AFLP markers suggest low population genetic differentiation of the black rockfish Sebastes schlegelii

AFLP markers were used to investigate the population genetic differentiation among populations of Sebastes schlegelii from China and Japan. A total of 405 bands were amplified for 180 individuals from 9 populations by 3 pairs of selective primers. S. schlegelii exhibited high Nei's gene diversity with an average value of 0.29 for all populations. No significant genealogical branches or clusters corresponding to sampling localities were detected by UPGMA tree. The results of AMOVA analysis and pairwise F_ST values showed no genetic divergence among different geographic populations. The result of STRUCTURE demonstrated all populations of S. schlegelii examined in the study shared one single gene pool.     

The histopathology and prevalence of Henneguya sebasta and Kudoa clupeidae in the rockfish, Sebastes paucispinis of southern California

The pathogenesis of two histozoic myxosporidans, Henneguya sebasta and Kudoa clupeidae, was studied from the Pacific rockfish, Sebastes paucispinis. Infection of the bulbus and truncus arteriosus with H. sebasta was observed in 30 of 100 fish. The parasite metastasized throughout the tissue causing necrosis, hyperplasia and hypertrophy of the connective tissue and smooth muscle. K. clupeidae, found in 37 of 100 fish, caused necrosis and atrophy of host skeletal muscle. The unattractive appearance of Kudoa cysts in rockfish filets detracted from their commercial value.     

Agronomic characterization, genetic diversity and association analysis of cotton cultivars using simple sequence repeat molecular markers

Cotton is the most important textile plant in the world and is one of the most important crops for the production of oilseed. Because of its worldwide economic importance, new cultivars are constantly being released in the world and consequently in the Greek market, as Greece is the largest producer in Europe. We used simple sequence repeat (SSR) markers for the identification and the phylogenetic analysis of the most widely cultivated cotton cultivars in Greece. Initially, we used 12 pairs of SSR molecular markers for the analysis of 29 cultivars of Gossypium hirsutum and an interspecific hybrid (G. hirsutum x G. barbadense). Of the 12 pairs of SSR primers, 11 amplified polymorphic products, while one pair did not amplify any product. Globally, 17 polymorphic marker loci were identified. Two to four different alleles were amplified at each genomic locus, with a mean of 2.53 alleles per locus. Among the 30 genotypes that we analyzed, the polymorphism information content ranged from 0 to 0.548, with a mean of 0.293. Three main groups were formed among the 30 genotypes when a phylogenetic analysis was performed using UPGMA. Computational analysis of each molecular marker separately showed an association of SSR markers with agronomic traits such as fiber quality. To our knowledge, this is the first in-depth molecular analysis of cotton cultivars grown in Greece using SSR markers. An analysis of association of SSR markers with fiber quality traits of 29 cotton cultivars is reported for the first time.     

Isolation, characterisation and mapping of simple sequence repeat loci in potato

Solanum tuberosum L. DNA sequences containing simple sequence repeat (SSR) motifs were extracted from the EMBL database, cDNA and selectively enriched small-insert DNA libraries. Enrichment was achieved using either triplex affinity capture or single-strand hybridisation selection. One hundred and twelve primer pairs which successfully amplified products of the correct size from potato DNA were ultimately designed and synthesised. Ninety-eight of these revealed length polymorphisms in a panel of four diploid and two tetraploid clones, in agreement with the high information content of this class of markers which has been found in other species. All of the markers were assigned a quality score of 1–5 based on their potential usefulness. Eighty-nine loci from 65 of the primer pairs were located on two genetic linkage maps of potato by segregation analysis of the amplified alleles. Fifty-two of the SSRs were clearly single locus. The maps were aligned using 23 SSR primer pairs and 13 RFLP loci mapped in both populations. The markers described constitute a class which should replace Restriction Fragment Length Polymorphisms (RFLP) as the markers of choice for future genetic studies in potato. The sequences of the primers, together with other information on these markers are provided. Received: 12 January 1998 / Accepted: 25 March 1998     

Genetic relationships among cherry species with transferability of simple sequence repeat loci

Sweet and sour cherries are two economically important species in the world. The capability to distinguish among cherry genotypes in breeding, cultivation and germplasm collection is extremely important for scientific as well as economic reasons. In the present research, sixteen simple sequences repeat (SSR) loci were used to estimate the relationships among sweet, sour, duke and wild cherries. All of the SSR markers showed high transferability across the studied species that allowed us to study genetic diversity in them. Totally 96 alleles were generated with SSR loci, of which 93 were found polymorphic with 97.57 % polymorphism. Values of genetic similarity between genotypes varied from 0.16 to 0.97 which indicated high level of genetic diversity. On the basis of their genetic similarities, SSR analysis allowed to group the genotypes into three main clusters according to their species. These results have an important implication for cherry germplasm characterization, improvement, and conservation.     

Estimation of effective population size for the long-lived darkblotched rockfish Sebastes crameri

We report the variance effective population size (Ne) in darkblotched rockfish (Sebastes crameri) utilizing the temporal method for overlapping generations, which requires a combination of age-specific demography and genetic information from cohorts. Following calculations of age-specific survival and reproductive success from fishery data, we genotyped a sample (n = 1087) comprised by 6 cohorts (from 1995 to 2000) across 7 microsatellite loci. Our Ne estimate (Ne) plus 95% confidence interval was (Ne) = 9157 [6495-12 215], showing that the breeding population number could be 3-4 orders of magnitude smaller than the census population size (N) = 24 376 210). Our estimates resemble closely those found for fishes with similar life history, suggesting that the small (Ne)/(N) ratio for S. crameri is most likely explained by a combination of high variance in reproductive success among individuals, genetic structure, and demographic perturbations such as historical fishing. Because small (Ne)/(N) ratios have been commonly associated with potential loss of genetic variation, our estimates need careful consideration in rockfish management and conservation.     

Analysis of genetic diversity of Guizotia abyssinica from Ethiopia using inter simple sequence repeat markers

Within and among population genetic diversity of 37 Guizotia abyssinica populations from Ethiopia were analyzed using inter simple sequence repeats (ISSRs). Five primers amplified a total of 118 genomic DNA fragments across a total of 370 individuals of which 106 were polymorphic (89.83%). The average number of polymorphic bands per primer was 21.2. More bands were generated by primer UBC 888 (BDB(CA)(7.) The total genetic diversity (Ht) and the coefficient of genetic differentiation (Gst) were 0.4115 and 0.0918 respectively, while the within population genetic diversity (Hs) and the among population genetic diversity(Dst) were 0.3738 and 0.03776 respectively suggesting more variability within the populations than among them. The standard genetic distances between the G. abyssinica populations of the eight regions ranged from 0.0281 (between Wollo and Gojam) to 0.1148 (between Jimma and Hararghe). Generally, the standard genetic distances are smaller between populations of neighboring regions and highest between those of Jimma and the other regions, ranging from 0.0696 (between Jimma and Shewa) to 0.1148 (between Jimma and Hararghe). The ISSR based UPGMA clustering using the standardized genetic distances matrix also placed populations from neighboring regions closer than those from farther apart areas, while the UPGMA clustering by regions based on the standard genetic distances produced three clusters following the proximity and the contiguity of the regions. The mean Shannon Weaver diversity indices for the populations of the eight regions ranged from 0.8197 (Jimma) to 0.9176 (Hararghe), with a mean of 0.8841 for the whole material.     

白黄侧耳Pleurotus cornucopiae微卫星间区(ISSR)分析

本试验对我国1982年至2004年22年间栽培的白黄侧耳Pleurotus cornucopiae 30个菌株进行了锚定ISSR分析,试验表明,引物P4和P5都能对白黄侧耳P.cornucopiae进行多态性扩增,P4将供试菌株扩增出45个条带,大小在200～20000bp,P5将供试菌株扩增出39个条带,大小在500～15000bp,扩增出的条带100%具多态性。聚类分析在遗传相似性61%的水平下将30个供试菌株划分为15个类群,即15个具一定遗传差异的菌株;具有相同ISSR图谱、遗传相似性程度100%的可能为同一菌株,属于同物异名。试验表明我国的食用蕈菌野生环境面临人工栽培种质的污染,采自河北、山东、云南自然环境下的白黄侧耳P.cornucopiae与此前大量栽培的一些商业品种具完全相同的ISSR指纹图谱,聚类分析相似性系数100%。     

Population genetic structure of wild and hatchery black rockfish Sebastes inermis in Korea, assessed using cross-species microsatellite markers

The population structure of the black rockfish, Sebastes inermis (Sebastidae), was estimated using 10 microsatellite loci developed for S. schlegeli on samples of 174 individuals collected from three wild and three hatchery populations in Korea. Reduced genetic variation was detected in hatchery strains [overall number of alleles (N(A)) = 8.07; allelic richness (A(R)) = 7.37; observed heterozygosity (H(O)) = 0.641] compared with the wild samples (overall N(A) = 8.43; A(R) = 7.83; H(O) = 0.670), but the difference was not significant. Genetic differentiation among the populations was significant (overall F(ST) = 0.0237, P < 0.05). Pairwise F(ST) tests, neighbor-joining tree, and principal component analyses showed significant genetic heterogeneity among the hatchery strains and between wild and hatchery strains, but not among the wild populations, indicating high levels of gene flow along the southern coast of Korea, even though the black rockfish is a benthic, non-migratory marine species. Genetic differentiation among the hatchery strains could reflect genetic drift due to intensive breeding practices. Thus, in the interests of optimal resource management, genetic variation should be monitored and inbreeding controlled within stocks in commercial breeding programs. Information on genetic population structure based on cross-species microsatellite markers can aid in the proper management of S. inermis populations.     

Genetic diversity analysis of Bt cotton genotypes in Pakistan using simple sequence repeat markers

The popularity of genetically modified insect resistant (Bt) cotton has promoted large scale monocultures, which is thought to worsen the problem of crop genetic homogeneity. Information on genetic diversity among Bt cotton varieties is lacking. We evaluated genetic divergence among 19 Bt cotton genotypes using simple sequence repeat (SSR) markers. Thirty-seven of 104 surveyed primers were found informative. Fifty-two primers selected on the basis of reported intra-hirsutum polymorphism in a cotton marker database showed a high degree of polymorphism, 56% compared to 13% for randomly selected primers. A total of 177 loci were amplified, with an average of 1.57 loci per primer, generating 38 markers. The amplicons ranged in size from 98 to 256 bp. The genetic similarities among the 19 genotypes ranged from 0.902 to 0.982, with an average of 0.947, revealing a lack of diversity. Similarities among genotypes from public sector organizations were higher than genotypes developed by private companies. Hybrids were found to be more distant compared to commercial cultivars and advanced breeding lines. Cluster analysis grouped the 19 Bt cotton genotypes into three major clusters and two independent entries. Cultivars IR-3701, Ali Akbar-802 and advanced breeding line VH-259 grouped in subcluster B2, with very narrow genetic distances despite dissimilar parentage. We found a very high level of similarity among Pakistani-bred Bt cotton varieties, which means that genetically diverse recurrent parents should be included to enhance genetic diversity. The intra-hirsutum polymorphic SSRs were found to be highly informative for molecular genetic diversity studies in these cotton varieties.     

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.     

Assessing genetic diversity and population structure in a citrus germplasm collection utilizing simple sequence repeat markers (SSRs)

Twenty-four simple sequence repeat (SSR) markers were used to detect molecular polymorphisms among 370 mostly sexually derived Citrus accessions from the collection of citrus germplasm maintained at the University of California, Riverside. A total of 275 alleles were detected with an average of 11.5 alleles per locus and an average polymorphism information content of 0.625. Genetic diversity statistics were calculated for each individual SSR marker, the entire population, and for specified Citrus groups. Phylogenetic relationships among all citrus accessions and putative non-hybrid Citrus accessions were determined by constructing neighbor-joining trees. There was strong support for monophyly at the species level when hybrid taxa were removed from the data set. Both of these trees indicate that Fortunella clusters within the genus Citrus but Poncirus is a sister genus to Citrus. Additionally, Citrus accessions were probabilistically assigned to populations or multiple populations if their genotype indicated an admixture by a model-based clustering approach. This approach identified five populations in this data set. These separate analyses (distance and model based) both support the hypothesis that there are only a few naturally occurring species of Citrus and most other types of Citrus arose through various hybridization events between these naturally occurring forms.Electronic Supplementary Material Supplementary material is available for this article at and is accessible for authorized users.     

Genome-wide identification and characterization of simple sequence repeat loci in grape phylloxera, Daktulosphaira vitifoliae

A genome-wide sequence search was conducted to identify simple sequence repeat (SSR) loci in phylloxera, Daktulosphaira vitifoliae, a major grape pest throughout the world. Collectively, 1524 SSR loci containing mono-, di-, tri-, tetra-, penta-, and hexanucleotide motifs were identified. Among them, trinucleotide repeats were the most abundant in the phylloxera genome (34.4%), followed by hexanucleotide (20.4%) and dinucleotide (19.6%) repeats. Mono-, tetra- and pentanucleotide repeats were found at a frequency of 1.3, 11.2 and 12.9%, respectively. The abundance and inherent variations in SSRs provide valuable information for developing molecular markers. The high levels of allelic variation and codominant features of SSRs make this marker system a useful tool for genotyping, diversity assessment and population genetic studies of reproductive characteristics of phylloxera in agricultural and natural populations.     

Influence of habitat discontinuity, geographical distance, and oceanography on fine-scale population genetic structure of copper rockfish (Sebastes caurinus)

The copper rockfish is a benthic, nonmigratory, temperate rocky reef marine species with pelagic larvae and juveniles. A previous range-wide study of the population-genetic structure of copper rockfish revealed a pattern consistent with isolation-by-distance. This could arise from an intrinsically limited dispersal capability in the species or from regularly-spaced extrinsic barriers that restrict gene flow (offshore jets that advect larvae offshore and/or habitat patchiness). Tissue samples were collected along the West Coast of the contiguous USA between Neah Bay, WA and San Diego, CA, with dense sampling along Oregon. At the whole-coast scale (approximately 2200 km), significant population subdivision (F(ST) = 0.0042), and a significant correlation between genetic and geographical distance were observed based on 11 microsatellite DNA loci. Population divergence was also significant among Oregon collections (approximately 450 km, F(ST) = 0.001). Hierarchical amova identified a weak but significant 130-km habitat break as a possible barrier to gene flow within Oregon, across which we estimated that dispersal (N(e)m) is half that of the coast-wide average. However, individual-based Bayesian analyses failed to identify more than a single population along the Oregon coast. In addition, no correlation between pairwise population genetic and geographical distances was detected at this scale. The offshore jet at Cape Blanco was not a significant barrier to gene flow in this species. These findings are consistent with low larval dispersal distances calculated in previous studies on this species, support a mesoscale dispersal model, and highlight the importance of continuity of habitat and adult population size in maintaining gene flow.     

PCR-multiplexes for a genome-wide framework of simple sequence repeat marker loci in cultivated sunflower

Simple sequence repeat (SSR) and other DNA sequence-tagged site markers can be genotyped more rapidly and cost efficiently by simultaneously amplifying multiple loci (multiplex PCR). The development of PCR-multiplexes for a nearly genome-wide framework of 78 SSR marker loci in cultivated sunflower ( Helianthus annuus L.) is described herein. The most outstanding single-locus SSR markers in the public collection (300 out of 1,089) were identified and screened for polymorphisms among 24 elite inbred lines, preparatory to selecting SSR markers for testing in multiplex PCRs. The selected SSR markers produced robust PCR products, amplified a single locus each, were polymorphic among elite inbred lines (minimum, mean and maximum heterozygosities were 0.08, 0.53 and 0.85, respectively), and supply a dense genome-wide framework of predominantly or completely codominant, single-locus DNA markers for molecular breeding and genomics research in sunflower. Thirteen six-locus multiplex PCRs were developed for 78 SSR marker loci strategically positioned throughout the sunflower genome (three to five per linkage group) by identifying compatible SSR primer combinations and optimizing multiplex PCR protocols. The multiplexed SSR markers, when coupled with 17 complementary SSR marker loci, create a 'standard genotyping' set ideal for first-pass scans of the genome, as are often needed when screening bulked-segregant DNA samples or mapping phenotypic trait loci. The minimum, mean and maximum heterozygosities of the multiplexed SSR markers were 0.38, 0.62 and 0.83, respectively. The PCR-multiplexes increase genotyping throughput, reduce reagent costs, and are ideal for repetitive genotyping applications where common sets of SSR marker loci are required or advantageous.     

Association analysis and population structure of flowering-related traits in super sweet corn inbred lines with simple sequence repeat markers

This study assessed the genetic and phenotypic variation of 90 super sweet corn inbred lines and performed association analyses of six agronomical traits using 100 simple sequence repeats (SSR), ultimately detecting 590 alleles, with an average of 5.90 alleles per locus. The average genetic diversity and Polymorphism information content values were 0.54 and 0.50, respectively. Using population structure analysis, inbred lines were divided into three major groups and one admixed group. Association analysis was performed with a general linear model using a Q-matrix (Q GLM) and a mixed linear model using Q and K-matrices (Q + K MLM). Q GLM found 33 marker-trait associations involving 20 SSR markers that were associated with six agronomic traits. Q + K MLM identified four marker-trait associations involving three markers that were associated with traits of days of tasseling (DT) and days of silking (DS). Q GLM and Q + K MLM detected four significant marker-trait associations (SMTAs), with a level of significance of P < 0.01. In overlapping SMTAs, phi051 was associated with DT, umc1708 was associated with DS, and umc2341 was associated with two traits: DT and DS. The detection of loci associated with traits in this study may provide greater opportunities to improve quality by marker-assisted selection (MAS). Finally, these results will be helpful for breeders in choosing parental lines for crossing combinations as well as markers for using MAS in super sweet corn breeding programs in Korea.     

Rate and directionality of mutations and effects of allele size constraints at anonymous, gene-associated, and disease-causing trinucleotide loci.

We studied the patterns of within- and between-population variation at 29 trinucleotide loci in a random sample of 200 healthy individuals from four diverse populations: Germans, Nigerians, Chinese, and New Guinea highlanders. The loci were grouped as disease-causing (seven loci with CAG repeats), gene-associated (seven loci with CAG/CCG repeats and eight loci with AAT repeats), or anonymous (seven loci with AAT repeats). We used heterozygosity and variance of allele size (expressed in units of repeat counts) as measures of within-population variability and GST (based on heterozygosity as well as on allele size variance) as the measure of genetic differentiation between populations. Our observations are: (1) locus type is the major significant factor for differences in within-population genetic variability; (2) the disease-causing CAG repeats (in the nondisease range of repeat counts) have the highest within-population variation, followed by the AAT-repeat anonymous loci, the AAT-repeat gene-associated loci, and the CAG/CTG-repeat gene-associated loci; (3) an imbalance index beta, the ratio of the estimates of the product of effective population size and mutation rate based on allele size variance and heterozygosity, is the largest for disease-causing loci, followed by AAT- and CAG/CCG-repeat gene-associated loci and AAT-repeat anonymous loci; (4) mean allele size correlates positively with allele size variance for AAT- and CAG/CCG-repeat gene-associated loci and negatively for anonymous loci; and (5) GST is highest for the disease-causing loci. These observations are explained by specific differences of rates and patterns of mutations in these four groups of trinucleotide loci, taking into consideration the effects of the past demographic history of the modern human population.