Model-based Population Structure Research Articles

Genetic Diversity and Population Structure of Cacao (Theobroma cacao L.) Germplasm from Sierra Leone and Togo Based on KASP–SNP Genotyping

Cacao (Theobroma cacao L.) is a tropical tree species belonging to the Malvaceae, which originated in the lowland rainforests of the Amazon. It is a major agricultural commodity, which contributes towards the Gross Domestic Product of West African countries, where it accounts for about 70% of the world’s production. Understanding the genetic diversity of genetic resources in a country, especially for an introduced crop such as cacao, is crucial to their management and effective utilization. However, very little is known about the genetic structure of the cacao germplasm from Sierra Leone and Togo based on molecular information. We assembled cacao germplasm accessions (235 from Sierra Leone and 141 from Togo) from different seed gardens and farmers’ fields across the cacao-producing states/regions of these countries for genetic diversity and population structure studies based on single nucleotide polymorphism (SNP) markers using 20 highly informative and reproducible KASP–SNPs markers. Genetic diversity among these accessions was assessed with three complementary clustering methods, including model-based population structure, discriminant analysis of principal components (DAPC), and phylogenetic trees. STRUCTURE and DAPC exhibited some consistency in the allocation of accessions into subpopulations or groups, although some discrepancies in their groupings were noted. Hierarchical clustering analysis grouped all the individuals into two major groups, as well as several sub-clusters. We also conducted a network analysis to elucidate genetic relationships among cacao accessions from Sierra Leone and Togo. Analysis of molecular variance (AMOVA) revealed high genetic diversity (86%) within accessions. A high rate of mislabeling/duplicate genotype names was revealed in both countries, which may be attributed to errors from the sources of introduction, labeling errors, and lost labels. This preliminary study demonstrates the use of KASP–SNPs for fingerprinting that can help identify duplicate/mislabeled accessions and provide strong evidence for improving accuracy and efficiency in cacao germplasm management as well as the distribution of correct materials to farmers.

Assessment of genetic diversity and population structure of U.S. Polypay sheep from breed origins to future genomic selection.

Knowledge of past and present genetic diversity within a breed is critical for the design and optimization of breeding programs as well as the development of strategies for the conservation of genetic resources. The Polypay sheep breed was developed at the U.S. Sheep Experiment Station (USSES) in 1968 with the goal of improving productivity in Western U.S. range flocks. It has since flourished in the more intensively managed production systems throughout the U.S. The genetic diversity of the breed has yet to be documented. Therefore, the primary objective of this study was to perform a comprehensive evaluation of the genetic diversity and population structure of U.S. Polypay sheep using both pedigree- and genomic-based methods. Pedigree data from 193 Polypay flocks participating in the National Sheep Improvement Program (NSIP) were combined with pedigree records from USSES (n = 162,997), tracing back to the breed's origin. A subset of these pedigreed sheep from 32 flocks born from 2011 to 2023 were genotyped with the GGP Ovine 50K BeadChip containing 51,867 single nucleotide polymorphisms (SNPs). Four subgroups were used for the pedigree-based analyses: 1) the current generation of animals born in 2020-2022 (n = 20,701), 2) the current generation with a minimum of four generations of known ancestors (n = 12,685), 3) only genotyped animals (n = 1,856), and 4) the sires of the current generation (n = 509). Pedigree-based inbreeding for the full population was 2.2%, with a rate of inbreeding of 0.22% per generation. Pedigree-based inbreeding, Wright's inbreeding, and genomic inbreeding based on runs of homozygosity were 2.9%, 1.3%, and 5.1%, respectively, for the genotyped population. The effective population size ranged from 41 to 249 for the pedigree-based methods and 118 for the genomic-based estimate. Expected and observed heterozygosity levels were 0.409 and 0.403, respectively. Population substructure was evident based on the fixation index (FST), principal component analysis, and model-based population structure. These analyses provided evidence of differentiation from the foundation flock (USSES). Overall, the Polypay breed exhibited substantial genetic diversity and the presence of a population substructure that provides a basis for the implementation of genomic selection in the breed.

Genetic diversity and population structure of maize inbred lines using phenotypic traits and single nucleotide polymorphism (SNP) markers

Understanding germplasm’s genetic diversity is essential for developing new and improved cultivars with stable yields under diverse environments. The objective of this study was to determine the genetic diversity and population structure of 128 maize inbred lines sourced from the International Institute of Tropical Agriculture (IITA), the International Maize and Wheat Improvement Centre (CIMMYT), and the University of KwaZulu-Natal (UKZN) using 11,450 informative single nucleotide polymorphism (SNP) markers. The inbred lines revealed highly significant (p < 0.001) levels of variability for the key phenotypic traits. The SNP markers had a mean gene diversity (GD) and polymorphic information content (PIC) of 0.40 and 0.31, respectively, indicating the existence of substantial genetic variation across the germplasm panel. The model-based population structure analysis identified three subpopulations (K = 3) among the inbred lines. This corroborated the phylogenetic analysis using phenotypic traits and molecular markers which classified the inbred lines into three groups. The findings of this study identified considerable genetic diversity for the selection of inbred lines with favourable alleles for multiple traits and could be useful to initiate marker-assisted selection (MAS) to identify significant loci associated with agronomic performance and multiple-stress tolerance.

Prioritization of Microsatellite Markers Linked with Drought Tolerance Associated Traits in Chickpea (Cicer arietinum L.)

Background: Being a vital source of high-quality dietary protein, chickpea is an unavoidable legume. The present investigation was performed to study the applicability of the microsatellite markers linked with drought tolerance in Indian chickpea genotypes collected from different genetic background. Methods: In Rabi 2021-22, forty chickpea genotypes including national check for drought tolerance, elite cultivars, released varieties and advanced breeding lines were screened employing forty microsatellite markers linked with drought tolerance associated traits. Results: Among forty drought tolerance related microsatellite markers, twenty-six were found to be polymorphic and produced a total of 66 alleles, with a mean of 2.5 alleles per locus. Genotype NCPGR127 had highest numbers of alleles, gene diversity and polymorphism information content tracked by genotype TR19. These genotypes may be used for selecting drought tolerant genotypes through marker assistant selection (MAS). Model-based population structure analysis clearly distinguished the drought tolerant genotypes including ICC4958, JG74, JAKI9218, JG16, JG6, JG14 and JG11. Principle coordinate analysis (PCoA) and analysis of molecular variance (AMOVA) further confirmed these results. Findings of the present investigation have a greater potential for further utilization in breeding of drought specific chickpea cultivar(s).

Genome size, genetic diversity, and phenotypic variability imply the effect of genetic variation instead of ploidy on trait plasticity in the cross-pollinated tree species of mulberry.

Elucidation of genome size (GS), genetic and phenotypic variation is the fundamental aspect of crop improvement programs. Mulberry is a cross-pollinated, highly heterozygous tree eudicot, and comprised of huge ploidy variation with great adaptability across the world. However, because of inadequate information on GS, ploidy-associated traits, as well as the correlation between genetic and phenotypic variation hinder the further improvement of mulberry. In this present research, a core set of 157 germplasm accessions belonging to eight accepted species of Morus including promising functional varieties were chosen to represent the genetic spectrum from the whole germplasm collection. To estimate the GS, accessions were subjected to flow cytometry (FCM) analysis and the result suggested that four different ploidies (2n = 2x, 3x, 4x, and 6x) with GS ranging from 0.72±0.005pg (S-30) to 2.89±0.015pg (M. serrata), accounting~4.01 fold difference. The predicted polyploidy was further confirmed with metaphase chromosome count. In addition, the genetic variation was estimated by selecting a representative morphologically, diverse population of 82 accessions comprised of all ploidy variations using simple sequence repeats (SSR). The estimated average Polymorphism Information Content (PIC) and expected heterozygosity showed high levels of genetic diversity. Additionally, three populations were identified by the model-based population structure (k = 3) with a moderate level of correlation between the populations and different species of mulberry, which imply the effect of genetic variation instead of ploidy on trait plasticity that could be a consequence of the high level of heterozygosity imposed by natural cross-pollination. Further, the correlation between ploidies, especially diploid and triploid with selected phenotypic traits was identified, however, consistency could not be defined with higher ploidy levels (>3x). Moreover, incite gained here can serve as a platform for future omics approaches to the improvement of mulberry traits.

HETEROSIS AND HETEROTIC GROUPING EFFECTS ON GRAIN YIELD, HEIGHT, TILLER DENSITY, AND DAYS TO HEADING IN HYBRID RICE (ORYZA

Heterotic groups are necessary for high vigor in hybrid rice. However, hybrids produced from crosses between parents from different rice subspecies (i.e., Indica × Japonica) have extensive incompatibility issues exhibited by low seed sets. The study objectives were to evaluate the heterosis in grain yield and yield-related traits between hybrids produced from low and high parental genetic distances (PGDs) and demonstrate the heterotic group approach in rice. From PGDs, eight and three hybrids were assigned to the low and high PGD hybrid groups, respectively. Neighbor-joining clustering and model-based population structure analyses classified the hybrid parents into four heterotic groups, with the low and high PGD hybrid groups found consisting of intra-subpopulation and intersubpopulation crosses, respectively. Replicated yield trials conducted at Beaumont, Texas, transpired in 2019 and 2020. The hybrids exhibited normal seed sets, with at least one of each hybrid's parents determined to possess the wide compatibility S5n allele necessary for normal seed sets in wide crosses. Trait and standard heterosis values estimates included the number of days to heading, plant height, tiller density, and grain yield. Higher trait values and heterosis for tiller density and grain yield occurred in the high than the low PGD hybrid group, especially in the inter-subpopulation crosses with indica rice. PGD had consistent positive correlations with heterosis for grain yield (r = 0.41 to 0.60) and tiller density (0.28 to 0.36) in both years. PGDs aid in determining highly heterotic cross combinations for tiller density and grain yield and in forming heterotic groups. Heterotic grouping is advisable through cluster and structure analyses of genome-wide markers instead of identifying genetically-distant crosses based on pedigree information.

Morpho-physiological screenings and molecular analysis of west sumatra rice genotypes under submergence stress

This study investigates the submergence tolerance level of 14 rice genotypes by morpho-physiological and molecular analyses of Sub1 alleles. IR64-Sub1 was used as a submergence tolerant check. The submergence screenings were conducted by submerging 14-days-old seedlings in water tanks for 14 days while molecular analysis was conducted using 14 Sub1 linked markers. The results showed that 5 tested genotypes, namely Inpari 48 Blas, Mundam Putiah, Batang Piaman, Banang Pulau and Pulau Sijunjung, recorded high survival rates (SR) of 80% to 100% under submergence stress. PCR-based identification of the Sub1 alleles confirmed that several tested genotypes carry Sub1A and Sub1C, but not all were expressed in their phenotypic performance towards submergence. IR64-Sub1 and Batang Piaman not only showed well-adaptation towards submergence by maintaining lower elongation (&lt;20%) and less chlorophyll content change (TCC) (&lt;30%) but were also equipped with the Sub1A allele. These genotypes potentially provide good phenotypic and genotypic performance under submergence stress conditions. Additionally, based on population structure analysis, these genotypes were grouped into 3 clusters, of which 35.71% are pure accessions, while the remaining 64.29% have admixture ancestry between populations 1, 2 and 3. The data in model-based population structure and UPGMA dendrogram supported that rice genotypes in this study have 3 well-differentiated genetic populations and admixtures. Most genotypes have a close genetic relationship with Nei’s similarity index ranging from 0.571 to 0.893.

Population structure and genetic diversity of a germplasm for hybrid breeding in rye (Secale cereale L.) using high-density DArTseq-based silicoDArT and SNP markers

Investigating genetic structure and diversity is crucial for the rye hybrid breeding strategy, leading to improved plant productivity and adaptation. The present study elucidated the population structure and genetic diversity of 188 rye accessions, comprising 94 pollen fertility restoration lines (RF) and 94 cytoplasmic male-sterile (CMS) lines with Pampa sterilizing cytoplasm using SNP and silicoDArT markers from the diversity array technology (DArT)-based sequencing platform (DArTseq). Expected heterozygosity (He) and Shanon’s diversity (I) indexes varied slightly between marker systems and groups of germplasms (He = 0.34, I = 0.51 for RF and CMS lines genotyped using SNPs; He = 0.31, I = 0.48, and He = 0.35, I = 0.53 for RF and CMS using silicoDArTs, respectively). ANOVA indicated moderate variation (7%) between RF and CMS breeding materials. The same parameter varied when chromosome-assigned markers were used and ranged from 5.8% for 5R to 7.4% for 4R. However, when silicoDArT markers were applied, the respective values varied from 6.4% (1R) to 8.2% (3R and 4R). The model-based (Bayesian) population structure analysis based on the total marker pool identified two major subpopulations for the studied rye germplasm. The first one (P1) encompasses 93 RF accessions, and the second one (P2) encompasses 94 CMS and one RF accession. However, a similar analysis related to markers assigned to selected chromosomes failed to put plant materials into any of the populations in the same way as the total marker pool. Furthermore, the differences in grouping depended on marker types used for analysis.

Genetic Characterization and Population Structure of Pea (Pisum sativum L.) by Molecular Markers against Rust (Uromyces viciae-fabae) in Newly Developed Genotypes

The understanding of the genetic diversity of germplasm of any crop is necessary for genetic improvement. Pea (Pisum sativum L.) is a very important legume crop that provides protein and several essential vitamins, carbohydrates, and minerals. The genetic diversity and population structure of pea germplasm consisted of 115 entries of Australian accessions and 4 entries of Indian varieties used as checks with varying responses and severities of rust, which were analysed using 31 polymorphic SSR (Simple Sequence Repeats) markers. The combination of the markers revealed that 78 alleles were present at 32 loci. It was also observed that each marker had three alleles with an average PIC (Polymorphic Information Content) value of 0.272. The population structure analysis showed the genetic differentiation of the entries. The model-based population structure grouped the entries into three sub-populations of SP1, SP2, and SP3 having 37, 35, and 32 entries, respectively with 15 entries as admixtures. AMOVA (Analysis of Molecular Variance) disclosed that there was 56% variation among the individuals and 20% within the population. A mean fixation index (Fst) of 0.240 among the pea entries exhibited relatively significant variation in population. This study provides basic information to select parental lines for developing rust resistant varieties to meet the ultimate goal of sustainable agriculture.

Analysis of genetic diversity and population structure of oilseed crop noug (Guizotia abyssinica) accessions collected from Ethiopia.

Noug is an Ethiopian indigenous oilseed crop cultivated primarily for its oil and various economic importance. Evaluating the extent of genetic diversity within and among populations is one of the most important steps in breeding and conservation measures. Thus, this study aimed to uncover the extent of genetic diversity and population structure of noug accessions collected from different regions of Ethiopiausing microsatellite markers. A total of 161 accessions from fourteen regions of Ethiopia, including some from Eritrea using 13 microsatellite markers were analyzed. All the 13 microsatellite markers were polymorphic and highly informative with a mean PIC value of 0.82. The analysis generated a total of 158 alleles with a mean of 12.15 per locus. The overall mean of Shannon information index and heterozygosity/gene diversity were 1.57 and 0.74, respectively suggesting the presence of higher genetic diversity across the collection regions. AMOVA revealed that 96.06% of the total genetic variation was attributed to within populations while only 3.94% was attributed to among populations. Likewise, the dendrogram clustering, PCoA, and the model-based population structure analysis didn't exactly corresponded the grouping of the genotypes according to their regions of origin. The microsatellites used in the present study are highly informative and could be targeted for developing markers forfuture marker-assisted breeding. Genotypes collected from Shewa, Wollo, Gojjam, Tigray, and B/G showed a higher genetic diversity and private alleles as compared to other populations. Hence, these areas can be considered as hotspots which could help for the identification of genotypes that can be used in breeding programs as well as for the implementation of further conservation programs.

Assessment of Genetic Diversity and Discovery of Molecular Markers in Durian (Durio zibethinus L.) in China

Durian (Durio zibethinus L.) is a crop of economic and health importance globally. Efforts are being made to revamp China’s only successful commercial-scale durian plantations in Hainan; however, their genetic base is unknown. Therefore, the present study was undertaken to assess the genetic base and population structure of 32 genotypes in durian plantation sites in Hainan, China, and develop simple sequence repeat (SSR) markers by whole genome sequencing through restriction site-associated DNA sequencing technology to facilitate germplasm conservation and breeding. The results from identity by state (IBS), phylogenetic tree, population structure, and principal component analysis grouped the 32 genotypes into two clusters/sub-populations. Based on IBS, genotypes in Cluster I are largely duplicated genotypes; however, results from the model-based population structure demonstrated that most of the genotypes in Sub-population II shared a common genetic background with those in Sub-population I/Cluster I. The results revealed that the core durian collection in the plantation sites in Hainan include D24, D101, MSW, JH, D163, HFH, and NLX-5. In addition, we developed a total of 79,178 SSR markers with varied lengths and amplicon sizes. The genetic diversity and population structure reported in this study will be useful for durian conservation and utilization. In addition, the discovered and developed SSR markers will lay the foundation for molecular breeding via marker-assisted selection, quantitative trait loci mapping, and candidate gene discovery and validation.

Genetic diversity and population structure of modern Bulgarian and foreign durum wheat based on microsatellite and agronomic data

The genetic variation and population structure of a panel of 90 durum wheat (Triticum durum desf.) consisting of 62 varieties and breeding lines originating from two agro-ecological zones in Bulgaria (Northern and Southern Bulgaria) and 28 introduced varieties from South–western, Central and Eastern Europe, and the USA were determined by 34 microsatellite markers (SSR). The genetic diversity in the modern durum wheat was 0.5612 with 6.88 alleles per locus. Model-based population STRUCTURE analysis identified two sub-populations (K = 2) separating the South Bulgarian varieties (SP1) from all others (SP2), including South-Western, Central-Eastern European and North Bulgarian ones. Subsequent genetic structure analysis at K = 4 revealed an additional division of each sub-population into two (SP1-2, SP1-4, SP2-1, SP2-3). DAPC analysis and UPGMA dendrogram based on SSR data were in excellent agreement with the Subpopulations defined by STRUCTURE analysis. The Principal Component Analysis (PCA) revealed that among the studied 5 agronomically important traits the correlation between grain yield and plant height was the highest and distinguished 10 varieties and advanced breeding lines from Southern Bulgaria (SP1-2 and SP1-4) as most promising in regard to yield stability. This study showed a good relationship between the genetic and phenotypic population structures according to the division of the genotypes by their agro-geographical origin. It will be useful for both breeders and farmers and could serve as a fundament for durum wheat improvement programs under drought prone environmental conditions.

Morpho-genetic screening and population structure analysis of Capsicum landraces of North-eastern Himalayan regions of India

ABSTRACT North-eastern Himalayan (NEH) region of India possesses numerous unique and traditionally important Capsicum landraces. The extent of phenotypic variation and phylogenetic relationship of the NEH Capsicum landraces is poorly understood. Therefore, Capsicum landraces consisting of 34 Capsicum annuum L., 5 C. chinense Jacq. and 57 C. frutescens L, that were collected from different states NEH region of India, were studied for morpho-genetic diversity. Accessions were agro-morphologically characterised using the IPGRI minimal descriptors. Genetic diversity analysis was done using 20 microsatellite markers spanning all 13 linkage groups of Capsicum. Multivariate analyses indicated that C. frutescens accessions were agro-morphologically different from both C. annuum and C. chinense. On an average, 3.6 alleles per locus were detected. Considerable genetic diversity (polymorphic information content, PIC = 0.46) was found within the accessions. The phylogenetic and model-based population structure analyses classified the landraces into two to three groups with varied species homogeneity with a majority of members in a cluster belonging to the same species. This study provides important information on the morpho-agronomic variability and genetic structure of chilli landraces of northeastern India which will be useful to identify groups with similar genetic backgrounds for conservation and effective selection of parents for future breeding programme.

Genetic characterization of cultivated apple (Malus x domestica Borkh.) in Morocco using microsatellite (SSR) markers

Genetic diversity of 27 apple genotypes from four geographical regions of Morocco was analyzed using 26 simple sequence repeat (SSR) primers. In total, 195 polymorphic SSR alleles were detected, with sizes ranging from 78 to 209 bp. The results obtained for the average number of alleles per locus (7.5), effective number of alleles (4.62), Shannon information index (1.66), expected heterozygosity (0.76), observed heterozygosity (0.74) and polymorphism information content (0.76) showed a moderate level of polymorphism, which suggests that Moroccan apple cultivars exhibit significant genetic diversity. Over the 26 SSR loci used, the probability of identity P (ID) was 4.62 10 −29 indicating that most markers were highly discriminating and powerful for cultivars characterization. The principal coordinate analysis and hierarchical classification suggested the presence of four well defined groups, which was confirmed later by model based population structure. Furthermore, strong genetic differentiation between these four groups was also detected (FST = 0.28) . Most of the individuals segregated into the four groups showing a membership coefficient greater than 0.80, which indicates their better genetic integrity. A parentage analysis, however, shows that cultivars from the four regions are minimally hybridized. After comparing SSR profiles and genotypes names, we conclude that the problem of homonyms and/or labeling errors appear in the studied cultivars.Thus, based on genetic profiles, two individuals (Beldi 1/Beldi 2 and Laakri 5/Laakri 6) found to be duplicated. Additionally, some cultivars with the same name are grouped in different clusters suggesting the existence of possible homonymy. Lastly, the present work confirms the usefulness of SSR markers for the elimination of duplications and characterization of diversity and hybrid characters of apple genotypes in Morocco.

Assessing Population Structure and Genetic Diversity in US Suffolk Sheep to Define a Framework for Genomic Selection.

Long-term sustainability of breeds depends on having sufficient genetic diversity for adaptability to change, whether driven by climatic conditions or by priorities in breeding programs. Genetic diversity in Suffolk sheep in the United States was evaluated in four ways: 1) using genetic relationships from pedigree data [(n = 64 310 animals recorded in the US National Sheep Improvement Program (NSIP)]; 2) using molecular data (n = 304 Suffolk genotyped with the OvineHD BeadChip); 3) comparing Australian (n = 109) and Irish (n = 55) Suffolk sheep to those in the United States using molecular data; and 4) assessing genetic relationships (connectedness) among active Suffolk flocks (n = 18) in NSIP. By characterizing genetic diversity, a goal was to define the structure of a reference population for use for genomic selection strategies in this breed. Pedigree-based mean inbreeding level for the most recent year of available data was 5.5%. Ten animals defined 22.8% of the current gene pool. The effective population size (Ne) ranged from 27.5 to 244.2 based on pedigree and was 79.5 based on molecular data. Expected (HE) and observed (HO) heterozygosity were 0.317 and 0.306, respectively. Model-based population structure included 7 subpopulations. From Principal Component Analysis, countries separated into distinct populations. Within the US population, flocks formed genetically disconnected clusters. A decline in genetic diversity over time was observed from both pedigree and genomic-based derived measures with evidence of population substructure as measured by FST. Using these measures of genetic diversity, a framework for establishing a genomic reference population in US Suffolk sheep engaged in NSIP was proposed.

Genetic Diversity, Population Structure and Linkage Disequilibrium Analyses in Tropical Maize Using Genotyping by Sequencing.

Several maize breeding programs in India have developed numerous inbred lines but the lines have not been characterized using high-density molecular markers. Here, we studied the molecular diversity, population structure, and linkage disequilibrium (LD) patterns in a panel of 314 tropical normal corn, two sweet corn, and six popcorn inbred lines developed by 17 research centers in India, and 62 normal corn from the International Maize and Wheat Improvement Center (CIMMYT). The 384 inbred lines were genotyped with 60,227 polymorphic single nucleotide polymorphisms (SNPs). Most of the pair-wise relative kinship coefficients (58.5%) were equal or close to 0, which suggests the lack of redundancy in the genomic composition in the majority of inbred lines. Genetic distance among most pairs of lines (98.3%) varied from 0.20 to 0.34 as compared with just 1.7% of the pairs of lines that differed by <0.20, which suggests greater genetic variation even among sister lines. The overall average of 17% heterogeneity was observed in the panel indicated the need for further inbreeding in the high heterogeneous genotypes. The mean nucleotide diversity and frequency of polymorphic sites observed in the panel were 0.28 and 0.02, respectively. The model-based population structure, principal component analysis, and phylogenetic analysis revealed three to six groups with no clear patterns of clustering by centers-wise breeding lines, types of corn, kernel characteristics, maturity, plant height, and ear placement. However, genotypes were grouped partially based on their source germplasm from where they derived.

Analysis of parental genetic diversity and its impact on grain yield and quality of japonica hybrid rice in northern China

The relationship between parental genetic differences and the quality and yield of japonica hybrid rice strongly influences japonica hybrid rice breeding. In this study, 137 parental lines of japonica hybrid rice were genotyped using 8K rice SNP-Chips to characterize their genetic diversity, population structure, and indica-genotype proportion. The genetic diversity of total parental lines averaged 0.264, with values of 0.287 for restorer lines and 0.148 for the sterile lines. The introduction of indica lineage increased the genetic diversity of restorer lines relative to that of sterile lines. By model-based population structure analysis, the 137 lines were divided into 14 groups. According to the grouping results, eight restorer lines and five sterile lines were selected from different groups for cross breeding, yielding 40 japonica hybrid rice combinations (F1). Investigation of the yield and quality of these combinations showed that high-yield combinations could be obtained by increasing parental genetic distance to 0.8–0.9, a result accomplished largely by the introduction of indica genomic components of restorer lines. To further improve grain quality, the genetic distance between parents should be reduced to 0.4–0.5, suggesting an indica-genotype proportion of 30%–40% for restorer lines. This study may provide a reference for breeding of japonica hybrid rice.

Genetic diversity and selective sweeps in historical and modern Canadian spring wheat cultivars using the 90K SNP array

Previous molecular characterization studies conducted in Canadian wheat cultivars shed some light on the impact of plant breeding on genetic diversity, but the number of varieties and markers used was small. Here, we used 28,798 markers of the wheat 90K single nucleotide polymorphisms to (a) assess the extent of genetic diversity, relationship, population structure, and divergence among 174 historical and modern Canadian spring wheat varieties registered from 1905 to 2018 and 22 unregistered lines (hereinafter referred to as cultivars), and (b) identify genomic regions that had undergone selection. About 91% of the pairs of cultivars differed by 20–40% of the scored alleles, but only 7% of the pairs had kinship coefficients of < 0.250, suggesting the presence of a high proportion of redundancy in allelic composition. Although the 196 cultivars represented eight wheat classes, our results from phylogenetic, principal component, and the model-based population structure analyses revealed three groups, with no clear structure among most wheat classes, breeding programs, and breeding periods. FST statistics computed among different categorical variables showed little genetic differentiation (< 0.05) among breeding periods and breeding programs, but a diverse level of genetic differentiation among wheat classes and predicted groups. Diversity indices were the highest and lowest among cultivars registered from 1970 to 1980 and from 2011 to 2018, respectively. Using two outlier detection methods, we identified from 524 to 2314 SNPs and 41 selective sweeps of which some are close to genes with known phenotype, including plant height, photoperiodism, vernalization, gluten strength, and disease resistance.

Genetic variability and population structure of Ethiopian chickpea (Cicer arietinum L.) germplasm.

Evaluation of the genetic diversity and an understanding of the genetic structure and relationships of chickpea genotypes are valuable to design efficient germplasm conservation strategies and crop breeding programs. Information is limited, in these regards, for Ethiopian chickpea germplasms. Therefore, the present study was carried out to estimate the genetic diversity, population structure, and relationships of 152 chickpea genotypes using simple sequence repeats (SSR) markers. Twenty three SSR markers exhibited polymorphism producing a total of 133 alleles, with a mean of 5.8 alleles per locus. Analyses utilizing various genetic-based statistics included pairwise population Nei's genetic distance, heterozygosity, Shannon's information index, polymorphic information content, and percent polymorphism. These analyses exemplified the existence of high genetic variation within and among chickpea genotypes. The 152 genotypes were divided into two major clusters based on Nei's genetic distances. The exotic genotypes were grouped in one cluster exclusively showing that these genotypes are distinct to Ethiopian genotypes, while the patterns of clustering of Ethiopian chickpea genotypes based on their geographic region were not consistent because of the seed exchange across regions. Model-based population structure clustering identified two discrete populations. These finding provides useful insight for chickpea collections and ex-situ conservation and national breeding programs for widening the genetic base of chickpea.

Assessment of the genetic diversity and population structure of groundnut germplasm collections using phenotypic traits and SNP markers: Implications for drought tolerance breeding.

Profiling the genetic composition and relationships among groundnut germplasm collections is essential for the breeding of new cultivars. The objectives of this study were to assess the genetic diversity and population structure among 100 improved groundnut genotypes using agronomic traits and high-density single nucleotide polymorphism (SNP) markers. The genotypes were evaluated for agronomic traits and drought tolerance at the International Crop Research Institute for the Semi-Arid Tropics (ICRISAT)/India across two seasons. Ninety-nine of the test genotypes were profiled with 16363 SNP markers. Pod yield per plant (PY), seed yield per plant (SY), and harvest index (HI) were significantly (p < 0.05) affected by genotype × environment interaction effects. Genotypes ICGV 07222, ICGV 06040, ICGV 01260, ICGV 15083, ICGV 10143, ICGV 03042, ICGV 06039, ICGV 14001, ICGV 11380, and ICGV 13200 ranked top in terms of pod yield under both drought-stressed and optimum conditions. PY exhibited a significant (p ≤ 0.05) correlation with SY, HI, and total biomass (TBM) under both test conditions. Based on the principal component (PC) analysis, PY, SY, HSW, shelling percentage (SHP), and HI were allocated in PC 1 and contributed to the maximum variability for yield under the two water regimes. Hence, selecting these traits could be successful for screening groundnut genotypes under drought-stressed and optimum conditions. The model-based population structure analysis grouped the studied genotypes into three sub-populations. Dendrogram for phenotypic and genotypic also grouped the studied 99 genotypes into three heterogeneous clusters. Analysis of molecular variance revealed that 98% of the total genetic variation was attributed to individuals, while only 2% of the total variance was due to variation among the subspecies. The genetic distance between the Spanish bunch and Virginia bunch types ranged from 0.11 to 0.52. The genotypes ICGV 13189, ICGV 95111, ICGV 14421, and ICGV 171007 were selected for further breeding based on their wide genetic divergence. Data presented in this study will guide groundnut cultivar development emphasizing economic traits and adaptation to water-limited agro-ecologies, including in Ethiopia.