欧洲重要玉米群体特征及其利用途径分析

欧洲本土玉米种质多属硬粒型,具有较强的早熟性和抗逆性,导入欧洲优良玉米种质是拓宽我国适宜机械化种质基础的有效途径。通过整合分析欧洲西南、东南和北部玉米种质的配合力及杂种优势研究结果,发现有应用潜力的23个优良玉米群体,包括10个西班牙群体、6个法国群体、2个葡萄牙群体和5个瑞士群体。建议在适应性改良的基础上,将群体Enano Norteno/Vasco、EZS22与我国A群种质,群体Ain、Alegia、Bade、Berrobi、Lazcano、Tuy与我国B群种质构建复合群体,开展改良,拓宽我国玉米种质类群的遗传基础。     

8个合成群体改良玉米杂交种郑单958的育种潜力分析

玉米群体含有有利等位基因, 可作为改良杂交种的优异种质。针对持续改良我国主要玉米杂交种郑单958产量性状和商品品质的需求, 文章以8个合成群体为供体, 郑单958亲本自交系为受体, 组配16个测交组合。2009和2010年分别在北京顺义和河南新乡测量产量和籽粒容重。4个遗传参数评价显示, 合成群体可以作为新的有利等位基因供体改良杂交种性状, 其中WBMC-4和陕综3号两个群体具有同时改良杂交种产量和籽粒容重的潜力, 可分别用于改良亲本自交系郑58和昌7-2, 以及拓宽我国主要玉米类群PA和四平头的种质基础。     

405份CIMMYT引进小麦种质的遗传多样性分析

为了明确国际玉米改良中心(CIMMYT)引进普通小麦种质材料的遗传多样性特点,为其利用提供参考依据,本研究从均匀分布于小麦基因组的420对SSR引物中选择出条带清晰、多态性较好的62对引物对引自CIMMYT的405份普通小麦种质系进行遗传多样性检测。结果表明,62对SSR引物在405份CIMMYT材料中共检测到198个等位变异,每对引物检测到等位变异的数目为2~8个,平均每对SSR引物能够检测到3.19个等位变异。单个SSR引物的PIC值介于0.03~0.79之间,平均值0.48。405份CIMMYT材料A、B、D基因组之间多态性位点数和等位变异数相差不大,PIC平均值B基因组(0.53)A基因组(0.52)D基因组(0.39)。聚类分析结果显示,62对SSR引物能够将405份CIMMYT材料区分开来,在0.1285遗传距离处将供试材料分为24个类群,类型较为丰富,不同类群的材料在农艺性状和品质性状上存在差异。     

基于SSR标记的30份玉米种质遗传完整性分析

利用70对SSR引物,对30份玉米地方品种种质进行遗传完整性检测,每一份种质包含来自两个不同繁种年份的供试亚群体。取样方法为DNA混合取样。结果表明,30份种质的供试亚群体之间的遗传相似系数除红包谷(统一编号00230080)为0.77外,其他都大于0.80。聚类分析表明,除二黄(统一编号00210055)和红包谷两份种质的亚群体出现分支外,其他28份种质亚群体分支都按照同一种质群分别聚类。本文同时探讨了个别种质亚群体之间遗传分化的原因,以及SSR标记作为玉米种质遗传完整性检测方法的可行性。     

玉米抗腐霉茎腐病种质标记基因型鉴定与遗传多样性分析

腐霉茎腐病(Pythium stalk rot)是玉米生产上的重要病害。本研究利用14个与8个抗玉米茎腐病基因连锁的分子标记对196份抗腐霉茎腐病玉米种质进行抗病标记基因型鉴定,并采用42对多态性SSR标记对54份抗病自交系进行遗传多样性分析,以期阐明玉米抗腐霉茎腐病种质的标记基因型和遗传背景,并为资源的有效利用、新基因的挖掘和杂种优势模式确定提供参考信息。14个与抗病基因连锁的分子标记将196份抗性种质鉴定为128种标记基因型,表明存在多样的抗性基因组合方式。191份种质获得与齐319、X178或1145中一个或多个的相同的扩增,表明97.45%种质可能含有与3个抗玉米茎腐病材料相同的抗病基因;粤61、郑653、赤L136、白53和18--14共5份种质均未扩增出与齐319、X178和1145相同的标记基因型,可能携带其他抗茎腐病基因;遗传背景相近的抗性种质分属不同的标记基因型,表明抗病种质携带的抗病基因可能在育种选择中发生了分离。42对多态性SSR引物在54份抗病材料中共检测出119个等位基因(Na),多态位点百分率(PPB)为99.17%,平均有效等位基因数(Ne)为1.7070,平均Nei′s基因多样性(H)为0.3999,平均Shannon′s信息指数(I)为0.5844,平均多态信息含量(PIC)为0.5527,变幅为0.2061～0.7844;通过UPGMA聚类分析,54份抗病材料被划分为2个类群,共6个亚群中,分别是旅大红骨亚群、BSSS亚群、塘四平头亚群、PA亚群、PB亚群、Lan亚群,表现出较高的遗传多样性。结果表明,我国6个杂种优势群中均含有较为丰富的抗腐霉茎腐病种质资源,其中PA亚群包含的抗病种质最多。     

120份欧美玉米自交系的遗传多样性分析

为了拓宽黄淮海区玉米自交系的遗传基础,加快欧美优异种质的融入与利用,本研究利用SSR分子标记对120份来自美国和塞尔维亚及2份中国的玉米自交系进行遗传多样性和聚类分析。结果表明:29个多态性SSR标记共检测到115个等位位点,平均3.97个,位点多态性信息指数(PIC)平均为0.50,较好地揭示了自交系间的遗传多样性;观测杂合度(Ho)仅为0.03,表明参试自交系遗传稳定、纯合度高;美国SS、美国NSS、塞尔维亚和中国骨干自交系4个群之间相比,美国NSS群的等位位点数(3.55)、Shannon信息指数(0.93)最高,而塞尔维亚群的有效等位位点数(2.37)最高,表明美国NSS和塞尔维亚自交系群比其他两个群遗传多样性高;4个自交系群间的遗传距离介于0.1403~0.4695之间,美国NSS群与美国SS群、塞尔维亚群之间较小(0.1419,0.1403),与中国骨干自交系群之间最大(0.4695),4个群的遗传一致度介于0.6253~0.8691之间,美国NSS群与美国SS、塞尔维亚两个群之间的遗传一致度较高,表明美国与塞尔维亚自交系之间基因交流频繁,亲缘关系较近;聚类分析将122份玉米自交系分为9大主要类群,美国SS种质、NSS种质自交系被明显的区分开,并且SS种质被分为2个主要类群(Ⅰ和Ⅸ),NSS种质被分为6个主要类群(Ⅱ-Ⅶ),来自塞尔维亚的材料分散在美国NSS种质类群。本研究结果为来自欧美的自交系在玉米育种中合理利用提供可靠依据。     

热带、亚热带玉米育种素材的遗传改良

以泰国玉米品种与适应种质共122份为素材,采用改良穗行、顶交或测交方案,按精准的育种目标与定向设计,创制出具有鲜明独特特征的开放授粉品种(Open pollinate varieties,OPVs)。育种素材选择考虑表现优良、广适性、遗传多样性等3个因素;合成系统考虑实现遗传混合与重组、均等比较遗传贡献、施之温和选择压力、充分交配达到遗传平衡(遗传组成母本性状相近)等4条要素。相继创制Suwan 1复合种及其(半)硬粒型衍生种(Suwan 2、3复合种,Suwan 5、KS24综合种),含有不同血缘的马齿型KS6、KS28,Non-Suwan 1血缘的马齿型Caripeno DMR、KS27、KS23等。对10个OPVs采用S1选择法分别实施了C2～C13轮选择,从中育成近50个自交系,组配并发放16个优良单(三)交种。目前泰国各单位育成的每个杂交种中,至少有一个亲本系来源于Suwan(KS)种质。文章还依据合成OPVs及选系理论,对合成OPVs遗传成分适度多样化、亲缘关系、优势群与模式和合成OPVs对杂交优势育种的启示问题加以探讨。     

中国黍稷种质资源抗黑穗病鉴定评价

采用人工对种子饱和接种的方法,对来自我国14省（区）的6526份黍稷种质资源进行了抗黑穗病鉴定。筛选出高抗种质11份,占0．17％;抗病种质574份,占8．80％;这些种质均可作为我国黍稷种质遗传改良的亲本材料应用,有些丰产性和品质性状优良的种质,黑穗病高发地区可在生产上直接利用。     

野生马氏珠母贝子一代的遗传多样性

分析了海南省三亚与广西省北海两地野生贝群体内交配所得子代两群体 (SS、BB)和群体间交配(SS♀ ×BB♂ →BS)所得子代群体 (BS)各 8个个体的遗传多样性。筛选的 2 0个含 1 0碱基的随机引物中 ,其中 1 4个产生稳定的可重复的多态扩增结果 ,共检测出 1 2 4个位点。用修正的Shannon表型多态性指数量化三个群体的遗传多态度 ,SS、BB、BS三群体的多态度分别为 0 2 47,0 2 3 7,0 2 61。SS与BB ,SS与BS ,BB与BS三群体间的遗传相似度分别为 87 2 4% ,80 3 9% ,83 90 %。讨论了不同地域之间进行马氏珠母贝育种及遗传多样性保护工作的可行性     

北沙柳群体遗传多样性和遗传结构分析

以内蒙古北沙柳(Salix psammophila)国家种质资源库内9个群体(P1~P9)288个无性系为实验材料,利用TP-M13-SSR技术,选取22对具有多态性EST-SSR北沙柳引物,采用毛细管电泳对PCR产物进行检测,分析北沙柳遗传多样性、分化程度和群体遗传结构,为北沙柳种质资源库遗传管理、无性系鉴定、品种选育、遗传改良和构建指纹图谱提供理论依据。结果显示:(1)22对EST-SSR引物共检测到222个等位基因,各位点平均等位基因数(A)为10,四倍体基因型丰富度(G)和特异基因型(G1)总和分别为1 460和802个,平均特异基因型比率(P1)和种质鉴别率(P2)分别为45.86%和13.21%。(2)9个群体平均等位基因数(A)为7.475,基因型丰富度(G)为15.586,观察杂合度(Ho)和期望杂合度(He)分别为0.577和0.638。以期望杂合度He为标准,北沙柳群体遗传多样性水平最低的是P1和P9。(3)北沙柳群体遗传分化系数仅为0.02,AMOVA分子变异分析显示,北沙柳群体大部分遗传变异来自群体内(97%),群体间变异仅为3%。(4)三维主成分、聚类和Structure群体遗传结构分析显示,9个群体被划分为2个组,Mantel检验表明北沙柳遗传距离与地理距离极显著相关(r=0.684 P0.001)。研究表明,北沙柳种质资源具有丰富的遗传多样性,这是其具有耐旱、耐寒、耐高温、耐沙埋和抗风蚀等适应性较强的分子基础;北沙柳的遗传变异集中在群体内;分布区群体呈现由中心向边缘群体扩张分化的趋势。     

Use of SSRs for establishing heterotic groups in subtropical maize

Heterotic groups and patterns are of fundamental importance in hybrid breeding. The objectives of our research were to: (1) investigate the relationship of simple sequence repeats (SSR) based genetic distances between populations and panmictic midparent heterosis (PMPH) in a broad range of CIMMYT maize germplasm, (2) evaluate the usefulness of SSR markers for defining heterotic groups and patterns in subtropical germplasm, and (3) examine applications of SSR markers for broadening heterotic groups by systematic introgression of other germplasm. Published data of two diallels and one factorial evaluated for grain yield were re-analyzed to calculate the PMPH in population hybrids. Additionally, 20 pools and populations widely used in CIMMYT's breeding program were assayed with 83 SSR markers covering the entire maize genome. Correlations of squared modified Roger's distance (MRD²) and PMPH were mostly positive and significant, but adaption problems caused deviations in some cases. For intermediate- and early-maturity subtropical germplasm, two heterotic groups could be suggested consisting of a flint and dent composite. We concluded that the relationships between the populations obtained by SSR analyses are in excellent agreement with pedigree information. SSR markers are a valuable complementation to field trials for identifying heterotic groups and can be used to introgress exotic germplasm systematically.Communicated by F. Salamini     

Allozyme polymorphisms of maize populations from southwestern China

Maize (Zea mays L.) is one of the most-important food crops in southwestern China. The diversity of maize populations from southwestern China has been evaluated on the basis of agronomic and morphological data, but not on marker data. Our objectives were to evaluate the allozyme polymorphism of these populations, and group the populations on the basis of allozyme data. We analyzed 27 maize populations from southwestern China and two populations [BS13(S)C2 and Lancaster] from the USA for genetic variation at 18 allozyme loci. We found a total of 69 alleles at 18 allozyme loci with an average of 3.8 alleles per locus. Compared with inbreds, hybrids, and populations from the U.S. Corn Belt, the 27 Chinese populations had a significantly higher (p<0.01) number of allozyme alleles per locus. Maize populations from southwestern China have accumulated abundant genetic diversity, and might be valuable germplasm for broadening the genetic base of U.S. Corn Belt breeding germplasm. The analyses of allele-frequency distributions and the expected heterozygosity also reflected the differences between the Chinese and the U.S. germplasm. The Chinese populations might be valuable germplasm for complementing U.S. Corn Belt breeding germplasm. The analysis of gene diversity showed that 77% of the allozyme variation resided within populations and 23% between populations. This result suggested that breeders should identify one or a few Chinese populations with the best agronomic performance, and exploit the genetic variation within these selected populations. Cluster analysis classified the 29 populations into four main groups. Groupings based on allozyme data could be useful for classifying the populations into different heterotic groups and, consequently, exploiting them in hybrid breeding. Received: 12 October 2000 / Accepted: 13 March 2001     

Genetic characterization of a core set of a tropical maize race Tuxpeño for further use in maize improvement

The tropical maize race Tuxpe?o is a well-known race of Mexican dent germplasm which has greatly contributed to the development of tropical and subtropical maize gene pools. In order to investigate how it could be exploited in future maize improvement, a panel of maize germplasm accessions was assembled and characterized using genome-wide Single Nucleotide Polymorphism (SNP) markers. This panel included 321 core accessions of Tuxpe?o race from the International Maize and Wheat Improvement Center (CIMMYT) germplasm bank collection, 94 CIMMYT maize lines (CMLs) and 54 U.S. Germplasm Enhancement of Maize (GEM) lines. The panel also included other diverse sources of reference germplasm: 14 U.S. maize landrace accessions, 4 temperate inbred lines from the U.S. and China, and 11 CIMMYT populations (a total of 498 entries with 795 plants). Clustering analyses (CA) based on Modified Rogers Distance (MRD) clearly partitioned all 498 entries into their corresponding groups. No sub clusters were observed within the Tuxpe?o core set. Various breeding strategies for using the Tuxpe?o core set, based on grouping of the studied germplasm and genetic distance among them, were discussed. In order to facilitate sampling diversity within the Tuxpe?o core, a minicore subset of 64 Tuxpe?o accessions (20% of its usual size) representing the diversity of the core set was developed, using an approach combining phenotypic and molecular data. Untapped diversity represents further use of the Tuxpe?o landrace for maize improvement through the core and/or minicore subset available to the maize community.     

Genetic Characterization of a Core Set of a Tropical Maize Race Tuxpe?o for Further Use in Maize Improvement

The tropical maize race Tuxpeño is a well-known race of Mexican dent germplasm which has greatly contributed to the development of tropical and subtropical maize gene pools. In order to investigate how it could be exploited in future maize improvement, a panel of maize germplasm accessions was assembled and characterized using genome-wide Single Nucleotide Polymorphism (SNP) markers. This panel included 321 core accessions of Tuxpeño race from the International Maize and Wheat Improvement Center (CIMMYT) germplasm bank collection, 94 CIMMYT maize lines (CMLs) and 54 U.S. Germplasm Enhancement of Maize (GEM) lines. The panel also included other diverse sources of reference germplasm: 14 U.S. maize landrace accessions, 4 temperate inbred lines from the U.S. and China, and 11 CIMMYT populations (a total of 498 entries with 795 plants). Clustering analyses (CA) based on Modified Rogers Distance (MRD) clearly partitioned all 498 entries into their corresponding groups. No sub clusters were observed within the Tuxpeño core set. Various breeding strategies for using the Tuxpeño core set, based on grouping of the studied germplasm and genetic distance among them, were discussed. In order to facilitate sampling diversity within the Tuxpeño core, a minicore subset of 64 Tuxpeño accessions (20% of its usual size) representing the diversity of the core set was developed, using an approach combining phenotypic and molecular data. Untapped diversity represents further use of the Tuxpeño landrace for maize improvement through the core and/or minicore subset available to the maize community.     

Incorporation of tropical maize germplasm into inbred lines derived from temperate × temperate-adapted tropical line crosses: agronomic and molecular assessment

Exotic maize ( Zea mays L.) germplasm may allow for increased flexibility and greater long-term progress from selection if it can be incorporated at high rates into U.S. breeding programs. Crosses were made between a temperate line, NC262A, and each of eight different lines consisting of 100% temperate-adapted tropical germplasm. Pedigree selection was used to generate a set of 148 F(5)S(2) lines that were evaluated in testcrosses with FR992/FR1064 in nine North Carolina environments. Several entries had grain yield, grain moisture content and standability that were comparable to three commercial checks. The best testcrosses outyielded the cross NC262A x FR992/FR1064 by 9.5 to 10.9%, suggesting that a significant amount of tropical germplasm was retained in these lines and that this germplasm combined well with the Stiff Stalk tester. Previous researchers had suggested that tropical alleles could be rapidly lost during inbreeding in populations derived from tropical x temperate bi-parental crosses, leading to the development of lines that possess significantly less than 50% tropical germplasm. F(5)S(5) sub-lines corresponding to the 14 best testcrosses were genotyped at 47 to 49 polymorphic simple sequence repeat (SSR) loci across all ten chromosomes to estimate the amount of tropical germplasm that was retained. The estimated genetic contribution from the tropical parent ranged from 32 to 70%, with the average being 49%. Only two of the 14 lines deviated significantly from a 50%-tropical/50%-temperate ratio, suggesting limited overall selection against germplasm from the tropical parents. These experiments collectively demonstrated that tropical maize germplasm can be incorporated at high rates into a temperate line via pedigree breeding methods in order to derive new inbred lines with acceptable agronomic performance.     

Relationships among maize inbred lines and populations from European and North-American origins as estimated using RFLP markers

RFLP markers have proven to be a reliable and highly informative tool for characterizing genetic diversity in maize. Joint analysis of inbred lines and populations should provide valuable information with respect to (1) a better understanding of the genetic basis of present elite germplasm and (2) the identification of populations that may prove to be useful sources of genetic diversity for breeding programs. Sixty-two inbred lines of known heterotic groups and ten maize populations, some of them significant contributors to the genetic basis of the heterotic groups, were assayed at 28 RFLP loci. Joint data analyses first underlined that the populations displayed a large number of alleles that were absent in the set of inbred lines. Associations among inbreds and populations further proved consistent with pedigree data of the inbreds and provided new information on the genetical basis of heterotic groups. In particular, European flint inbreds were revealed to be as close to the Northeastern U.S. flint population studied as to the typical European populations. These results advocate the analysis of larger sets of populations by means of molecular markers in order to (1) gain insight into the history of maize germplasm and (2) set up appropriate strategies for the use of genetic resources in breeding programs. Received: 23 February 1998 / Accepted: 5 February 1999     

Molecular characterization of global maize breeding germplasm based on genome-wide single nucleotide polymorphisms

Characterization of genetic diversity is of great value to assist breeders in parental line selection and breeding system design. We screened 770 maize inbred lines with 1,034 single nucleotide polymorphism (SNP) markers and identified 449 high-quality markers with no germplasm-specific biasing effects. Pairwise comparisons across three distinct sets of germplasm, CIMMYT (394), China (282), and Brazil (94), showed that the elite lines from these diverse breeding pools have been developed with only limited utilization of genetic diversity existing in the center of origin. Temperate and tropical/subtropical germplasm clearly clustered into two separate groups. The temperate germplasm could be further divided into six groups consistent with known heterotic patterns. The greatest genetic divergence was observed between temperate and tropical/subtropical lines, followed by the divergence between yellow and white kernel lines, whereas the least divergence was observed between dent and flint lines. Long-term selection for hybrid performance has contributed to significant allele differentiation between heterotic groups at 20% of the SNP loci. There appeared to be substantial levels of genetic variation between different breeding pools as revealed by missing and unique alleles. Two SNPs developed from the same candidate gene were associated with the divergence between two opposite Chinese heterotic groups. Associated allele frequency change at two SNPs and their allele missing in Brazilian germplasm indicated a linkage disequilibrium block of 142 kb. These results confirm the power of SNP markers for diversity analysis and provide a feasible approach to unique allele discovery and use in maize breeding programs.     

Broadening the genetic base of European maize heterotic pools with US Cornbelt germplasm using field and molecular marker data

Maize (Zea mays L.) breeders are concerned about the narrowing of the genetic base of elite germplasm. To reverse this trend, elite germplasm from other geographic regions can be introgressed, but due to lack of adaptation it is difficult to assess their breeding potential in the targeted environment. The objectives of this study were to (1) investigate the relationship between European and US maize germplasm, (2) examine the suitability of different mega-environments and measures of performance to assess the breeding potential of exotics, and (3) study the relationship of genetic distance with mid-parent heterosis (MPH). Eight European inbreds from the Dent and Flint heterotic groups, 11 US inbreds belonging to Stiff Stalk (SS), non-Stiff Stalk (NSS), and CIMMYT Pool 41, and their 88 factorial crosses in F₁ and F₂ generations were evaluated for grain yield and dry matter concentration. The experiments were conducted in three mega-environments: Central Europe (target mega-environment), US Cornbelt (mega-environment where donor lines were developed), and Southeast Europe (an intermediate mega-environment). The inbreds were also fingerprinted with 266 SSR markers. Suitable criteria to identify promising exotic germplasm were F₁ hybrid performance in the targeted mega-environment and F₁ and parental performance in the intermediate mega-environment. Marker-based genetic distances reflected relatedness among the inbreds, but showed no association with MPH. Based on genetic distance, MPH, and F₁ performance, we suggest to introgress SS germplasm into European Dents and NSS into European Flints, in order to exploit the specific adaptation of European flint germplasm and the excellent combining ability of US germplasm in European maize breeding programs.     

The strategy and potential utilization of temperate germplasm for tropical germplasm improvement: a case study of maize (<Emphasis Type="Italic">Zea mays</Emphasis> L.)

The organization of maize (Zea mays L.) germplasm into genetically divergent heterotic groups is the foundation of a successful hybrid maize breeding program. In this study, 94 CIMMYT maize lines (CMLs) and 54 United States germplasm enhancement of maize (GEM) lines were assembled and characterized using 1,266 single nucleotide polymorphisms (SNPs) with high quality. Based on principal component analysis (PCA), the GEM lines and CMLs were clearly separated. In the GEM lines, there were two groups classified by PCA corresponding to the heterotic groups “stiff stalk” and “non-stiff stalk”. CMLs did not form obvious subgroups by PCA. The allelic frequency of each SNP differed in GEM lines and CMLs. In total, 3.6% alleles (46/1,266) of CMLs are absent in GEM lines and 4.4% alleles (56/1,266) of GEM lines are absent in CMLs. The performance of F1 plants (n = 654) produced by crossing between different groups based on pedigree information was evaluated at the breeding nurseries of two CIMMYT stations. Genomic estimated phenotypic values of plant height and days to anthesis for a testing set of 45 F1 crosses were predicted based on the training data of 600 F1 crosses using a best linear unbiased prediction method. The prediction accuracy benefitted from the adoption of the markers associated with quantitative trait loci for both traits; however, it does not necessarily increase with an increase in marker density. It is suggested that genomic selection combined with association analysis could improve prediction efficiency and reduce cost. For hybrid maize breeding in the tropics, incorporating GEM lines which have unique alleles and clear heterotic patterns into tropically adapted lines could be beneficial for enhancing heterosis in grain yields.