Comparative analysis of cultivated melon groups (Cucumis melo L.) using random amplified polymorphic DNA and simple sequence repeat markers

Random amplified polymorphic DNA (RAPD) and simple sequence repeat (SSR) markers were used to characterize genetic relationships among 46 accessions in two C. melo L. subsp. melo (Cantalupensis, Inodorus) and subsp.agrestis (Conomon, and Flexuosus) groups. Genetic distance (GD) estimates were made among and between accessions in four melon market classes [Galia, Ogen, Charentais, and Shipper (European and U.S. types)] of Cantalupensis, one market class of Inodorus (Cassaba and Honey Dew), one accession of Conomon, and one accession of Flexuosus by employing three GD estimators; simple matching coefficient, Jaccard's coefficient, and Nei's distance-D. Differences detected among 135 RAPD bands and 54 SSR bands (products of 17 SSR primers) were used to calculate GD. Band polymorphisms observed with 21 RAPD primers and 7 SSR primers were important (p =0.01) in the detection of genetic differences. Estimators of GD were highly correlated (p 0.0001; r_s = 0.64 to0.99) when comparisons were made between estimation methods within a particular marker system. Lower correlations (r_s = 0.17 to 0.40) were detected (P > 0.001) between marker systems using any one estimator. The GD of the Conomon and Flexuosus accessions was significantly different (p> 0.001)from the mean GD of all the market classes examined. The mean GD (Jaccard's coefficient) among accessions of Ogen, Galia, Cassaba, Charentais, European shipper, and U.S. shipper groups was 0.11 ± 0.04, 0.33± 0.09, 0.21 ± 0.04, 0.26 ± 0.10, 0.17± 0.05 and 0.22 ± 0.08, respectively. Market classes were distinct (p > 0.001), such that GDs between Galia and other accessions were the largest(mean GD 0.34 to 0.35), and GDs between Ogen and other accessions were the smallest (mean GD 0.29 to 0.30). Contrasts between the U.S. shipper cultivar Top Mark and accessions within any market class was relatively large (mean GD = 0.42 ± 0.06). Empirical estimations of variances associated with each marker type in the accessions examined indicated that, per band, lower coefficients of variation can be attained in the estimation of GD when using RAPDs compared to SSRs. Nevertheless, the genetic relationships identified using these markers were generally similar. The disparity between the analyses of the two markers made may be related to the amount of genome coverage which is characteristic of a particular marker system and/or its efficiency in sampling variation in a population. Results of RAPD marker analysis suggest that 80 marker bands were adequate for assessing the genetic variation present in the accessions examined. This revised version was published online in July 2006 with corrections to the Cover Date.     

Conformity and genetic relatedness estimation in crop species having a narrow genetic base: the case of cucumber (Cucumis sativus L.)*

A set of 155 SSR (107) and SCAR (48) markers were used to evaluate 53 cucumber (Cucumis sativus L.) accessions of diverse origin to characterize genetic relationships and to define a standard marker array that was most effective in detecting genetic differences in this germplasm array. A multivariate marker‐based analysis of diverse germplasm using this standard marker array (17 SSR and 5 SCAR markers) was compared with results from a set of 70 previously reported RAPD markers, and then used to explore the potential value of these genetic markers for plant variety protection (PVP) and the establishment of essential derivation (ED) threshold values in this species using elite lines and hybrids and backcross progeny. Diversity analysis allowed identification of distinctly different lines that were used for the construction of three sets of backcross families (BC₁‐BC₃). While general genetic relationships among accessions were similar in SSR/SCAR analyses (r_s= 0.65) using two genetic distance (GD) estimators, differences in accession relationships were detected between RAPD and SSR/SCAR marker evaluations regardless of the estimator used. The GDs among elite germplasm with known pedigrees were relatively small (0.06‐0.23 for any pairwise comparison). GD values decreased and degree of fixation (at three to seven loci depending on the mating) increased with increased backcrossing such that recurrent parent allelic fixation occurred in least one family of each of the BC₃ families. In many instances the degree of fixation of loci was not uniformly achieved in the BC₃. Although the level of genetic polymorphisms will likely restrict the use of molecular markers for PVP and the establishment of ED values, the use of single nucleotide differences will likely provide opportunities to define specific functional distances that have potential for PVP in cucumber. Nevertheless, without an expanded, genetically robust standard marker array (e.g. 50 codominant markers), ED threshold values will be difficult to define in this species, and perhaps will require the appraisal of single nucleotide polymorphisms as discriminators of difference in this species.     

Inter and intra-species Inter Simple Sequence Repeat (ISSR) variations in the genus Cicer

Intra and inter-species ISSR variation and use of ISSR markers in determination of genetic relationship were investigated in an accession collection representing twoperennial and six annual Cicerspecies. Screening of Ciceraccessions with SSR primers revealed highly reproducible amplicon profiles with relatively high multiplex ratios. Many of the primers generated amplicon profiles with which not only the differences among species can readily be identified, but also polymorphisms within species could be detected more efficiently. PCR products at 150 gel positions detected using six SSR primers in Cicer accessions were treated as dominant DNA markers and utilized to compute the distances among accessions and species. Cluster analysis of accessions and species revealed groupings that corroborate our previous studies of relationships based on allozyme and AFLP analysis. Consistent with the AFLP analysis carried out in the same accession collection, ISSR-based groupings indicated that perennial C. incisumis genetically close to the annuals of the second crossability group (C. pinnatifidum,C. bijugum, C. judaicum) while C. reticulatum is the closest wild species to the cultivated chickpea. ISSR-based variation estimates were relatively higher when compared to previous estimates computed from RAPD and AFLP data. Technically, ISSR analysis combines the PCR-based targeting of microsatellite-associated polymorphisms with no prior sequence requirement and stringent PCR conditions. Similarly, when compared to AFLP analysis, it is less technically demanding allowing to survey polymorphic loci in the genome. Thus, ISSR-PCR technology is a reliable, fast, and cost-effective marker system that can be used to study genetic variation and genetic relationships in the genusCicer. This revised version was published online in July 2006 with corrections to the Cover Date.     

Genetic diversity assessment in cultivated cardoon by AFLP (amplified fragment length polymorphism) and microsatellite markers

Cultivated cardoon (Cynara cardunculus L. var. altilis DC) belongs, together with globe artichoke (C. (cardunculus L. var. sylvestris L.) and wild cardoon (C. cardunculus L. var., sylvestris (Lamk) Fiori). to the family Asteraceae (Compositae). Cultivated cardoon is of regional importance in Italy. Spain and southern France, where it is used for the preparation of traditional dishes. It has been shown to have potential as a source of oil from its seeds, inulin from its roots and various biopharmaceuticals from its leaves. Levels of genetic diversity and relatedness between eleven Italian and 10 Spanish accessions were assessed by DNA profiling with eight AFLP primer combinations and at five microsatellite loci. The AFLP analysis of genetic similarities showed that the Spanish and Italian accessions represent two distinct gene pools; substantial variation was present within each accession. On the other hand a limited variation was detectable by applying SSR markers.     

Inter and intra-population variability of <Emphasis Type="Italic">Jatropha curcas</Emphasis> (L.) characterized by RAPD and ISSR markers and development of population-specific SCAR markers

Jatropha curcas (Euphorbiaceae) is an oil-bearing species with multiple uses and considerable potential as a bioenergy crop. The present investigation has been undertaken to assess the extent of genetic diversity in a representative set of 42 accessions of J. curcas encompassing different crop growing regions in India along with a non-toxic genotype from Mexico as a prelude for utilization of promising and genetically divergent materials in the breeding programmes. Molecular polymorphism was 42.0% with 400 RAPD primers and 33.5% with 100 ISSR primers between accessions indicating modest levels of genetic variation in the Indian germplasm. The within-population variation based on RAPD polymorphism was 64.0% and was on par with the inter-population variation. Polymorphic ISSR markers have been identified that could differentiate the Indian accessions from the Mexican genotype and two of them were converted to SCAR markers. The SCAR primer pair ISPJ1 amplified a 543 bp fragment in all the Indian populations, while ISPJ2 with a specific amplicon of 1,096 bp was specific to the Mexican genotype. Population-specific bands have been identified for the accession from Kerala (2 RAPD markers), Neemuch-1 from Rajasthan (1 each of RAPD and ISSR markers) and the non-toxic genotype from Mexico (17 RAPD and 4 ISSR markers), which serve as diagnostic markers in genotyping. The study indicates an immediate need for widening the genetic base of J. curcas germplasm through introduction of accessions with broader geographical background.     

Chinese melon (<Emphasis Type="Italic">Cucumis melo</Emphasis> L.) diversity analyses provide strategies for germplasm curation,genetic improvement,and evidentiary support of domestication patterns

The genetic diversity of melon market types (Cucumis melo L., 2n = 2x = 24) in China, an important secondary center of diversity, has not been examined. Therefore, reference accessions from India and Africa, Crete/Greece, Japan, Europe, U.S.A., Spain, and 68 Chinese cultigens (fresh-market non-netted thin-skinned; non-netted thick-skinned; netted thick-skinned; and non-netted thin-skinned, and vegetable) were evaluated by using 17 10-mer RAPD primers (32 mapped loci), days to flower, sex expression, lateral-branch number, and fruit number and weight per plant. While Chinese thin-skinned melons differed from vegetable melon types only in sex expression, the U.S. Western Shipping market type reference accession “Top Mark” and Chinese thick-skinned melons were similar for all of the morphological traits examined. The average similarity (Jaccard Coefficient) between any two pairs of accessions examined as estimated by RAPD variation was 0.47 ± 0.14. Within-group genetic similarities ranged between 0.94 (thin-skinned type) and 0.08 (non-netted thick-skinned type). The average/standard deviation, maximum, and minimum similarity between any two Chinese reference accessions was 0.41 ± 0.13, 0.75, and 0.12, respectively. Cluster analysis partitioned accessions into two main branches consisting of Group Cantalupensis and Inodorus reference accessions (clade 1) and Chinese accessions (clade 2). A second cluster analysis partitioned China, India, and Africa accessions into one major group, and accessions from Japan, Europe, and U.S.A. into another. Results indicate that Chinese accessions are a rich source of genetic diversity for plant improvement, and that molecular assessments support previously described theoretical melon domestication patterns constructed from historical and archeological evidence.     

Assessment of genetic variability in grapefruits (Citrus paradisi Macf.) and pummelos (C. maxima (Burm.) Merr.) using RAPD and SSR markers

The genetic variability of 38 grapefruit (Citrus paradisi Macf.) and three pummelos (C. maxima (Burm.) Merr..) accessions was evaluated using RAPD, and single sequence repeat (SSR) analyses. Approximately49% of the 198 RAPD were polymorphic, and 4.6 alleles per SSR loci were identified. PIC values changed from 0.093 to 0.450. A UPGMA phenetic tree was constructed and two main grapefruit groups were identified. The grapefruit accessions `do Cabo' and `Siamesa-Filipinas'clustered very close to the pummelos in Group A. The Group B consisted of three sub-groups, which comprised all of the other grapefruit accessions. The majority of grapefruit accessions showed a narrow genetic base suggesting that the observed morphological polymorphism within the group must be associated with somatic mutations, which were not detected by these molecular markers. This revised version was published online in August 2006 with corrections to the Cover Date.     

Molecular diversity and genome-wide linkage disequilibrium patterns in a worldwide collection of <Emphasis Type="Italic">Oryza sativa</Emphasis> and its wild relatives

Genetic diversity analysis within a species is vital for understanding evolutionary processes at the population and genomic levels. We report a detailed study of molecular diversity, polymorphism and linkage disequilibrium in three groups of rice (Oryza) germplasm accessions based on 176 SSR markers. The first group included 65 rice (O. sativa L.) accessions introduced from seven countries, including five regions of China. The second group included 58 US rice varieties released in the past 25 years. The third group consisted of 54 accessions of rice wild relatives represented by ten different species. The number of alleles per SSR marker ranged from 4 to 32 with a mean of 16 alleles and the polymorphism information content values ranged from 0.43 to 0.91 with a mean of 0.70. The variation in SSR alleles was a significant contribution to the genetic discrimination of the 177 accessions within the three Oryza groups. Analysis of molecular variance identified deviation from Hardy–Weinberg equilibrium. Principal coordinates analysis clearly separated the accessions into their respective three groups. Neighbor-joining phylogenetic cluster reflects the ordination of each accession. Linkage disequilibrium (D′) averaged 0.75 in wild Oryza spp., and about 0.5 in both US and international O. sativa accessions. Our results showed that LD among adjacent loci in both O. sativa and Oryza spp. accessions is strong enough to be detecting marker-trait association via genome-wide scans.     

小扁豆种质资源SSR标记遗传多样性及群体结构分析

从145对SSR引物中筛选到14对多态性引物,对选取国家种质库的440份小扁豆种质资源进行SSR标记遗传多样性分析,共检测出87个等位变异,平均每个SSR位点6.2143个;平均Shannon-Weaver指数(I)为1.1869。16个不同地理来源群体间表现出显著的遗传多样性差异,国外群体的遗传多样性水平(0.9837)远高于国内群体(0.3485)。PCA、UPGMA法聚类分析和Structure群体结构分析结果相互间完全吻合。440份参试材料从遗传结构上可划分为8个组群,揭示国外群体遗传分化大,群体间的亲缘关系较远;国内群体与之相反。研究结果显示,山西、宁夏和甘肃省是我国小扁豆资源遗传多样性最丰富、遗传关系较复杂的地区,应对该区域小扁豆资源进一步搜集、保护和研究。同时,应继续加强小扁豆资源的国外引种与交流,做进一步系统研究和开发利用。     

应用RAPD分析四川马铃薯地方品种与部分栽培品种间遗传关系

为探讨四川省马铃薯地方品种与栽培品种间遗传关系,评价其在遗传研究与育种利用价值,指导杂交亲本选配,对21份地方品种和10个栽培品种进行了RAPD分析。选取8份差异较大的材料对170条RAPD引物进行筛选,获得20条多态性高、条带清晰、稳定的RAPD引物。20条RAPD引物共扩增出191个位点,其中多态性位点172个;平均多态性位点比率90.1%,平均多态性信息量(PIC)为0.822;栽培品种、地方品种平均PIC分别为0.823和0.814。遗传距离与聚类分析表明：31份材料间平均遗传距离0.4274,变幅为0.1481~0.5852,地方品种间平均遗传距离和变幅均高于栽培品种间,地方品种与栽培品种间平均遗传距离为0.4496;表明地方品种中可能存在更广泛的遗传变异,具有较高的育种利用价值。大部分地方品种出乎意料与栽培品种聚在不同的类中,与供试栽培品种间亲缘关系较远,可能具有较高的杂交组配潜力;而N5-33、N5-38和N6-22可能分别源自于大西洋、疫不加与南湖塔(或米拉),值得深入对比研究。     

ICRISAT花生微核心种质青枯病抗性鉴定

对ICRISAT花生微核心种质155份材料进行抗青枯病鉴定,获得ICG9249和ICG12625两份抗青枯病材料,平均抗性达到了91.7%。与中国核心高抗5份种质共同作为材料,以SSR技术对其亲缘关系和遗传多样性进行了分析。在选用的58对SSR引物中,24对引物能扩增出稳定的多态性条带,这些引物能在抗青枯病花生种质基因组DNA中扩增出2~7个DNA片段。结果表明,7份抗青枯病种质的遗传距离为0.17~0.71,平均为0.49。其中ICG12625和撮豆、富川大花生的遗传距离最大（0.71）,嵊县小红毛和富川大花生的遗传距离最小（0.17）。经过统计,两两品种之间遗传距离达0.50以上的有12个组合,说明了这些抗青枯病种质资源的遗传多样性。根据DNA扩增结果,绘制了抗青枯病种质的指纹图谱,明确了其SSR分子特性。通过聚类分析结果和植物学性状调查结果显示,ICG12625与其它种质距离较远,且具有优良的植物学性状,可以作为疏枝亚种的亲本材料加以研究利用。     

基于SSR的四川花生遗传多样性分析

[目的]研究旨在了解四川花生资源的遗传多样性及表型性状与分子标记的关联分析,为花生分子育种及资源库构建提供理论依据。[方法]鉴定分析57份不同来源花生资源材料的4个农艺性状及4个品质性状,并利用SSR标记研究57份花生材料的遗传多样性,对SSR标记与表型性状进行聚类及关联分析。[结果]表型性状鉴定结果显示花生资源的8个性状中,6个变异较大、多样性较好。67对SSR引物中,有效引物39对,获得多态性条带53条,平均每个引物扩增1.36条,平均Nei"s 基因多样性0.2288、平均Shannon"s 指数0.3695,最远遗传距离为0.51。SSR分子标记聚类分析将57份资源聚为2大类群,GLM分析发现多个与蛋白质含量、株高、含糖量的关联标记。[结论]研究结果表明,四川不同区域间花生遗传多样性较丰富,品种类型单一,聚类及关联分析结果可为四川花生突破性新品种选育的亲本选择提供提供重要参考。     

Population structure and linkage disequilibrium of ICRISAT foxtail millet (Setaria italica (L.) P. Beauv.) core collection

Use of diverse germplasm is a key factor which allows high level of resolution due to extensive recombination in the history. Therefore, population used in association mapping should posses as many phenotypes as possible. One of the methods to obtain most of the phenotypes is to construct the core collection. The ICRISAT foxtail millet core collection consisting of 155 accessions was genotyped using 72 simple sequence repeat (SSR) markers to investigate the genetic diversity, population structure and linkage disequilibrium (LD). A high degree of molecular diversity among the accessions was found, with an average of 16.69 alleles per locus. STRUCTURE analyses classify the accessions into four subpopulations (SP) based on SSR allelic diversity. The Neighbor joining clustering and the principal coordinate analysis were in accordance with the racial classification. The distribution of molecular genetic variation among and within the four SP and three races showed high degree of variability within each group, and low level of genetic distance (GD) among the groups. LD decay of <40 cM of GD in foxtail millet core collection was observed, which suggests that it could be possible to achieve resolution down to the 40 cM level. From this investigation, it is evident that the foxtail millet core collection developed at ICRISAT is very diverse and could be a valuable resource for trait association mapping, crop breeding and germplasm management.     

Molecular Marker based Genetic Diversity Analysis in Rice (Oryza sativa L.) using RAPD and SSR markers

The availability of an array of molecular marker systems allowed comparing the efficiency of two of these marker systems to estimate the relationships among various taxa. The objective of this study was to assess the genetic diversity among 40 cultivated varieties and five wild relatives of rice, Oryza sativa L. involving simple sequence repeat (SSR) randomly amplified polymorphic DNA (RAPD) markers. The accessions were evaluated for polymorphisms after amplification with 36 decamer primers and 38 SSR primer pairs. A total of 499 RAPD markers were produced among the 40 cultivated varieties and five wild relatives with a polymorphism percentage of 90.0. Out of 38 SSR primer pairs used, only one locus viz., RM115 was monomorphic. The average Polymorphism Information Content (PIC) value was 0.578 and it ranged from a low of zero (RM 115) to a high of 0.890 (RM 202). The Mantel matrix correspondence test was used to compare the similarity matrices and the correlation coefficient was 0. 582. The test indicated that clusters produced based on RAPD and SSR markers were not conserved since matrix correlation value was 0.582 as against the minimum required value of 0.800. The two marker systems contrasted most notably in pair-by-pair comparisons of relationships. SSR analysis resulted in a more definitive separation of clusters of genotypes indicating a higher level of efficiency of SSR markers for the accurate determination of relationships between accessions that are too close to be accurately differentiated by RAPD markers. This revised version was published online in July 2006 with corrections to the Cover Date.     

DNA profiling of pineapple cultivars in Japan discriminated by SSR markers

We developed 18 polymorphic simple sequence repeat (SSR) markers in pineapple (Ananas comosus) by using genomic libraries enriched for GA and CA motifs. The markers were used to genotype 31 pineapple accessions, including seven cultivars and 11 breeding lines from Okinawa Prefecture, 12 foreign accessions and one from a related species. These SSR loci were highly polymorphic: the 31 accessions contained three to seven alleles per locus, with an average of 4.1. The values of expected heterozygosity ranged from 0.09 to 0.76, with an average of 0.52. All 31 accessions could be successfully differentiated by the 18 SSR markers, with the exception of ‘N67-10’ and ‘Hawaiian Smooth Cayenne’. A single combination of three markers TsuAC004, TsuAC010 and TsuAC041, was enough to distinguish all accessions with one exception. A phenogram based on the SSR genotypes did not show any distinct groups, but it suggested that pineapples bred in Japan are genetically diversed. We reconfirmed the parentage of 14 pineapple accessions by comparing the SSR alleles at 17 SSR loci in each accession and its reported parents. The obtained information will contribute substantially to protecting plant breeders’ rights.     

不同地理来源旱稻种质资源的遗传多样性分析

用38对SSR引物对144份不同地理来源的旱稻种质资源进行遗传多样性分析。结果表明,共检测到137个等位变异,平均每对引物检测到3.6个,等位变异范围2~9。Nei基因多样性指数（He）在0.440（RM162）~0.854（RM335）之间,平均0.598。旱稻种质资源亚种间SSR多样性差异明显,籼稻的等位基因数目和Nei基因多样性指数（Na = 3.5,He = 0.558）明显高于粳稻（Na = 3.2,He = 0.415）。Nei基因多样性指数以亚洲最高,非洲最低,亚洲其他（He = 0.594）>中国（He = 0.593）>南美（He = 0.545）>非洲（He = 0.512）。AMOVA分析表明,旱稻种质资源的遗传变异主要来自亚种内（占总变异的76.3％）,亚种间遗传分化极显著。系统聚类能较好地区分籼粳亚种,但不能区分地理组。旱稻种质资源丰富的遗传多样性为水稻节水抗旱品种的选育提供了条件。     

The taxonomic characterisation of annual Beta germplasm in a genetic resources collection using RAPD markers

Summary Annual beets in the genus Beta section Beta represent an important genetic resource. Representative accessions of annual beets from a beet germplasm collection were analysed using RAPD to assess the patterns of variation and relationships among them. Using arbitrary primers, markers showing variation across accessions were identified. A dendrogram of similarity was produced using these molecular markers. All the accessions analysed were classified into three major groups corresponding to species or subspecies macrocarpa, adanensis and maritima. Macrocarpa was shown to be the most divergent group in this section. Using RAPD molecular markers, it was possible to ascribe an accession to one of three taxonomic groups and overcome much of the confusion encountered when morphological traits are used for identification. The group of maritima was found to be more polymorphic than either the group of macrocarpa or adanensis at both accession and subspecies levels.     

Genetic relationship of Mediterranean mandarins (Citrus deliciosa Tenore) using RAPD markers

Summary Random amplified polymorphic DNA (RAPD) analysis was carried out to evaluate polymorphism and genetic similarity between 39 Mediterranean mandarin genotypes. One hundred eleven amplification products were identified using 21 random primers. An average of 2.2 RAPD markers was obtained for each primer, corresponding to 42% of the amplification products. Genotype-specific RAPD markers were also found, mainly in known hybrids. UPGMA cluster analysis revealed the low level of genetic variation between accessions of Mediterranean mandarins, whereas their hybrids with other Citrus species showed greater genetic dissimilarity. Twenty accessions yielded very similar patterns, suggesting either that they could be a single clone, or that the technique was not able to detect genomic variation. However, for the other specimens genetic polymorphism can easily be detected by RAPD, although the genetic variation between accessions was quite low. The large number of hybrids and the low polymorphism between accessions support the hypothesis that Mediterranean mandarins are all true hybrid of Common mandarins (Citrus reticulata Blanco).     

大麦遗传多样性及连锁不平衡分析

为了合理评价引进种质资源,为大麦基因发掘及育种组合配置提供依据,选用分布于全基因组的64个SSR标记,对221份大麦材料进行了基因型分析。共检测到192个等位变异,变幅为2~7个;基因频率变异范围为0.0090~0.9729,平均0.3333;全部位点的基因多样性变化范围在0.0528~0.7807,平均0.4813;多态性信息含量(PIC)变异范围在0.0514~0.7464,平均0.4113。供试材料间遗传相似系数变幅为0.4844~0.9792,平均0.7023。221份材料被划分成两大群7个亚群,国内地方品种与1份北京品种为一大群,国内育种品种与所有国外引进品种为另一群。遗传结构分析与聚类结果基本一致,两大类群间的遗传距离为0.3358,且第二大群多样性比第一大群丰富。2016个SSR位点成对组合中,不论共线性组合还是非共线性组合,都存在一定程度的连锁不平衡(LD)。D′统计概率(P<0.01)支持的LD成对位点830个,占全部位点组合的41.2%,D′平均值为0.4,整体LD水平较高。栽培品种的LD水平高于地方品种,且现代遗传改良的目标性状集中于2H、4H、6H和7H染色体。     

棉花品种资源群体结构与连锁不平衡分析

用基因组扫描的方法,利用棉花9个连锁群上的79个微卫星标记(Simple sequence repeat,SSR),对收集的204份陆地棉品种(系)组成的品种资源群体进行群体结构和连锁不平衡(Linkage disequilibrium,LD)分析.结果表明:本研究群体可划分为3个群体,其中两个群体分别由3个亚群体组成...