基于SV标记的杂柑遗传多样性分析及分子身份证构建

向芝菲1,何 淙1,耿远来1,邱 婷1,余 蔷1,张颖梓1,2,杨星星3,贺邓敏4,戴素明1,2,李大志1,2,李 娜1,2*

1湖南农业大学园艺学院,长沙 410128;2岳麓山实验室果树品种创制中心,长沙 410128;3湖南省农作物种质资源保护与良种繁育中心,长沙 410219;4安化县无病虫柑橘良种繁殖场,湖南安化 413599)

要:【目的】探究杂柑品种遗传多样性并构建身份证,为杂柑的品种鉴定与保护提供技术支撑。【方法】选用16个杂柑品种为材料,基于7个农艺性状和34对SV标记引物进行遗传多样性分析与分子身份证构建,并采用UPGMA法构建聚类图。【结果】7个农艺性状存在16种变异类型,平均多样性指数为0.518;从34对SV标记引物中筛选出8对SV标记引物,利用这8对SV标记引物可区分14个杂柑品种,并构建了其分子身份证;8对SV标记引物共检测到19个等位基因,多态性信息含量指数为0.393,Nei's基因多样性为0.492,期望杂合度为0.508,表明16个杂柑品种遗传多样性较丰富;聚类分析将16个杂柑品种划分为5类。【结论】构建14个杂柑品种的DNA分子身份证,为杂柑苗期的鉴定提供技术支撑。

关键词:杂柑;结构变异;DNA分子标记;遗传多样性;分子身份证

中国柑橘产业规模位居世界之首,产量约占全球1/3[1]。现有栽培柑橘品种主要由柚、宽皮橘和枸橼三个原始种杂交而来。由于柑橘种(属)间存在广泛的杂交亲和性,其遗传背景高度复杂,进而演化出极为丰富的栽培品种多样性[2]。由人工或自然杂交培育而成的柑橘类水果统称为杂柑,数量繁杂众多,兼具多种亲本种质的复合特性。杂柑以鲜食为主,其易剥皮、多汁、化渣、风味浓郁、少籽或无籽的特点深受消费者喜爱。近年来,受杂柑销售价格持续上涨的驱动,苗木市场呈现爆发式增长态势。然而,市场繁荣背后衍生出品种混杂、套牌经营及假冒伪劣等乱象,严重制约了杂柑良种的有序发展,亟须建立高效、精准的品种鉴定技术体系。

形态学鉴定与分子标记相结合的方法常应用于鉴定植物品种[3-5]。但柑橘属易发生自然杂交和体细胞突变,遗传背景极为复杂,难以区分同类或近似品种[6]。分子标记具有不受环境影响、操作简便快速准确等特点,在柑橘品种鉴定和遗传多样性分析等方面发挥着关键作用[7-9]。简单序列重复(simple sequence repeats,SSR)因多态性高、共显性遗传等特点,成为了品种鉴定的主流标记[10-11]。冯意斯等[12]筛选出2对SSR标记用于沃柑实生后代三倍体的遗传鉴定。宋放等[13]筛选出3对SSR引物用于清见×鄂柑一号杂交后代的鉴定。SSR标记的多态性水平为10%~30%,其带型复杂且难以判读,需通过聚丙烯酰胺凝胶电泳或高成本的毛细管电泳技术进行基因分型检测[4,14]

引入DNA测序(next-generation sequencing,NGS)技术后,单核苷酸多态性(single nucleotide polymorphism,SNP)已成为分子遗传学研究的主导[15]。然而,SNP无法完全捕获表型相关差异,相比之下,大片段结构变异(structural variation,SV,>50bp的插入、缺失、倒置和易位变异)比SNP更容易引起基因表达的变化。因此,在表型多样性研究中具有不可忽视的重要性[16]。SV开发的分子标记对基因表达和蛋白质功能的影响大于SNP标记[17],导致健康个体之间出现表型差异[18]。目前,SV标记主要用于人类的群体遗传学及水稻、高粱等作物研究,在果树中报道较少[19-21]

在柑橘中,SV标记已应用于冰糖橙与瓯柑芽变品种的鉴定[22-23]。此外,Wang等[24]也曾基于234个柑橘种质的全基因组变异图谱(包括SV)组装了山金柑的染色体水平基因组,探究了柑橘中无融合生殖的遗传学和进化问题。本研究基于表型性状及柑橘基因组测序数据开发SV标记,并应用于16个杂柑品种的遗传多样性评估及品种鉴别研究,通过筛选、开发并验证兼具高有效性和显著多态性的SV分子标记,分析供试杂柑种质资源的遗传多样性,进而构建杂柑种质的DNA分子身份证体系。本研究成果将为深入解析杂柑资源遗传多样性机制以及建立品种鉴别技术提供重要的理论依据与数据支撑。

1 材料和方法

1.1 植物材料

16份杂柑试验材料由国家柑橘改良中心长沙分中心、湖南省农作物种质资源保护与良种繁育中心和安化县无病虫柑橘良种繁殖场等地提供(表1)。将采集的各地幼嫩杂柑叶片标记后放入自封袋中,置于-80 ℃冰箱备用。

表1 供试杂柑品种信息
Table 1 Information on citrus hybrids

序号 品种名称 选育国家 采样地 序号 品种名称 选育国家 采样地No. Variety name Breeding countries Sampling sites No. Variety name Breeding countries Sampling sites1 清见 日本 湖南安化 9 春香 日本 湖南长沙Kiyomi Japan Anhua,Hunan Haruka Japan Changsha,Hunan 2 天草 日本 湖南安化 10 春见 日本 湖南长沙Amakusa Japan Anhua,Hunan Harumi Japan Changsha,Hunan 3 南香 日本 湖南安化 11 甘平 日本 湖南常德Nankou Japan Anhua,Hunan Kanpei Japan Changde,Hunan 4 西之香 日本 湖南安化 12 红美人 日本 湖南长沙Nishinoka Japan Anhua,Hunan Ehime Japan Changsha,Hunan 5 W.默科特 美国 湖南安化 13 不知火 日本 湖南长沙W.Murcott America Anhua,Hunan Shiranuhi Japan Changsha,Hunan 6 默科特 美国 湖南安化 14 金秋砂糖橘 中国 湖南长沙Murcott America Anhua,Hunan Jinqiu Shatangju China Changsha,Hunan 7 沃柑 以色列 湖南长沙 15 明日见 日本 湖南长沙Orah Israel Changsha,Hunan Asumi Japan Changsha,Hunan 8 大雅柑 中国 湖南长沙 16 阳光1号 中国 湖南长沙Dayagan China Changsha,Hunan Yangguang No.1 China Changsha,Hunan

1.2 农艺性状调查

参照《柑橘种质资源描述规范和数据标准》[25],对16个杂柑品种的2年生苗期植株进行农艺性状调查,观察记录树姿、叶型、叶身形状、叶尖形状、叶基形状、翼叶形状、叶缘等质量形状并进行赋值编码(表2)。

表2 杂柑农艺性状赋值
Table2 Assignment of quality traits of citrus hybrids

性状 赋值Trait Assignment of values树姿 直立=1,开张=2,披垂=3 Tree habit Upright=1,Spreading=2,Weeping=3叶型 单叶=1,单身复叶=2,三出复叶=3 Leaf type Simple=1,Unifoliate=2,Trifoliate=3叶身形状 椭圆形=1,卵圆形=2,倒卵圆形=3,披针形=4,菱形=5,Leaf blade 圆形=6 shape Elliptic=1,Ovate=2,Obovate=3,Lanceolate=4,Rhombic=5,Orbicular=6叶尖形状 钝圆=1,渐尖=2,急尖=3,短尖=4,长尾状=5 Leaf apex Obtuse=1,Acuminate=2,Acute=3,Mucronate=4,shape Caudate=5叶基形状 狭楔形=1,楔形=2,广楔形=3,圆形=4 Leaf base Narrowly cuneate=1,Cuneate=2,Broadly Cuneate=3,shape Rounded=4翼叶形状 心形=1,倒三角形=2,倒卵圆形=3,倒披针形=4,线形=5 Winged leaf Cordate=1,Obdeltoid=2,Obovate=3,Oblanceolate=4,shape Linear=5叶缘 全缘=1,浅波缘=2,锯齿缘=3 Leaf margin Entire=1,Undulate=2,Serrate=3

1.3 SV位点筛选及引物的设计与筛选

从NCBI中下载已发布的21个柑橘基因组数据,以甜橙基因组(ASM1810577v1//GCA_018105775.1)为参考基因组,与其余20个柑橘基因组数据进行比对,生成比对文件;利用SVIM-asm软件搜索比对文件,去除冗余后获得252 629个SV变异位点(插入、缺失>50bp)。合并后的252629个核心SV在柑橘染色体上整体分布较为均匀,但单个品种经SVIM-asm软件鉴定出的原始SV在染色体上的分布则不均匀。根据215524个SV位点,并利用Primer3 Input工具、UCSC的In-Silico PCR工具进行引物设计与筛选。引物设计区域限制在变异位点上下游200bp序列,结合电子PCR扩增结果,以不同品种间变异较大的位点作为候选位点。候选位点的扩增片段长度变化范围为100~1000bp,将各扩增条带大小进行排序,长度相差小于50bp视为同一大小条带,并进行合并处理,长度相差大于50bp则为不同条带,最终筛选出多态性高、品种间条带差异大的34对引物。引物长度为18~24 bp,退火温度为56~61 ℃。将PCR电泳扩增条带符合预期的34对SV标记引物送至擎科生物技术有限公司(长沙合成部)合成。

1.4 DNA的提取及PCR扩增、电泳分析

采用CTAB法提取柑橘叶片总DNA,并使用1%琼脂糖凝胶电泳检测DNA质量,同时使用酶标仪测定DNA浓度以及OD260/280,筛选合格的总DNA质量浓度稀释至约100 ng·μL-1,置于-20 ℃冰箱保存待用。

PCR扩增体系(20 μL):2×Taq MasterMix(诺唯赞)10 μL,10 nmol·L-1正、反向引物各0.5 μL,基因组DNA(100ng·μL-1)1 μL,ddH2O补足至20 μL。

PCR扩增程序:94 ℃预变性5 min;94 ℃变性30 s,56.0~60.5 ℃退火40 s,72 ℃延伸40 s,循环35次;72 ℃延伸10min。

根据预期扩增条带大小,使用2%琼脂糖凝胶电泳对PCR产物进行检测,电压110V,时间1~2h,扩增产物采用紫外凝胶成像系统观察并拍照。

1.5 DNA分子身份证的构建

利用柑橘染色体上均匀分布的8个SV标记,获得16份杂柑品种的扩增条带信息,按照标记位点染色体信息的排布顺序依次串联,将数据转换为二元矩阵;对应位置无条带记为0,有条带则记为1,获得每个杂柑品种的扩增条带组合信息;利用草料二维码生成器将每个杂柑对应的0、1数据字符串转化为直观的条形码和二维码分子身份证。二维码分子身份证需通过草料二维码生成器进行识别。

1.6 杂柑DNA分子身份证的应用

供试样品为前期已建立DNA分子身份证的杂柑品种,由外单位送样并随机编号,委托课题组外志愿者对检测样品随机给出盲检号,封存样品信息。利用筛选的8对引物进行盲测,通过比较供试样品与标准样品扩增图谱间位点的差异性和一致性,判断供试品种的真实身份。参考NY/T 3436—2019标准《柑橘属品种鉴定SSR分子标记法》[26],以标准品种的电泳图谱作为对照,杂柑品种真实性判定标准如下:

不同品种判定:供试样品与标准样品间存在≥2个差异位点。

近似品种判定:供试样品与标准样品间存在1个差异位点。

极近似或相同品种判定:供试样品与标准样品间无差异位点。

1.7 数据处理与分析

利用Microsoft Excel2016、SPSS25软件计算杂柑农艺性状的遗传多样性指数H'(Shannon-Weaver法)[27];利用DataFormater软件将0、1数据转换成bp数据;使用Popgene32软件计算等位基因数(Na),有效等位基因数(Ne),Shannon’s信息指数(I),观测杂合度(Ho),期望杂合度(He)和Nei’ s基因多样性指数(H)。用PowerMarkerV3.25软件计算主要等位基因频率(major allele frequency,MAF)和引物多态性信息含量(polymorphism information content,PIC);使用NTSYSpc2.10e软件计算遗传相似系数,利用其中的SAHN程序和算术平均数不加权对组法(unweighted pairgroup method arithmetic averages,UPG-MA)进行聚类分析,绘制16个杂柑品种的UPGMA聚类图[28];参考《中国柑橘品种》第二版[29],对16个杂柑品种进行溯源,利用Microsoft Visio2010绘制系谱图。

2 结果与分析

2.1 16个杂柑品种苗期农艺性状多样性分析

对16个杂柑品种的7个农艺性状进行统计分析,结果表明16个杂柑品种存在16种变异类型,平均多样性指数为0.518,整体存在一定变异(表3和表4)。16个杂柑品种均为直立型树姿、单叶叶型,其多样性指数均为0,表明16份杂柑种质在树姿、叶型上完全一致,多样性极低;叶身形状以卵圆形为主,占比56.25%,其多样性指数为0.865,表明该性状存在较大的遗传变异,多样性中等;叶尖形状以渐尖为主,占比87.5%,其多样性指数较低,仅0.463,表明该性状变异较小;叶基形状以楔形为主,占比68.75%,其多样性指数较高,为0.831,表明该性状具有较大的遗传变异;翼叶形状以倒披针形为主,占比62.5%,其多样性指数最高,为0.900,表明该性状的遗传多样性较丰富,各类别分布较均匀;叶缘以波状为主,占比75%,其多样性指数中等,为0.562,表明该性状存在一定的遗传变异。综上所述,16份杂柑在叶身形状、叶基形状、翼叶形状和叶缘等性状上虽存在一定变异,但无法在苗期阶段对杂柑进行完全鉴别,且苗期表型性状易受环境和栽培条件影响,形态学鉴定只能作为鉴定品种的辅助方式。

表3 16个杂柑品种苗期农艺性状调查结果
Table3 Survey results of quality traits of 16citrus hybrids at seedling stage

品种名称 树姿 叶型 叶身形状 叶尖形状 叶基形状 翼叶形状 叶缘Variety name Tree habit Leaf type Leaf blade shape Leaf apex shape Leaf base shape Winged leaf shape Leaf margin清见 直立 单叶 卵圆形 渐尖 楔形 线形 波状Kiyomi Upright Simple Ovate Acuminate Cuneate Linear Undulate天草 直立 单叶 椭圆形 渐尖 楔形 倒披针形 波状Amakusa Upright Simple Elliptic Acuminate Cuneate Oblanceolate Undulate南香 直立 单叶 卵圆形 渐尖 楔形 倒披针形 波状Nankou Upright Simple Ovate Acuminate Cuneate Oblanceolate Undulate西之香 直立 单叶 披针形 渐尖 楔形 倒披针形 波状Nishinoka Upright Simple Lanceolate Acuminate Cuneate Oblanceolate Undulate W.默科特 直立 单叶 卵圆形 渐尖 广楔形 线形 波状W.Murcott Upright Simple Ovate Acuminate Broadly Cuneate Linear Undulate默科特 直立 单叶 披针形 渐尖 广楔形 倒披针形 波状Murcott Upright Simple Lanceolate Acuminate Broadly Cuneate Oblanceolate Undulate沃柑 直立 单叶 披针形 渐尖 楔形 倒披针形 锯齿Orah Upright Simple Lanceolate Acuminate Cuneate Oblanceolate Serrate大雅柑 直立 单叶 卵圆形 渐尖 楔形 倒三角形 锯齿Dayagan Upright Simple Ovate Acuminate Cuneate Obdeltoid Serrate春香 直立 单叶 卵圆形 短尖 狭楔形 倒披针形 波状Haruka Upright Simple Ovate Mucronate Narrowly Cuneate Oblanceolate Undulate春见 直立 单叶 卵圆形 渐尖 楔形 倒披针形 波状Harumi Upright Simple Ovate Acuminate Cuneate Oblanceolate Undulate甘平 直立 单叶 披针形 渐尖 狭楔形 线形 波状Kanpei Upright Simple Lanceolate Acuminate Narrowly Cuneate Linear Undulate红美人 直立 单叶 卵圆形 渐尖 楔形 倒披针形 波状Ehime Upright Simple Ovate Acuminate Cuneate Oblanceolate Undulate不知火 直立 单叶 卵圆形 渐尖 广楔形 倒三角形 波状Shiranuhi Upright Simple Ovate Acuminate Broadly Cuneate Obdeltoid Undulate金秋砂糖橘 直立 单叶 卵圆形 钝圆 楔形 倒披针形 锯齿Jinqiu Shatangju Upright Simple Ovate Obtuse Cuneate Oblanceolate Serrate明日见 直立 单叶 披针形 渐尖 楔形 线形 波状Asumi Upright Simple Lanceolate Acuminate Cuneate Linear Undulate阳光1号 直立 单叶 披针形 渐尖 楔形 倒披针形 锯齿Yangguang No.1 Upright Simple Lanceolate Acuminate Cuneate Oblanceolate Serrate

表4 16个杂柑品种苗期农艺性状遗传多样性分析
Table4 Analysis of genetic diversity of quality traits at seedling stage of 16citrus hybrids

符合赋值性状的品种数 分布频次性状 多样性指数Number of germplasms with assigned trait values Distribution frequency Shannon-Wiener dive-Trait1 2 3 4 5 6 1 2 3 4 5 6 rsity index(H′)树姿Tree habit 16--///1--///0叶型Leaf type 16--//1--///0叶身形状Leaf blade shape 1 9-6/0.0625 0.5625-0.375 0//0.8649叶尖形状Leaf apex shape 1 14-1-0.0625 0.875 0-0.0625-/0.4634叶基形状Leaf base shape 2 11 3-/0.125 0 0.6875 0.1875-//0.831 3翼叶形状Winged leaf shape -2-10 4-0.125 0-0.625 0 0.2500/0.9003叶缘Leaf margin -12 4//-0.7500 0.2500///0.5624

注:“-”代表16个杂柑品种无该类型,“/”代表该指标无该类型。
Note:“-” indicates that the corresponding quality type was not present in the 16 hybrid citrus varieties,while “/” indicates that the indicator did not possess this specific type.

2.2 SV标记引物的筛选结果

基于34个SV位点开发的标记引物均能扩增出条带目的片段,其中24对引物的扩增产物经电泳检测显示主带清晰、多态性高、条带重复性好。进一步从24对引物中筛选出分布于8对染色体中的8对引物(7号染色体除外)(表5),8对引物扩增产物长度均为200~500 bp,用于杂柑分子身份证的构建(图1)。

图1 基于8对SV标记引物的标准样品琼脂糖凝胶扩增结果
Fig.1 Agarose gel amplification results based on8pairs of SV-labeled primer amplification standard samples

表5 8个SV标记信息
Table5 Data for8SV Markers

编号 标记名称 正向引物(5′→3′) 反向引物(5′→3′)No. Label name Forward primers(5′→3′) Reverse primers(5′→3′)1 chr1:29803181 AGTGGGATCGAATGTCACTCT ACAGAATTCACCAACGAGCTG 2 chr2:1013046 AACAGCCAGCACAGACCT TCACACCTGACGCCTCCT 3 chr3:2080210 TCTGCAGGAGCTTGGCAC ACCACAAACATGCCAGGAA 4 chr4:31281339 ACAGAACAGGCACGGAAAC AGGAGAGTTGACCACGTGG 5 chr5:6730856 TGCCTCTTTCGCCACCTG TACCGGTACCGCTCTCCC 6 chr6:798504 TGGTATGAGGCTTAGCAGGC GCTACTGGCTTGGCATGGA 7 chr8:3205311 CGCCATTTCCCCTGTGCT AGCAGAGGACTTGTTTAGGGT 8 chr9:3657639 TGCATTCAATCGGCATTACG GTGAAACCGGCACAAGGT

2.3 基于SV标记的16个杂柑品种区分情况

8对SV标记引物的扩增结果(图1)显示,西之香、明日见和阳光1号均表现出特异性扩增带型,可通过单对引物实现有效区分,其中阳光1号可同时被2个SV标记(chr1:29803181、chr8:3205311)鉴别(表6)。基于8个标记组合,除大雅柑和春见外,可有效区分14个品种(表7和表8),区分率达87.5%。在柑橘属品种鉴定标准中,当供试样品与标准样品差异位点数≥2时,可判定为不同品种。在本研究采用的8个标记组合中,14个品种与标准样品均有2个及以上的差异位点,符合品种鉴定标准。因此,后续杂柑品种真实性分析仍采用该8个标记。

表6 杂柑品种鉴别的单一标记
Table6 Single-marker identification of citrus hybrids

杂柑品种名称 标记Name of citrus hybrids Marker阳光1号Yangguang No.1 chr1:29803181、chr8:3205311明日见Asumi chr4:31281339西之香Nishinoka chr6:798504

表7 杂柑品种鉴别的组合标记
Table7 Identification of citrus hybrids by marker combinations

品种名称 引物组合一 引物组合二Variety name Primer combination 1 Primer combination2红美人Ehime chr1:29803181+chr2:1013046/阳光1号 chr1:29803181+chr2:1013046/Yangguang No.1天草Amakusa chr1:29803181+chr2:1013046+chr4:31281339 chr1:29803181+chr2:1013046+chr3:2080210南香 chr1:29803181+chr2:1013046+chr4:31281339 chr1:29803181+chr2:1013046+chr3:2080210+chr5:Nankou 6730856默科特 chr1:29803181+chr2:1013046+chr4:31281339 chr1:29803181+chr2:1013046+chr3:2080210+chr5:Murcott 6730856+chr6:798504春香 chr1:29803181+chr2:1013046+chr4:31281339 chr1:29803181+chr2:1013046+chr3:2080210+chr5:Haruka 6730856不知火 chr1:29803181+chr2:1013046+chr4:31281339 chr1:29803181+chr2:1013046+chr3:2080210+chr5:Shiranuhi 6730856+chr6:798504+chr8:3205311+chr9:3657639金秋砂糖橘 chr1:29803181+chr2:1013046+chr4:31281339 chr1:29803181+chr2:1013046+chr3:2080210 Jinqiu Shatangju明日见 chr1:29803181+chr2:1013046+chr4:31281339 chr1:29803181+chr2:1013046+chr3:2080210+chr5:Asumi 6730856+chr6:798504+chr8:3205311+chr9:3657639清见 chr1:29803181+chr2:1013046+chr4:31281339+chr9:3657639 chr1:29803181+chr2:1013046+chr3:2080210+chr5:Kiyomi 6730856+chr6:798504+chr8:3205311西之香 chr1:29803181+chr2:1013046+chr4:31281339+chr9:3657639 chr1:29803181+chr2:1013046+chr3:2080210+chr5:Nishinoka 6730856 W.默科特 chr1:29803181+chr2:1013046+chr4:31281339+chr9:3657639 chr1:29803181+chr2:1013046+chr3:2080210 W.Murcott沃柑 chr1:29803181+chr2:1013046+chr4:31281339+chr9:3657639 chr1:29803181+chr2:1013046+chr3:2080210+chr5:Orah 6730856甘平Kanpei chr1:29803181+chr2:1013046+chr4:31281339+chr9:3657639 chr1:29803181+chr2:1013046+chr3:2080210

表8 8个标记扩增条带的多态性及16个杂柑品种的遗传多样性
Table8 Polymorphisms of8pairs of primer amplification bands and the genetic diversity of 16citrus hybrids

有效等位 主要等位 Shannon’s多态 多态性信息 Nei's基因多观测杂合度 期望杂合度等位基因数 基因数 基因频率 性信息指数 含量指数 样性指数引物名称 Number of Effective Shannon's Observed Expected Primer name Major allele Polymorphism Nei's gene alleles,Na number of heterozygosity,heterozygosity,frequency,information Ho He information diversity alleles,Ne MAF index,I content,PIC index,Hchr1:29803181 2 1.438 0.813 0.483 0.250 0.315 0.258 0.305 chr2:1013046 2 1.822 0.656 0.644 0.688 0.466 0.349 0.451 chr3:2080210 2 1.992 0.531 0.691 0.563 0.514 0.374 0.498 chr4:31281339 4 3.303 0.406 1.279 0.813 0.720 0.643 0.697 chr5:6730856 2 1.992 0.531 0.691 0.688 0.514 0.374 0.498 chr6:798504 2 1.882 0.625 0.662 0.625 0.484 0.359 0.469 chr8:3205311 3 2.073 0.563 0.798 0.813 0.534 0.412 0.518 chr9:3657639 2 1.992 0.531 0.691 0.563 0.514 0.374 0.498总计Total 19平均值Average 2.375 2.062 0.582 0.742 0.625 0.508 0.393 0.492

利用8个SV标记对16个杂柑品种进行遗传多样性分析。由表8可知,8个SV标记共检测到19个等位基因,平均每对引物扩增出2.375个等位基因。不同标记间的等位基因数目存在差异,6个SV标记为二等位基因,1个SV标记为三等位基因,1个SV标记为四等位基因。有效等位基因数(Ne)平均为2.062,主要等位基因频率(MAF)平均为0.582,表明各位点均检测到一定程度的等位变异。观测杂合度(Ho)平均值为0.625,高于期望杂合度(He)平均值0.508,说明供试材料具有较高的杂合水平,遗传背景较为复杂。Shannon’s信息指数(I)、Nei’s基因多样性指数(H)和多态性信息含量(PIC)平均值分别为0.742、0.492和0.393,说明供试引物整体具有较好的多态性,有效地揭示了材料间的遗传差异。其中,chr4:31281339位点的I、PIC和H值均为最高,分别达到1.279、0.643和0.697,表明该位点多态性丰富,为高多态性引物;而chr1:29803181位点的I、PIC和H值较低,分别为0.483、0.258和0.305,多态性相对较弱。

2.4 16个杂柑品种的聚类分析

利用8个SV标记对16份杂柑种质进行聚类分析,结果(图2)表明,在遗传相似系数为0.52处,16份杂柑种质可分为两大类,第一类为清见等13份种质,第二类为春香、金秋砂糖橘和阳光1号;当遗传相似系数为0.60时,第二类中的3份种质完全区分,即春香、金秋砂糖橘和阳光1号单独为一类;在遗传相似系数为0.64处,第一类中的13份杂柑可进一步分为两类,清见等8份种质为一类,南香等5份种质为另一类。

图2 基于SV标记的16个杂柑品种UPGMA聚类分析
Fig.2 UPGMA analysis of 16hybrid citrus cultivars based on SV markers

参考《中国柑橘品种》[29],查阅16个杂柑品种的遗传背景并构建系谱图(图3)。从遗传背景分析聚类结果,以具有单胚性状的清见为母本或其后代为亲本选育的7个日本品种及中国选育的大雅柑聚为第一类;无清见血统的美国W.默科特和默科特、以色列沃柑、日本的红美人和南香为第二类;中国的阳光1号、金秋砂糖橘和无清见血统的日本品种春香则单独为1类。在16个杂柑品种中,仅大雅柑和春见因亲缘关系极近难以区分,其余14份均可鉴别。这一结果印证以分子标记为基础的聚类分析倾向聚集亲缘关系近的品种。

图3 16个杂柑品种的系谱图
Fig.3 Pedigree of 16citrus hybrids

2.5 14个杂柑品种的DNA分子身份证构建

基于8对SV特征引物的扩增结果,将扩增图谱上同一位置条带的有和无,转化为0、1组成的数字信息。按照引物在1号到9号染色体上的排列顺序,以及扩增片段由小到大的顺序将各位点赋值的0、1数字串联排序,获得每个杂柑品种的数据信息组合,构建每个品种唯一的19位0、1数据字符串。利用在线条形码和二维码生成技术将每个杂柑对应的0、1数据字符串转化为直观的条形码和二维码分子身份证,14个杂柑品种的DNA分子身份证信息如表9所示。以品种清见为例,通过草料二维码生成器扫码后,分子身份证信息如图4所示。

图4 杂柑品种清见的字符串、条形码和二维码分子身份证及扫码内容示例
Fig.4 Examples of the character string,barcode and QR code molecular ID card and scan code content of the Kiyomi of citrus hybrids

表9 杂柑品种的DNA分子身份证信息
Table9 DNA molecular ID information of citrus hybrids

序号 品种名称 字符串和条形码 品种二维码No. Variety name Strings and barcodes QR code of cultivars1 清见Kiyomi2 天草Amakusa3 南香Nankou4 西之香Nishinoka5 W.默科特W.Murcott6 默科特Murcott7 沃柑Orah8 春香Haruka9 甘平Kanpei10 红美人Ehime11 不知火Shiranuhi12 金秋砂糖橘Jinqiu Shatangju13 明日见Asumi14 阳光1号Yangguang No.1

2.6 杂柑DNA分子身份证的验证

为了验证构建的杂柑分子身份证的可行性,由外单位送检了12份已知分子身份证信息的样品,将12份样品随机编号后进行盲检。利用8个SV标记对供试样品进行扩增,扩增结果见图5,将供试样品扩增图谱与已建立杂柑分子身份证信息进行逐一比对。结果(表10)显示,12份供试样品的鉴定结果与真实品种名称完全匹配。由此证明,已构建的杂柑分子身份证可用于杂柑品种的苗期真实性鉴定。

图5 8个SV标记用于12份杂柑样品真实性验证结果
Fig.5 The authenticity verification results of8SV marks used for 12 citrus hybrids samples

表10 12份杂柑样品真实性鉴定结果
Table 10 Authenticity identification results of 12 citrus hybrids samples

送样号 盲检号 品种名称 转换0,1字符 匹配品种 真实品种信息 差异位点Sample submis-Blind No. Convert0,1 characters Differential sites sion No. Variety name Matching variety Real variety information1-1 1号 未知 1011100011111110101 甘平 甘平 0 No.1 Unknown Kanpei Kanpei 2-1 2号 未知 1010110011110110111 不知火 不知火 0 No.2 Unknown Shiranuhi Shiranuhi 3-1 3号 未知 1011111001111110111 清见 清见 0 No.3 Unknown Kiyomi Kiyomi 4-1 4号 未知 1010101001111110111 天草 天草 0 No.4 Unknown Amakusa Amakusa 5-1 5号 未知 1111011100010110101 春香 春香 0 No.5 Unknown Haruka Haruka 6-1 6号 未知 1110111100111110110 红美人 红美人 0 No.6 Unknown Ehime Ehime 7-1 7号 未知 1011100011111110101 甘平 甘平 0 No.1 Unknown Kanpei Kanpei 8-1 8号 未知 1111100100110110111 金秋砂糖橘 金秋砂糖橘 0 No.2 Unknown Jinqiu Shatangju Jinqiu Shatangju 9-1 9号 未知 1110111100111110110 红美人 红美人 0 No.3 Unknown Ehime Ehime 10-1 10号 未知 1010110101111110110 默科特 默科特 0 No.4 Unknown Murcott Murcott 11-1 11号 未知 1011110101011110110 沃柑 沃柑 0 No.5 Unknown Orah Orah 12-1 12号 未知 1111100100110110111 金秋砂糖橘 金秋砂糖橘 0 No.6 Unknown Jinqiu Shatangju Jinqiu Shatangju

3 讨 论

3.1 16个杂柑品种的遗传多样性分析

本研究统计了16份杂柑种质的苗期农艺性状,并基于柑橘基因组测序数据筛选出8个高多态性的SV标记进行遗传多样性分析。农艺性状差异小则难以从表型性状上直接对品种进行区分。8个分子标记PIC变化范围为0.258~0.643,平均值为0.393。通常认为PIC>0.5的标记为高多态性,而PIC<0.25则被视为低多态性[3]。本研究除chr1:29803181(PIC=0.258)外,其余7个位点的PIC>0.3,多数引物多态性良好,其中chr4:31281339(PIC=0.643)为高多态性引物。与余歆等[30]利用Indel标记对橘柚杂种进行遗传多样性分析结果相比(PIC=0.055~0.450,平均值为0.281),本研究的SV标记多态性更高。此外,Nei's基因多样性(0.492)与PIC全基因组平均值(0.393)表明16个杂柑品种具有高度遗传多样性;观测杂合度的平均值(0.625)高于期望杂合度(0.508),表明品种杂合度高,证实了长期杂交育种导致了遗传背景的高度复杂。

3.2 16个杂柑品种的聚类分析

通常基于基因组数据、分子标记与形态学对柑橘的遗传背景进行分析[31]。遗传相似系数可以反映不同品种间亲缘关系的远近[32]。李沛等[33]基于柑橘重测序与表型数据对宽皮柑橘进行聚类分析,将供试材料分为七大亚群,其中具有爱媛系列遗传背景的杂柑聚为一类,橘柚杂种聚为一类,沙糖橘系列杂交种则聚为另一类。本研究基于柑橘基因组数据与开发的SV标记,在遗传相似系数0.52处,将16个杂柑品种分为了两大类,以清见或其后代为亲本选育的7个日本品种、以色列选育的沃柑、美国选育的W.默科特和默科特等聚为一类,这类品种均为直立树姿、单叶叶型,叶身形状以卵圆形、披针形为主,叶尖多为渐尖,叶缘多呈波状。中国选育的金秋砂糖橘、阳光1号和日本选育的春香聚为一类。其中,金秋砂糖橘叶尖为钝圆、叶缘呈锯齿状;阳光1号叶身为披针形、叶缘呈锯齿状;春香叶尖为短尖、叶缘呈波状,三者与第一类杂柑品种的农艺性状差异明显。此外,金秋砂糖橘与阳光1号是清见的第3或4代杂交种,亲缘关系较远;而春香则无清见血缘;春香与阳光1号均是橘柚杂种[30]。因此,金秋砂糖橘、阳光1号、春香划为第二类的可信度较高。

3.3 分子身份证构建

传统的品种鉴定方法主要依赖叶片和果实形态特征,而苗期则主要依赖叶片形态特征。本研究统计分析了16份杂柑品种的苗期农艺性状,其树姿均为直立,叶型均为单叶,叶身形状集中于卵圆形、披针形,叶尖多为渐尖,多数品种的叶缘呈波状。苗期叶片性状高度相似,且易受环境因素干扰,难以区分亲缘关系较近的品种。分子标记是种质鉴定与新品种保护的重要分子手段,突破了传统鉴定方法的限制[34]。该技术基于PCR扩增特定基因组序列,其分子指纹图谱在DNA水平上直观呈现个体差异,具有环境稳定性和个体特异性两大优势[35]。从本研究开发的SV标记中筛选出8对高多态性引物,应用于16个杂柑品种的鉴定。利用琼脂糖凝胶电泳平台显示SV标记扩增条带的信息,通过人工读带的方式将条带信息转换为0、1字符矩阵,再转化成条形码与二维码,构建了14个杂柑品种的分子身份证,可应用于杂柑品种的鉴定。在16个杂柑品种中,仅大雅柑与春见无法利用所筛选的8个SV标记进行有效区分。8个SV标记位点在大雅柑和春见中完全一致,且两者的叶身形状(卵圆形)、叶尖形状(渐尖)、叶基形状(楔形)等农艺性状高度重合,从表型层面和分子层面皆证实了两者具有高度接近的亲缘关系,遗传背景显著重叠。遗传背景分析表明,两者具有相同母本,大雅柑为清见与新生系3号椪柑的杂交后代,春见则是清见与F-2432椪柑的杂交后代。鉴于父本属于近缘椪柑品系,两者实际亲缘关系比普通半同胞更近[36],需采用更高分辨率的分子标记加以区分。

4 结 论

本研究对16个杂柑品种的苗期表型性状进行了系统分析,并基于柑橘全基因组测序数据筛选获得8个SV标记。结果表明,苗期表型性状差异小,难以作为品种鉴别的有效依据;而8对SV标记引物组合可实现14个杂柑品种的有效区分。进一步的遗传多样性及聚类分析结果表明供试品种遗传背景复杂、遗传多样性丰富。在此基础上,将8对SV标记的扩增结果转化为字符串编码并进行组合,成功构建了14个杂柑品种独一无二的DNA分子身份证。研究结果为杂柑品种苗期鉴定与品种保护提供了有力的技术支撑。

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Genetic diversity analysis and fingerprinting of citrus hybrid varietiesbased on SV markers

XIANG Zhifei1,HE Cong1,GENG Yuanlai1,QIU Ting1,YU Qiang1,ZHANG Yingzi1,2,YANG Xingxing3,HE Dengmin4,DAI Suming1,2,LI Dazhi1,2,LI Na1,2*

(1College of Horticulture,Hunan Agricultural University,Changsha 410128,Hunan,China;2Yuelushan Laboratory,Pomology Variety Innovation Center,Changsha 410128,Hunan,China;3Hunan Provincial Crop Germplasm Resources Protection and Improved Seed Breeding Center,Changsha 410219,Hunan,China;4Anhua County Pest-Free Citrus Breeding Farm,Anhua 413599,Hunan,China)

Abstract: 【Objective】Citrus hybrids have gained significant popularity among consumers and hold broad market prospects due to their desirable characteristics,including juiciness,easy-to-separate segments,rich flavor,low-seed or seedless flesh,and easy peeling. However,with the increasing number of commercial varieties and the expansion of planting areas,issues such as variety mixing and counterfeit labeling have become increasingly prominent. These problems are particularly difficult to identify at the seedling stage,which severely restricts the healthy development of the citrus industry. Therefore,it is urgent to establish rapid and accurate variety identification techniques to protect breeders' rights. To address this need,the present study utilized structural variation (SV) molecular markers to analyze the genetic diversity of 16 citrus hybrids and constructed their corresponding molecular identification profiles. This research aims to provide technical support for the identification and protection of citrus hybrids germplasm resources,while also offering data references for further exploration of their genetic background.【Methods】This study selected 16 popular citrus hybrids as materials. Genetic diversity analysis and molecular fingerprint construction were based on 7 qualitative traits and 34 pairs of SVmarker primers. Data for qualitative traits were processed using Microsoft Excel2016,and the genetic diversity index (H) was calculated using SPSS 25 following the Shannon-Weaver method. PCR products amplified by the 34 SV marker primer pairs were detected via agarose gel electrophoresis,and banding patterns were scored as “0” and “1”. The Data Formatter software was used to convert the binary (0/1) data into fragment size (bp) data. Popgene 32 software was used to calculate the number of alleles(Na),the effective number of alleles(Ne),the Shannon's information(I),the observed heterozygosity (Ho),the expected heterozygosity (He) and the Nei's gene diversity (H). The Power Marker V3.25 was used to calculate the major allele frequency (MAF) and polymorphism information content (PIC).Cluster analysis was performed using NTSYSpc2.10e software to calculate genetic similarity coefficients,and a dendrogram was constructed using the UPGMA method.【Results】The results showed that the 7 qualitative traits across the 16 citrus hybrids exhibited 16 variation types,with an average diversity index of 0.517 5. While there was some variation among the 16 citrus hybrids accessions in traits such as leaf blade shape,leaf base shape,wing leaf shape,and leaf margin,these traits were insufficient to fully distinguishing the tangor varieties at the seedling stage. Furthermore,seedling phenotypic traits are easily influenced by environment and cultivation conditions,indicating that morphological identification can only serve as an auxiliary method for variety identification. Eight SV marker primers exhibiting good polymorphism were selected from the successfully 34 amplified primers;these eight primers could collectively distinguish 14 citrus hybrids. Among them,the varieties Nishinoka,Asumi,and Yangguang No.1 possessed unique genotypes distinguishable using just one primer pair. A total of 19 alleles were detected by the eight SV marker primers. The number of alleles (Na) was 2.375,the effective number of alleles (Ne) was 2.062,the major allele frequency (MAF) was 0.582,the polymorphism information content (PIC) was 0.393,the Nei's gene diversity (H) was 0.492,the average Shannon's information (I) was 0.742,the observed heterozygosity (Ho) was 0.625,and the expected heterozygosity(He) was0.508. These results indicate that the eight SV marker primers possess good polymorphism and that the tested 16 citrus hybrids have a high degree of heterozygosity and relatively rich genetic diversity. Cluster analysis revealed that at a genetic similarity coefficient of 0.64,the 16 citrus hybrids could be divided into five groups. Varieties bred using Kiyomi (a monoembryonic trait) as a female parent or its descendants as parents,were mainly clustered into the first group. Varieties without Kiyomi ancestry were primarily clustered into the second group. Yangguang No.1,Haruka,and Jinqiu Shatangju each formed separate groups,indicating significant differences in their genetic backgrounds compared to the other 13 citrus hybrids accessions. Using the amplification results from the eight selected SV marker primers,unique molecular fingerprints were constructed for 14 citrus hybrids. Subsequently,six samples with established molecular fingerprint information provided by an external institution were tested,verifying that the established citrus hybrids molecular fingerprints can be used for authenticity identification of citrus hybrids at the seedling stage.【Conclusion】This study statistically analyzed the seedling phenotypic traits of 16 citrus hybrids and found them to be relatively consistent,making it difficult to directly identify varieties based on morphological characteristics at the seedling stage.Based on citrus whole-genome sequencing data,eight SV markers were developed and screened.14 citrus hybrids could be distinguished combinations of these eight SV marker primers. Furthermore,the amplification results of the eight SV markers were converted into character strings and combined to successfully construct the unique DNA molecular fingerprints for 14 citrus hybrids. Corresponding barcode and QR code molecular fingerprints were generated using a QR code generator. Additionally,the results of genetic diversity and cluster analysis of the 16 citrus hybrids indicated that the tested varieties havecomplex genetic backgrounds and rich genetic diversity. In summary,the above research findings provide effective technical support for the identification and protection of citrus hybrids at the seedling stage.

Key words: Citrus hybrids;Structural variation;Molecular markers of DNA;Genetic diversity;Molecular ID card

DOI: 10.13925/j.cnki.gsxb.20250559

中图分类号:S666.1

文献标志码:A

文章编号:1009-9980(2026)05-1084-15

收稿日期:2025-10-10

接受日期:2025-12-11

基金项目:国家柑橘产业技术体系项目(CARS-26);湖南省水果产业技术体系专项(HARS-09)

作者简介:向芝菲,女,在读硕士研究生,研究方向为柑橘育种。E-mail:1515426295@qq.com

*通信作者 Author for correspondence. E-mail:1112lina@hunau.edu.cn