(P<0.05)、1.68倍(P<0.05)、3.06倍(P<0.05);红、蓝单色光均导致光合色素含量和净光合速率(net photosyn-thetic rate,Pn)显著降低,而红蓝复合光促进叶绿素b(chlb)、类胡萝卜素(car)含量和Pn的增加,并且随着红光比例的增加,叶绿素含量、car含量、chla/chlb、Pn呈显著降低趋势;红蓝单色光和复合光导致气孔导度(stomatal conductance,Gs)(除RB41处理外)和蒸腾速率(transpiration rate,Tr)(除RB21和RB41处理外)呈降低趋势.主成分分析结果显示,红蓝1:1复合光(RB11)更利于金秋砂糖橘新梢生长发育、物质积累和光合作用.综上,该研究为建立金秋砂糖橘苗木快速繁育的LED补光技术提供了理论依据.

There is little information on the impact of agrometeorological factors on late-maturing citrus varieties. Here, several indices of the agronomic and physiological quality of ‘Orah’ mandarin fruit during three consecutive years were studied along with the metabolic traits under different climatic conditions. The average yield was high in the dry-hot valleys. However, the yield and yield efficiency were the lowest in areas with humid-sparse sunlight. The fruit in the dry-hot valleys and south subtropical regions were large and had seed number beyond 15.38, while the fruit in areas with humid-sparse sunlight were reddish and had few seeds. A statistical analysis of the total soluble solids (TSS) within three years showed that the fruit with highest amounts were in the mid-subtropical regions (≥ 14.03%), followed by the dry-hot valleys. The fruit of tropical rainforest areas (titratable acid ≥ 0.67%) were considered to contain the highest percentage of acid. A metabolic analysis showed that the contents of several metabolites, such as malic acid and proline, varied noticeably across different climatic regions. Correlation and factor analyses of the agronomic, physiological and metabolic indices with meteorological parameters revealed that the fruit yield and quality in the dry-hot valleys were superior to those observed in other regions and that temperature, in particular at the degreening and overwintering stages, along with the hours of sunshine significantly resulted in a considerable degree of variation in the indicators of fruit heterogeneity, such as weight, TSS, malic acid and proline.

在桂中南柑橘园区武鸣区、德保县、西乡塘区、来宾市、隆安县、马山县、上林县、钟山县等8个市(县、区)选取104个具代表性的柑橘园采集土壤样本,定量测定土壤pH、有机质和矿质元素含量等,并进行主成分和聚类系统分析,以探明桂中南柑橘园区土壤养分丰缺状况.结果表明:桂中南柑橘园土壤pH值以酸性为主,最适宜柑橘生长的微酸性土壤(5.5≤pH<6.5)占比仅为19.2％;49.0％的橘园土壤有机质含量不足;土壤碱解氮及有效镁、有效锌、有效铜、有效硼含量普遍不足,低于适量水平的比例分别为51.0％、93.3％、93.3％、89.4％、92.3％,特别是镁和锌缺失严重,缺失水平占比分别为59.6％和63.5％;有效磷和有效钙主要处于适宜水平,适量以上水平的占比分别为76.0％和71.2％;土壤有效钾丰缺并存,不足、适宜、超标的比例分别为42.3％、24.0％、33.7％;有效铁、有效锰含量丰富,处于适量以上水平的比例分别为83.7％和89.4％;主成分和聚类分析表明,德保县、钟山县和武鸣区果园的土壤养分综合状况要好于其他市(县、区).可见,桂中南柑橘产区生产上应当注意调节土壤pH,适当补充氮、镁和锌肥及增施有机肥,减少铜制剂用量,控制土施硼肥,并重视磷、钙和钾肥的补充与平衡.

[目的]探讨施用氯化钾对脐橙叶片营养、果实产量及品质的影响,分析土壤和植株中氯元素含量与积累状况.[方法]以9年生纽荷尔脐橙为试材,于2018—2019年连续进行了两年田间试验.脐橙果园土壤一个为酸性、一个为碱性.氯化钾年施用量处理为250 g/株(T1)、500 g/株(T2)、1000 g/株(T3),以硫酸钾556 g/株为对照(CK).在果实成熟期,测定了春梢和秋梢叶片中的N、P、K、Ca、Mg、Cl元素和相对叶绿素含量,测产并取样测定了果实品质及Cl-含量,在施肥后测定了0—20和20—40 cm土壤中的Cl-含量.[结果]1)施用不同量氯化钾后果皮、果肉中氯元素含量没有显著变化,土壤和叶片中氯元素含量显著增加.T1处理在酸性土中氯元素含量较碱性土中多,与CK相比,T1处理酸性土中氯元素含量平均增加50.20％,而碱性土增加28.02％;T2处理氯元素含量在酸性土与碱性土中相差不大;T3处理氯元素含量在碱性土中大于酸性土中,与CK相比,酸性土增加79.70％,碱性土增加99.36％.2)T1处理下,在酸性土上脐橙春、秋梢叶片氯元素含量较CK分别增加了21.9％和8.0％,在碱性土上分别增加25.5％和12.7％;T2处理下,在酸性土上分别增加51.9％和45.0％,碱性土上分别增加33.3％和19.3％;T3处理下,在碱性土上分别增加109.7％和98.7％,而在酸性土上分别增加63.8％和58.0％.施用氯化钾后叶片中相对叶绿素、氮和钙元素含量没有显著变化,钾和部分磷元素含量随氯化钾施用量的增多呈增加趋势,镁元素含量略有下降.3)施用氯化钾对果实产量、单果重、亮度、黄色度、可溶性固形物和可滴定酸含量均没有显著影响,部分果实红色度在施用氯化钾代替硫酸钾后显著提高,维生素C含量随氯化钾浓度的增高有增加趋势.[结论]短期施用氯化钾对果实中氯元素含量无显著影响,土壤和叶片中氯元素含量则显著增加,但均处在安全阈值以内.短期施用氯化钾对柑橘果实产量及品质无显著不良影响,叶片营养受影响较小,因此,酸、碱性土壤脐橙园短期内施用适量的氯化钾代替硫酸钾是可行的.

[目的]土壤pH影响土壤锰(Mn)有效性,酸性土壤易出现Mn过量问题,我国柑橘主要分布在南方红黄壤区,柑橘园酸性或强酸性土壤比例高,柑橘园土壤Mn过量较普遍.为此,我们研究了4种柑橘砧木对Mn过量胁迫的耐受性和生理响应,以期为Mn过量土壤上适宜砧木的选择提供依据.[方法]选用枳、资阳香橙、红橘和沙田柚4种常用柑橘砧木苗为材料,采用蛭石与珍珠岩1:1的基质进行了营养液栽培试验,营养液中Mn处理包括0.01(对照)、0.05、0.25、1.25和6.25 mmol/L 5个浓度.观察砧木苗的生长反应和中毒症状,处理60天时,测定叶绿素含量和光合参数;处理67天终止处理,测定砧木苗生长量、生物量、过氧化物酶活性、营养元素含量等生理生化指标,并用隶属函数对砧木过量锰的耐受性进行综合评价.[结果]柑橘砧木苗出现锰中毒的症状为叶片失绿,出现褐色坏死斑点;根量变少,呈现褐色斑点.4种砧木苗均在Mn 0.25 mmol/L处理时出现Mn中毒症状,其中枳最先出现症状且最严重,资阳香橙最迟出现症状且最轻;4种砧木在Mn 0.05 mmol/L处理时即出现Mn过量胁迫,表现为地上部和地下部鲜重和干重显著下降,根冠比升高(红橘除外)、叶绿素含量下降、净光合速率降低、气孔开度下降、胞间CO2浓度上升.Mn过量(＞0.05 mmol/L)胁迫使4种砧木叶片细胞膜受损,相对电导率和MDA含量上升;清除活性氧的SOD和POD活性上升,CAT活性下降.Mn过量胁迫影响柑橘砧木的营养元素吸收和转运,叶片和根系Mn含量上升,但随Mn胁迫浓度升高,Mn从根系到叶片的迁移率先降低后升高;Mn过量胁迫使砧木叶片K、P、Ca、Mg、Fe、Zn元素含量下降,根系K、P、Fe、Zn含量上升而Ca、Mg含量下降.[结论]不同砧木对Mn过量胁迫耐受性存在明显的差异,综合评价耐性强弱顺序为:资阳香橙＞沙田柚＞红橘＞枳,高锰土壤的柑橘园可选用资阳香橙做砧木以减轻锰害.

为了探究不同LED光质及配比对红桔幼苗生长和叶绿素荧光特性的影响,以长出两片叶的红桔幼苗为试验材料,设置LED白光(对照)、红光(R)、蓝光(B)、红蓝复合光(R1B1、R4B1,数字指复合光中不同色光的峰面积之比)、红绿蓝复合光(R4G1B1)等6个光照处理,水培培养2个月后观测幼苗的形态参数、生物量、光合色素含量和叶绿素荧光特征参数,并对相关指标进行主成分分析.结果 表明,与对照相比,红、蓝单色光和复合光对红桔幼苗生长明显不利;高比例红蓝复合光添加绿光(R4G1B1),对红桔幼苗生长无明显不利,且株高和株叶面积分别比对照大18.8％(p＜0.05)和28.7％ (p＜0.05),更有利于地上部分(茎、叶)的形态建成和光吸收.红、蓝单色光和复合光,导致幼苗根茎叶的生物量呈降低趋势;高比例红蓝复合光添加绿光(R4G1B1),导致幼苗叶干质量比对照高39.3％(p＜0.05),其他生物量指标与对照无显著差异.在红蓝复合光中,R1B1的光合色素含量无显著变化,R4B1显著抑制了叶绿素a和叶绿素b的合成,R4B1添加绿光后(R4G1B1)使叶绿素a合成有一定恢复.红光导致幼苗的光合作用能力显著降低,蓝光则呈相反趋势,而红蓝复合光和红绿蓝复合光的光合作用能力处于红、蓝单色光之间.经主成分分析,LED红绿蓝复合光(R4G1B1)优于对照和其他处理.

[目的]研究资阳香橙(Citrusjunos Sieb.ex Tanaka)×枳(Poncirus trifoliate Raf.)杂交的8个F1代株系(ZZ1、ZZ6、ZZ7、ZZ31、ZZ42、ZZ60、ZZ65、ZZ948)在pH 8.22的碱性土壤上耐碱性差异,为选育新的耐碱砧木积累数据和材料.[方法]测量了8个杂种砧木及其亲本在碱性土壤上的株高、茎粗、黄化指数、叶片光合色素以及营养元素含量,应用AHP-TOPSIS法对这些砧木的耐碱性做出综合评价.[结果]播种生长23个月的杂种砧木,株高差异显著,在68.52～228.23 cm范围均有分布,其中ZZ6最矮,约为枳株高的1/2;ZZ65最高,约为资阳香橙株高的1.6倍.总体上,砧木茎粗与株高相呼应,株高较高的砧木茎粗值也较大.统计杂种砧木黄化指数得出,ZZ6黄化指数最低,ZZ7、ZZ31和ZZ948黄化指数较低,ZZ1黄化指数中等,ZZ42和ZZ60黄化指数较高,ZZ65黄化指数最高.随砧木黄化指数的升高,叶片叶绿素a、叶绿素b和叶绿素a+b含量随之降低.砧木叶片元素测定结果显示,叶片中活性铁含量与砧木黄化指数呈显著负相关,叶片P含量与黄化指数呈显著正相关,全铁和其余元素含量与叶片黄化无显著相关性.通过AHP-TOPSIS法综合评价得到砧木耐碱性排序为资阳香橙＞ZZ6 ＞ZZ31 ＞ZZ948 ＞ZZ7 ＞ZZ1 ＞ZZ60 ＞ZZ42 ＞ZZ65＞枳.[结论]筛选出3个耐碱性强的砧木品种(ZZ6、ZZ31和ZZ948),其中ZZ6为矮化耐碱砧木资源.

Rare earth elements (REEs) can affect the growth and development of plants. However, few studies have been carried out on the effects of REEs on citrus seedlings. In this study, the growth parameters, toxicity symptoms, chlorophyll content, and La content of three citrus rootstocks are analyzed under different concentrations of La, a representative REE. The results show that the growth of citrus rootstock seedlings was stimulated at La ≤ 0.5 mmol·L−1 and inhibited at concentrations above 1 mmol·L−1. The chlorophyll and carotenoid contents of trifoliate orange (Poncirus trifoliata L. Raf.) and Ziyang Xiangcheng (C. junos Sieb. ex Tanaka) leaves of plants grown at low concentrations of La (≤1.5 mmol·L−1) were similar to those of the control but were significantly reduced at 4 mmol·L−1 La. Toxic symptoms gradually appeared with increasing La concentrations, with yellowed leaves and burst veins appearing at 4 mmol·L−1 La. The symptoms of toxicity were most severe in trifoliate orange, followed by Shatian Pomelo (Citrus grandis var. shatinyu Hort) and then Ziyang Xiangcheng. Moreover, in leaves, the Ca content was significantly negatively correlated with La content (p < 0.01). These results indicate that La has a hormesis effect on the growth of citrus rootstocks. Of the studied citrus seedlings, Ziyang Xiangcheng is the most resistant to La.

[目的]研究石灰水喷施浓度和覆盖率对'纽荷尔'脐橙和'沃柑'的果面温度、叶面温度、日灼发生率、果实品质等影响,以确定日灼防控的适宜喷施浓度和覆盖率.[方法]以'纽荷尔'脐橙和'沃柑'杂柑为材料,设置5个石灰水质量浓度0(CK)、5、10、20、40 g·L-1和2个喷施覆盖率30％和50％,于夏季高温来临前对树冠进行喷施.[结果]与对照相比,喷施石灰水能显著降低叶面和果面温度,但其降温效果具有阈值.随喷施浓度和覆盖率的升高,叶面反光率升高,日灼程度和日灼发生率降低.质量浓度40 g·L-1覆盖率50％的处理叶面反光率最高,日灼发生率和日灼程度最低.喷施石灰水能显著增加果实硬度,影响维生素C含量、色度L值、可溶性固形物含量和可滴定酸含量.主成分分析表明,采用石灰水质量浓度为40 g·.L-1、喷施覆盖率为50％提高'纽荷尔'脐橙和'沃柑'果实品质的效果最好.[结论]喷施石灰水能显著降低果实和叶片日灼,且对果实品质无不良影响,在日灼易发区,推荐喷施石灰水质量浓度为40g·L-1、覆盖率为50％.

Cadmium (Cd) is a primary heavy metal causing crops toxicity, however, Cd uptake by citrus is little studied and largely unknown. In this study, nine (9) citrus rootstock cultivars were selected and grown under Cd stress at concentrations of 0, 2.5, 10, 20, 50, and 100 mg L-1 (Cd0, Cd2.5, Cd10, Cd20, Cd50 and Cd100, respectively) for 30 d, and citrus growth, Cd concentration, Cd transport ratio (TR%), and Cd uptake factor (PUF%) were measured. Results showed that after 30 d treatments, all selected citrus rootstocks remained alive under a relatively low Cd concentrations (Cd0, Cd2.5 and Cd10), but the mortality rate increased with increasing Cd concentrations beyond Cd20, and all citrus completely died at Cd100. Cd exposure significantly suppressed seedling growth. At 20 % growth reduction, tissue Cd concentrations were Cleopatra mandarin (C. reticulate Blanco) < Brazil sour orange (C. aurantium) < 'Swingle' citrumelo (C. paradisi x Poncirus. trifoliate Raf.) < Ziyang Xiangcheng (C. junos Sieb. ex Tanaka) < Carrizo citrange (C. sinensis Osb. x P. trifoliate Raf.) < Goutou sour orange (C. aurantium) < Yichang Cheng (C. ichangensis Swingle) < Red tangerine (C. tangerine) < Trifoliate orange (P. trifoliata Raf.). Moreover, the Cd accumulation in the roots was much higher than in the leaves, and the accumulation was elevated with increasing Cd concentration. Principal component analysis (PCA), including fresh weight growth rate of root and shoot, Cd concentration in root and shoot, transport ratio (TR%), plant uptake factor (PUF%), indicated that selected 9 cultivars could be classified into 4 categories: (1) Trifoliate orange possessed a weak capacity for Cd uptake and accumulation, and its growth was less affected, (2) Goutou sour orange had a weak Cd uptake capacity, but a strong capacity for Cd accumulation and translocation, (3) Ziyang Xiangcheng and Cleopatra mandarin exhibited relatively a strong capacity for both Cd uptake and translocation, (4) The others did not clearly show changes in physiological Cd transport features. This comprehensive evaluation showed that Trifoliate orange was high tolerance to Cd, and Goutou sour orange was low tolerance to Cd, whereas Ziyang Xiangcheng and Cleopatra mandarin were intolerant of Cd.

为筛选适于杂柑新品种“中柑所5号”(商品名“金秋砂糖桔”)的砧木,2016-2018年连续3年对四川仁寿区试点飞龙枳、枳、资阳香橙和红桔砧金秋砂糖桔(2015年3月定植2年生嫁接大苗)的生长结果进行比较,2018年对广西隆安、平南、灵川和云南元阳4个生态区试点枳和资阳香橙砧金秋砂糖桔(2016年3月定植2年生嫁接大苗)的生长结果进行比较.结果 表明,四川仁寿区试点,树冠由大到小依次为红桔、资阳香橙、枳和飞龙枳砧,单株产量3年平均值分别为37.18、27.02、18.72和12.97 kg,单位树冠体积产量(生产效率)3年平均值分别为4.97、6.22、9.25和19.26 kg/m3;单果质量由大到小依次为为资阳香橙、红桔、飞龙枳、枳砧;果实可溶性固形物以枳和飞龙枳砧较高,资阳香橙砧次之,红桔砧最低.广西和云南4个区试点资阳香橙和枳砧的差异趋势,与四川仁寿这两种砧木的差异趋势基本相同.推荐生产上酸性和中性土壤用枳砧,碱性土壤用资阳香橙砧,高密度栽培用飞龙枳砧.

Background Copper (Cu) toxicity has become a potential threat for citrus production, but little is known about related mechanisms. This study aims to uncover the global molecular response of mRNAs, long non-coding RNAs (lncRNAs), circular RNAs (circRNAs) and microRNAs (miRNAs) to Cu toxicity and to construct their competing endogenous RNAs (ceRNAs) network in citrus.Results In this study, tolerance of four commonly used rootstocks to Cu toxicity was first evaluated, and ‘Ziyang Xiangcheng’ (Citrus junos ) was proved to be tolerant rootstock. Then the Cu-treated and -untreated root (CuR, CKR) and leaf (CuL, CKL) of ‘Ziyang Xiangcheng’ was selected to perform whole-genome transcriptome sequencing. In total, 5734 and 222 mRNAs, 164 and 5 lncRNAs, 45 and 17 circRNAs, and 147 and 130 miRNAs were identified to be differentially expressed (DE) in CuR/CKR and CuL/CKL, respectively. Gene ontology enrichment analysis of these DEmRNAs and targets of DElncRNAs and DEmiRNAs showed that most were annotated to oxidation-reduction, phosphorylation, membrane, and ion binding. The ceRNA network was constructed with the predicted DEmRNAs-DEmiRNAs and DElncRNAs-DEmiRNAs pairs, which further revealed regulatory roles of these DERNAs in Cu toxicity.Conclusions A large number of mRNAs, lncRNAs, circRNAs, and miRNAs were altered in response to Cu toxicity in citrus, and they may play crucial roles in mitigation of Cu toxicity through the ceRNA regulatory network.

Abstract Changes in the accumulation patterns of mineral nutrients at different development stages of fruit reflect the requirements of citrus trees for different nutrients, and this information provides an essential reference for rational fertilization. In this study, changes in the contents of 11 nutrients in the whole fruit, fruit pulp, and peel were studied during the whole developmental period of the fruit of ‘Seike’ and ‘Newhall’ navel oranges. We found that the two navel orange cultivars showed very similar changes in nutrients. Specifically, the N, P, Mg, S, Mn, and Zn contents were high in the young fruit stage (April), the K and Fe contents were high in the fruit expansion stage (July and August), and the Ca content was high in the fruit maturation stage (October). As the fruit developed, the N, P, Mg, S, Zn, and B contents decreased to the lowest levels at fruit maturity in November. In addition, the contents of N, P, K, Fe, Zn, and Cu were ranked as fruit pulp > whole fruit > peel, while Ca, Mn, and B contents were ranked as fruit peel > whole fruit > fruit pulp. N, P, K, and Mg accumulated in the fruit in June and July, in contrast to the June to September period for the micro-elements. During these accumulation periods, it is recommended that suitable fertilizers be applied in a timely manner.

In this study, 9 pairs of Simple Sequence Repeat (SSR) molecular marker primers were screened for construction of the fingerprint of CRIC 5 (Citrus reticulata Blanco cv. Ehime No. 30 × Citrus reticulata Blanco cv. Shiyueju). In these screened primer pairs, 5 primer pairs(CSSR038、SS16、CSSR052、SS9、CSSR014) showed the same bands with its male parent Shatangju, 3 primer pairs (CSSR020, SS12, CSSR037) with its female parent Ehime No. 30, and the bond of 1 primer pair is different from both male and female parents. By using these primers for fingerprinting, two unknown citrus samples (from Jianyang and Ziyang,Sichuan, respectively) were identified as citrus variety CRIC 5. Thus, SSR based DNA molecular marker technique is a powerful tool for discriminating this new citrus cultivar.

Copper (Cu) is an element necessary for citrus,which plays an important role in the process of citrus growth and development.Copper fungicides have been widely used to control citrus canker and anthracnose since the 19th century,resulting in accumulation of copper in soils of citrus orchards.Otherwise,the available copper content of virgin soil in the citrus production areas of China is relatively low.Leaf nutrient of citrus was influenced by soil nutrient status.Copper deficiency and excess would cause stresses in citrus orchards.This paper summarized the effects of copper stress on citrus growth and metabolism,the factors effecting copper stress,and the tolerance of citrus rootstocks to copper stress.The research progress of heavy metal stress-associated proteins was also introduced.Copper participates in several physiological processes of plants.Cu-deficient plants exhibit a reduction in electron transport during photosynthesis due to decreases of plastocyanin synthesis and the contents of chlorophylls and carotenoids.Copper as a cofactor of enzymes,has an influence on the activity of antioxidant enzyme that scavenge reactive oxygen species (ROS).Copper deficiency affects the lignification process by decreasing lignin,hemicellulose and acetyl contents of cell walls.The uptake of zinc is inhibited in copper-deficient plants.Citrus orchards with high organic matter content,high pH,and rarely use of copper fungicides,are more likely to have Cu-deficient.Visual symptoms of deficiency are characterized by curved or "S-shaped" branches with large,dark green and overdeveloped leaves.In severe cases,reddish brown droplets of gum cover the twigs.As the deficiency becomes acute,the twigs start to die.Copper toxicity in plants affects physiological and biochemical processes,resulting in the inhibition of shoot and root growth.Leaf chlorosis,black and shorter roots have been observed on copper toxicity plants.The excess Cu decreases the concentration of chlorophyll,which results in a reduction in the energy transfer from the antennae of the PSII to the reaction centers.And net photosynthetic rate is significantly reduced.Furthermore,excess copper reduces the ability of the plant to explore the soil for water and essential nutrients.It has been reported that high copper inhibits the uptake and activity of Zn2+,Fe2+,Mg2+,et al.An excess of Cu also leads to serious damage to the root and leaves ultra-structure of citrus.The membrane system of chloroplast and mitochondria is damaged greatly.A thin and twisted cell wall,degeneration of the middle lamella,cellular plasmolysis can be observed in the root cell of copper toxicity plants.Many researches revealed that high copper stresses would result in oxidative stress due to enhanced ROS production.In order to scavenge ROS and alleviate their deleterious effects in cells,plants have increased activities of SOD,CAT and peroxidases (APX and POX).The availability and mobility of Cu in the soils are related to organic matter content and soil pH.High organic matter content and high pH could reduce the availability of copper in soil.It can effectively alleviate the copper toxicity of citrus when soil pH was 6.5 or over 6.5.The application of fertilizer can also affect the uptake of copper by citrus.Nitrogen (N) fertilizer applied in the NH4+ form would result in some degree of soil acidification,which could enhance the leaching of nutrients in sandy soil.Excessive applications of N and P fertilizers in citrus orchards would cause copper deficiency.Previous study showed that increased Ca availability in the rooting environment would ameliorate the effects of Cu phytotoxicity.And sufficient P supply has positive effect on citrus seedling under excess copper.The interaction of rootstock with Cu toxicity in citrus trees has been evaluated in some researches.Results showed that,'Swingle citrumelo'rootstock might have better tolerance than'Sunki mandarin'and'Rangpur lime'.And rough lemon is more tolerant to Cu phytotoxicity than'Cleopatra mandarin'.Plants have developed various mechanisms,including avoidance of uptake,chelation,effiux,autoxidation,and intracellular sequestration,to overcome Cu toxicity.The storage of Cu in the root cell walls and vacuole may keep the ion sequestered from the metabolic center.The conversion of Cu2+ to no-toxic complex compound by protein,organic acid or phenolic compounds,is one of the important detoxification mechanisms.The improvement of antioxidant system is also a manifestation of alleviating Cu stress.Heavy metal binding proteins and transporters play important roles in resistance to copper stress.Various protein families related to Cu uptake and transportation were found in plants.CsMT1 was identified in sweet orange,and mainly expressed in leaves and flowers.COPT gene family encode Cu transporter with high affinity,and 6 COPT family members has been found in Arabidopsis.Researches indicated HMA1 and HMA5-HMA8 were related to Cu transport between organelles.Recently,12 MTP genes were identified in sweet orange,named as CitMTP1 and CitMTP3 to CitMTP12 based on their sequence similarity to Arabidopsis thaliana MTPs.

[目的]了解重庆柑橘园土壤微量营养元素养分状况.[方法]在重庆15个柑橘主产县(区)选取567个代表性柑橘园采集土壤样本进行测定分析.[结果]果园土壤pH值变幅pH 4.1～8.7,但仅有20.99％的土壤pH适宜柑橘生长(pH值5.5～6.5),53.62％的土样pH高于6.5,并有35.63％的土样pH高于7.5.土壤有机质匮乏,有机质偏低或缺乏比例达68.79％.土壤有效Fe、Mn、Zn、Cu、B的平均含量分别为40.91 mg· kg-1、15.69 mg·kg-1、1.39 mg· kg-1、1.06 mg· kg-1、0.37mg· kg-1,土壤有效Fe、Mn、Zn、Cu、B含量处于适宜及以上水平的比例分别占77.08％、0.18％、53.62％、73.02％、23.28％;总体上土壤有效Fe、Cu含量水平较高,有效Zn、B含量较低,有效Mn含量缺乏.[结论]柑橘生产上应注意调节土壤pH值,结合叶片营养诊断适量补充含Mn、B、Zn的微量元素肥料或有机肥.