Genetic Diversity In Durum Wheat Research Articles

Genetic diversity of durum wheat (Triticum turgidum ssp. durum) to mitigate abiotic stress: Drought, heat, and their combination.

Drought and heat are the main abiotic constraints affecting durum wheat production. This study aimed to screen for tolerance to drought, heat, and combined stresses in durum wheat, at the juvenile stage under controlled conditions. Five durum wheat genotypes, including four landraces and one improved genotype, were used to test their tolerance to abiotic stress. After 15 days of growing, treatments were applied as three drought levels (100, 50, and 25% field capacity (FC)), three heat stress levels (24, 30, and 35°C), and three combined treatments (100% FC at 24°C, 50% FC at 30°C and 25% FC at 35°C). The screening was performed using a set of morpho-physiological, and biochemical traits. The results showed that the tested stresses significantly affect all measured parameters. The dry matter content (DM) decreased by 37.1% under heat stress (35°C), by 37.3% under severe drought stress (25% FC), and by 53.2% under severe combined stress (25% FC at 35°C). Correlation analyses of drought and heat stress confirmed that aerial part length, dry matter content, hydrogen peroxide content, catalase, and Glutathione peroxidase activities could be efficient screening criteria for both stresses. The principal component analysis (PCA) showed that only the landrace Aouija tolerated the three studied stresses, while Biskri and Hedhba genotypes were tolerant to drought and heat stresses and showed the same sensitivity under combined stress. Nevertheless, improved genotype Karim and the landrace Hmira were the most affected genotypes by drought, against a minimum growth for the Hmira genotype under heat stress. The results showed that combined drought and heat stresses had a more pronounced impact than simple effects. In addition, the tolerance of durum wheat to drought and heat stresses involves several adjustments of morpho-physiological and biochemical responses, which are proportional to the stress intensity.

Genetic Diversity of Durum Wheat (Triticum turgidum L. ssp. durum, Desf) Germplasm as Revealed by Morphological and SSR Markers.

Ethiopia is considered a center of origin and diversity for durum wheat and is endowed with many diverse landraces. This research aimed to estimate the extent and pattern of genetic diversity in Ethiopian durum wheat germplasm. Thus, 104 durum wheat genotypes representing thirteen populations, three regions, and four altitudinal classes were investigated for their genetic diversity, using 10 grain quality- and grain yield-related phenotypic traits and 14 simple sequence repeat (SSR) makers. The analysis of the phenotypic traits revealed a high mean Shannon diversity index (H' = 0.78) among the genotypes and indicated a high level of phenotypic variation. The principal component analysis (PCA) classified the genotypes into three groups. The SSR markers showed a high mean value of polymorphic information content (PIC = 0.50) and gene diversity (h = 0.56), and a moderate number of alleles per locus (Na = 4). Analysis of molecular variance (AMOVA) revealed a high level of variation within populations, regions, and altitudinal classes, accounting for 88%, 97%, and 97% of the total variation, respectively. Pairwise genetic differentiation and Nei's genetic distance analyses identified that the cultivars are distinct from the landrace populations. The distance-based (Discriminant Analysis of Principal Component (DAPC) and Minimum Spanning Network (MSN)) and model-based population stratification (STRUCTURE) methods of clustering grouped the genotypes into two clusters. Both the phenotypic data-based PCA and the molecular data-based DAPC and MSN analyses defined distinct groupings of cultivars and landraces. The phenotypic and molecular diversity analyses highlighted the high genetic variation in the Ethiopian durum wheat gene pool. The investigated SSRs showed significant associations with one or more target phenotypic traits. The markers identify landraces with high grain yield and quality traits. This study highlights the usefulness of Ethiopian landraces for cultivar development, contributing to food security in the region and beyond.

Turkish durum wheat conserved ex‐situ and in situ unveils a new hotspot of unexplored genetic diversity

AbstractDurum wheat (Triticum turgidum L.) is the 10th most cultivated crop and is a vital food source for human consumption. Genetic diversity in durum wheat is still an unexplored subject, and gene banks are filled with accessions waiting to be screened. Here, four different groups of durum wheat, Turkish and foreign cultivars, and in situ and ex situ landraces were evaluated for population structure and genetic diversity. A collection of 129 durum wheat accessions were genotyped, with a total of 6,357 markers (SilicoDArT, SNP [single‐nucleotide polymorphism], and simple sequence repeats [SSRs]). The highest mean allele number per marker (1.562) was obtained with SNP markers in ex situ landraces; the lowest mean allele number per marker (0.788) was obtained with SSR markers in the foreign cultivars. The minimum percentage of polymorphic loci was 38.70% observed with SSR markers in foreign cultivars; the maximum was 76.20% in SilicoDArT markers in ex situ landraces. According to Neighbor‐Joining analyses, the studied collection was divided into groups of cultivars and landraces, with some level of admixtures. Structure and principal coordinate analysis obtained distinct clusters for ex situ landraces and foreign cultivars, supported by Neighbor‐Joining analysis. A significant level of intergroup and intragroup variation was observed, and Turkish ex situ landraces were found as the most diverse and distinct group in the collection. Turkish landraces may be a promising source of novel allelic diversity that can be used in durum wheat breeding worldwide.

SSR markers and seed quality traits revealed genetic diversity in durum wheat (Triticum durum Desf.).

Genetic diversity and differences among durum-wheat cultivars evolved in various regions of the world are important for sustainable production in the current climate change scenario. Information regarding genetic differences was also important for the correct choice of parental material for the selection of high quality cultivars. Two elite and six obsolete cultivars of durum-wheat were characterized with 25-simple sequence repeats (SSR) markers. All accessions were evaluated for 2-agronomic-traits (Yield (Y) and Thousand-Kernel-Weight (TKW)) and 11 grain quality-traits (grain protein content (GPC), grain moisture contents (H), carotene content (CT), sedimentation test (SDS), gluten content (GC), gluten index (GI), semolina color index (L*, a*, b*) and alveographic parameters (W and P/L)) under randomized complete block design with three replication for two crop seasons (2015-2017). Genetic characterization through SSR markers revealed 126 alleles with an average of 5.04 alleles locus-1 and had average 0.79 polymorphism information content (PIC). The comparisons revealed that elite accessions were more productive in terms of grain yield and TKW, whereas obsolete accessions showed high GPC and end-use quality-traits. The generated dendrogram based on SSR markers, agronomic, seed quality-traits clearly differentiate the genotypes in two main groups obsolete and elite accessions. Analysis of correlation revealed a significant association between the traits TKW, Y, b*, a*, GPC, GC, SDS and H. High genetic diversity found between elite and obsolete cultivars for parameters such as yield, end-use quality and their correlation with SSR markers could help breeders for an eventual breeding program on durum-wheat.

The study of genetic diversity in a minicore collection of durum wheat genotypes using agro-morphological traits and molecular markers

The evaluation of genetic diversity in a gene pool contributes to the effective selection of genotypes and truncates the breeding time. In the present study, 96 durum wheat genotypes were evaluated for (1) genotypic diversity using two DNA marker systems: CAAT box-derived polymorphism (CBDP) and inter-simple sequence repeats (ISSR) markers and (2) phenotypic diversity using several drought-adaptive traits under rainfed conditions for two cropping seasons. Our results revealed that the ISSR primers produced 99 bands across the genotypes, the average of which was 6 fragments per primer, whereas CBDP primers generated 70 polymorphic bands, with an average of 5.3 fragments per primer. The values of marker index (MI) and polymorphism information content (PIC) indicated that CBDP markers were more efficient than ISSR markers for detection of genetic diversity in durum wheat. The average of PIC values for the CBDP and ISSR markers were 0.40 and 0.23, respectively. Based on the values of Shannon index (I) ICARDA population had a higher than CIMMYT population and the heterozygosis values confirmed these results. Dendrogram was created with a neighbor-joining clustering method. The studied genotypes were divided into five and seven groups based on data from the CBDP and ISSR markers, respectively, which was supported by principal coordinate analyses. The results of genotype by trait biplot analysis showed different patterns of interaction accessions and traits across years. High level of diversity among the studied accessions based on each studies trait was observed.

Evaluation of genetic diversity of durum wheat (Triticum durum desf.) genotypes using inter-simple sequence repeat (ISSR) and caat box-derived polymorphism (CBDP) markers

Evaluation of genetic diversity is the key principal for plant breeding, providing an opportunity to discover novel characters and alleles for breeders. In the present study, 69 durum wheat genotypes were investigated for genetic diversity using several CAAT box-derived polymorphism (CBDP) and inter-simple sequence repeat (ISSR) markers. Twelve CBDP and sixteen ISSR primers amplified a total of 115 and 160 polymorphic fragments with a mean of 9.58 and 10 fragments per primer, respectively. CBDP primers showed the higher mean values for informativeness parameters such as polymorphic information content (PIC), resolving power (Rp) and marker index (MI) in comparison with ISSR primers. The results of analysis of molecular variance (AMOVA) indicated that the highest proportion of genetic variance referred within populations. Furthermore, CBDP primers indicated high values for all genetic parameters. Besides, the highest values of genetic parameters including number of observed (Na) and effective alleles (Ne), Shannon?s information index (I) and Nei?s gene diversity (He) were estimated for Iranian durum wheat landraces. Cluster analysis based on each molecular technique classified all durum wheat genotypes into three main groups, so that the results of principal coordinate analysis (PCoA) supported the grouping patterns. As a result, the grouping pattern observed by ISSR primers was clearer than CBDP primers and grouped all samples based on their origins. However, Mantel?s coefficient correlation test illustrated the higher positive correlation (0.54) between both marker techniques. Hence, the use of these markers in combination with each other to evaluate the genetic diversity is recommended.

Applicability of CAAT Box-derived Polymorphism (CBDP) Markers for Analysis of Genetic Diversity in Durum Wheat

Progress in plant molecular tools has been resulted in the development of gene-targeted and functional marker systems. CAAT box region is a different pattern of nucleotides with a consensus sequence, GGCCAATCT, which situated upstream of the start codon of eukaryote genes and plays an important role during transcription. In the present study, several CAAT box-derived polymorphism (CBDP) primers were used for fingerprinting in mini-core collection of durum wheat (including internationally developed breeding lines and Iranian landraces). Twelve selected primers amplified 98 loci, of which all were polymorphic. The average values of the polymorphism information content (PIC) and resolving power (Rp) were 0.31 and 9.16, respectively, indicating a high level of variability among studied genotypes. Analysis of molecular variance (AMOVA) indicated that 92% of the total variation resided among populations. The values of the percentage polymorphic bands (PPL), the observed (Na) and effective (Ne) number of alleles, Nei’s gene diversity (He) and Shannon’s information index (I) for Iranian landraces were higher than the breeding lines. The Fandendrogram obtained by cluster analysis grouped all individuals into three main clusters. Our results showed a remarkable level of genetic diversity among studied durum wheat, especially among Iranian landraces, which can be interest for future breeding programs. More importantly, the present study also revealed that CBDP technique was efficient and powerful tool to assess genetic diversity in wheat germplasm. Hence, this technique could be employed individually or in combination with other molecular markers to evaluate genetic diversity and relations among different species.

A Whole Genome DArTseq and SNP Analysis for Genetic Diversity Assessment in Durum Wheat from Central Fertile Crescent.

Until now, little attention has been paid to the geographic distribution and evaluation of genetic diversity of durum wheat from the Central Fertile Crescent (modern-day Turkey and Syria). Turkey and Syria are considered as primary centers of wheat diversity, and thousands of locally adapted wheat landraces are still present in the farmers’ small fields. We planned this study to evaluate the genetic diversity of durum wheat landraces from the Central Fertile Crescent by genotyping based on DArTseq and SNP analysis. A total of 39,568 DArTseq and 20,661 SNP markers were used to characterize the genetic characteristic of 91 durum wheat land races. Clustering based on Neighbor joining analysis, principal coordinate as well as Bayesian model implemented in structure, clearly showed that the grouping pattern is not associated with the geographical distribution of the durum wheat due to the mixing of the Turkish and Syrian landraces. Significant correlation between DArTseq and SNP markers was observed in the Mantel test. However, we detected a non-significant relationship between geographical coordinates and DArTseq (r = -0.085) and SNP (r = -0.039) loci. These results showed that unconscious farmer selection and lack of the commercial varieties might have resulted in the exchange of genetic material and this was apparent in the genetic structure of durum wheat in Turkey and Syria. The genomic characterization presented here is an essential step towards a future exploitation of the available durum wheat genetic resources in genomic and breeding programs. The results of this study have also depicted a clear insight about the genetic diversity of wheat accessions from the Central Fertile Crescent.

Genetic diversity reduction in improved durum wheat cultivars of Morocco as revealed by microsatellite markers

ABSTRACT It has been argued that genetic diversity in crop varieties has been on the decline in recent times due to plant breeding. This can have serious consequences for both the genetic vulnerability of crops and their plasticity when responding to changes in production environments. It is, therefore, vital for plant breeding programs to maintain sufficient diversity in the cultivars deployed for multi-period cultivation. In this study, to understand the temporal genetic diversity in durum wheat, 21 improved durum wheat cultivars released in Morocco, since 1956 and five exotic cultivars currently used in crossing programs were analyzed using 13 microsatellite markers. The analysis revealed a total of 44 alleles and average genetic diversity of 0.485 with genetic distances ranging from 0.077 to 0.846 at 13 microsatellite loci in Moroccan durum wheat cultivars. All the durum cultivars of Morocco could be distinguished using the 13 microsatellite markers. The total number of alleles and unique alleles were highest in cultivars developed before 1990, decreasing in cultivars developed during the 1990s and 2000s, indicating that recent durum breeding efforts have reduced allelic richness in recent cultivars. Thus, deployment of exotic durum wheat lines in breeding programs could enhance genetic diversity in durum wheat cultivars.

Genotyping by sequencing transcriptomes in an evolutionary pre-breeding durum wheat population

The genetic diversity in durum wheat, Triticum turgidum durum, has been strongly reduced since the domestication of the wild Triticum turgidum dicoccoides. Monitoring durum wheat composite crosses incorporating related tetraploid taxa, such as wild and domesticated emmer wheat, is a suitable evolutionary pre-breeding method. Transcriptome sequencing paves the way for a genomic survey of single nucleotide polymorphisms (SNPs) segregating in such populations, offering the possibility of genotyping by sequencing to use these resources in genome-wide association studies (GWAS) and genomic selection (GS) programs. Evolutionary Pre-breeding pOpulation (EPO) is an evolutionary durum wheat pre-breeding population. Sequencing the transcriptome of 179 durum wheat lines (175 from EPO) led to the detection of 103,262 SNPs on two reference transcriptomes: one from the International Wheat Genome Sequencing Consortium and one assembled de novo on durum wheat. Using strict filtering to remove dubious heterozygous SNPs, EPO genetic diversity was eventually described with 76,188 high-confidence SNPs. The percentage of missing genotyping data depended on the expression level, and 88 individuals out of 175 were genotyped per SNP on average. Using the 3B pseudo-molecule of bread wheat, the transcription and diversity levels were shown to be higher in distal regions than in proximal regions, but SNPs were available throughout the chromosomes. Assuming good synteny with Hordeum, the trend was similar on the 14 chromosomes of the durum wheat genome. EPO hosts a high level of diversity, has a number of SNPs in low linkage disequilibrium (<40 Mb) and would be well suited for GWAS and GS programs.

The climate of the zone of origin of Mediterranean durum wheat (Triticum durum Desf.) landraces affects their agronomic performance

The genetic diversity of durum wheat (Triticum durum Desf.) is held by landraces, which are generally considered to be endemic to a particular region to which they are well adapted. To evaluate the effect of climate in the countries of origin on their agronomic performance, 172 durum wheat landraces from 21 Mediterranean countries were grown in northeastern Spain. Average long-term climatic data of the main wheat-growing areas in each country of origin allowed us to identify four climatic zones in the Mediterranean Basin, steadily varying from warm and dry to cool and wet. The phenology, biomass, and yield of landraces were affected by the climatic zone of origin. The climatic zone accounted for 32.8, 28.3 and 14.5 % of variance for days to anthesis, plant height, and grain filling rate, respectively. The number of days to heading and anthesis steadily increased when moving from the warmest and driest zone of origin to the coldest and wettest one. Landraces collected in the warmest and driest zone had a smaller biomass, a lower chlorophyll content in the flag leaf, more fertile tillers, spikes and grains m−2, a lower grain filling rate, lighter grains, and lower yields than those originated in colder and wetter zones. Landraces collected in countries with high solar radiation showed a shorter cycle until anthesis and smaller height and biomass accumulation, while higher temperatures after anthesis resulted in more tillers and spikes. Landraces from countries with high potential evapotranspiration during grain filling had significantly lower grain filling rates and grain weight.

Genetic diversity of durum wheat as determined by AFLP in fluorescence

The DNA of fifteen Italian cultivars of durum wheat (Triticum turgidum L. ssp. durum) were analyzed by in fluorescence amplified fragment length polymorphism (fAFLP) in order to obtain the characteristic fingerprintings of genotypes and assess their genetic relatedness. Among 64 combinations of fluorescence labelled primers, three different combinations were chosen as producing a total of 6630 AFLP fragments, 2277 (34.3 %) of them being polymorphic. By using this fAFLP methodology a DNA fingerprinting of each durum wheat cultivar was generated for genotype identification. Analysis of the genetic relationships show the low variability among durum wheat cultivars.

Nucleotide-binding site (NBS) profiling of genetic diversity in durum wheat

Molecular markers are effective tools to investigate genetic diversity for resistance to pathogens. NBS (nucleotide-binding site) profiling is a PCR (polymerase chain reaction)-based approach to studying genetic variability that specifically targets chromosome regions containing R-genes and R-gene analogues. We used NBS profiling to measure genetic diversity among 58 accessions of durum wheat. Mean polymorphism rates detected using MseI and AluI as restriction enzymes were 34% and 22%, respectively. Mean number of polymorphisms per enzyme-primer combination was equal to 23.8 +/- 5.9, ranging from 13 to 31 polymorphic bands. In total, 96 markers over 190 indicated a good capacity to discriminate between accessions (the polymorphic index content ranging from 0.30 to 0.50). The results obtained with NBS profiling were compared with simple sequence repeat (SSR) and amplified fragment length polymorphism (AFLP) data of the same set of accessions. The genetic distances computed with 190 NBS profiling markers were in close agreement with those obtained with AFLP and SSR markers (r = 0.73 and 0.76, respectively). Our results indicate that NBS profiling provides an effective means to investigate genetic diversity in durum wheat.

Genetic Diversity in Durum Wheat Based on RFLPs, Morphophysiological Traits, and Coefficient of Parentage

Estimation of genetic diversity present in gene pools is an important determination for breeding programs. This study was conducted to determine the level of variation in durum wheat cultivars (Triticum turgidum L. var durum) based on different measures. Genetic diversity in durum wheat was measured in a collection of 113 improved cultivars and landraces of diverse ecogeographical origin by means of restriction fragment length polymorphism (RFLP), morphophysiological traits, and coefficient of parentage (COP). Thirty‐nine clones and a single restriction enzyme were used to measure the RFLP‐based genetic distance. Average taxonomic distances were calculated for the morphophysiological traits evaluated in four location‐years. Lower genetic distances were observed for both RFLP and morphophysiological traits for the improved cultivars and for some landraces from Morocco and Jordan, while genetic distances were larger for the rest of the landraces. Patterns of variation for morphophysiological traits were associated with days to heading, plant height, and harvest index. Landraces contained 99% of the total fragments observed in the pool of improved varieties and showed 13% unique fragments. Coefficient of parentage analysis revealed 15 ancestral lines that contributed 72% of the genetic make up of improved cultivars. Thirty‐nine different ancestors contributed to the remaining 28%. Correlation of distances based on different measures was higher for average taxonomic distance and Nei's genetic distance (r = 0.47) while COP relationship with the other two measures was lower. Narrower genetic diversity in breeding lines based on the measures used, suggests the utilization of other sources of variation.

Evaluation of Lines Derived from Wild Emmer Chromosome Substitutions: II. Agronomic Traits

Improving yield and other agronomic traits in durum wheat(Triticum turgidum L. var. durum) depends on adequate genetic diversity. Genetic diversity in durum wheat is limited. An accession of wild emmer (Triticum turgidum L. var. dicoccoides) with high protein concentration was used to develop a complete set of ‘Langdon’ (T. dicoccoides) [LDN(DIC)] substitution lines. This study was conducted evaluate the potential of using these substitution lines as parents for deriving lines with acceptable agronomic traits. Each of the 14 substitution lines and Langdon were crossed to a common male parent, ‘Vic’. Parents, F2:4, and F2:5 lines were grown in replicated trials at two locations in North Dakota in 1989 and 1991, respectively. Days to heading, plant height, grain yield, and kernel weight were measured. Population means and genetic variances were compared to those of the Langdon/Vic population to identify substitution lines that conferred favorable agronomic characteristics to derived lines. Heritabilities were estimated based on parent‐offspring regression and variance components. All substitution populations except these with LDN(DIC) 4B and 5B were earlier in heading date than the Langdon/Vic population. Langdon dicoccoides substitution populations 1A, 2A, 4A, 6A, 7A, 1B, 4B, 5B, and 6B were significantly shorter than the Langdon/Vic population. Langdon dicoccoides substitution population 4B had higher yield than the Langdon/Vic population. Langdon dicoccoides substitution populations 2A, 3A, and 5B had a mean kernel weight greater than the Langdon/Vic population. Our data suggests that there is a possibility of deriving lines with high grain yield and good agronomic traits from LDN(DIC) 4B.