Genetic diversity and linkage disequilibrium in Chinese bread wheat (Triticum aestivum L.) revealed by SSR markers

Two hundred and fifty bread wheat lines, mainly Chinese mini core accessions, were assayed for polymorphism and linkage disequilibrium (LD) based on 512 whole-genome microsatellite loci representing a mean marker density of 5.1 cM. A total of 6,724 alleles ranging from 1 to 49 per locus were identified in all collections. The mean PIC value was 0.650, ranging from 0 to 0.965. Population structure and principal coordinate analysis revealed that landraces and modern varieties were two relatively independent genetic sub-groups. Landraces had a higher allelic diversity than modern varieties with respect to both genomes and chromosomes in terms of total number of alleles and allelic richness. 3,833 (57.0%) and 2,788 (41.5%) rare alleles with frequencies of <5% were found in the landrace and modern variety gene pools, respectively, indicating greater numbers of rare variants, or likely new alleles, in landraces. Analysis of molecular variance (AMOVA) showed that A genome had the largest genetic differentiation and D genome the lowest. In contrast to genetic diversity, modern varieties displayed a wider average LD decay across the whole genome for locus pairs with r(2)>0.05 (P<0.001) than the landraces. Mean LD decay distance for the landraces at the whole genome level was <5 cM, while a higher LD decay distance of 5-10 cM in modern varieties. LD decay distances were also somewhat different for each of the 21 chromosomes, being higher for most of the chromosomes in modern varieties (<5 ～ 25 cM) compared to landraces (<5 ～ 15 cM), presumably indicating the influences of domestication and breeding. This study facilitates predicting the marker density required to effectively associate genotypes with traits in Chinese wheat genetic resources.     

Genetic Diversity and Core Collection Evaluations in Common Wheat Germplasm from the Northwestern Spring Wheat Region in China

Fluorescence microsatellite markers were employed to reveal genetic diversity of 340 wheat accessions consisting of 229 landraces and 111 modern varieties from the Northwest Spring Wheat Region in China. The 340 accessions were chosen as candidate core collections for wheat germplasm in this region. A core collection representing the genetic diversity of these accessions was identified based on a cluster dendrogram of 78 SSR loci. A total of 967 alleles were detected with a mean of 13.6 alleles (5–32) per locus. Mean PIC was 0.64, ranged from 0.05 to 0.91. All loci were distributed relatively evenly in the A, B and D wheat genomes. Mean genetic richness of A, B and D genomes for both landraces and modern varieties was B > A > D. However, mean genetic diversity indices of landraces changed to B > D > A. As a whole, genetic diversity of the landraces was considerably higher than that of the modern varieties. The big difference of genetic diversity indices in the three genomes suggested that breeding has exerted greater selection pressure in the D than the A or B genomes in this region. Changes of allelic proportions represented in the proposed core collection at different sampling scales suggested that the sampling percentage of the core collection in the Northwest Spring Wheat Region should be greater than 4% of the base collection to ensure that more than 70% of the variation is represented by the core collection. Electronic supplementary material Electronic supplementary material is available for this article at and accessible for authorised users.     

An estimation of the minimum number of SSR loci needed to reveal genetic relationships in wheat varieties: Information from 96 random accessions with maximized genetic diversity

Genetic relationships among common wheat varieties from the 10 wheat growing regions of China were assessed using SSR markers. The wheat varieties included 33 modern varieties and 63 landraces selected from the national gene bank collection of China. One hundred and four pairs of selected primers detected a total of 802 alleles, of which 234 were specific to A genome, 309 to B genome, and 221 to D genome. The average genetic richness per locus (A _ij /loci) for A, B and D genomes were 6.88, 7.92 and 7.62, respectively. Their average genetic dispersion indices (H _t ) were 0.637, 0.694 and 0.656, respectively. The B genome showed the highest genetic diversity among the three wheat genomes. The landraces had a higher genetic diversity than the modern varieties, and the major difference between the landraces and the modern varieties in China existed in the D genome, followed by B and A genomes. The majority of the accessions (65.6%) had heterogeneity at the 112 loci detected. The highest heterogeneity locus percentages were 9.09 and 12.73 in the modern varieties and the landraces, respectively. SSR data were analyzed with NTSYS-pc software. The genetic similarities between accessions were estimated with the DICE coefficient. The accessions clustered into two groups, the modern varieties and the landraces by the un-weighted pair-group method using arithmetic average (UPGMA). The trend of correlation coefficients between genetic similarity matrices based on different numbers of random alleles and that of 802 alleles showed that 550 alleles were sufficient to construct a robust dendrogram. The separated simulations from six sub-samples revealed that 550 alleles were the minimum number required to confidently determine the genetic relationships. It was shown that the number of alleles (loci) needed do not have a strong association with the number of wheat lines in the sample size. These data suggested that 73 loci with good polymorphism are needed to reflect genetic relationships among accessions with more than 90% certainty. In the dendrogram, most accessions from the same wheat region were clustered together, and those from geographically adjacent regions usually appeared in the same small group. This indicated that genetic diversity of Chinese common wheat has a close association with their geographic distribution and ecological environment.     

Identification of unique alleles and assessment of genetic diversity of rabi sorghum accessions using simple sequence repeat markers

Genetic diversity among 42 sorghum accessions representing landraces (19), advanced breeding lines (16), local cultivars (2) and release varieties (5) with 30 simple sequence repeat (SSR) markers revealed 7.6 mean number of alleles per locus showing 93.3% polymorphism and an average polymorphism information content of 0.78 which range from 0.22 (Xtxp12) and 0.91(Xtxp321). The average heterozygosity and effective number of alleles per locus were 0.8 and 6.65 respectively. Cluster analysis based on microsatellite allelic diversity clearly demarcated the accessions into ten clusters. A total of 24 unique alleles were obtained from seven SSR loci in 23 accessions in a size range of 110–380 bp; these unique alleles may serve as diagnostic tools for particular region of the genome of respective genotypes. Selected SSR markers from different linkage groups provided an accurate way of determining genetic diversity at the molecular level.     

Assessment of genetic diversity among Syrian durum (<Emphasis Type="Italic">Triticum</Emphasis> ssp. <Emphasis Type="Italic">durum</Emphasis>) and bread wheat (<Emphasis Type="Italic">Triticum aestivum</Emphasis> L.) using SSR markers

Genetic diversity among 49 wheat varieties (37 durum and 12 bread wheat) was assayed using 32 microsatellites representing 34 loci covering almost the whole wheat genome. The polymorphic information content (PIC) across the tested loci ranged from 0 to 0.88 with average values of 0.57 and 0.65 for durum and bread wheat respectively. B-genome had the highest mean number of alleles (10.91) followed by A genome (8.3) whereas D genome had the lowest number (4.73). The correlation between PIC and allele number was significant in all genome groups accounting for 0.87, 074 and 0.84 for A, B and D genomes respectively, and over all genomes, the correlation was higher in tetraploid (0.8) than in hexaploid wheat varieties (0.5). The cluster analysis discriminated all varieties and clearly divided the two ploidy levels into two separate clusters that reflect the differences in genetic diversity within each cluster. This study demonstrates that microsatellites markers have unique advantages compared to other molecular and biochemical fingerprinting techniques in revealing the genetic diversity in Syrian wheat varieties that is crucial for wheat improvement.     

Assessment of genetic diversity among Syrian durum (Triticum turgidum ssp. durum) and bread wheat (Triticum aestivum L.) using SSR markers

Genetic diversity among 49 wheat varieties (37 durum and 12 bread wheat) was assayed using 32 microsatellites representing 34 loci covering almost the whole wheat genome. The polymorphic information content (PIC) across the tested loci ranged from 0 to 0.88 with average values of 0.57 and 0.65 for durum and bread wheat respectively. B genome had the highest mean number of alleles (10.91) followed by A genome (8.3) whereas D genome had the lowest number (4.73). The correlation between PIC and allele number was significant in all genome groups accounting for 0.87, 074 and 0.84 for A, B and D genomes respectively, and over all genomes, the correlation was higher in tetraploid (0.8) than in hexaploid wheat varieties (0.5). The cluster analysis discriminated all varieties and clearly divided the two ploidy levels into two separate clusters that reflect the differences in genetic diversity within each cluster. This study demonstrates that microsatellites markers have unique advantages compared to other molecular and biochemical fingerprinting techniques in revealing the genetic diversity in Syrian wheat varieties that is crucial for wheat improvement.     

Wheat storage proteins: diversity of HMW glutenin subunits in wild emmer from Israel

Summary The diversity of HMW glutenin subunits in the tetraploid wild progenitor of wheat, Triticum turgidum var. dicoccoides was studied electrophoretically in 231 individuals representing 11 populations of wild emmer from Israel. The results show that (a) The two HMW glutenin loci, Glu-A1 and Glu-B1, are rich in variation, having 11 and 15 alleles, respectively, (b) Genetic variation in HMW glutenin subunits is often severely restricted in individual populations, supporting an island population genetic model, (c) Significant correlations were found between glutenin diversity and the frequencies of specific glutenin alleles and physical (climate and soil) and biotic (vegetation) variables. Our results suggest that: (a) at least part of the glutenin polymorphisms in wild emmer can be accounted for by environmental factors and (b) the endosperm of wild emmer contains many allelic variants of glutenin storage proteins that are not present in bread wheat and could be utilized in breeding varieties with improved bread-making qualities.     

Genetic diversity in a collection of old and new bread wheat cultivars from Iran as revealed by simple sequence repeat-based analysis

Genetic diversity in a collection of 70 bread wheat ( Triticum aestivum ) genotypes was studied using 73 microsatellite [simple sequence repeat (SSR)] loci evenly spaced on wheat chromosomes. A total of 592 alleles with an average of 8.53 allele/locus were detected, of which 185 (31.25%) occurred only in a specific group of genotypes. A set of SSR markers consisted of 22 loci with polymorphic information content values of 0.80 or higher were selected for rapid fingerprinting of many genotypes. Average of gene diversity was 0.74 ± 0.017, and significant difference between observed and maximum theoretical values of gene diversity in the analysed SSR loci was obtained using a paired t -test. Genetic distance-based clustering methods including unweighted pair group method with arithmetic average and neighbour joining (NJ) were used for grouping of genotypes. The resulted dendrogram based on NJ and number of differences coefficient hinted of the existence of three groups. This grouping was in agreement with the pedigree information and confirmed by high within-group bootstrap value. A comparatively higher genetic diversity in the studied wheat collection as revealed by presence of high allelic diversity and large number of specific alleles could be utilised in development of new cultivars with desired characteristics.     

Genetic diversity analysis of traditional and improved Indonesian rice (Oryza sativa L.) germplasm using microsatellite markers

The archipelago of Indonesia has a long history of rice production across a broad range of rice-growing environments resulting in a diverse array of local Indonesian rice varieties. Although some have been incorporated into modern breeding programs, the vast majority of these landraces remain untapped. To better understand this rich source of genetic diversity we have characterized 330 rice accessions, including 246 Indonesian landraces and 63 Indonesian improved cultivars, using 30 fluorescently-labeled microsatellite markers. The landraces were selected across 21 provinces and include representatives of the classical subpopulations of cere, bulu, and gundil rices. A total of 394 alleles were detected at the 30 simple sequence repeat loci, with an average number of 13 alleles per locus across all accessions, and an average polymorphism information content value of 0.66. Genetic diversity analysis characterized the Indonesian landraces as 68% indica and 32% tropical japonica, with an indica gene diversity of 0.53 and a tropical japonica gene diversity of 0.56, and a Fst of 0.38 between the two groups. All of the improved varieties sampled were indica, and had an average gene diversity of 0.46. A set of high quality Indonesian varieties, including Rojolele, formed a separate cluster within the tropical japonicas. This germplasm presents a valuable source of diversity for future breeding and association mapping efforts.     

香稻资源遗传多样性的比较

利用60个水稻SSR标记, 对来自国内外的370份香稻材料的遗传多样性进行了比较分析。结果共检测到361个等位基因, 每个位点的等位基因变幅为2~10个, 平均Nei基因多样性指数(He)为0.663, 变幅为0.104(RM308)~0.885(RM2634)。籼粳亚种间的遗传多样性具有明显差异, 籼稻的等位基因数和Nei基因多样性指数均高于粳稻。地方品种的遗传多样性高于选育品种, 选育品种等位基因数仅为地方品种的86.5%。分子方差分析表明, 香稻材料中总变异的43.08%是由于亚种间的遗传差异引起的。不同稻区的遗传分化程度总体介于1.69%~14.40%之间。其中, 华南与西南、华中与西南地方品种间遗传差异的分化程度达显著水平。聚类分析将参试材料明显分为籼粳两大类, 同时地域相同(稻区)、相邻省份的香稻材料基本归为同一类群。     

西南冬麦区地方品种HMW-GS组成遗传多样性研究

采用十二烷基硫酸钠-聚丙烯酰胺凝胶电泳(SDS-PAGE)对西南冬麦区(云南、贵州、四川)3个省份共计560份小麦地方品种的高分子量谷蛋白亚基(HMW-GS)组成进行了研究。结果表明:Glu-1位点共有22种等位基因,其中Glu-A1位点4种、Glu-B1位点11种、Glu-D1位点7种;亚基null、7 8和2 12在各自位点的频率最高,分别为89.64%、68.21%和96.43%。亚基组成类型共有46种,以null/7 8/2 12和null/7 9/2 12为主,频率分别为50.89%和11.79%。在这些材料中筛选出一些含有1、2*、17 18、14 15、5 10等优质亚基的材料,其中有52份材料含有优质亚基组合。     

SSR allelic diversity changes in 480 European bread wheat varieties released from 1840 to 2000

A sample of 480 bread wheat varieties originating from 15 European geographical areas and released from 1840 to 2000 were analysed with a set of 39 microsatellite markers. The total number of alleles ranged from 4 to 40, with an average of 16.4 alleles per locus. When seven successive periods of release were considered, the total number of alleles was quite stable until the 1960s, from which time it regularly decreased. Clustering analysis on Neis distance matrix between these seven temporal groups showed a clear separation between groups of varieties registered before and after 1970. Analysis of qualitative variation over time in allelic composition of the accessions indicated that, on average, the more recent the European varieties, the more similar they were to each other. However, European accessions appear to be more differentiated as a function of their geographical origin than of their registration period. On average, western European countries (France, The Netherlands, Great Britain, Belgium) displayed a lower number of alleles than southeastern European countries (former Yugoslavia, Greece, Bulgaria, Romania, Hungary) and than the Mediterranean area (Italy, Spain and Portugal), which had a higher number. A hierarchical tree on Neis distance matrix between the 15 geographical groups of accessions exhibited clear opposition between the geographical areas north and south of the arc formed by the Alps and the Carpathian mountains. These results suggest that diversity in European wheat accessions is not randomly distributed but can be explained both by temporal and geographical variation trends linked to breeding practices and agriculture policies in different countries.Electronic Supplementary Material Supplementary material is available for this article at     

云南栽培稻种SSR遗传多样性比较

采用64个SSR标记对96份云南水稻（Oryza sativa）地方品种和选育品种的遗传多样性进行比较分析。结果发现64个标记都具有多态性,共检测到741个等位基因,每个多态性位点检测到的等位基因数为2—29个,平均11．57个：Nei基因多样性指数（He）范围在0．345（RM321）-0．932（RM1）之间,平均为0．56。水稻品种的遗传多样性并非按地理位置均匀分布,而是在相似系数为0．17的水平上明显分为2个不同类群,即籼稻类群和粳稻类群,且籼粳亚种间的SSR多样性差异不明显,籼稻平均等位基因数（Ap）和Nei基因多样性指数（Ap=10．6,He=0．46）与粳稻品种（Ap=10．7,He=0．48）十分接近,可能与这些品种间存在一定频率的基因交流有关。糯稻和非糯稻在籼稻群和粳稻群中都有表现,没有特别的分布规律。云南栽培稻选育品种与地方稻亲缘关系较近,其遗传基础可能来源于云南水稻地方品种。本研究结果表明,SSR标记能较好地区分云南栽培稻品种,且云南水稻地方品种遗传多样性丰富,存在大量的优质性状可供育种实践选择。     

云南栽培稻种SSR 遗传多样性比较

采用64个SSR标记对96份云南水稻(Oryz a sativa)地方品种和选育品种的遗传多样性进行比较分析。结果发现64个标记都具有多态性, 共检测到741个等位基因, 每个多态性位点检测到的等位基因数为2-29个, 平均11.57个; Nei基因多样性指数(He)范围在0.345(RM321)-0.932(RM1)之间, 平均为0.56。水稻品种的遗传多样性并非按地理位置均匀分布, 而是在相 似系数为0.17的水平上明显分为2个不同类群, 即籼稻类群和粳稻类群, 且籼粳亚种间的SSR多样性差异不明显, 籼稻平均等位基因数(Ap)和Nei基因多样性指数(Ap=10.6, He=0.46)与粳稻品种(Ap=10.7, He=0.48)十分接近, 可能与这些品种间存在一定频率的基因交流有关。糯稻和非糯稻在籼稻群和粳稻群中都有表现, 没有特别的分布规律。云南栽培稻选育品种与地方稻亲缘关系较近, 其遗传基础可能来源于云南水稻地方品种。本研究结果表明, SSR标记能较好地区分云南栽培稻品种, 且云南水稻地方品种遗传多样性丰富, 存在大量的优质性状可供育种实践选择。     

Allelic reduction and genetic shift in the Canadian hard red spring wheat germplasm released from 1845 to 2004

Analysis of genetic diversity changes in existing gene pools of cultivated crops is important for understanding the impact of plant breeding on crop genetic diversity and developing effective indicators for genetic diversity of cultivated plants. The objective of this study was to assess genetic diversity changes in 75 Canadian hard red wheat (Triticum aestivum L.) cultivars released from 1845 to 2004 using 31 simple sequence repeats (SSRs) markers. A total of 267 SSR alleles were detected, and their allelic frequencies ranged from 0.01 to 0.97, with an average of 0.14. Significant allelic reduction was observed at only four SSR loci for the cultivars released from 1970 onwards. However, 51 alleles (about 19%) present in pre-1910 cultivars were undetected in cultivars released after 1990 and were spread over 27 SSR loci. The proportion of SSR variation accounted for by six breeding periods was 12.5%, by four ancestral families, 16.5%, and by eight breeding programs, 8.4%. The average genetic diversity measured by three different band-sharing methods did not change significantly among cultivars released from different breeding periods, breeding programs, and ancestral families. However, genetic shift was obvious in the cultivars released over the six breeding periods, reflecting well the various breeding efforts over years. These results clearly show the allelic reduction and genetic shift in the Canadian hard red spring wheat germplasm released over time. Consequently, more effort needs to be made to broaden the wheat breeding base and conserve wheat germplasm.     

新疆冬春麦区小麦地方品种贮藏蛋白遗传多样性研究

采用SDS-聚丙烯酰胺凝胶电泳（SDS-PAGE）对236份新疆小麦地方品种的高分子量麦谷蛋白亚基（HMW-GS）的组成进行了分析。结果表明：Glu-Ⅰ位点共有19种等位基因,其中Glu-Al位点3种,Glu-Bl位点7种,Glu—D1住点9种;亚基null、7＋8、2＋12在各自的位点上出现频率最高,分别达到91．95％、85．17％、80．93％;亚基组成类型共有21种,主要为null／7＋8／2＋12,频率达70．34％;同时筛选出33份含有1、2^＊、13＋16、14＋15、5＋10、1．5＋10、174-18等优质亚基的材料,可作为优质基因源。利用酸性聚丙烯酰胺凝胶电泳（A-PAGE）对其中的65份地方品种进行醇溶蛋白多样性分析。结果表明：电泳出现64条迁移率不同的谱带,构成65种组合,其中ω区出现的谱带最多,达17条;其次是β和γ区各16条,α区出现的谱带数最少,为15条。从每条谱带在65份材料中出现的频率看,总的变异范围为1．54％～93．85％;α、β、γ和ω4个分区多样性指数（H1）分别为0．498、0．386、0．523和0．348,表明新疆麦区小麦地方品种贮藏蛋白位点存在丰富的遗传多样性。     

Identifying loci influencing 1,000-kernel weight in wheat by microsatellite screening for evidence of selection during breeding

Chinese wheat mini core collection (262 accessions) was genotyped at 531 microsatellite loci representing a mean marker density of 5.1 cM. One-thousand-kernel weights (TKW) of lines were measured in five trials (three environments in four growing seasons). Structure analysis based on 42 unlinked SSR loci indicated that the materials formed two sub-populations, viz., landraces and modern varieties. A large difference in TKW (7.08 g, P<0.001) was found between the two sub-groups. Therefore, TKW is a major yield component that was improved in the past 6 decades; it increased from a mean 31.5 g in the 1940s to 44.64 g in the 2000s, representing a 2.19 g increase in each decade. Analyses based on a mixed linear model (MLM), population structure (Q) and relative kinship (K) revealed 22 SSR loci that were significantly associated with mean TKW (MTKW) of the five trials estimated by the best linear unbiased predictor (BLUP) method. They were mainly distributed on chromosomes of homoeologous groups 1, 2, 3, 5 and 7. Six loci, cfa2234-3A, gwm156-3B, barc56-5A, gwm234-5B, wmc17-7A and cfa2257-7A individually explained more than 11.84% of the total phenotypic variation. Favored alleles for breeding at the 22 loci were inferred according to their estimated effects on MTKW based on mean difference of varieties grouped by genotypes. Statistical simulation showed that these favored alleles have additive genetic effects. Frequency changes of alleles at loci associated with TKW are much more dramatic than those at neutral loci between the sub-groups. The numbers of favored alleles in modern varieties indicate there is still considerable genetic potential for their use as markers for genome selection of TKW in wheat breeding. Alleles that can be used globally to increase TKW were inferred according to their distribution by latitude and frequency of changes between landraces and the modern varieties.     

小麦全基因组抗赤霉病QTL关联位点特异性SSR标记的筛选、等位变异及效应解析

赤霉病是小麦主要的流行病害之一。借助标记辅助选择将不同数量性状基因座（quantitative trait loci，QTL）聚合是防治赤霉病有效且环保的方法，可以从源头上控制赤霉病并降低籽粒中毒素含量。抗赤霉病QTL在小麦全基因组均有分布，但除了Fhb1、Fhb2等少数位点有比较可靠的鉴别标记，绝大部分位点缺乏有效的位点特异性鉴别标记。简单重复序列（simple sequence repeat，SSR）标记多态性丰富，可以区分自然群体中不同等位变异，方便用于标记辅助育种。基于此，搜集了不同文献中报道的与赤霉病关联的SSR标记386个，并用这些标记构建全基因组赤霉病抗性QTL一致性图谱，接着对这些关联标记进行拷贝数分析，进而选择位点内的单拷贝SSR标记，将这些单拷贝标记在156个品种组成的自然群体中进行扩增，并与三季大田和三季温室环境下赤霉病抗性进行关联，筛选与赤霉病抗性关联的单拷贝SSR标记，明确这些标记在自然群体中的有效等位变异和效应。结果表明，共8个单拷贝SSR标记至少在两季试验中与表型显著关联(P<0.05)，涉及2B、2D、3B、5A、5B、6A、6D、7A染色体，有5个单拷贝标记位点存在有效等位变异。中国地方品种和日本品种携带更多的有利变异，且有利等位变异数目越多的品种赤霉病抗性越好。研究分析的QTL位点及其关联的单拷贝SSR标记可用于赤霉病抗病育种，有利于提高品种赤霉病抗性水平和育种效率。     

Detection of genetic diversity in closely related bread wheat using microsatellite markers

Wheat microsatellites (WMS) were used to estimate the extent of genetic diversity among 40 wheat cultivars and lines, including mainly European elite material. The 23 WMS used were located on 15 different chromosomes, and revealed a total of 142 alleles. The number of alleles ranged from 3 to 16, with an average of 6.2 alleles per WMS. The average dinucleotide repeat number ranged from 13 to 41. The correlation coefficient between the number of alleles and the average number of repeats was only slight (r _s = 0.55). Based on percentage difference a dendrogram is presented, calculated by the WMS-derived data. All but two of the wheat cultivars and lines could be distinguished. Some of the resulting groups are strongly related to the pedigrees of the appropriate cultivars. Values for co-ancestry (f) of 179 pairs of cultivars related by their pedigrees (f0.1) averaged 0.29. Genetic similarity (GS) based on WMS of the same pairs averaged 0.44. The rank correlation for these pairs was slight, with r _s = 0.55, but highly significant (P<0.001). The results suggest that a relatively small number of microsatellites can be used for the estimation of genetic diversity and cultivar identification in elite material of hexaploid bread wheat.     

Trends in Genetic Diversity Change of Spring Bread Wheat Cultivars Released in Russia in 1929–2003

Using genealogy analysis, we studied genetic diversity of 340 cultivars of spring bread wheat that were released on the territory of Russia in 1929–2003. Trends in the temporal change of genetic diversity were inferred from analysis of a set of n × m matrices, where n is the number of the released cultivars and m is the number of original ancestors. The pool of original ancestors of the spring bread wheat cultivars for the total period of study included 255 landraces, of which 88 were from the former USSR and modern Russia. The original ancestors showed great differences in their presence in the cultivar sets examined and, consequently, in their importance for the gene pool of Russian spring wheats. The distributions of contributions of dominant original ancestors to cultivar diversity were significantly different in different regions, indicating that the ancestors were specific for the cultivation conditions. During the last 75 years, the genetic diversity of the spring bread wheat cultivars has been increasing owing to the wide use of foreign material in Russian breeding programs. However, our analysis showed that about 60 landraces, including the Russian ones, were lost during the studied time period. The lost part makes up 35% of the gene pool of the Russian original ancestors. It is reasonable to assume that the lost landraces carried a gene complex f or adaptation to specific Russian environments. Specificity of the contributions of the original ancestors in the sets of cultivars produced in different breeding centers was established. A comparative analysis of genetic similarity of cultivars was carried out using coefficients of parentage. Significant differences in this parameter between breeding institutes and regions of cultivation were revealed.