Linkage Disequilibrium Decay Research Articles

Genetic diversity and genomic inbreeding in Japanese Black cows in the islands of Okinawa Prefecture evaluated using single-nucleotide polymorphism array.

Maintaining genetic diversity and inbreeding control are important in Japanese Black cattle production, especially in remote areas such as the islands of Okinawa Prefecture. Using a single-nucleotide polymorphism (SNP) array, we evaluated the genetic diversity and genomic inbreeding in Japanese Black cows from the islands of Okinawa Prefecture and compared them to those from other locations across Japan. Linkage disequilibrium decay was slower in cows in the islands of Okinawa Prefecture. The estimated effective population size declined over time in both populations. The genomic inbreeding coefficient (FROH ) was estimated using long stretches of consecutive homozygous SNPs (runs of homozygosity; ROH). FROH was higher in the cows on the islands of Okinawa Prefecture than on other locations. In total, 818 ROH fragments, including those containing NCAPG and PLAG1, which are major quantitative trait loci for carcass weight in Japanese Black cattle, were present at significantly higher frequencies in cows in the islands of Okinawa Prefecture. This suggests that the ROH fragments are under strong selection and that cows in the islands of Okinawa Prefecture have low genetic diversity and high genomic inbreeding relative to those at other locations. SNP arrays are useful tools for evaluating genetic diversity and genomic inbreeding in cattle.

Population Structure and Genetic Diversity of Seven Chinese Indigenous Chicken Populations in Guizhou Province.

To investigate the population structure and genetic diversity of indigenous chicken breeds in Guizhou, a total of 150 individual samples were collected from 12 breeds, including seven local chicken breeds in Guizhou Province, three Chinese native breeds found in other provinces, and two commercial breeds. The genotype datasets were obtained using a 50K single nucleotide polymorphism array method, and then a series of population analyses were performed. The obtained population parameters and linkage disequilibrium decay indicated a higher degree of genetic diversity in Guizhou chickens than in commercial breeds. Two Guizhou local breeds, Wumeng black-bone and Weining, were clustered with a breed from a neighboring province, Xinwen black-bone, which exhibited similar ancestral composition patterns. A newly found breed, Wumeng crested, had high genetic diversity and displayed genetic differences from other Guizhou breeds. These findings provide insight into the establishment of efficient conservation and utilization programs for Guizhou chicken breeds.

A New Diversity Panel for Winter Rapeseed (Brassica napus L.) Genome-Wide Association Studies

A diverse population (429 member) of canola (Brassica napus L.) consisting primarily of winter biotypes was assembled and used in genome-wide association studies. Genotype by sequencing analysis of the population identified and mapped 290,972 high-quality markers ranging from 18.5 to 82.4% missing markers per line and an average of 36.8%. After interpolation, 251,575 high-quality markers remained. After filtering for markers with low minor allele counts (count > 5), we were left with 190,375 markers. The average distance between these markers is 4463 bases with a median of 69 and a range from 1 to 281,248 bases. The heterozygosity among the imputed population ranges from 0.9 to 11.0% with an average of 5.4%. The filtered and imputed dataset was used to determine population structure and kinship, which indicated that the population had minimal structure with the best K value of 2–3. These results also indicated that the majority of the population has substantial sequence from a single population with sub-clusters of, and admixtures with, a very small number of other populations. Analysis of chromosomal linkage disequilibrium decay ranged from ~7 Kb for chromosome A01 to ~68 Kb for chromosome C01. Local linkage decay rates determined for all 500 kb windows with a 10kb sliding step indicated a wide range of linkage disequilibrium decay rates, indicating numerous crossover hotspots within this population, and provide a resource for determining the likely limits of linkage disequilibrium from any given marker in which to identify candidate genes. This population and the resources provided here should serve as helpful tools for investigating genetics in winter canola.

Genome-Wide Association Study of Root System Development at Seedling Stage in Rice.

Root network structure plays a crucial role in growth and development processes in rice. Longer, more branched root structures help plants to assimilate water and nutrition from soil, support robust plant growth, and improve resilience to stresses such as disease. Understanding the molecular basis of root development through screening of root-related traits in rice germplasms is critical to future rice breeding programs. This study used a small germplasm collection of 137 rice varieties chosen from the Korean rice core set (KRICE_CORE) to identify loci linked to root development. Two million high-quality single nucleotide polymorphisms (SNPs) were used as the genotype, with maximum root length (MRL) and total root weight (TRW) in seedlings used as the phenotype. Genome-wide association study (GWAS) combined with Principal Components Analysis (PCA) and Kinship matrix analysis identified four quantitative trait loci (QTLs) on chromosomes 3, 6, and 8. Two QTLs were linked to MRL and two were related to TRW. Analysis of Linkage Disequilibrium (LD) decay identified a 230 kb exploratory range for detection of candidate root-related genes. Candidates were filtered using RNA-seq data, gene annotations, and quantitative real-time PCR (qRT-PCR), and five previously characterized genes related to root development were identified, as well as four novel candidate genes. Promoter analysis of candidate genes showed that LOC_Os03g08880 and LOC_Os06g13060 contained SNPs with the potential to impact gene expression in root-related promoter motifs. Haplotype analysis of candidate genes revealed diverse haplotypes that were significantly associated with phenotypic variation. Taken together, these results indicate that LOC_Os03g08880 and LOC_Os06g13060 are strong candidate genes for root development functions. The significant haplotypes identified in this study will be beneficial in future breeding programs for root improvement.

Population structure of Nepali spring wheat (Triticum aestivum L.) germplasm

BackgroundAppropriate information about genetic diversity and population structure of germplasm improves the efficiency of plant breeding. The low productivity of Nepali bread wheat (Triticum aestivum L.) is a major concern particularly since Nepal is ranked the 4th most vulnerable nation globally to climate change. The genetic diversity and population structure of Nepali spring wheat have not been reported. This study aims to improve the exploitation of more diverse and under-utilized genetic resources to contribute to current and future breeding efforts for global food security.ResultsWe used genotyping-by-sequencing (GBS) to characterize a panel of 318 spring wheat accessions from Nepal including 166 landraces, 115 CIMMYT advanced lines, and 34 Nepali released varieties. We identified 95 K high-quality SNPs. The greatest genetic diversity was observed among the landraces, followed by CIMMYT lines, and released varieties. Though we expected only 3 groupings corresponding to these 3 seed origins, the population structure revealed two large, distinct subpopulations along with two smaller and scattered subpopulations in between, with significant admixture. This result was confirmed by principal component analysis (PCA) and UPGMA distance-based clustering. The pattern of LD decay differed between subpopulations, ranging from 60 to 150 Kb. We discuss the possibility that germplasm explorations during the 1970s–1990s may have mistakenly collected exotic germplasm instead of local landraces and/or collected materials that had already cross-hybridized since exotic germplasm was introduced starting in the 1950s.ConclusionWe suggest that only a subset of wheat “landraces” in Nepal are authentic which this study has identified. Targeting these authentic landraces may accelerate local breeding programs to improve the food security of this climate-vulnerable nation. Overall, this study provides a novel understanding of the genetic diversity of wheat in Nepal and this may contribute to global wheat breeding initiatives.

Population structure, diversifying selection, and local adaptation in Pinus patula.

Climate change is predicted to affect natural and plantation forests. The responses of conifers to overcome changing environments will depend on their adaptation to local conditions; however, intraspecific adaptive genetic variation is unknown for most gymnosperms. Studying genetic diversity associated with phenotypic variability along environmental gradients will enhance our understanding of adaptation and may reveal genetic pools important for conservation and management. We used target enrichment and genome skimming to obtain single nucleotide polymorphisms (SNPs) from 61 individuals of Pinus patula, a pine tree native to Mexico widely used in plantation forestry. We investigated the adaptive genetic variation of two varieties with morphological and distributional differences potentially related to genetic and adaptive divergence. Population structure and haplotype network analyses revealed that genetic diversity between P. patula var. patula and P. patula var. longipedunculata was structured, even within populations of P. patula var. longipedunculata. We observed high genetic diversity, low inbreeding rate, and rapid linkage disequilibrium (LD) decay in the varieties. Based on outlier tests, loci showing signatures of natural selection were detected in geographically distant P. patula var. longipedunculata populations. For both varieties, we found significant correlations between climate-related environmental variation and SNP diversity at loci involved in abiotic stress, cell transport, defense, and cell wall biogenesis, pointing to local adaptation. Overall, significant intraspecific adaptive genetic variation in P. patula was detected, highlighting the presence of different genetic pools and signs of local adaptation that should be considered in forestry and conservation.

Characterization and association mapping for drought adaptation in Ethiopian sorghum (Sorghum bicolor (L.) Moench) germplasm

Knowledge of drought related traits and their mechanisms of drought adaptation are the key component in selecting genotypes that withstand the effects of drought in sorghum. The objectives of this study were to assess genetic variability among sorghum germplasm, to map QTL associated with root and shoot traits, and to identify tightly linked SSR markers. The experiment was carried out at Jimma University under greenhouse condition. One hundred thirty-six sorghum genotypes were characterized for twelve traits using a high throughput root phenotyping platform in a randomized complete block design with three replications. Among these genotypes, 108 of them were used for studying population structure and trait-marker association analysis using 39 SSR markers. The analysis of variance indicated that highly significant difference (P < 0.01) were observed among the genotypes for all the studied traits. The coefficients of correlation showed that there was a significant positive and negative association among different drought related traits. The first three principal components (PCs) with eigenvalues greater than one accounted for 56.4% of the total genotype variation, the remaining 43.60% accounted for the last nine principal components. All 136 genotype were grouped into four clusters whereby a different member within a cluster being assumed to be more closely related in terms of the trait under consideration with each other than that member in different clusters is. Moderate genotypic variation was exhibited for leaf area, shoot fresh weight, shoot dry weight, root to shoot ratio and root angle. Highest phenotypic variation was exhibited for leaf area, shoot fresh weight, shoot dry weight, root dry weight and root to shoot ratio. Broad sense heritability ranged from 19.35% for root length to 71.08% for shoot fresh weight and high heritability was recorded for shoot fresh weight (71.08%), leaf area (70.22%) and root angle (66.22%). High heritability combined with high genetic advance was observed for shoot fresh weight, root angle, and leaf area. The 108 genotypes were grouped into three distinct subgroups. The plots of LD (r2) showed a clear trend on linkage disequilibrium decay and based on trend line it is around 15–20 cM. A total of 25 significant marker-trait associations/QTLs (P ≤ 0.05) were detected with 14 SSR markers.

LDkit: a parallel computing toolkit for linkage disequilibrium analysis

BackgroundLinkage disequilibrium (LD) analysis is broadly utilized in genetics to understand the evolutionary and demographic history and helps geneticists identify genes associated with interested inherited traits, such as diseases. There are some tools for linkage disequilibrium analysis either in a local or online way; however, there has been no such tool supporting both graphical user interface (GUI) and parallel computing.ResultsWe developed a GUI software called LDkit for LD analysis, which supports parallel computing. The LDkit supports both variant call format (VCF) and PLINK ‘ped + map’ format. At the same time, users could also just analyze a subset of individuals from the whole population. The LDkit reads the data by block and then paralleled the computation process by monitoring the usage of processes. Assessment on the Human 1000 genome data showed that when paralleled with 32 threads, the running time was reduced to less than 6 minutes from ~77 minutes using the chromosome 22 dataset with 1,103,547 SNPs and 2504 individuals.ConclusionsThe software LDkit can be effectively used to calculate and plot LD decay, LD block, and linkage disequilibrium analysis between a site and a given region. Most importantly, both graphical user interface (GUI) and stand-alone packages are available for users’ convenience. LDkit was written in JAVA language under cross-platform support.

Genome-Wide Population Genetic Analysis of Commercial, Indigenous, Game, and Wild Chickens Using 600K SNP Microarray Data.

Following chicken domestication, diversified chicken breeds were developed by both natural and artificial selection, which led to the accumulation of abundant genetic and phenotypic variations, making chickens an ideal genetic research model. To better understand the genetic structure of chicken breeds under different selection pressures, we genotyped various chicken populations with specific selection targets, including indigenous, commercial, gamecock, and wild ancestral chickens, using the 600K SNP array. We analyzed the population structure, genetic relationships, run of homozygosity (ROH), effective population number (Ne), and other genetic parameters. The wild ancestral population, red junglefowl (RJF), possessed the highest diversity, in comparison with all other domesticated populations, which was supported by linkage disequilibrium decay (LD), effective population number, and ROH analyses. The gamecock breeds, which were subjected to stronger male-biased selection for fighting-related traits, also presented higher variation than the commercial and indigenous breeds. Admixture analysis also indicated that game breed is a relatively independent branch of Chinese local breeds. Following intense selection for reproductive and productive traits, the commercial lines showed the least diversity. We also observed that the European local chickens had lower genetic variation than the Chinese local breeds, which could be attributed to the shorter history of the European breed. ROH were present in a breed specific manner and 191 ROH island were detected on four groups (commercial, local, game and wild chickens). These ROH islands were involved in egg production, growth and silky feathers and other traits. Moreover, we estimated the effective sex ratio of these breeds to demonstrate the change in the ratio of the two sexes. We found that commercial chickens had a greater sex imbalance between females and males. The commercial lines showed the highest female-to-male ratios. Interestingly, RJF comprised a greater proportion of males than females. Our results show the population genetics of chickens under selection pressures, and can aid in the development of better conservation strategies for different chicken breeds.

Genetic Dissection of Growth Traits in a Unique Chicken Advanced Intercross Line.

The advanced intercross line (AIL) that is created by successive generations of pseudo-random mating after the F2 generation is a valuable resource, especially in agricultural livestock and poultry species, because it improves the precision of quantitative trait loci (QTL) mapping compared with traditional association populations by introducing more recombination events. The growth traits of broilers have significant economic value in the chicken industry, and many QTLs affecting growth traits have been identified, especially on chromosomes 1, 4, and 27, albeit with large confidence intervals that potentially contain dozens of genes. To promote a better understanding of the underlying genetic architecture of growth trait differences, specifically body weight and bone development, in this study, we report a nine-generation AIL derived from two divergent outbred lines: High Quality chicken Line A (HQLA) and Huiyang Bearded (HB) chicken. We evaluate the genetic architecture of the F0, F2, F8, and F9 generations of AIL and demonstrate that the population of the F9 generation sufficiently randomized the founder genomes and has the characteristics of rapid linkage disequilibrium decay, limited allele frequency decline, and abundant nucleotide diversity. This AIL yielded a much narrower QTL than the F2 generations, especially the QTL on chromosome 27, which was reduced to 120 Kb. An ancestral haplotype association analysis showed that most of the dominant haplotypes are inherited from HQLA but with fluctuation of the effects between them. We highlight the important role of four candidate genes (PHOSPHO1, IGF2BP1, ZNF652, and GIP) in bone growth. We also retrieved a missing QTL from AIL on chromosome 4 by identifying the founder selection signatures, which are explained by the loss of association power that results from rare alleles. Our study provides a reasonable resource for detecting quantitative trait genes and tracking ancestor history and will facilitate our understanding of the genetic mechanisms underlying chicken bone growth.

Marker-trait association identified candidate starch biosynthesis pathway genes for starch and amylose–lipid complex gelatinization in wheat (Triticum aestivum L.)

During processing of wheat flour, its starch component undergoes gelatinization, an important physicochemical property, affecting cooking and nutrition quality of food products. Genetic loci controlling gelatinization properties of starch and amylose–lipid complex is unknown in wheat. In this study gelatinization properties were measured in a set of 226 wheat varieties using differential scanning calorimetry and their thermograms identified two endothermic peaks: first peak of starch gelatinization and second peak of amylose–lipid complex. The four parameters (onset temp, peak temp, conclusion temp, and enthalpy) of both gelatinization peaks showed wide variation among the varieties. Marker-trait association studies using the genotyping data of 258 SSRs and gelatinization data on the wheat varieties identified 24 and 6 markers associated for starch and amylose–lipid complex gelatinization properties, respectively. Using wheat reference genome sequence and LD decay information, 12 starch biosynthesis pathway genes were identified, which were co-located within 50 Mb of the associated markers. Four out of 12 genes (SSIV, SBEIIb, PHO, and PUL) were located within 5.2 Mb. Out of 24, 17 markers were involved in epistatic interactions. These markers are novel for wheat starch gelatinization properties, and would be useful for gene discovery and marker assisted selection for the improvement of starch quality in wheat.

Whole genome analyses revealed genomic difference between European taurine and East Asian taurine.

European taurine and East Asian taurine are two main clades in Bos taurus, but their genomic differences are not clearly elucidated. Here, we sequenced 16 Mongolian cattle genomes and compared them to the 92 genomes of 10 representative breeds worldwide. We found the highest LD level in Mishima cattle and the fastest LD decay in European taurine. Phylogenetic analysis revealed that Mongolian, Hanwoo and Mishima cattle were clustered into East Asian taurine. From selective sweep, gene annotation, functional enrichment and differential expression analysis, we identified selective signals including genes and/or pathways related to rapid growth and large body size in European taurine, and superior meat quality in East Asian taurine. Our findings will help us understand the evolutionary history and formation process of the breeds and provide theoretical materials regarding the genetic mechanism underlying breed characteristics and molecular breeding programmes of the taurine clades in the future.

Population genetic structure and marker-trait associations in East and West African Striga hermonthica with varying phenotypic response to Fusarium oxysporum f.sp. strigae isolates Foxy-2 and FK3.

To examine the genetic basis for the variable susceptibility of Striga hermonthica from differing zones of sub-Saharan Africa to Fusarium oxysporum f.sp. strigae (Fos) isolates Foxy-2 and FK3, 10 S.hermonthica populations from Eastern and Western Africa were phenotyped for their susceptibility response to Foxy-2 and FK3, and then genotyped with 22 simple sequence repeat (SSR) markers. There is low genetic differentiation between East African and West African S.hermonthica populations (i.e. the proportion of the total genetic variance contained in the subpopulation relative to the total genetic variance, FST =0.012, P<0.05), but intermediate genetic differentiation (FST =0.143, P<0.01) underlies the S.hermonthica groups that are differentiated by their phenotypic responses to Fos isolates. An expressed sequence tag SSR (EST-SSR) marker Y53 (P<0.01) and a genomic SSR marker E1009 (P<0.05) were associated with the S.hermonthica class susceptible to Foxy-2 and FK3 (groupA). A divergent S.hermonthica class, consisting of groups with intermediate susceptibility to Foxy-2 (groupB) and susceptibility to either FK3 (groupC) or Foxy-2 (groupD), showed no marker-trait association, instead demonstrated linkage disequilibrium decay. Owing to point substitutions and insertion-deletion mutations, the unique, protein-coding nucleotide sequence at the E1009 locus in groupA was partly dissimilar to groupB, but was totally distinct from groupsC and D. These findings implied that the inconsistent effectiveness of a Fos isolate is better explained by genomic variation in S.hermonthica, rather than by S.hermonthica sampling zones.

Genome-wide association studies of fruit quality traits in jujube germplasm collections using genotyping-by-sequencing.

Chinese jujube (Ziziphus jujuba Mill.) is an important fruit crop and harbors many highly diverse traits of potential economic importance. Fruit size, stone size, and fruit cracking have an important influence on the commercial value of jujube. This study is the first to conduct a genome-wide association study (GWAS) on 180 accessions of jujube and focuses on locating single-nucleotide polymorphisms (SNPs) associated with nine important fruit quality traits. Genotyping was performed using genotyping-by-sequencing and 4651 high-quality SNPs were identified. A genetic diversity analysis revealed the presence of three distinct groups, and rapid linkage disequilibrium decay was observed in this jujube population. Using a mixed linear model, a total of 45 significant SNP-trait associations were detected, among which 33 SNPs had associations with fruit size-related traits, nine were associated with stone size-related traits, and three with fruit cracking-related traits. In total, 21 candidate genes involved in cell expansion, abiotic stress responses, hormone signaling, and growth development were identified from the genome sequences of jujube. These results are useful as basic data for GWAS of other jujube traits, and these significant SNP loci and candidate genes should aid marker-assisted breeding and genomic selection of improved jujube cultivars.

Population structure, genetic diversity, and selective signature of Chaka sheep revealed by whole genome sequencing

BackgroundChaka sheep, named after Chaka Salt Lake, are adapted to a harsh, highly saline environment. They are known for their high-grade meat quality and are a valuable genetic resource in China. Furthermore, the Chaka sheep breed has been designated a geographical symbol of agricultural products by the Chinese Ministry of Agriculture.ResultsThe genomes of 10 Chaka sheep were sequenced using next-generation sequencing, and compared to that of additional Chinese sheep breeds (Mongolian: Bayinbuluke and Tan; Tibetan: Oula sheep) to explore its population structure, genetic diversity and positive selection signatures. Principle component analysis and a neighbor-joining tree indicated that Chaka sheep significantly diverged from Bayinbuluke, Tan, and Oula sheep. Moreover, they were found to have descended from unique ancestors (K = 2 and K = 3) according to the structure analysis. The Chaka sheep genome demonstrated comparable genetic diversity from the other three breeds, as indicated by observed heterozygosity (Ho), expected heterozygosity (He), runs of homozygosity (ROH), linkage disequilibrium (LD) decay. The enrichment analysis revealed that in contrast to Mongolian or Tibetan lineage groups, the genes annotated by specific missense mutations of Chaka sheep were enriched with muscle structure development (GO:0061061) factors including insulin-like growth factor 1 (IGF1), growth differentiation factor 3 (GDF3), histone deacetylase 9 (HDAC9), transforming growth factor beta receptor 2 (TGFBR2), and calpain 3 (CAPN3), among others. A genome-wide scan using Fst and XP-CLR revealed a list of muscle-related genes, including neurofibromin 1 (NF1) and myomesin 1 (MYOM1), under potential selection in Chaka sheep compared with other breeds.ConclusionsThe comprehensive genome-wide characterization provided the fundamental footprints for breeding and management of the Chaka sheep and confirmed that they harbor unique genetic resources.

Genetic diversity and population structure analysis of chickpea (Cicer arietinum L.) advanced breeding lines using whole-genome DArTseq-generated SilicoDArT markers

Chickpea (Cicer arietinum L.) is the third most important legume crop as a stable protein source in human feed. Breeding efforts in chickpea need to find the genotypes with diverse genome background for crossing to produce progenies that are used in the evaluation of favorable traits. In this study, we employed DArTseq-generated SilicoDArT markers for assessment of genetic diversity, population structure and linkage disequilibrium in a panel of 90 chickpea advanced breeding lines. Totally, 9824 SilicoDArT markers generated through DArTseq genotyping and, after filtering, 2053 markers with an average of 265.5 markers per chromosome were used for genetic diversity analysis. Polymorphism information content (PIC) value of SilicoDArT markers ranged from 0.05 to 0.50, with an average of 0.25. Extensive and low level of LD decay in long distances with average r2 = 0.15 was observed. Chickpea genotypes showed high genetic diversity with average kinship value and genetic distance of − 0.54 and 0.36, respectively. Results of cluster analysis, population structure and discriminant analysis of principal component (DAPC) were consistent together in grouping chickpea genotypes into four distinct clusters. These findings demonstrated the efficiency of SilicoDArT markers for large-scale diversity analysis in chickpea, and results can be used for future genomic studies in chickpea such as genome-wide association study and genomic selection for important traits such as seed yield and resistance to abiotic and biotic stresses.

QTL mapping and candidate gene analysis of cadmium accumulation in polished rice by genome-wide association study

Cadmium (Cd) accumulation in rice is a serious threat to food safety and human health. Breeding rice varieties with low Cd accumulation is one of the most effective approaches to reducing health risks from Cd-polluted rice. However, the genetic basis of Cd accumulation in grains, especially in indica rice varieties, has not been fully elucidated. The evaluation of Cd-accumulation capacity was conducted among 338 diverse rice accessions grown in Cd-contaminated soils with different Cd contents. Thirteen rice lines with relatively low Cd accumulation, including six indica rice lines, were identified. Then, 35 QTLs significantly associated with Cd accumulation were identified through sequencing-based SNP discovery and a genome-wide association study (GWAS) in the two experimental years, and only qCd8-1 was detected in both years. Among of them, nine QTLs were co-localized with identified genes or QTLs. A novel QTL, qCd1-3, with the lowest P value was selected for further LD decay analysis and candidate gene prediction. We found differential expression of OsABCB24 between high-Cd-accumulative and low-Cd-accumulative accessions, suggesting it may be a candidate gene for qCd1-3 associated with low Cd accumulation. These results may be helpful for further exploiting novel functional genes related to Cd accumulation and developing rice variety with low Cd accumulation through marker-assisted breeding.

Identification and tagging of QTLs for arjunolic acid in Terminalia arjuna among Indian sub populations by association mapping and linkage disequilibrium

The content of cardiotonic arjunolic acid in Terminalia arjuna vary among the population. We studied the population structure and the association between the molecular markers and its active ingredient among 140 plants collected from various agroclimatic zones in India. Large variation was detected for the arjunolic acid in this study showing suitableness of the genotypes. The maximum arjunolic acid content was approximately 238 per cent higher than the lowest value for the genotypes and was found to be considerably correlated to bark thickness, bark fresh weight and bark dry weight. The population structure studies described the existence of nine subpopulations. As the distance increased between the associated markers, Linkage disequilibrium (LD) reduction and a considerable reduction in LD decay was ascertained. Eleven QTL regions associated with arjunolic acid were identified from a genome-wide marker-trait association study. Fine-scale resolution detected significant LD among 3.4 per cent RAPD paired loci and 8.7 per cent ISSR paired loci and 6.7 per cent RAPD paired loci and 13.3 per cent ISSR paired loci. Importantly LD decay found to start at a distance of &gt;20bp from the loci on the genome of T. arjuna accessions. Finally, association mapping (AM) in arjun tightly linked to OPT09 which can be a possible substitute to QTL mapping methodology.

Identification of candidate tolerance genes to low-temperature during maize germination by GWAS and RNA-seq approaches

BackgroundMaize (Zea mays L.) is one of the main agricultural crops with the largest yield and acreage in the world. However, maize germplasm is very sensitive to low temperatures, mainly during germination, and low temperatures significantly affect plant growth and crop yield. Therefore, the identification of genes capable of increasing tolerance to low temperature has become necessary.ResultsIn this study, fourteen phenotypic traits related to seed germination were used to assess the genetic diversity of maize through genome-wide association study (GWAS). A total of 30 single-nucleotide polymorphisms (SNPs) linked to low-temperature tolerance were detected (−log10(P) > 4), fourteen candidate genes were found to be directly related to the SNPs, further additional 68 genes were identified when the screen was extended to include a linkage disequilibrium (LD) decay distance of r2 ≥ 0.2 from the SNPs. RNA-sequencing (RNA-seq) analysis was then used to confirm the linkage between the candidate gene and low-temperature tolerance. A total of ten differentially expressed genes (DEGs) (|log2 fold change (FC)| ≥ 0.585, P < 0.05) were found within the set distance of LD decay (r2 ≥ 0.2). Among these genes, the expression of six DEGs was verified using qRT-PCR. Zm00001d039219 and Zm00001d034319 were putatively involved in ‘mitogen activated protein kinase (MAPK) signal transduction’ and ‘fatty acid metabolic process’, respectively, based on Gene Ontology (GO) and Kyoto Encyclopedia of Genes and Genomes (KEGG) enrichment analyses. Thus, these genes appeared to be related to low-temperature signal transduction and cell membrane fluidity.ConclusionOverall, by integrating the results of our GWAS and DEG analysis of low-temperature tolerance during germination in maize, we were able to identify a total of 30 SNPs and 82 related candidate genes, including 10 DEGs, two of which were involved in the response to tolerance to low temperature. Functional analysis will provide valuable information for understanding the genetic mechanism of low-temperature tolerance during germination in maize.

Phenotypic and genetic variation in phosphorus-deficiency-tolerance traits in Chinese wheat landraces

BackgroundPhosphorus deficiency is a major limiting factors for affecting crop production globally. To understand the genetic variation of phosphorus-deficiency-tolerance, a total of 15 seedling traits were evaluated among 707 Chinese wheat landraces under application of phosphorus (AP) and non-application of phosphorus (NP). A total of 18,594 single-nucleotide polymorphisms and 38,678 diversity arrays technology sequencing markers were used to detect marker-trait associations under AP and NP.ResultsTop ten genotypes with extremely tolerance and bottommost ten genotypes with extremely sensitivity were selected from 707 Chinese wheat landraces for future breeding and genetic analysis. A total of 55 significant markers (81 marker-trait associations) for 13 traits by both CMLM and SUPER method. These were distributed on chromosomes 1A, 1B, 2A, 2B, 2D, 3A, 4B, 5A, 5B, 6A, 6B, 6D, 7A and 7B. Considering the linkage disequilibrium decay distance, 25 and 12 quantitative trait loci (QTL) were detected under AP and NP, respectively (9 QTL were specific to NP).ConclusionsThe extremely tolerant landraces could be used for breeding phosphorus-deficiency-tolerant cultivars. The QTL could be useful in wheat breeding through marker-assisted selection. Our findings provide new insight into the genetic analysis of P-deficiency-tolerance, and will be helpful for breeding P-deficiency-tolerant cultivars.