[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. · 1.18 Impact Factor
[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.
Biocontrol Science and Technology 01/2012; 22(7):813-835. · 0.71 Impact Factor
[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. · 1.18 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: 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: Little is known about the genetic impacts of modern plant breeding on specific breeding target loci. Resequencing cloned genes can identify all mutations in single genes for population-based analyses of genetic changes in improved gene pools. Ninety-five wheat cultivars released in Canada from 1845 to 2004 were sequenced at the wheat leaf rust resistance locus Lr21. Characterization of the DNA fragment of length 4,071 bp, covering the Lr21 gene from -92 to +4,261, revealed 13 SNPs, four indels, 10 haplotypes, and 4 major haplotype groups. A new SCAR marker was developed to identify the resistant haplotype and haplotype groups. Non-synonymous polymorphic sites and haplotype numbers were increased over the 100 years of wheat breeding. Nucleotide diversity of the wheat cultivars was gradually reduced from 1845 to 1993 and increased after the release of the first Lr21 wheat cultivar AC Cora in 1994. Positive selection measured with Tajima's D was observed in the cultivars released before 1935. At least two recombination events were inferred in those cultivars released before 1993. Linkage disequilibrium at the locus was decreased over time. These findings demonstrate not only the effectiveness of the wheat breeding in the improvement of leaf rust resistance, but also are useful to understand the genetic influences of a long-term artificial selection on individual loci.
Theoretical and Applied Genetics 03/2010; 121(2):271-81. · 3.66 Impact Factor
[show abstract][hide abstract] ABSTRACT: Little is known about the genetic diversity of pale flax (Linum bienne Mill.), the wild progenitor of cultivated flax (L. usitatissimum L.), and ex situ germplasm of pale flax was scarce. Effort was made to collect 34 pale flax accessions and five landrace accessions of cultivated
flax in Turkey. The inter simple sequence repeat (ISSR) technique was applied to characterize this set of flax germplasm,
along with one Turkish cultivar, one Russian cultivar, five winter and four dehiscent type accessions of cultivated flax.
Twenty-four ISSR primer pairs detected a total of 311 DNA fragments, of which 298 bands were polymorphic across 493 flax samples
(roughly 10 samples per accession). These polymorphic bands had frequencies ranging from 0.002 to 0.998 and averaging 0.38.
Accession-specific ISSR variation (Fst values) ranged from 0.469 to 0.514 and averaged 0.493. There was 49.3% ISSR variation resided among these 50 accessions,
35.9% harbored among landrace, winter, dehiscent types of cultivated flax and pale flax, and 38.2% present among 34 pale flax
accessions. Pale flax displayed more ISSR variation than landraces and dehiscent type, but less than winter type, of cultivated
flax. Clustering 493 individual plants revealed that these assayed plants were largely grouped according to their plant types
and that pale flax was genetically more close to the dehiscent type, followed by the winter type and landrace, of cultivated
flax. Pale flax collected within the geographic range of 180km displayed a significant spatial genetic autocorrelation. Genetic
distances among the pale flax accessions were significantly associated with their geographic distances and elevation differences.
These findings are significant for understanding flax domestication and its primary gene pool.
KeywordsFlax domestication-Flax wild relative-Genetic diversity-ISSR marker-
[show abstract][hide abstract] ABSTRACT: Grassland in North America is expected to expand northward as the climate becomes warmer and drier under many climate change scenarios. Successful adaptation of plant species to climate change depends on regeneration success. This paper aims to identify the spatial variation in seed germination characteristics of Festuca hallii populations and to quantify the effect of genetic, geographic, demographic, or climatic factors on the variation. Seeds were collected from 15 populations in five ecoregions over a wide geographic range in Canada. Seeds were germinated at 7 growth chambers with constant temperatures from 5 to 35 °C with 5 °C increments. Thermal time models were constructed to generate germination thresholds. Correlations between germination parameters and genetic variation, longitude, latitude, population size, geographic distance to the nearest neighbour, mean annual temperature (MAT) and mean annual precipitation (MAP) were assessed. Base temperatures (Tb, minimal or base temperature permitting germination) of the 15 populations fell into a narrow range within 2.2 °C with an average of 1.1 °C. Tb was positively correlated with latitude and negatively with longitude and the thermal time requirement for 50% germination was negatively correlated with latitude. Seed mass was negatively correlated with MAT and positively correlated with MAP. High final germination percentage was reached at a wide temperature range from 5 to 20 °C with the highest germination percentage at 10 °C. Germination rate index (GRI) increased with increasing temperature from 5 to 20 °C. Final germination percentage at 5 °C was negatively correlated with MAT and positively correlated with MAP. GRIs at 5 and 10 °C were positively correlated with MAP but not with MAT. GRI at 5 °C was positively correlated with longitude. Germination was not correlated with any genetic and demographic attributes assayed. Population-wise variation in temperature and precipitation affects seed mass, an important attribute determining seed germinability. Sites with greater precipitation and lower temperature had heavier seeds, which usually had lower thermal time requirements for germination and faster germination. The warmer and drier future climate as predicted for the Canadian prairie may reduce regeneration success of this species in the current distribution range, particularly after disturbances followed by sexual regeneration from seeds.
[show abstract][hide abstract] ABSTRACT: Genetic diversity is essential for predicting plant evolutionary potential and for formulating conservation strategies. However, little is known about the genetic variation of plains rough fescue [Festuca hallii (Vasey) Piper], a widespread and diagnostic grass in the Fescue Prairie. We used the amplified fragment length polymorphism (AFLP) technique to assess the genetic variation of 30 fragmented populations of F. hallii across the northern Canadian Prairie and its associations with 12 geographical, fragmentation and environmental attributes. Three AFLP primer pairs were used to screen 840 samples, representing approximately 30 samples from each population, and 246 polymorphic bands were scored. The fescue plant was genetically diverse, as revealed by the proportion of polymorphic bands (0.870–0.967), the mean band frequency (0.364–0.457) and the within-population variation (69.4–85.4). The genetic variation was not highly differentiated, with only 6.5% of the total AFLP variation residing among populations. A Mantel test revealed a significant correlation between genetic and geographical distances (r = 0.39; P < 0.004) and a spatial autocorrelation up to 60 km among populations was detected. The AFLP variation displayed a longitudinal decline and was significantly associated with environmental attributes related to moisture, indicating local adaptation. However, the AFLP variation was not significantly associated with the estimated population size and geographical distance to the nearest neighbor, suggesting that fragmentation has not generated considerable genetic impact on the fescue populations. Implications for fescue conservation, restoration and management are discussed.
[show abstract][hide abstract] ABSTRACT: Public concerns about crop uniformity intro- duced by modern plant breeding and genetic vulnerability to biotic and abiotic stresses have been one of the major forces driving long-term efforts in plant germplasm conservation for future food security. However, such concerns have gained little empirical support, as recent molecular diversity analyses of improved crop gene pools did not reveal much reduction from early to recent breeding efforts. We conducted a genome-wide examination of 75 Canadian hard red spring wheat (Triticum aestivum L.) cultivars released from 1845 to 2004 using 370 simple sequence repeat (or SSR) markers that were widely distributed over all 21 wheat chro- mosomes. A total of 2280 SSR alleles were detected. Allelic reduction occurred in every part of the wheat genome and a majority of the reduced alleles resided in only a few early cul- tivars. Signifi cant allelic reduction started in the 1930s. Considering 2010 SSR alleles detected in the 20 earliest cultivars, 38% of them were retained, 18% were new, and 44% were lost in the 20 most recent cultivars. The net reduction of the total SSR variation in 20 recent cultivars was 17%. This clear-cut evidence not only sup- ports the contention that modern plant breed- ing reduces the genetic diversity of Canadian wheat, but also underlies the need for conserv- ing wheat germplasm and introducing genetic diversity into wheat breeding.
[show abstract][hide abstract] ABSTRACT: Current molecular characterization of ex situ plant germplasm has placed more emphasis on cultivated gene pools and less on exotic gene pools representing wild relative species. This study attempted to characterize a selected set of germplasm accessions representing various Avena species with the hope to establish a reference set of exotic oat germplasm for oat breeding and research. The amplified fragment length polymorphism (AFLP) technique was applied to screen 163 accessions of 25 Avena species with diverse geographic origins. For each accession, 413 AFLP polymorphic bands detected by five AFLP primer pairs were scored. The frequencies of polymorphic bands ranged from 0.006 to 0.994 and averaged 0.468. Analysis of molecular variance revealed 59.5% of the total AFLP variation resided among 25 oat species, 45.9% among six assessed sections of the genus, 36.1% among three existing ploidy levels, and 50.8% among eight defined genome types. All the species were clustered together according to their ploidy levels. The C genome diploids appeared to be the most distinct, followed by the Ac genome diploid A. canariensis. The Ac genome seemed to be the oldest in all the A genomes, followed by the As, Al and Ad genomes. The AC genome tetraploids were more related to the ACD genome hexaploids than the AB genome tetraploids. Analysis of AFLP similarity suggested that the AC genome tetraploid A. maroccana was likely derived from the Cp genome diploid A. eriantha and the As genome diploid A. wiestii, and might be the progenitor of the ACD genome hexaploids. These AFLP patterns are significant for our understanding of the evolutionary pathways of Avena species and genomes, for establishing reference sets of exotic oat germplasm, and for exploring new exotic sources of genes for oat improvement.
Theoretical and Applied Genetics 09/2008; 117(3):333-42. · 3.66 Impact Factor
[show abstract][hide abstract] ABSTRACT: The Avena sterilis L. collection in the Plant Gene Resources of Canada (PGRC) consists of 11,235 accessions originating from 27 countries and is an invaluable source of genetic variation for genetic improvement of oats, but it has been inadequately characterized, particularly using molecular techniques. More than 35 accessions have been identified with genes for resistance to oat crown and stem rusts, but little is known about their comparative genetic diversity. This study attempted to characterize a structured sample of 369 accessions representing 26 countries and two specific groups with Puccinia coronata avenae (Pc) and Puccinia graminis avenae (Pg) resistance genes using microsatellite (SSR) markers. Screening of 230 SSR primer pairs developed from other major crop species yielded 26 informative primer pairs for this characterization. These 26 primer pairs were applied to screen all the samples and 125 detected alleles were scored for each accession. 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 0.01 to 0.99 and averaged 0.28. More than 90% of the SSR variation resided within accessions of a country. Accessions from Greece, Liberia, and Italy were genetically most diverse, while accessions from Egypt, Georgia, Ethiopia, Gibraltar, and Kenya were most distinct. Seven major clusters were identified, each consisting of accessions from multiple countries and specific groups, and these clusters were not well congruent with geographic origins. Accessions with Pc and Pg genes had similar levels of SSR variation, did not appear to cluster together, and were not associated with the other representative accessions. These SSR patterns are significant for understanding the progenitor species of cultivated oat, managing A. sterilis germplasm, and exploring new sources of genes for oat improvement.
Theoretical and Applied Genetics 05/2007; 114(6):1029-38. · 3.66 Impact Factor
[show abstract][hide abstract] ABSTRACT: Genetic diversity assessment of improved crop germplasm can facilitate the expansion of the genetic base in a plant breeding program, but little effort has been made to assess the Cana- dian soybean (Glycine max (L.) Merr.) gene pool established over the past century. Simple sequence repeat (SSR) markers were applied to assess the genetic diversity of 45 Canadian soybean cultivars released from 1934 to 2001 and 37 exotic germplasm accessions. Thirty- seven SSR primer pairs were applied and 234 polymorphic bands were scored for each accession. The frequencies of the scored bands ranged from 0.01 to 0.90 and averaged 0.17. The proportion of total SSR variation occur- ring between exotic and Canadian germplasm was 9%; among the Canadian cultivars of three breeding periods 10%; and between the cul- tivars of maturity groups 0 and 00 4%. More diversity was found for exotic germplasm than the Canadian. More diversity was observed in the cultivars of the recent breeding period than the early. The Canadian cultivars were clustered into seven major groups, partially congruent to the known pedigrees, and they were more related to germplasm from Russia, Sweden, and Ukraine and less to the Asian germplasm. The six genetically most distinct cultivars were PS86 RR, Gaillard, Manitoba Brown, Beech- wood, Maple Isle, and 92B91. These fi ndings are useful for the selection of genetically distinct or less related soybean materials to improve the genetic background of the soybean gene pool.
[show abstract][hide abstract] ABSTRACT: Molecular characterization of ex situ plant germplasm, although more attainable than before, has rarely been applied to a whole germplasm collection of 2000 accessions or larger. The benefits of screening large numbers of accessions have not been well recognized for germplasm management and utilization. Challenges also exist in identifying duplicated and genetically related accessions and in validating developed core subsets. Here we show how a new approach using an average marker-based dissimilarity of an accession in a collection can be applied to identify both redundancy and distinctness in a plant germplasm collection. Application of this dissimilarity measure to 2727 flax accessions genotyped by 149 randomly amplified polymorphic DNA (RAPD) markers revealed that up to 22% of accessions could be deemed to be redundant. Up to 500 of the most distinct flax accessions were identified and these can be directly screened for traits of interest to broaden the genetic base in a flax improvement programme. These results demonstrate that molecular screening of a large number of accessions with an informative diversity analysis can facilitate the management and utilization of ex situ plant germplasm.
[show abstract][hide abstract] ABSTRACT: Sinapis alba L. is a major specialty crop grown as a condiment in western Canada, but little is known about its genetic diversity. The objective of this study was to assess the level and pattern of genetic diversity in a collection of 127 S. alba accessions held at Plant Gene Resources of Canada using amplified fragment length polymorphism (AFLP) markers. Five AFLP primer pairs were applied, and 134 polymorphic bands were scored for each accession. These scored bands had frequencies of occurrence ranging from 0.02 to 0.99 with an average of 0.69. More AFLP variation was found within single (79.1%) than between (20.9%) S. alba accessions. A small degree of AFLP difference (1.7%) was observed among the accessions of various regions, while relatively large variation (9.2%) existed among the accessions of various countries. A large AFLP difference (15.6%) also existed between the yellow- and brown-seeded accessions, but only 6.2% difference was observed between the cultivar and landrace accessions. Two distinct groups of S. alba germplasm were identified on the basis of the seed colour (yellow or brown), although a few mixtures also existed. No apparent ‘duplicated’ accessions were observed. The most diverse accessions were from Italy, Spain, France and Greece. Among the most genetically distinct accessions were SA97 from Portugal, SA89 and SA88 from France, SA83 from Russia and SA57 from Italy. These findings are significant not only for managing S. alba germplasm, but also for identifying diverse germplasm that can be used by plant breeders to improve S. alba seed yield and quality parameters.
[show abstract][hide abstract] ABSTRACT: Genetic diversity changes in wheat germplasm have been studied using different molecular markers, but little is known about the impact of plant breeding on the transcribed segments of the wheat genome. The objective of this study was to assess diversity changes in 75 Canadian hard red wheat cultivars released from 1845 to 2004 using 37 EST-derived microsatellite (eSSR) markers. These markers were derived from at least 19 transcribed sequences with putative functions assigned and sampled 17 wheat chromosomes. A total of 138 eSSR alleles was detected, and their allelic frequencies ranged from 0.01 to 0.99 with an average of 0.41. Allelic counts were significantly reduced at three loci for cultivars released after 1990. Sixteen alleles at 14 loci in pre-1910 cultivars were lost in cultivars released after 1990. The lost alleles had frequencies ranging from 0.03 to 0.17 and averaging 0.07. Partitioning the eSSR variation showed the four ancestral families accounted for 14.7% of the variation, followed by the six breeding periods with 12.8% and the eight breeding programs with 5.8%. A genetic shift was observed in the cultivars released over the six breeding periods, reflecting the various breeding efforts. These results illustrate the impact of the Canadian wheat breeding on the transcriptional segments of the wheat genome. These findings, along with those from genomic SSR markers, suggest the Canadian wheat breeding programs have reduced genetic diversity in the hard red spring wheat.
Theoretical and Applied Genetics 06/2006; 112(7):1239-47. · 3.66 Impact Factor
[show abstract][hide abstract] ABSTRACT: Based on agro-botanical characterization data, 3101 accessions of cultivated flax (Linum usitatissimum L. subsp. usitatissimum) from the flax collection held by Plant Gene Resources of Canada (PGRC) were grouped into four infraspecific groups according
to the classification proposed by Kulpa and Danert (1962) . The objective of this study was to investigate phenotypic and
RAPD variation within and among the four groups to better understand phenotypic and genotypic differentiation within the genepool
of cultivated flax. The results of the phenotypic characterization of characters defining the convarieties (capsule dehiscence,
plant height, technical stem length and 1000 seed weight) and of other quantitative (petal width, oil content in seeds) and
qualitative (RAPD, petal colour, anther colour, petal longitudinal folding and margin folding, ciliation of capsule septa,
seed colour) are presented using descriptive statistics. The most frequent convariety in the PGRC genebank was intermediate
flax (convar. usitatissimum; 80.7 %), followed by fibre flax (convar. elongatum Vav. et Ell. in Wulff; 13.4%), large-seeded flax (convar. mediterraneum [Vav. ex Ell.] Kulpa et Danert; 5.6%) and dehiscent flax (convar. crepitans [Boenningh.] Kulpa et Danert; 0.3%). Analyses of RAPD data and two qualitative characters (longitudinal and marginal folding
of petals) did not show marked differences among the proposed convarieties. However, differences among the convarieties in
quantitative traits defining them (plant height, technical stem length and seed size) were considerable. Patterns of variation
among the convarieties for other quantitative characters (petal width and seed oil content), as well as the frequencies of
character expressions of four qualitative characters (petal colour, anther colour, ciliation of capsule septa and seed colour)
were significantly associated with the four proposed convarieties, underlining the phenotypic and genotypic validity of this
grouping. The patterns of geographic distribution of the convarieties and important characters showed that certain convarieties
dominate in some areas of origin. The infraspecific classification and the presented characterization data increase the transparency
of genetic diversity available in cultivated flax and in particular in the PGRC flax collection.
[show abstract][hide abstract] ABSTRACT: A phylogenetic analysis was conducted on 34 alleles of 2.5 kb sized stearoyl-ACP desaturase II (sad2), obtained from 30 accessions of cultivated and pale flax (Linum spp.), to elucidate the history of flax domestication. The analysis supports a single domestication origin for extant cultivated flax. The phylogenetic evidence indicates that flax was first domesticated for oil, rather than fibre. The genetic diversity of the sad2 locus in cultivated flax is low when compared to that of the pale flax assayed. An absolute archaeological date could be applied to the synonymous substitution rate of sad2 in cultivated flax, yielding a high estimate of 1.60-1.71x10(-7) substitutions/site/year. The occurrence of nonsynonymous substitutions at conserved positions of the third exon in alleles from cultivated flax suggests that the locus may have been subjected to an artificial selection pressure. The elevated synonymous substitution rate is also compatible with a population expansion of flax since domestication, followed by a population decline in historic times. These findings provide new insight into flax domestication and are significant for the continuous exploration of the flax germplasm for utilization.
Theoretical and Applied Genetics 01/2006; 112(1):58-65. · 3.66 Impact Factor