Genetic Diversity and Molecular Characterization of Iranian Durum Wheat Landraces (Triticum turgidum durum (Desf.) Husn.) Using DArT Markers

Genome-wide association analysis of tan spot disease resistance in durum wheat accessions from Tunisia

Background: Tunisia harbors a rich collection of unexploited durum wheat landraces (Triticum durum ssp. durum) that have been gradually replaced by elite cultivars since the 1970s. These landraces represent an important potential source for broadening the genetic background of elite durum wheat cultivars and for the introgression of novel genes for key traits, including disease resistance, into these cultivars. Methods: In this study, single nucleotide polymorphism (SNP) markers were used to investigate the genetic diversity and population structure of a core collection of 235 durum wheat accessions consisting mainly of landraces. The high phenotypic and genetic diversity of the fungal pathogen Pyrenophora tritici-repentis (cause of tan spot disease of wheat) in Tunisia allowed the assessment of the accessions for tan spot resistance at the adult plant stage under field conditions over three cropping seasons. A genome-wide association study (GWAS) was performed using a 90k SNP array. Results: Bayesian population structure analysis with 9191 polymorphic SNP markers classified the accessions into two groups, where groups 1 and 2 included 49.79% and 31.49% of the accessions, respectively, while the remaining 18.72% were admixtures. Principal coordinate analysis, the unweighted pair group method with arithmetic mean and the neighbor-joining method clustered the accessions into three to five groups. Analysis of molecular variance indicated that 76% of the genetic variation was among individuals and 23% was between individuals. Genome-wide association analyses identified 26 SNPs associated with tan spot resistance and explained between 8.1% to 20.2% of the phenotypic variation. The SNPs were located on chromosomes 1B (1 SNP), 2B (4 SNPs), 3A (2 SNPs), 3B (2 SNPs), 4A (2 SNPs), 4B (1 SNP), 5A (2 SNPs), 5B (4 SNPs), 6A (5 SNPs), 6B (2 SNPs), and 7B (1 SNP). Four markers, one on each of chromosomes 1B, and 5A, and two on 5B, coincided with previously reported SNPs for tan spot resistance, while the remaining SNPs were either novel markers or closely related to previously reported SNPs. Eight durum wheat accessions were identified as possible novel sources of tan spot resistance that could be introgressed into elite cultivars. Conclusion: The results highlighted the significance of chromosomes 2B, 5B, and 6A as genomic regions associated with tan spot resistance.

Phenotypic evolution in durum wheat (Triticum durum Desf.) based on SNPs, morphological traits, UPOV descriptors and kernel-related traits

Durum wheat is a worldwide staple crop cultivated mainly in the Mediterranean basin. Progress in durum wheat breeding requires the exploitation of genetic variation among the gene pool enclosed in landraces, old cultivars and modern cultivars. The aim of this study was to provide a more comprehensive view of the genetic architecture evolution among 123 durum wheat accessions (41 landraces, 41 old cultivars and 41 modern cultivars), grown in replicated randomized complete block in two areas, Metaponto (Basilicata) and Foggia (Apulia), using the Illumina iSelect 15K wheat SNP array and 33 plant and kernel traits including the International Union for the Protection of new Varieties of Plants (UPOV) descriptors. Through DAPC and Bayesian population structure five groups were identified according to type of material data and reflecting the genetic basis and breeding strategies involved in their development. Phenotypic and genotypic coefficient of variation were low for kernel width (6.43%) and for grain protein content (1.03%). Highly significant differences between environments, genotypes and GEI (Genotype x Environment Interaction) were detected by mixed ANOVAs for agro-morphological-quality traits. Number of kernels per spike (h2 = 0.02) and grain protein content (h2 = 0.03) were not a heritability character and highly influenced by the environment. Nested ANOVAs revealed highly significant differences between DAPC clusters within environments for all traits except kernel roundness. Ten UPOV traits showed significant diversity for their frequencies in the two environments. By PCAmix multivariate analysis, plant height, heading time, spike length, weight of kernels per spike, thousand kernel weight, and the seed related traits had heavy weight on the differentiation of the groups, while UPOV traits discriminated moderately or to a little extent. The data collected in this study provide useful resources to facilitate management and use of wheat genetic diversity that has been lost due to selection in the last decades.

Harnessing genome-wide genetic diversity, population structure and linkage disequilibrium in Ethiopian durum wheat gene pool

Yanyang Liu, Henan Academy of Agricultural Sciences (HNAAS), China; Landraces are an important genetic source for transferring valuable novel genes and alleles required to enhance genetic variation. Therefore, information on the gene pool's genetic diversity and population structure is essential for the conservation and sustainable use of durum wheat genetic resources. Hence, the aim of this study was to assess genetic diversity, population structure, and linkage disequilibrium, as well as to identify regions with selection signature. Five hundred (500) individuals representing 46 landraces, along with 28 cultivars were evaluated using the Illumina Infinium 25K wheat SNP array, resulting in 8,178 SNPs for further analysis. Gene diversity (GD) and the polymorphic information content (PIC) ranged from 0.13-0.50 and 0.12-0.38, with mean GD and PIC values of 0.34 and 0.27, respectively. Linkage disequilibrium (LD) revealed 353,600 pairs of significant SNPs at a cut-off (r2 > 0.20, P < 0.01), with an average r2 of 0.21 for marker pairs. The nucleotide diversity (π) and Tajima's D (TD) per chromosome for the populations ranged from 0.29-0.36 and 3.46-5.06, respectively, with genome level, mean π values of 0.33 and TD values of 4.43. Genomic scan using the Fst outlier test revealed 85 loci under selection signatures, with 65 loci under balancing selection and 17 under directional selection. Putative candidate genes co-localized with regions exhibiting strong selection signatures were associated with grain yield, plant height, host plant resistance to pathogens, heading date, grain quality, and phenolic content. The Bayesian Model (STRUCTURE) and distance-based (principal coordinate analysis, PCoA, and unweighted pair group method with arithmetic mean, UPGMA) methods grouped the genotypes into five subpopulations, where landraces from geographically non-adjoining environments were clustered in the same cluster. This research provides further insights into population structure and genetic relationships in a diverse set of durum wheat germplasm, which could be further used in wheat breeding programs to address production challenges sustainably.

Genetic approaches to exploit landraces for improvement of Triticum turgidum ssp. durum in the age of climate change

Addressing the challenges of climate change and durum wheat production is becoming an important driver for food and nutrition security in the Mediterranean area, where are located the major producing countries (Italy, Spain, France, Greece, Morocco, Algeria, Tunisia, Turkey, and Syria). One of the emergent strategies, to cope with durum wheat adaptation, is the exploration and exploitation of the existing genetic variability in landrace populations. In this context, this review aims to highlight the important role of durum wheat landraces as a useful genetic resource to improve the sustainability of Mediterranean agroecosystems, with a focus on adaptation to environmental stresses. We described the most recent molecular techniques and statistical approaches suitable for the identification of beneficial genes/alleles related to the most important traits in landraces and the development of molecular markers for marker-assisted selection. Finally, we outline the state of the art about landraces genetic diversity and signature of selection, already identified from these accessions, for adaptability to the environment.

Marker-trait association analyses revealed major novel QTLs for grain yield and related traits in durum wheat

The growing global demand for wheat for food is rising due to the influence of population growth and climate change. The dissection of complex traits by employing a genome-wide association study (GWAS) allows the identification of DNA markers associated with complex traits to improve the productivity of crops. We used GWAS with 10,045 single nucleotide polymorphism (SNP) markers to search for genomic regions associated with grain yield and related traits based on diverse panels of Ethiopian durum wheat. In Ethiopia, multi-environment trials of the genotypes were carried out at five locations. The genotyping was conducted using the 25k Illumina Wheat SNP array to explore population structure, linkage disequilibrium (LD), and marker-trait associations (MTAs). For GWAS, the multi-locus Fixed and Random Model Circulating Probability Unification (FarmCPU) model was applied. Broad-sense heritability estimates were high, ranging from 0.63 (for grain yield) to 0.97 (for thousand-kernel weight). The population structure based on principal component analysis, and model-based cluster analysis revealed two genetically distinct clusters with limited admixtures. The LD among SNPs declined within the range of 2.02-10.04 Mbp with an average of 4.28 Mbp. The GWAS scan based on the mean performance of the genotypes across the environments identified 44 significant MTAs across the chromosomes. Twenty-six of these MTAs are novel, whereas the remaining 18 were previously reported and confirmed in this study. We also identified candidate genes for the novel loci potentially regulating the traits. Hence, this study highlights the significance of the Ethiopian durum wheat gene pool for improving durum wheat globally. Furthermore, a breeding strategy focusing on accumulating favorable alleles at these loci could improve durum wheat production in the East African highlands and elsewhere.

Genetic diversity and marker trait association for phytophthora resistance in chilli

BACKGROUND

Chilli is an important commercial crop with positive returns tendency. Phytophthora root rot causes drastic damage to chilli plant. Dearth of detecting marker trait associations is a major hinderance in practicing marker assisted selection in chilli breeding.

METHODS AND RESULTS

Herein, 110 chilli accessions were assessed for 15 agronomic traits under control and disease infected conditions for two crop seasons (2018-2019). The SSR genotyping revealed high values of major allele frequency (MAF = 0.70), genetic diversity (GD = 0.39) and Polymorphic Information Content (PIC = 0.31). Principal coordinate analysis and population structure analysis showed distribution of diverse genotypes in all groups by dividing 110 genotypes in three populations and nine sub-populations. The UPGMA based Archaeopteryx tree was in concordance with population structure analysis. Linkage disequilibrium analysis evaluated that LD decays within 3-10 bp. Marker trait association (MTA) revealed the associations of 35 SSRs with 14 morphological traits. The significant MTA for marker CAeMS073 with relative leaf damage (RLD, 0.183 R²) under control and treated conditions was consistently observed in both models. The markers, CAMS173 and CAMS194 were found to be strongly associated with RLD and Disease Index (DI), respectively. The absence of MTA was detected for height of first branch.

CONCLUSION

The MTAs reported in this study can facilitate marker assisted breeding for developing chilli germplasm resistant against Phytophthora capsici.

Morphological characterization and genetic diversity analysis of Tunisian durum wheat (Triticum turgidum var. durum) accessions

BACKGROUND

Tunisia is considered a secondary center of diversification of durum wheat and has a large number of abandoned old local landraces. An accurate investigation and characterization of the morphological and genetic features of these landraces would allow their rehabilitation and utilization in wheat breeding programs. Here, we investigated a diverse collection of 304 local accessions of durum wheat collected from five regions and three climate stages of central and southern Tunisia.

RESULTS

Durum wheat accessions were morphologically characterized using 12 spike- and grain-related traits. A mean Shannon-Weaver index (H') of 0.80 was obtained, indicating high level of polymorphism among accessions. Based on these traits, 11 local landraces including Mahmoudi, Azizi, Jneh Khotifa, Mekki, Biskri, Taganrog, Biada, Badri, Richi, Roussia and Souri were identified. Spike length (H' = 0.98), spike shape (H' = 0.86), grain size (H' = 0.94), grain shape (H' = 0.87) and grain color (H' = 0.86) were the most polymorphic morphological traits. The genetic diversity of these accessions was assessed using 10 simple sequence repeat (SSR) markers, with a polymorphic information content (PIC) of 0.69. Levels of genetic diversity were generally high (I = 0.62; He = 0.35). In addition, population structure analysis revealed 11 genetic groups, which were significantly correlated with the morphological characterization. Analysis of molecular variance (AMOVA) showed high genetic variation within regions (81%) and within genetic groups (41%), reflecting a considerable amount of admixture between landraces. The moderate (19%) and high (59%) levels of genetic variation detected among regions and among genetic groups, respectively, highlighted the selection practices of farmers. Furthermore, Mahmoudi accessions showed significant variation in spike density between central Tunisia (compact spikes) and southern Tunisia (loose spikes with open glume), may indicate an adaptation to high temperature in the south.

CONCLUSION

Overall, this study demonstrates the genetic richness of local durum wheat germplasm for better in situ and ex situ conservation and for the subsequent use of these accessions in wheat breeding programs.

Development of novel EST microsatellite markers for genetic diversity analysis and correlation analysis of velvet antler growth characteristics in Sika deer

BACKGROUND

Sika deer is one of the most popular and valued animals in China. However, few studies have been conducted on the microsatellite of Sika deer, which has hampered the progress of genetic selection breeding. To develop and characterize a set of microsatellites for Sika deer which provide helpful information for protection of Sika deer natural resources and effectively increase the yield and quantity of velvet antler.

RESULTS

We conducted a transcriptome survey of Sika deer using next-generation sequencing technology. One hundred eighty-two thousand two hundred ninety-five microsatellite markers were identified in the transcriptome, 170 of 200 loci were successfully amplified across panels of 140 individuals from Shuangyang Sika deer population. And 29 loci were found to be obvious polymorphic. Number of alleles is from 3 to 14. The expected heterozygosity ranged from 0.3087 to 0.7644. The observed heterozygosity ranged from 0 to 0.7698. The polymorphism information content values of those microsatellites varied ranged from 0.2602 to 0.7507. The marker-trait association was tested for 6 important and kernel characteristics of two-branched velvet antler in Shuangyang Sika deer through one-way analysis of variance. The results showed that marker-trait associations were identified with 8 different markers, especially M009 and M027.

CONCLUSIONS

This study not only provided a large scale of microsatellites which were valuable for future genetic mapping and trait association in Sika deer, but also offers available information for molecular breeding in Sika deer.

Whole Genome Scan Reveals Molecular Signatures of Divergence and Selection Related to Important Traits in Durum Wheat Germplasm

The first breeding program in the world for durum wheat was conceived in Italy in the early 1900s. Over the decades, pressure exerted by natural and artificial selection could have progressively reduced the genetic diversity of the durum wheat germplasm. In the present study, a large panel of Italian durum wheat accessions that includes landraces, old and modern cultivars was subjected to genotyping using the Illumina iSelect 15K wheat SNP array. The aim was to assess the impact that selection has in shaping Italian durum wheat genetic diversity and to exploit the patterns of genetic diversity between populations to identify molecular signatures of divergence and selection. Relatively small differences in genetic diversity have been observed among accessions, which have been selected and cultivated in Italy over the past 150 years. Indeed, directional selection combined with that operated by farmers/breeders resulted in the increase of linkage disequilibrium (LD) and in changes of the allelic frequencies in DNA regions that control important agronomic traits. Results from this study also show that major well-known genes and/or QTLs affecting plant height (RHT), earliness (VRN, PPD) and grain quality (GLU, PSY, PSD, LYC, PPO, LOX3) co-localized with outlier SNP loci. Interestingly, many of these SNPs fall in genomic regions where genes involved in nitrogen metabolism are. This finding highlights the key role these genes have played in the transition from landraces to modern cultivars. Finally, our study remarks on the need to fully exploit the genetic diversity of Italian landraces by intense pre-breeding activities aimed at introducing a new source of adaptability and resistance in the genetic background of modern cultivars, to contrast the effect of climate change. The list of divergent loci and loci under selection associated with useful agronomic traits represents an invaluable resource to detect new allelic variants for target genes and for guiding new genomic selection programs in durum wheat.

In-depth genome diversity, population structure and linkage disequilibrium analysis of worldwide diverse safflower (Carthamus tinctorius L.) accessions using NGS data generated by DArTseq technology

Safflower (Carthamus tinctorius L.) is one of the most important oilseed crops for its seed oil rich in unsaturated fatty acids. Precise utilization of diverse genetic resources is fundamental in breeding programs to improve high yield genotypes with desirable traits. In this study, for the first time we report successful application of DArTseq technology; an efficient genotyping-by-sequencing (NGS); to analysis genetic diversity and population structure of 89 safflower accessions from worldwide origins. Totally, 19,639 DArTseq markers (10,130 SilicoDArTs and 9509 SNPs) generated through DArTseq genotyping. After filtering the data, 3431 polymorphic DArTseq markers (1136 SilicoDArTs and 2295 SNPs) used for genetic diversity, population structure and linkage disequilibrium analysis in safflower genotypes. All the SilicoDArT and SNP markers showed high reproducibility and call rate. Polymorphism information content (PIC) values ranged from 0.1 to 0.5, while ≥ 0.50% of SilicoDArTs and ≥ 0.64% SNPs showed PIC values more than median. Genotypes grouping using DArTseq markers resulted in three distinct clusters. Results showed weak correlation between safflower diversity pattern and origins. Analysis of molecular variance revealed that the majority of genetic variation was attributed to the differences among varieties within cluster populations and there was no significant molecular variance between origins. However, safflower of accessions belonged to Iran, Turkey, Pakistan and India indeed appear to be genetically similar and grouped close in referred cluster, while the accessions from Near East (Afghanistan, China) being distinct. Our results were in agreement with hypothesis that safflower domesticated in somewhere west of Fertile Crescent and then expanded through Africa and Europe. Present study using a panel of globally diverse safflower accessions and large number of DArTseq markers set the stage for future analysis of safflower domestication using large germplasm from proposed domestication centers. Also, studied germplasm in this study can be used as a valuable source for future genomic studies in safflower for mapping desirable traits through genome-wide association mapping studies.

Genomic analysis of Spanish wheat landraces reveals their variability and potential for breeding

Background

One of the main goals of the plant breeding in the twenty-first century is the development of crop cultivars that can maintain current yields in unfavorable environments. Landraces that have been grown under varying local conditions include genetic diversity that will be essential to achieve this objective. The Center of Plant Genetic Resources of the Spanish Institute for Agriculture Research maintains a broad collection of wheat landraces. These accessions, which are locally adapted to diverse eco-climatic conditions, represent highly valuable materials for breeding. However, their efficient use requires an exhaustive genetic characterization. The overall aim of this study was to assess the diversity and population structure of a selected set of 380 Spanish landraces and 52 reference varieties of bread and durum wheat by high-throughput genotyping.

Results

The DArTseq GBS approach generated 10 K SNPs and 40 K high-quality DArT markers, which were located against the currently available bread and durum wheat reference genomes. The markers with known locations were distributed across all chromosomes with relatively well-balanced genome-wide coverage. The genetic analysis showed that the Spanish wheat landraces were clustered in different groups, thus representing genetic pools providing a range of allelic variation. The subspecies had a major impact on the population structure of the durum wheat landraces, with three distinct clusters that corresponded to subsp. durum, turgidum and dicoccon being identified. The population structure of bread wheat landraces was mainly biased by geographic origin.

Conclusions

The results showed broader genetic diversity in the landraces compared to a reference set that included commercial varieties, and higher divergence between the landraces and the reference set in durum wheat than in bread wheat. The analyses revealed genomic regions whose patterns of variation were markedly different in the landraces and reference varieties, indicating loci that have been under selection during crop improvement, which could help to target breeding efforts. The results obtained from this work will provide a basis for future genome-wide association studies.

Whole-genome diversity, population structure and linkage disequilibrium analysis of globally diverse wheat genotypes using genotyping-by-sequencing DArTseq platform

In this study, 129 wheat genotypes from globally diverse origins were genotyped using DArTseq (SilicoDArT and SNP) markers. After filtering markers for quality-filtering, 14,270 SilicoDArTs and 6484 SNPs were retained and used for genetic diversity, population structure and linkage disequilibrium analyses. The highest number of SilicoDArT and SNP markers mapped on genome A and B compared to genome D. In both marker types, polymorphism information content (PIC) values ranged from 0.1 to 0.5, while > 0.80% of SilicoDArTs and > 0.44% SNPs showed PIC value more than median (0.25%). Un-weighted Neighbor Joining cluster analysis and Bayesian-based model population structure grouped wheat genotypes into three and four clusters, respectively. Principal component analysis and discriminant analysis of principal component results showed highly match with cluster and population structure analysis. Linkage disequilibrium (LD) was more extensive in both marker types, while graphical display of LD decay for both marker types showed that LD declined in the region close to 15 kbp, where r 2-values corresponded to r 2 = 0.16. Overall, our genetic diversity analysis showed high level of variation in studied wheat genotypes, even though there was no relationship between wheat grouping and origins. This might be attributed to admixture level that occurred during long-term natural selection of wheat genotypes in different parts of the world. Highly diverse wheat genotypes used in this study may possess unique genes and are useful sources in breeding programs to improve grain yield and quality.