European Accessions Research Articles

Nineteenth century French rose (Rosa sp.) germplasm shows a shift over time from a European to an Asian genetic background.

Hybridization with introduced genetic resources is commonly practiced in ornamental plant breeding to introgress desired traits. The 19th century was a golden age for rose breeding in France. The objective here was to study the evolution of rose genetic diversity over this period, which included the introduction of Asian genotypes into Europe. A large sample of 1228 garden roses encompassing the conserved diversity cultivated during the 18th and 19th centuries was genotyped with 32 microsatellite primer pairs. Its genetic diversity and structure were clarified. Wide diversity structured in 16 genetic groups was observed. Genetic differentiation was detected between ancient European and Asian accessions, and a temporal shift from a European to an Asian genetic background was observed in cultivated European hybrids during the 19th century. Frequent crosses with Asian roses throughout the 19th century and/or selection for Asiatic traits may have induced this shift. In addition, the consistency of the results with respect to a horticultural classification is discussed. Some horticultural groups, defined according to phenotype and/or knowledge of their pedigree, seem to be genetically more consistent than others, highlighting the difficulty of classifying cultivated plants. Therefore, the horticultural classification is probably more appropriate for commercial purposes rather than genetic relatedness, especially to define preservation and breeding strategies.

Population structure and genome-wide association analysis for frost tolerance in oat using continuous SNP array signal intensity ratios.

Key messageInfinium SNP data analysed as continuous intensity ratios enabled associating genotypic and phenotypic data from heterogeneous oat samples, showing that association mapping for frost tolerance is a feasible option.Oat is sensitive to freezing temperatures, which restricts the cultivation of fall-sown or winter oats to regions with milder winters. Fall-sown oats have a longer growth cycle, mature earlier, and have a higher productivity than spring-sown oats, therefore improving frost tolerance is an important goal in oat breeding. Our aim was to test the effectiveness of a Genome-Wide Association Study (GWAS) for mapping QTLs related to frost tolerance, using an approach that tolerates continuously distributed signals from SNPs in bulked samples from heterogeneous accessions. A collection of 138 European oat accessions, including landraces, old and modern varieties from 27 countries was genotyped using the Infinium 6K SNP array. The SNP data were analyzed as continuous intensity ratios, rather than converting them into discrete values by genotype calling. PCA and Ward’s clustering of genetic similarities revealed the presence of two main groups of accessions, which roughly corresponded to Continental Europe and Mediterranean/Atlantic Europe, although a total of eight subgroups can be distinguished. The accessions were phenotyped for frost tolerance under controlled conditions by measuring fluorescence quantum yield of photosystem II after a freezing stress. GWAS were performed by a linear mixed model approach, comparing different corrections for population structure. All models detected three robust QTLs, two of which co-mapped with QTLs identified earlier in bi-parental mapping populations. The approach used in the present work shows that SNP array data of heterogeneous hexaploid oat samples can be successfully used to determine genetic similarities and to map associations to quantitative phenotypic traits.Electronic supplementary materialThe online version of this article (doi:10.1007/s00122-016-2734-y) contains supplementary material, which is available to authorized users.

Biochemical and pomological assessment of European pear accessions from Bosnia and Herzegovina

The research on 10 old and indigenous pear cultivars was conducted during 2012 and 2013 in Bosnia and Herzegovina. The following characteristics were determined: fruit weight, fruit length and width, stalk length and width, fruit flesh firmness; soluble solids content and total dry matter content of the fruit juice; pH, titratable acidity, vitamin C, total phenolics, total flavonoids and antioxidant activity of the fruit cell juice. On the basis of the Principal Component Analysis (PCA) of pomological fruit characteristics the studied cultivars were divided into four main groups. Based on the PCA of biochemical traits the studied cultivars can be divided into three groups. Extremely high phenolic content in the cvs Mioljnjača, Žutica, Poljakinja, Karamut and Gradišćanka recommends them for their inclusion in a breeding programme. The cvs Mioljnjača and Poljakinja are also characterised by large and firm fruit and since the antioxidant capacity affects the duration of fruit storage, it is expected that these traditionally grown varieties can survive longer and keep their valuable nutritional ingredients longer.

Evaluation of Turkish apricot germplasm using SSR markers: Genetic diversity assessment and search for Plum pox virus resistance alleles

Apricot (Prunus armeniaca L.) is an important fruit crop in Turkey, where a rich diversity of apricot cultivars and seedlings is prevalent. The genetic diversity of the Turkish apricot germplasm was investigated. The profiles of 18 simple sequence repeat (SSR) loci of 239 accessions in the genetic source collection of the country as well as those of European and Pakistani accessions were obtained. Eleven SSRs were selected from the apricot molecular linkage group 1 (LG1), and these are located close to the major Plum pox virus (PPV) resistance locus. The remaining seven SSRs represent the other six linkage groups. A high level of genetic diversity (He=0.74, Ho=0.63) was observed. Stark Early Orange (SEO)/Harlayne-type resistance alleles of three SSR loci (PGS1.21-240, PGS1.23-161 and PGS1.24-119) were found to be rare in the Turkish accessions (1.7%) but were abundantly found in the Pakistani accessions (41.7%). The genetic clustering analyses, the neighbor-joining tree constructed from the genetic distances of the proportions of shared alleles and the population genetic structure did not distinguish the European accessions from the Turkish accessions. However, ‘Harlayne’, ‘SEO’ and the putative resistant apricot accessions were grouped together, indicating a common heritage for the resistant accessions. SSR profiles of the accessions will improve the management of apricot gene banks, and information on the genetic variation in Turkish apricots will assist the international research community.

How just a few makes a lot: Speciation via reticulation and apomixis on example of European brambles (Rubus subgen. Rubus, Rosaceae)

New species are generated by many means, among which hybridization plays an important role. Interspecific hybrids can form isolated evolutionary units, especially when mechanisms increasing viability and fertility, like polyploidy and apomixis, are involved. A good model system to study reticulate evolution in plants is Rubus subgen. Rubus (brambles, blackberries), which only in Europe includes 748 accepted species, out of which only four are sexual diploids and all others are polyploid apomicts. We employed two molecular markers (ITS and cpDNA) to shed light on the evolutionary history of European bramble flora and main processes generating such high species diversity. We distinguished just six ancestral diploids (including two extinct ones) for both markers, which gave rise to all European polyploid accessions, and revealed an extreme reticulation in bramble evolution. We furthermore detected hybridogenous origins and identified putative parents for several taxa (e.g. ser. Nessenses), while in other groups (e.g. ser. Discolores) we could also infer the direction of hybridization. By comparing different cp haplotypes having clear geographic patterns, we hypothesize that the origin of European brambles can be attributed to both Holocene species range expansion and Pleistocene climate fluctuations.

Seed yield and essential oil content of fennel influenced by genetic variation and genotype × year interaction

Common fennel (Foeniculum vulgare Mill.) is an important medicinal plant with considerable geographical distribution in Iran. Variation in eighteen populations of fennel collected from different regions of Iran and two European accessions was evaluated based on agro-morphological traits, ISSR markers, seed yield and essential oil content. Accessions were planted in the field and studied for two consecutive agronomic years. The analysis of data on all 20 accessions showed that mean squares of genotypes, years, and genotype×year interaction was significant for most of the traits indicating wide variation for the studied traits in the fennel accessions influenced by the environment. Coefficients of genotypic variability revealed high genetic variation for seed yield per plant and harvest index suggesting the possibility of improving seed yield by means of selection particularly in the first year. Seed yield per plant had positive correlations with the number of effective umbels per plant and 1000-seed weight as yield components. Cluster analysis based on agro-morphological traits classified populations into 4 major groups in the first year. Similarly the UPGMA (unweighted pair group method with arithmetic mean) dendrogram obtained from ISSR molecular data based on SM (simple matching) classified populations into four groups. Agro-morphological and ISSR data matrices were not correlated and did not correspond to the geographical variation of the populations. In general, the results of this research showed that there was a considerable genetic variation in terms of seed yield and the other agronomic and molecular traits among accessions and depending on the objectives, this variation may be utilized to select superior genotypes for medicinal purposes and in plant breeding programs.

The role of climate adaptation in colonization success in Arabidopsis thaliana.

Understanding the genetic mechanisms that contribute to range expansion and colonization success within novel environments is important for both invasion biology and predicting species-level responses to changing environments. If populations are adapted to local climates across a species' native range, then climate matching may predict which genotypes will successfully establish in novel environments. We examine evidence for climate adaptation and its role in colonization of novel environments in the model species, Arabidopsis thaliana. We review phenotypic and genomic evidence for climate adaptation within the native range and describe new analyses of fitness data from European accessions introduced to Rhode Island, USA, in spring and fall plantings. Accessions from climates similar to the Rhode Island site had higher fitness indicating a potential role for climate pre-adaptation in colonization success. A genomewide association study (GWAS), and genotypic mean correlations of fitness across plantings suggest the genetic basis of fitness in Rhode Island differs between spring and autumn cohorts, and from previous fitness measurements in European field sites. In general, these observations suggest a scenario of conditional neutrality for loci contributing to colonization success, although there was evidence of a fitness trade-off between fall plantings in Norwich, UK, and Rhode Island. GWAS suggested that antagonistic pleiotropy at a few specific loci may contribute to this trade-off, but this conclusion depended upon the accessions included in the analysis. Increased genomic information and phenotypic information make A. thaliana a model system to test for the genetic basis of colonization success in novel environments.

Molecular and phenotypic characterization of variation related to pea enation mosaic virus resistance in lentil (Lens culinarisMedik.)

Jain, S., Porter, L. D., Kumar, A., Mir, R. R., Eigenbrode, S. D. and McPhee, K. E. 2014. Molecular and phenotypic characterization of variation related to pea enation mosaic virus resistance in lentil (Lens culinaris Medik.). Can. J. Plant Sci. 94: 1333–1344. Identification of genetically diverse lentil germplasm with resistance to pea enation mosaic virus (PEMV) through the combined approach of molecular marker analysis and phenotyping could prove useful in breeding programs. A total of 44 lentil (Lens culinaris Medik.) accessions, were screened for resistance to PEMV. Two accessions (PI 431663 and PI 432028) were identified with resistance to PEMV in field tests while several accessions were found resistant in greenhouse screenings. Thirty-six polymorphic simple sequence repeat (SSR) markers which produced 43 loci with 2 to 12 alleles per locus were used for genetic diversity analysis. The polymorphic information content (PIC) values for these markers ranged from 0.22–0.85 with a mean of 0.55 per marker. Using allelic data of 36 SSR primer pairs, dissimilarity ranging from 0.12 to 0.74 was calculated. Cluster analysis performed using the unweighted pair group method with arithmetic mean (UPGMA) determined that most of PEMV-resistant accessions were grouped in one cluster along with other accessions from Iran, Chile, Ethiopia, India, Pakistan, Turkey, Afghanistan and Lebanon. All the adapted cultivars originating from North and South America were grouped in another cluster along with some European accessions. The 44 accessions were classified into 4 subpopulations using Structure 2.2 software complimenting the results of UPGMA analysis and indicated the effect of geographical origin on the grouping of accessions. The results of this study can be used to select genetically diverse PEMV-resistant accessions for lentil improvement programs.

Phenotypic Performance of Timothy Accessions under Irrigated and Nonirrigated Conditions

ABSTRACTTimothy (Phleum pratense L.) is one of the most winter‐hardy, cool‐season perennial grasses used for forage production. However, its lack of tolerance to water stress requires supplemental irrigation for successful production in more arid areas of the world. A set of 112 timothy accessions and 6 check cultivars were evaluated for dry matter yield, in vitro true digestibility, neutral detergent fiber, crude protein, and water soluble carbohydrates across two production years at Lewiston, UT, and Tetonia, ID. Supplemental irrigation was not supplied at Tetonia. For each of the traits except water‐soluble carbohydrates, the variance due to the main effect of accessions differed from zero. There was also accession × environment interaction for each of the traits. Within‐environment broad‐sense heritability estimates differed from zero and ranged from 0.45 ±0.16 to 0.80 ±0.40. Thus, genetic determinants exerted substantial influence on the expression of the traits in each environment. Most of the commercial cultivars exhibited no benefit over the accessions for these traits, and there was a relationship between the accessions’ geographic origin and their potential for timothy improvement. Asian and Northwest and Northeast European accessions possessed the greatest potential for increasing timothy nutritive value under western North American conditions. Yet there was little evidence that any accessions would provide a yield improvement.

S-locus genotyping on stone fruits in Hungary: a review of the most recent achievements

Central Europe can be taken as a geographical and historical connection zone between the western growing countries and Asian gene centres of Prunus tree fruits. The determination of the S-genotype of stone fruit (mainly almond, plum, cherries and apricot) cultivars and landraces has both practical and theoretical significance. Our group has allocated complete S-genotypes for more than 200 cultivars and selections of almond, Japanese plum, sweet cherry and apricot. Among Eastern European almond cultivars, two novel cross-incompatibility groups (CIGs) were identified. S-alleles of a related species were also shown in P. dulcis accessions; a fact seems to be indicative of introgressive hybridization. Our results with Japanese plum clarified and harmonized two different allele nomenclatures and formed a basis for intensive international studies. In apricot, a total of 13 new S-alleles were identified from Eastern European and Asian accessions. Many Turkish and North African cultivars were classified into new CIGs, III–XVII. Results suggest that the mutation rendering apricot self-compatible might have occurred somewhere in south-east of Turkey and we were successful to confirm the presumed Irano-Caucasian origin of North African apricots based on the geographical distribution of S-alleles. In sweet cherry, new alleles have been identified and characterized from Turkish cultivars and selections. In addition, wild sweet cherry and sour cherry S-alleles were also shown indicating a a broader gene pool in Turkey as compared with international cultivars. We also used S-genotype information of Ukrainian sweet cherry cultivars to design crosses in a functional breeding program. Our results exhibit an increased number of S-alleles in tree fruit accessions native to the regions from Eastern Europe to Central Asia, which can be used to develop S-genotyping methods, to assist cultivation and draw inferences for crop evolution.

Characterization of accessions of ‘Reine Claude Verte’ plum using Prunus SRR and phenotypic traits

European plum (Prunus domestica L.) cv ‘Reine Claude Verte’ is highly appreciated for its excellent organoleptic qualities. Despite its increasing demand, this cultivar is in the process of being eradicated in many commercial orchards because of its generally erratic fruit setting. This situation led us to explore the behaviour of particular accessions with the aim of evaluating if some of them can crop more regularly. For this purpose, we initially evaluated the putative diversity of 24 European plum accessions of ‘Reine Claude Verte’ collected in different areas of Spain. For the molecular characterization, 16 Prunus SSRs were used. Eight of them were selected from previous works of SSRs transferability within the genus and the other eight were selected from a transferability screening of another 75 Prunus SSRs, in which 65 SSRs were conserved in the species. Morphological characterization was performed by evaluating 33 qualitative characters of leaves and fruits. Results allowed differentiating the accessions by their genotypic profile and their phenotype. The accessions were grouped in six genotypic profiles according to their genetic similarity and in seven clusters according to their fruit and leaf traits. High similarity was found between the ‘Reine Claude Verte’ commercial cultivars. Some of the prospected accessions sharing the same genotypic profile showed some morphological differences, whereas some accessions with different genotypic profiles presented fruit traits similar to ‘Reine Claude Verte’. The combined use of molecular and morphological characterization allowed identifying different clones of the cultivar that were selected for further agronomic evaluation.

USE OF CARROT GENETIC RESOURCES TO UNDERSTAND ROOT CAROTENOID CONTENT: PRELIMINARY STEPS TO AN ASSOCIATION MAPPING STUDY

Association mapping becomes one of the major genetic methods used to understand genetic control of complex traits. This method allows the use of natural populations with high resolution thanks to ancestral recombinations. Resolution is given by linkage disequilibrium (LD) extend. But false positives can be detected when phenotypic traits are correlated with underlying population stratification at non causal loci. Knowledge of population structure is then a preliminary step for association mapping studies. Here we investigated the population structure in cultivated carrot and the LD extend in the carotenoid isomerase gene, a key gene in the carotenoid biosynthesis pathway. An unexpected high LD for outcrossing species was found in this gene. Population stratification analysis confirmed the differentiation of the carrot germplasm in two clusters. The first one comprised European and American accessions, the second one Asian accessions. These are preliminary steps to perform association mapping studies to understand root carotenoid content in cultivated carrot.

Rps16-trnK DNA 서열에 의한 딜(Anethum graveolens L.)의 유전적 다양성과 유전 관계

딜(Anethum graveolens L.)은 세계적으로 중요한 초본으로 양념과 약용뿐만 아니라 소화제, 진정제, 마취제, 활력제로 오래 전부터 사용되어왔다. 딜은 지중해, 서아시아, 중국과 한국 등에서 분포한다. 20개국 100계통 간 rps16-trnK3 서열을 이용하여 유전적 다양성과 유연관계를 조사하였다. 배당된 서열은 747에서 779 염기쌍으로 삽입과 결실이 있었다. 비록 일부 삽입과 결실이 발견되었지만 서열 변이는 염기 치환에 기인하였다. 동아시아 계통이 중앙아시아와 유럽보다 북미에 근연하였다. 딜의 일부 계통은 지리적 분포와 계통도에서 위치가 일치하지 않았지만 rps16-trnK로 잘 분리되었다. Dill (Anethum graveolens L.) is an annual herb with a long history and it is mainly used as a spice and as a medicine that is effective as a digestive aid, a sedative, and a narcotic, and that helps remove bad breath. Dill grows wild in the districts along the shores of the Mediterranean Sea, West Asia, China, and Korea. An estimate of the phylogenetic relationships within dill accessions in 20 countries was inferred using data from the rps16-trnK3-intergenic spacer. The aligned data sets for dill ranged from 747 to 779 nucleotides (bp) as a result of the differences in the insert/delete nucleotides. The sequence variation within the dill accessions was mostly due to nucleotide substitutions, although several small insertions and deletions can be found. Among 100 accessions from 20 countries, the Eastern Asia accessions were more closely related to the North American accessions than to the Central Asia and European accessions. Although some accessions were not congruent completely with geographical locations, the dill accessions with rps16-trnK analysis resulted in plants with better-resolved clades.

Molecular polymorphism related to flowering trait variation in a Phaseolus vulgaris L. collection

The aim of this study was to investigate the flowering variation and the molecular polymorphism in key regulatory genes that control flowering in a Phaseolus vulgaris L. collection of 94 accessions from Europe and the Americas. The analysis of variance revealed that the difference in days-to-flowering between accessions was significant, with European accessions characterized by flowering precocity. Population structure analysis corroborated previous data on the genetic distinction between the Andean and Mesoamerican gene pools. A low level of admixture was detected. Genomic sequences of 15 gene fragments were obtained. About 7.0kb per accession were sequenced and a total of 48 nucleotide substitutions identified. A Mixed Linear Model analysis, including population structure and kinship, was used to identify marker-trait associations. Haplotype tagging single nucleotide polymorphisms (htSNPs) associated with the studied traits were detected: in PvVRN1 and PvPHYB with days-to-flowering, in PvMYB29 with number of flower buds per inflorescence and in PvTFL1z and PvFCA with inflorescence length. The two genes associated with days-to-flowering control belong to the photoperiod and vernalization pathways. In particular, the PvVRN1 gene appears to play an important role in regulating the adaptation process of common bean.

An analysis of genetic differentiation and geographical variation of spinach germplasm using SSR markers

To assess the genetic diversity of spinach germplasm, 250 individuals of 50 accessions collected from geographically diverse regions (West Asia, East Asia, Japan, Europe and the USA) were analysed using simple sequence repeat (SSR) markers. A total of 39 polymorphic alleles were identified, with an average of 6.5 alleles per locus for six loci. The overall gene diversity (0.62) in the entire set of individuals suggests that the germplasm has high genetic variability. The West Asian accessions showed the highest gene diversity, with a value of 0.57, followed by the East Asian accessions. These results help confirm the notion that spinach originated from West Asia. Hierarchical analysis of molecular variance revealed significant genetic differentiation among the geographical regions, which accounts for 26% of the total variation detected. Furthermore, pairwise Φstvalues indicate low genetic differentiation between the East Asian and Japanese germplasm accessions, both of which showed high genetic differentiation from the European accessions. The differentiation between the East Asian and European gene pools may be attributed to the founder effect associated with crop dissemination, as well as to the selection and genetic drift that occurred during the breeding process.

Germplasm diversity and differentiation ofHelianthus tuberosusL. revealed by AFLP marker and phenotypic traits

SUMMARYHelianthus tuberosusL. is regarded as one of the most important bioenergy crops because of its tolerance to arid conditions and its high biomass production. Future breeding programmes will rely on the available germplasm, thus necessitating a critical assessment of genetic diversity and differentiation in the species. The germplasm diversity and regional differentiation ofH. tuberosusL. was assessed for 60 accessions collected from East Asia and Europe by means of amplified fragment length polymorphisms (AFLPs), phenotypic traits and chemical analysis. The analysis did not reveal separate clusters for accessions from East Asia and Europe, with 5% for genetic and 0·27% for phenotypic variability, although some regional accessions were closely related to each other with respect to morphological, chemical and genetic variation. Both phenotypic and genetic relationships showed a moderate correlation with colour of tubers, which can be used as an important criterion for germplasm management of the crop. Three major genetic groups were identified from the accessions. Within the groups derived from the genetic data, both morphological and chemical traits were very variable. The most important features of Groups I, II and III were: Group I, strong sexual reproduction, higher above-ground biomass and nutrient content; Group II, longer vegetative growth; Group III, higher tuber yield and total sugar content. High diversity was found in both European and East Asian accessions as well as within each genetic group, suggesting that there is a strong base for future breeding from these plants.

Genetic structure and domestication of carrot (Daucus carota subsp. sativus) (Apiaceae)

Analyses of genetic structure and phylogenetic relationships illuminate the origin and domestication of modern crops. Despite being an important worldwide vegetable, the genetic structure and domestication of carrot (Daucus carota) is poorly understood. We provide the first such study using a large data set of molecular markers and accessions that are widely dispersed around the world. • Sequencing data from the carrot transcriptome were used to develop 4000 single nucleotide polymorphisms (SNPs). Eighty-four genotypes, including a geographically well-distributed subset of wild and cultivated carrots, were genotyped using the KASPar assay. • Analysis of allelic diversity of SNP data revealed no reduction of genetic diversity in cultivated vs. wild accessions. Structure and phylogenetic analysis indicated a clear separation between wild and cultivated accessions as well as between eastern and western cultivated carrot. Among the wild carrots, those from Central Asia were genetically most similar to cultivated accessions. Furthermore, we found that wild carrots from North America were most closely related to European wild accessions. • Comparing the genetic diversity of wild and cultivated accessions suggested the absence of a genetic bottleneck during carrot domestication. In conjunction with historical documents, our results suggest an origin of domesticated carrot in Central Asia. Wild carrots from North America were likely introduced as weeds with European colonization. These results provide answers to long-debated questions of carrot evolution and domestication and inform germplasm curators and breeders on genetic substructure of carrot genetic resources.

European Phaseolus coccineus L. landraces: Population Structure and Adaptation, as Revealed by cpSSRs and Phenotypic Analyses

Relatively few studies have extensively analysed the genetic diversity of the runner bean through molecular markers. Here, we used six chloroplast microsatellites (cpSSRs) to investigate the cytoplasmic diversity of 331 European domesticated accessions of the scarlet runner bean (Phaseolus coccineus L.), including the botanical varieties albiflorus, bicolor and coccineus, and a sample of 49 domesticated and wild accessions from Mesoamerica. We further explored the pattern of diversity of the European landraces using 12 phenotypic traits on 262 individuals. For 158 European accessions, we studied the relationships between cpSSR polymorphisms and phenotypic traits. Additionally, to gain insights into the role of gene flow and migration, for a subset of 115 accessions, we compared and contrasted the results obtained by cpSSRs and phenotypic traits with those obtained in a previous study with 12 nuclear microsatellites (nuSSRs). Our results suggest that both demographic and selective factors have roles in the shaping of the population genetic structure of the European runner bean. In particular, we infer the existence of a moderate-to-strong cytoplasmic bottleneck that followed the expansion of the crop into Europe, and we deduce multiple domestication events for this species. We also observe an adaptive population differentiation in the phenology across a latitudinal gradient, which suggests that selection led to the diversification of the runner bean in Europe. The botanical varieties albiflorus, bicolor and coccineus, which are based solely on flower colour, cannot be distinguished based on these cpSSRs and nuSSRs, nor according to the 12 quantitative traits.

Evidence from Genome-wide Simple Sequence Repeat Markers for a Polyphyletic Origin and Secondary Centers of Genetic Diversity of Brassica juncea in China and India

The oilseed Brassica juncea is an important crop with a long history of cultivation in India and China. Previous studies have suggested a polyphyletic origin of B. juncea and more than one migration from the primary to secondary centers of diversity. We investigated molecular genetic diversity based on 99 simple sequence repeat markers in 119 oilseed B. juncea varieties from China, India, Europe, and Australia to test whether molecular differentiation follows Vavilov's proposal of secondary centers of diversity in India and China. Two distinct groups were identified by markers in the A genome, and the same two groups were confirmed by markers in the B genome. Group 1 included accessions from central and western India, in addition to those from eastern China. Group 2 included accessions from central and western China, as well as those from northern and eastern India. European and Australian accessions were found only in Group 2. Chinese accessions had higher allelic diversity per accession (Group 1) and more private alleles per accession (Groups 1 and 2) than those from India. The marker data and geographic distribution of Groups 1 and 2 were consistent with two independent migrations of B. juncea from its center of origin in the Middle East and neighboring regions along trade routes to western China and northern India, followed by regional adaptation. Group 1 migrated further south and west in India, and further east in China, than Group 2. Group 2 showed diverse agroecological adaptation, with yellow-seeded spring-sown types in central and western China and brown-seeded autumn-sown types in India.

The use of microsatellite polymorphisms to characterise and compare genetic variability in Avena strigosa and A. barbata

Microsatellite (SSR) polymorphism was assessed across 90 diploid Avena strigosa Schreb. and tetraploid Avena barbata Pott ex Link accessions obtained from the USDA-ARS National Small Grains Collection using 105 genomic SSRs. Eleven polymorphic SSRs that detected 69 different alleles were identified and used to genotype the 90 accessions, which were chosen from a larger set of 385 accessions based on geographical source-diversity and variable reaction responses to five Australian pathotypes of the crown rust pathogen Puccinia coronata Corda f. sp. avenae Eriks. Eight diploid and eight tetraploid clades were identified among the 90 accessions. Diploid accessions displayed the lowest genetic diversity, with all accessions being at least 86 % similar, and included accessions from countries in the Americas such as Canada, USA, Argentina, Uruguay and Brazil, and European accessions from France, Romania and Poland. Although both species formed distinct clusters in the dendrogram, a few instances of diploids showing high similarity with tetraploids and vice versa were observed. An AMOVA analysis revealed 86 % of the total genetic variation to be distributed within the two oat species, while between-species differences accounted for only 14 %. Heterozygosity (H) index values of 0.32 and 0.40 were obtained for diploids and tetraploids respectively. Our study effectively differentiated A. strigosa and A. barbata, and identified 11 SSRs suitable for future characterisation of accessions of the two species.