[Show abstract][Hide abstract] ABSTRACT: Key message:
Maximizing crop yield while at the same time minimizing crop failure for sustainable agriculture requires a better understanding of the impacts of plant breeding on crop genetic diversity. This review identifies knowledge gaps and shows the need for more research into genetic diversity changes under plant breeding. Modern plant breeding has made a profound impact on food production and will continue to play a vital role in world food security. For sustainable agriculture, a compromise should be sought between maximizing crop yield under changing climate and minimizing crop failure under unfavorable conditions. Such a compromise requires better understanding of the impacts of plant breeding on crop genetic diversity. Efforts have been made over the last three decades to assess crop genetic diversity using molecular marker technologies. However, these assessments have revealed some temporal diversity patterns that are largely inconsistent with our perception that modern plant breeding reduces crop genetic diversity. An attempt was made in this review to explain such discrepancies by examining empirical assessments of crop genetic diversity and theoretical investigations of genetic diversity changes over time under artificial selection. It was found that many crop genetic diversity assessments were not designed to assess diversity impacts from specific plant breeding programs, while others were experimentally inadequate and contained technical biases from the sampling of cultivars and genomes. Little attention has been paid to theoretical investigations on crop genetic diversity changes from plant breeding. A computer simulation of five simplified breeding schemes showed the substantial effects of plant breeding on the retention of heterozygosity over generations. It is clear that more efforts are needed to investigate crop genetic diversity in space and time under plant breeding to achieve sustainable crop production.
[Show abstract][Hide abstract] ABSTRACT: Long-term conservation of 7.4 million ex situ seed accessions held in agricultural genebanks and botanic gardens worldwide is a challenging mission for human food security
and ecosystem services. Recent advances in seed biology and genomics may have opened new opportunities for effective management
of seed germplasm under long-term storage. Here, we review the current development of tools for assessing seed ageing and
research advances in seed biology and genomics, with a focus on exploring their potential as better tools for monitoring of
seed ageing. Seed ageing is found to be associated with the changes reflected in reactive oxygen species and mitochondria-triggered
programmed cell deaths, expression of antioxidative genes and DNA and protein repair genes, chromosome telomere lengths, epigenetic
regulation of related genes (microRNA and methylation) and altered organelle and nuclear genomes. Among these changes, the
signals from mitochondrial and nuclear genomes may show the most promise for use in the development of tools to predict seed
ageing. Non-destructive and non-invasive analyses of stored seeds through calorimetry or imaging techniques are also promising.
It is clear that research into developing advanced tools for monitoring seed ageing to supplement traditional germination
tests will be fruitful for effective conservation of ex situ seed germplasm.
[Show abstract][Hide abstract] ABSTRACT: Many in situ conservation programs have been developed to preserve plant landrace diversity and to promote its sustainable utilization, but little is known about the effectiveness of the developed programs in conserving plant genetic diversity. We investigated the effectiveness of an unregulated (i.e., unplanned or open) conservation system maintained by Thai farmers in conserving Thai elite cassava (Manihot esculenta Crantz) varieties. Specifically, we compared genetic diversity of 266 cassava clones that were collected from 80 farms in eight provinces with 16 cassava landraces and varieties released since the 1970s through genotyping with 35 informative simple sequence repeat (SSR) markers. The SSR analysis revealed a large regional heterogeneity in cassava diversity, with a strong genetic differentiation of the assayed clones among the 80 farms (19.8 %) and across the eight provinces (11.8 %). Significant associations were also found between SSR variation and farm agro-ecological factors or some farming practices. However, there was no significant genetic differentiation (0.9 %) between the 266 farm clones and 16 reference varieties. These findings suggest that the Thai elite cassava genetic diversity was fortuitously conserved by the farmers through farming with different sets of varieties. Implications of these findings are discussed with respect to on-farm conservation of plant genetic resources.
[Show abstract][Hide abstract] ABSTRACT: Genotyping by sequencing (GBS) has recently emerged as a promising genomic approach for assessing genetic diversity on a genome-wide scale. However, concerns are not lacking about the uniquely large unbalance in GBS genotype data. While some genotype imputation has been proposed to infer missing observations, little is known about the reliability of a genetic diversity analysis of GBS data with up to 90% of observations missing. Here we performed an empirical assessment of accuracy in genetic diversity analysis of highly incomplete SNP genotypes with imputations. Three large SNP genotype data sets for corn, wheat and rice were acquired, and missing data with up to 90% of missing observations were randomly generated and then imputed for missing genotypes with three map-independent imputation methods. Estimating heterozygosity and inbreeding coefficient from original, missing and imputed data revealed variable patterns of bias from assessed levels of missingness and genotype imputation, but the estimation biases were smaller for missing data without genotype imputation. The estimates of genetic differentiation were rather robust up to 90% of missing observations, but became substantially biased when missing genotypes were imputed. The estimates of topology accuracy for four representative samples of interested groups were generally reduced with increased levels of missing genotypes. Probabilistic principal component analysis based imputation performed better in terms of topology accuracy than those analyses of missing data without genotype imputation. These findings are not only significant for understanding the reliability of the genetic diversity analysis with respect to large missing data and genotype imputation, but also are instructive for performing a proper genetic diversity analysis of highly incomplete GBS or other genotype data.
[Show abstract][Hide abstract] ABSTRACT: Nuttall's salt-meadow, or alkali grass [Puccinellia nuttalliana (Shultes) Hitchc.], is a native grass species in North America, well known for its salt tolerance. Little information is available about the genetic diversity of natural populations of this species. Amplified fragment length polymorphism (AFLP) markers were used to examine the inter-population relationships and to compare variances within and among 23 populations collected from the Canadian Great Plains. Five AFLP primer pairs were employed to screen 15 genotypes (five sets of three half-sib plants) from each population, and 185 polymorphic AFLP bands were scored for each sample. The frequencies of these scored bands ranged from 0.02 to 0.99 with a mean of 0.60. The analysis of molecular variance revealed more than 96% of the total AFLP variation resided within populations. Populations were not highly differentiated with only 4% of the total AFLP variation residing among populations. A Mantel test revealed a significant but low correlation between genetic and geographic distances (r =0.29, P =0.024). Implications for P. nuttalliana conservation, germplasm sampling, and cultivar development are discussed.
Canadian Journal of Plant Science 11/2013; 93(6):1097-1104. DOI:10.4141/cjps2013-157 · 0.92 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: Recent advances in next generation sequencing technologies make genotyping by sequencing (GBS) more feasible for molecular characterization of plant germplasm with complex and unsequenced genomes. We used a GBS protocol consisting of Roche 454 pyrosequencing, genomic reduction and advanced bioinformatics tools to analyze genetic diversity of 24 diverse yellow mustard accessions. One and one half 454 pyrosequencing runs generated roughly 1.2 million sequence reads totaling about 392 million nucleotides. Application of the computational pipeline DIAL identified 512 contigs and 828 SNPs. The BLAST algorithm revealed alignments of 214 contigs with the sequences reported in NCBI nr/nt database. Sanger sequencing confirmed 95 % of 41 selected contigs and 94 % of 240 putative SNPs. The 454 scored SNPs were highly imbalanced among assayed samples. Diversity analysis of these SNPs revealed that 26.1 % of the total variation resided among landrace, cultivar and breeding lines and 24.7 % between yellow- and black-seeded germplasm. Cluster analysis showed that the black-seeded accessions were largely clustered together and the breeding lines were grouped with known origin. Computer simulation was performed to assess the impact of 454 SNPs missing and revealed considerable changes in allelic count, bias in detection of genetic structure, and large deviations from the expected genetic-distance matrix. These findings are useful for parental selection consideration in yellow mustard breeding, and our detailed analyses help illustrate the utility of GBS in genetic-diversity analysis of plant germplasm, particularly for genetic-relationship assessment.
[Show abstract][Hide abstract] ABSTRACT: Wild barley [Hordeum vulgare ssp. spontaneum (C. Koch) Thell.] is a part of the primary gene pool with valuable sources of beneficial genes for barley improvement. This study attempted to develop a core subset of 269 accessions representing 16 countries from the Plant Gene Resources of Canada (PGRC) collection of 3,782 accessions, and to characterize them using barley simple sequence repeat (SSR) markers. Twenty-five informative primer pairs were applied to screen all samples and 359 alleles were detected over seven barley chromosomes. Analyses of the SSR data showed the effectiveness of the stratified sampling applied in capturing country-wise SSR variation. The frequencies of polymorphic alleles ranged from 0.004 to 0.708 and averaged 0.072. More than 24% or 7% SSR variation resided among accessions of 16 countries or two regions, respectively. Accessions from Israel and Jordan were genetically most diverse, while accessions from Lebanon and Greece were most differentiated. Four and five optimal clusters of accessions were obtained using STRUCTURE and BAPS programs and partitioned 16.3% and 20.3% SSR variations, respectively. The five optimal clusters varied in size from 15 to 104 and two clusters had only country-specific accessions. A genetic separation was detected between the accessions east and west of the Zagros Mountains only at the country, not the individual, level. These SSR patterns enhance our understanding of the wild barley gene pool, and are significant for conserving wild barley germplasm and exploring new sources of useful genes for barley improvement.
[Show abstract][Hide abstract] ABSTRACT: The fungus Phoma macrostoma Mont. isolate 94-44B was registered as a bioherbicide for control of broadleaved weeds in Canada and the USA in 2011 and 2012, respectively. To obtain the registrations, the fungus had to be characterised both biologically and genetically. The objectives of this study were to demonstrate that bioherbicidal activity was associated with specific genetic markers and to determine whether bioherbicidal activity was a general trait of the species or only selected isolates. A collection of 64 isolates of P. macrostoma was established. A greenhouse bioassay and bioherbicidal-specific primers were used to determine bioherbicidal activity of all isolates. Only isolates originating from Canada thistle demonstrated the ability to reduce dandelion seedlings and display the 853 bp amplicon for the bioherbicidal-specific primer. Bioherbicidal isolates were consistently differentiated from all other isolates with two main genotypic groupings (I and II) arising from internal transcribed spacer (ITS) and amplified fragment length polymorphisms (AFLP) sequence analyses. Using AFLP, two biotypes of bioherbicidal isolates were also differentiated by the presence or absence of an AFLP marker at a single polymorphic locus. The genetic divergence among the bioherbicidal and nonbioherbicidal isolates of P. macrostoma was only 2.21% which was lower than that reported for other related Phoma sp. Other than the bioherbicidal trait, there was no apparent affiliation of the genetics with known varietal types, host or geographic origin. ITS sequence analysis and AFLP fingerprinting may be used as tools to detect bioherbicidal isolates of P. macrostoma.
[Show abstract][Hide abstract] ABSTRACT: Cultivated flax (Linum usitatissimum L.) is the earliest oil and fiber crop and its early domestication history may involve multiple events of domestication for oil, fiber, capsular indehiscence, and winter hardiness. Genetic studies have demonstrated that winter cultivated flax is closely related to oil and fiber cultivated flax and shows little relatedness to its progenitor, pale flax (L. bienne Mill.), but winter hardiness is one major characteristic of pale flax. Here, we assessed the genetic relationships of 48 Linum samples representing pale flax and four trait-specific groups of cultivated flax (dehiscent, fiber, oil, and winter) through population-based resequencing at 24 genomic regions, and revealed a winter group of cultivated flax that displayed close relatedness to the pale flax samples. Overall, the cultivated flax showed a 27% reduction of nucleotide diversity when compared with the pale flax. Recombination frequently occurred at these sampled genomic regions, but the signal of selection and bottleneck was relatively weak. These findings provide some insight into the impact and processes of flax domestication and are significant for expanding our knowledge about early flax domestication, particularly for winter hardiness.
Ecology and Evolution 03/2012; 2(3):622-35. DOI:10.1002/ece3.101 · 2.32 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: Many plant disease resistance (R) genes have been cloned, but the potential of utilizing these plant R-gene genomic resources for genetic inferences of plant domestication history remains unexplored. A population-based resequencing analysis of the genomic region near the Rrs2 scald resistance gene was made in 51 accessions of wild and cultivated barley from 41 countries. Fifteen primer pairs were designed to sample the genomic region with a total length of 10 406 bp. More nucleotide diversity was found in wild (π = 0.01846) than cultivated (π = 0.01507) barley samples. Three distinct groups of 29 haplotypes were detected for all 51 samples, and they were well mixed with wild and cultivated barley samples from different countries and regions. The neutrality tests by Tajima's D were not significant, but a significant (P < 0.05) case by Fu and Li's D* and F* was found in the barley cultivar samples. The estimate of selection intensity by K(a)/K(s) was 0.691 in wild barley and 0.580 in cultivated barley. The estimate of the minimum recombination events was 16 in wild barley and 19 in cultivated barley. A coalescence simulation revealed a bottleneck intensity of 1.5 to 2 since barley domestication. Together, the domestication signal in the genomic region was weak both in human selection and domestication bottleneck.
[Show abstract][Hide abstract] ABSTRACT: Crop domestication has been inferred genetically from neutral markers and increasingly from specific domestication-associated loci. However, some crops are utilized for multiple purposes that may or may not be reflected in a single domestication-associated locus. One such example is cultivated flax (Linum usitatissimum L.), the earliest oil and fiber crop, for which domestication history remains poorly understood. Oil composition of cultivated flax and pale flax (L. bienne Mill.) indicates that the sad2 locus is a candidate domestication locus associated with increased unsaturated fatty acid production in cultivated flax. A phylogenetic analysis of the sad2 locus in 43 pale and 70 cultivated flax accessions established a complex domestication history for flax that has not been observed previously. The analysis supports an early, independent domestication of a primitive flax lineage, in which the loss of seed dispersal through capsular indehiscence was not established, but increased oil content was likely occurred. A subsequent flax domestication process occurred that probably involved multiple domestications and includes lineages that contain oil, fiber, and winter varieties. In agreement with previous studies, oil rather than fiber varieties occupy basal phylogenetic positions. The data support multiple paths of flax domestication for oil-associated traits before selection of the other domestication-associated traits of seed dispersal loss and fiber production. The sad2 locus is less revealing about the origin of winter tolerance. In this case, a single domestication-associated locus is informative about the history of domesticated forms with the associated trait while partially informative on forms less associated with the trait.
Ecology and Evolution 01/2012; 2(1):139-52. DOI:10.1002/ece3.57 · 2.32 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: Recent advances in next-generation DNA sequencing (NGS) have enhanced the development of genomic resources such as contigs or single-nucleotide polymorphisms (SNPs) for evolutionary studies of a nonmodel species with a complex and unsequenced genome. This study presents an application of a NGS technique in combination with genomic reduction and advanced bioinformatics tools to identify contigs and SNPs from multiple samples of two Linum species. A full Roche 454 GS FLX run of 16 diverse Linum samples representing cultivated flax (Linum usitatissimum L.) and its wild progenitor (Linum bienne Mill.) generated approximately 1.6 million sequence reads with a total length of 498 Mbp. Application of the computational pipeline de novo identification of alleles identified 713 contigs and 1067 SNPs. A blast search revealed alignments of all 713 contigs with 491 existing Linum scaffolds and gene annotations associated with 512 contigs. Sanger sequencing confirmed 95% of 79 selected contigs and 94% of 272 SNPs and identified 211 new SNPs and 19 new indels. The scored 454 SNP data were highly imbalanced for assayed samples. These findings not only are useful for evolutionary studies of Linum species but also help to illustrate the utility of NGS technologies in SNP discovery for nonmodel organisms.
[Show abstract][Hide abstract] ABSTRACT: Flax (Linum usitatissimum L.) is the earliest oil and fibre crop, but little is known about its domestication process. Attempt was made here to assess
genetic relationships of 63 Linum accessions representing seven typical groups of cultivated flax and its wild progenitor, pale flax (Linum bienne Mill.), by using 49 informative expressed sequence tag-derived simple sequence repeat (EST-SSR) primer pairs. The seven groups
were pale flax from Turkey, pale flax from other countries, and five groups of cultivated flax (landrace, fibre, oil, winter,
and dehiscent). From these 63 samples, 366 polymorphic bands were detected, which likely represented 79 loci. These polymorphic
bands had frequencies that ranged from 0.016 to 0.984 and averaged 0.284. Group-specific EST-SSR variation (Fst values) ranged from 0.339 to 0.373 and averaged 0.349 and pairwise group EST-SSR variation ranged from 0.067 to 0.507.
A neighbor-joining clustering of these seven groups revealed that dehiscent flax clustered most closely to its wild progenitor,
pale flax, followed by oil flax and fibre flax. Winter flax clustered most closely to oil flax and less to pale flax. These
clustering patterns were essentially the same when individual samples were analyzed via neighbor-joining. These findings strongly
suggest that capsular dehiscence was among the first flax traits modified by human after initial domestication, reflecting
the importance that reducing capsular dehiscence likely played in early flax domestication.
KeywordsCultivated flax–Dehiscent flax–EST-SSR–Genetic relationship–
–Pale flax–Winter flax
[Show abstract][Hide abstract] ABSTRACT: Hairy prairie-clover [Dalea villosa (Nutt.) Spreng. var. villosa] is a threatened Canadian wildflower. To facilitate the efforts of conserving this threatened plant, amplified fragment length polymorphism (AFLP) technique was applied to assess genetic diversity in a remnant hairy prairie-clover population in the Canadian Prairie. Three AFLP primer pairs were employed to genotype 610 individual plants from the population and 15 plants from a North Dakota composite population, and 100 polymorphic AFLP bands were analyzed. The assayed plants displayed 23% AFLP variation present between the remnant population and the North Dakota composite population, but maintained a high level (91%) of AFLP variation within patches of the remnant population. The individual genetic distinctiveness measured by average AFLP dissimilarity was positively associated with latitude and negatively with elevation. The among-patch AFLP variation was significantly related to inter-patch distance, indicating local genetic differentiation within the remnant population. However, the proportions of within-patch AFLP variation were not associated with any patch characteristics assessed (i.e., patch size, perimeter, nearest neighbor distance, mean inter-patch distance). No fine-scale genetic structure was found within three large patches, suggesting little genetic correlations present for plants five meters apart. Some genetically distinctive and diverse patches were also identified. These findings indicate that the genetic risk of the remnant hairy prairie-clover population in the Canadian Prairie is low.
[Show abstract][Hide abstract] ABSTRACT: Next-generation DNA sequencing (NGS) technologies can survey sequence variation on a genome-wide scale, but their utility for crop genetic diversity analysis is poorly known. Many challenges remain in their applications, including sampling complex genomes, identifying single nucleotide polymorphisms (SNPs), and analyzing missing data. This study presented a practical application of the Roche 454 GS FLX Titanium technology in combination with genomic reduction and an advanced bioinformatics tool to analyze the genetic relationships of 16 diverse barley (Hordeum vulgare L.) landraces. A full 454 run generated roughly 1.7 million sequence reads with a total length of 612 Mbp. Application of the computational pipeline called DIAL (de novo identification of alleles) identified 2578 contigs and 3980 SNPs. Sanger sequencing of four barley samples confirmed 85 of the 100 selected contigs and 288 of the 620 putative SNPs and identified 735 new SNPs and 39 new indels. Several diversity analyses revealed the eastern and western division in the barley samples. The division is compatible with those inferred with 156 microsatellite alleles of the same 16 samples and consistent with our current knowledge about cultivated barley. These results help to illustrate the utility of NGS technologies for crop diversity studies. The NGS application also provides a new informative set of genomic resources for barley research.
The Plant Genome 11/2011; 4(3):226. DOI:10.3835/plantgenome2011.08.0022 · 3.93 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: Bluebunch wheatgrass (Pseudoroegneria spicata (Pursh) A. Löve) is a cool-season perennial grass native to semi-arid regions of western North America and has been used for habitat restoration. However, the genetic diversity of this species is poorly understood. A total of 172 expressed sequence tag-derived simple sequence repeat (eSSR) primer pairs that had been developed for wheat were characterized for genetic diversity studies of bluebunch wheatgrass. Of these, 12 eSSR primer pairs were found to be informative and were applied to screen 216 plants collected from six locations with two different elevations in the Thompson River valley of British Columbia. These analyses revealed a total of 106 eSSR polymorphic alleles (or bands) scorable for each sample. The number of polymorphic bands per primer pair ranged from 2 to 17 with a mean of 8.8. The frequencies of these bands ranged from 0.005 to 0.995 and averaged 0.146. Most (92.6%) of the eSSR variation detected was present within the 12 populations assessed. The between-population eSSR variability was significantly associated with their geographic distances, but not with their elevations. These findings are useful for genetic diversity and genetic mapping studies of this grass species and should facilitate the sampling and development of bluebunch wheatgrass germplasm for germplasm conservation and habitat restoration.
Canadian Journal of Botany 03/2011; 84(7):1122-1128. DOI:10.1139/b06-066 · 1.40 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: Fringed brome (Bromus ciliatus L.) is found in native stands throughout a large area of North America. Little is known about the genetic diversity of this species. The amplified fragment length polymorphism (AFLP) technique was applied to assess the genetic diversity of 16 fringed brome populations sampled in Canada from the provinces of Alberta, British Columbia, Quebec, and Saskatchewan. Four AFLP primer pairs were employed to screen 82 samples with four to six samples per population and 83 polymorphic AFLP bands scored for each sample. The frequencies of the scored bands in all assayed samples ranged from 0.01 to 0.99 and averaged 0.53. Analysis of molecular variance revealed that 52.6% of the total AFLP variation resided among the 16 populations and 20.6% among the four provinces. The five Quebec populations appeared to be genetically the most diverse and distinct. The AFLP variability observed was significantly associated with the geographic origins of the fringed brome populations. These findings are useful for sampling fringed brome germplasm from natural populations for germplasm conservation and should facilitate the development of genetically diverse regional cultivars for habitat restoration and revegetation.
Canadian Journal of Botany 03/2011; 83(10):1322-1328. DOI:10.1139/b05-112 · 1.40 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: The diversity of pale flax (Linum bienne Mill.) as the progenitor of cultivated flax (L. usitatissimum L.) has not been well documented and the domestication syndromes in cultivated flax are poorly understood. An attempt was
made to characterize 34 pale flax accessions and six cultivated flax accessions collected during 2007 summer in Turkey. A
total of 12 quantitative and 7 qualitative characters covering vegetative and generative plant parts, including phenological
traits, were assessed. The occurrence of yellow anthers well known in cultivated flax is reported for the first time in pale
flax. Pale flax displayed larger variation in vegetative plant parts and growth habit than the cultivated flax and more heterogeneity
within accessions. Within pale flax, a higher degree of variation was observed in many generative parts such as the flower
characters than in the capsule and seed characters. Based on the assayed characters, the pale flax from Turkey was grouped
into three clusters and these clusters were associated with site elevation and longitude, further confirming local genetic
differentiation in pale flax from Turkey. These findings are significant for further studies of flax domestication history
and useful for further exploitation of wild flax in genetic improvement of cultivated flax.
KeywordsCultivated flax–Domestication syndrome–Flax domestication–
[Show abstract][Hide abstract] ABSTRACT: Jerusalem artichoke (Helianthus tuberosus L.) is an old tuber crop with a recently renewed interest in multipurpose improvement, but little effort has been made to characterize its genetic resources. A study was conducted to assess ge-netic structure and genetic relatedness of 47 diverse Jerusalem artichoke accessions using RAPD, ISSR and SRAP markers. A total of 296 (87.1%) polymorphic bands were detected from 13 RAPD markers; 92 (80%) from six ISSR primers; and 194 (88.6%) for nine combinations of SRAP primers. Five optimal clusters were inferred by the STRUC-TURE program from the RAPD or ISSR data, while six optimal clusters were found from the SRAP data or combined marker data. Significant linear relationships between the distance matrices for all pairs of individual accessions were detected for all marker pairs and the estimated correlation coefficient was 0.40 for RAPD-ISSR, 0.53 for RAPD-SRAP, and 0.43 for ISSR-SRAP. Based on the combined data, the neighbor-joining clustering of the 47 accessions matched closely with those inferred from the STRUCTURE program. Three ancestral groups were observed for the Canadian germplasm. Most diverse germplasm harbored in the USA collection. These findings not only reveal the compatible patterns of genetic structure and relatedness inferred with three marker types, but also are useful for managing Jerusa-lem artichoke germplasm and utilizing diverse germplasm for genetic improvement.
American Journal of Plant Sciences 01/2011; 02(06). DOI:10.4236/ajps.2011.26090