New insights into Capsicum spp relatedness and the diversification process of Capsicum annuum in Spain

Capsaicinoid Profiles, Phenolic Content, and Antioxidant Properties of Chili Peppers Grown in Urban Settings

The Capsicum genus, native to the Americas and cultivated worldwide for culinary and medicinal purposes, includes five domesticated species with diverse fruit characteristics, pungency, and phytochemical profiles. However, the influence of casual urban backyard growing conditions on these traits remains unknown. In this study, we first assessed morphological production traits of 11 popular pepper cultivars over two growing seasons to establish a consistent baseline for cultivar performance. Next, we evaluated capsaicinoid and phenolic profiles of 47 pepper cultivars, which contribute to their pungency and antioxidant properties. Capsaicinoid profiles revealed species-specific ratios of capsaicin, dihydrocapsaicin, and nordihydrocapsaicin, with C. annuum and C. baccatum displaying an average 64:30:6 profile, C. chinense and C. frutescens showing a capsaicin-dominant 73:25:2 profile, and C. pubescens expressing a distinct dihydrocapsaicin-dominant 34:60:6 profile. Antioxidant activity positively correlated with capsaicinoid content (ABTS: R2 = 0.8264, p < 0.0001; FRAP: R2 = 0.8117, p < 0.0001), with C. chinense (Carolina Reaper) exhibiting the highest activity (FRAP = 111.8 µM TE/g). In LPS-activated macrophages, all cultivars suppressed nitric oxide production both at the enzymatic (66-89%, p < 0.001) and gene expression levels (4.2 to 5.3-fold reduction, p < 0.05). Interleukin IL-1β expression was upregulated (3.8 to 12.9-fold, p < 0.001), while no significant effects were noted on Cox-2, IL-6, and MCP-1 mRNA levels. These results provide novel insights into the molecular and biochemical adaptations of peppers grown in urban environments and underscore the importance of optimizing cultivation conditions to maximize their bioactive potential and health benefits.

Metabolite profiling reveals differential accumulation of secondary metabolites related to flavour and colour across four heirloom chilli landraces

Chillies from Northeast India exhibit wide variability in fruit morphology, pungency, bearing habit and crop duration. An untargeted metabolite profiling using LC-HRMS of four 'heirloom' pungent landraces viz. Naga chilli (AL-1), Dalle khursani (AL-2), Sohmynken khnai (AL-3), and J-41(B) was performed and compared with Kashi anmol (KA). While AL-2, J-41(B) and KA belong to C. annuum species, AL-1 is categorised as C. chinense and AL-3 is C. frutescens. A total of 6990 consistent peaks of monoisotopic masses were detected, out of which 2702 metabolites were identified using accurate mass error < 10 ppm. A higher number of differentially accumulated metabolites were seen in J-41(B) versus AL-3 (1376), followed by J-41(B) versus AL-2 (1365), J-41(B) versus AL-1 (1257), KA versus AL-2 (649), AL-3 versus KA (616), KA versus AL-1 (594) and J-41(B) versus KA (413). Variation among species was higher than variation within species. Pathway analysis identified fatty acid, carotenoid, flavonoid and capsaicinoid as key pathways. We identified eight major categories of metabolites, including fatty acids, sterol lipids, and flavonoids, which together account for over 70% of the significantly expressed metabolites across the genotypes. This study explores untargeted metabolites in various chilli species, offering insights into the biochemical and molecular mechanisms which may play a role in governing important fruit traits. Identification of key metabolites and underlying alleles for twenty-one genes across three pathways (flavonoid, capsaicinoid and carotenoid) suggests that the metabolites and associated alleles identified in this study can be used as biomarkers for further characterization of these heirloom chilli and could provide distinct parameter(s) in distinguishing improved cultivars from landraces. This will contribute towards breeding programs in aiding selection of fruits of the desirable traits.

Supplementary Information

The online version contains supplementary material available at 10.1007/s12298-025-01576-4.

Insights into the genetic architecture of Phytophthora capsici root rot resistance in chile pepper (Capsicum spp.) from multi-locus genome-wide association study

BACKGROUND

Phytophthora root rot, a major constraint in chile pepper production worldwide, is caused by the soil-borne oomycete, Phytophthora capsici. This study aimed to detect significant regions in the Capsicum genome linked to Phytophthora root rot resistance using a panel consisting of 157 Capsicum spp. genotypes. Multi-locus genome wide association study (GWAS) was conducted using single nucleotide polymorphism (SNP) markers derived from genotyping-by-sequencing (GBS). Individual plants were separately inoculated with P. capsici isolates, 'PWB-185', 'PWB-186', and '6347', at the 4-8 leaf stage and were scored for disease symptoms up to 14-days post-inoculation. Disease scores were used to calculate disease parameters including disease severity index percentage, percent of resistant plants, area under disease progress curve, and estimated marginal means for each genotype.

RESULTS

Most of the genotypes displayed root rot symptoms, whereas five accessions were completely resistant to all the isolates and displayed no symptoms of infection. A total of 55,117 SNP markers derived from GBS were used to perform multi-locus GWAS which identified 330 significant SNP markers associated with disease resistance. Of these, 56 SNP markers distributed across all the 12 chromosomes were common across the isolates, indicating association with more durable resistance. Candidate genes including nucleotide-binding site leucine-rich repeat (NBS-LRR), systemic acquired resistance (SAR8.2), and receptor-like kinase (RLKs), were identified within 0.5 Mb of the associated markers.

CONCLUSIONS

Results will be used to improve resistance to Phytophthora root rot in chile pepper by the development of Kompetitive allele-specific markers (KASP®) for marker validation, genomewide selection, and marker-assisted breeding.

Optimized Pepper Target SNP-Seq Applied in Population Structure and Genetic Diversity Analysis of 496 Pepper (Capsicum spp.) Lines

Peppers are a major vegetable crop worldwide. With the completion of additional genome assemblies, a multitude of single-nucleotide polymorphisms (SNPs) can be utilized for population structure and genetic diversity analysis. In this study, we used target SNP-sequencing as a new high-throughput sequencing technology, screening out 425 perfect SNPs for analyzing the genetic diversity and population structure among 496 pepper lines from five pepper species in China and abroad. The perfect SNP panel exhibited commendable discriminative ability, as indicated by the average values of polymorphism information content, observed heterozygosity, minor allele frequency, and genetic diversity, which were 0.346, 0.011, 0.371, and 0.449, respectively. Based on phylogenetic, population structure, and principal component analyses, 484 C. annuum lines were divided into four subpopulations according to the shape of fruit: blocky fruit, wide-horn fruit, narrow-horn fruit, and linear fruit. These subpopulations displayed clear clustering with minimal or no overlap. Moreover, F statistic (Fst) analysis revealed considerable distinctions among these subpopulations. Additionally, we established a set of 47 core SNPs that could effectively differentiate among all pepper lines. This core SNP set could precisely classify the C. annuum lines into four distinct fruit-shape groups. The blocky and narrow-horn fruit subpopulations displayed the lowest and highest genetic diversity, respectively. This study highlights the importance of fruit shape as a crucial trait in pepper breeding. Moreover, this work indicates the immense potential of optimized target SNP technology in the addition of foreground markers of important traits to improve molecular breeding efficiency, and demonstrates its broad application prospects in the genetic analysis and variety identification of peppers.

Tracing Back the History of Pepper (Capsicum annuum) in the Iberian Peninsula from a Phenomics Point of View

The Iberian Peninsula was the place where pepper (Capsicum annuum) entered Europe and dispersed to other continents but was also an important secondary center for its diversification. The current work evaluated the phenotypic diversity existing in this region and investigated how that evolved from Capsicum native areas (Mexico and Andean Region). For that purpose, the high-throughput phenotyping tool Tomato Analyzer was employed. Descriptors related to size and shape were the most distinctive among fruit types, reflecting a broad diversity for Iberian peppers. These traits likely reflected those suffering from more intensive human selections, driving the worldwide expansion of C. annuum. Iberian peppers maintained close proximity to the American accessions in terms of fruit phenomics. The highest similarities were observed for those coming from the southeastern edge of the Peninsula, while northwestern accessions displayed more significant differences. Common fruit traits (small, conical) suggested that Portuguese and Spanish landraces may have arisen from an ancient American population that entered the south of Spain and promptly migrated to the central and northern territories, giving rise to larger, elongated, and blocky pods. Such lineages would be the result of adaptations to local soil-climate factors prevailing in different biogeographic provinces.

Genetic diversity, gene flow, and differentiation among wild, semiwild, and landrace chile pepper (Capsicum annuum) populations in Oaxaca, Mexico

PREMISE

Capsicum annuum (Solanaceae) was originally domesticated in Mexico, where wild (C. annuum var. glabriusculum) and cultivated (C. annuum var. annuum) chile pepper populations (>60 landraces) are common, and wild-resembling individuals (hereafter semiwild) grow spontaneously in anthropogenic environments. Here we analyze the role of elevation and domestication gradients in shaping the genetic diversity in C. annuum from the state of Oaxaca, Mexico.

METHODS

We collected samples of 341 individuals from 28 populations, corresponding to wild, semiwild (C. annuum var. glabriusculum) and cultivated C. annuum, and closely related species Capsicum frutescens and C. chinense. From the genetic variation of 10 simple sequence repeat (SSR) loci, we assessed the population genetic structure, inbreeding, and gene flow through variance distribution analyses, genetic clustering, and connectivity estimations.

RESULTS

Genetic diversity (H_E ) did not differ across domestication levels. However, inbreeding coefficients were higher in semiwild and cultivated chiles than in wild populations. We found evidence for gene flow between wild populations and cultivated landraces along the coast. Genetic structure analysis revealed strong differentiation between most highland and lowland landraces.

CONCLUSIONS

Gene flow between wild and domesticated populations may be mediated by backyards and smallholder farms, while mating systems may facilitate gene flow between landraces and semiwild populations. Domestication and elevation may overlap in their influence on genetic differentiation. Lowland Gui'ña dani clustered with highland landraces perhaps due to the social history of the Zapotec peoples. In situ conservation may play an important role in preserving semiwild populations and private alleles found in landraces.

Assessment of genetic diversity and wilt disease resistance in hot pepper (Capsicum annuum) germplasm from Ethiopia

Hot pepper (Capsicum annuum L.) is an economically important crop in Ethiopia. Wide variability in hot pepper germplasm in Ethiopia is expected due to the presence of diverse environmental conditions and variation in farming systems. The present study was carried out to evaluate the resistance of 75 hot pepper accessions to wilt disease and assess their genetic diversity using SSR markers. Out of 75 accessions tested, the present study identified 23 accessions that showed resistance (R) with the value of 1-10% disease incidence. The genetic diversity assessment using 13 polymorphic SSR markers allowed the detection of 111 clear and scorable bands. The number of alleles per locus ranged from 5 to 13, with an average of 8.54. The PIC value ranged from 0.27 to 0.87 with an average of 0.59. The gene diversity indices were highly variable across SSR loci and ranged from 0.29 to 0.88 with mean genetic diversity of 0.62. Observed heterozygosity was also highly variable between loci (0.01-0.45) indicating that the accessions were not fixed to homozygosity. Furthermore, genetic diversity parameters were estimated among populations by grouping accessions based on their origin. Within populations, the PIC value ranged from 0.31 to 0.77. The genetic distances among the eight populations ranged from 0.15 to 0.48. The observed highest genetic diversity (0.80) in the Amhara region (Gojam) may indicate this area as the primary site for designing in situ conservation for this crop in Ethiopia. The research findings provide baseline information on disease resistance germplasm sources to be used for the breeding program, as well as the status of genetic diversity of the accessions for efficient conservation and proper utilization of the existing genetic resources in the country.

Global range expansion history of pepper (Capsicum spp.) revealed by over 10,000 genebank accessions

This study provides a deep population genomic analysis of 10,000 Capsicum accessions held in genebanks and representing a frame of the global diversity of the genus. By combining single nucleotide polymorphisms (SNPs) based data and passport information, we investigated the genomic diversity and population structure of wild and domesticated peppers, tracing back to routes of evolution and providing a model of Capsicum annuum distribution, which reflects human trade and historical/cultural influences. Our results highlight west–east routes of expansion, shedding light on the links between South and Mesoamerica, Africa, and East/South Asia, the latter two constituting important diversification centers of pepper diversity. Finally, we outline a roadmap for genebank management and future direction for better exploitation of germplasm resources.

Genebanks collect and preserve vast collections of plants and detailed passport information, with the aim of preserving genetic diversity for conservation and breeding. Genetic characterization of such collections has the potential to elucidate the genetic histories of important crops, use marker–trait associations to identify loci controlling traits of interest, search for loci undergoing selection, and contribute to genebank management by identifying taxonomic misassignments and duplicates. We conducted a genomic scan with genotyping by sequencing (GBS) derived single nucleotide polymorphisms (SNPs) of 10,038 pepper (Capsicum spp.) accessions from worldwide genebanks and investigated the recent history of this iconic staple. Genomic data detected up to 1,618 duplicate accessions within and between genebanks and showed that taxonomic ambiguity and misclassification often involve interspecific hybrids that are difficult to classify morphologically. We deeply interrogated the genetic diversity of the commonly consumed Capsicum annuum to investigate its history, finding that the kinds of peppers collected in broad regions across the globe overlap considerably. The method ReMIXTURE—using genetic data to quantify the similarity between the complement of peppers from a focal region and those from other regions—was developed to supplement traditional population genetic analyses. The results reflect a vision of pepper as a highly desirable and tradable cultural commodity, spreading rapidly throughout the globe along major maritime and terrestrial trade routes. Marker associations and possible selective sweeps affecting traits such as pungency were observed, and these traits were shown to be distributed nonuniformly across the globe, suggesting that human preferences exerted a primary influence over domesticated pepper genetic structure.

Conservation of floral, fruit and chromosomal diversity: a review on diploid and polyploid Capsicum annuum complex in India

Capsicum as a spice crop, has wild and cultivated forms admired globally, including Indian subcontinent with vast climatic ranges. Systematic representation of the Indian Capsicum is required to address species relationships and sustainable agriculture, in face of unpredictable climatic conditions. We have updated the catalogue of Indian 'C. annuum complex' with 28 landraces and populations from different agro-climatic regions. The agro-climatic influence on the origin of stable chili landraces in India is remarkable, especially in the North East. The floral and fruit morphotype standards and chromosomal attributes have been considered for four distinct 'C. annuum complex' members under three species. The highlights of study are: (1) comparative profiling of Indian Capsicum species revealing less infraspecific variation within C. frutescens and C. chinense than C. annuum, at par with cultivation status, (2) karyotype analysis of some unique diploid landraces of C. annuum, (3) karyotypic confirmation of the polyploid Dalle Khursani landraces exclusive to India. To obtain more information, we attempted to correlate diversity of fruit and floral morphotype with chromosomal diversity. Existence of elite and rare germplasm found in the regional pockets offer great scope for enriching the agricultural tradition. The present dataset may serve as a template to be continuously upgraded by taxonomists, genomicists and breeders.

Plant genomics in Africa: present and prospects

Plants are the world's most consumed goods. They are of high economic value and bring many health benefits. In most countries in Africa, the supply and quality of food will rise to meet the growing population's increasing demand. Genomics and other biotechnology tools offer the opportunity to improve subsistence crops and medicinal herbs in the continent. Significant advances have been made in plant genomics, which have enhanced our knowledge of the molecular processes underlying both plant quality and yield. The sequencing of complex genomes of African plant species, facilitated by the continuously evolving next-generation sequencing technologies and advanced bioinformatics approaches, has provided new opportunities for crop improvement. This review summarizes the achievements of genome sequencing projects of endemic African plants in the last two decades. We also present perspectives and challenges for future plant genomic studies that will accelerate important plant breeding programs for African communities. These challenges include a lack of basic facilities, a lack of sequencing and bioinformatics facilities, and a lack of skills to design genomics studies. However, it is imperative to state that African countries have become key players in the plant genome revolution and genome derived-biotechnology. Therefore, African governments should invest in public plant genomics research and applications, establish bioinformatics platforms and training programs, and stimulate university and industry partnerships to fully deploy plant genomics, particularly in the fields of agriculture and medicine.

Single nucleotide polymorphisms reveal genetic diversity in New Mexican chile peppers (Capsicum spp.)

BACKGROUND

Chile peppers (Capsicum spp.) are among the most important horticultural crops in the world due to their number of uses. They are considered a major cultural and economic crop in the state of New Mexico in the United States. Evaluating genetic diversity in current New Mexican germplasm would facilitate genetic improvement for different traits. This study assessed genetic diversity, population structure, and linkage disequilibrium (LD) among 165 chile pepper genotypes using single nucleotide polymorphism (SNP) markers derived from genotyping-by-sequencing (GBS).

RESULTS

A GBS approach identified 66,750 high-quality SNP markers with known map positions distributed across the 12 chromosomes of Capsicum. Principal components analysis revealed four distinct clusters based on species. Neighbor-joining phylogenetic analysis among New Mexico State University (NMSU) chile pepper cultivars showed two main clusters, where the C. annuum genotypes grouped together based on fruit or pod type. A Bayesian clustering approach for the Capsicum population inferred K = 2 as the optimal number of clusters, where the C. chinense and C. frutescens grouped in a single cluster. Analysis of molecular variance revealed majority of variation to be between the Capsicum species (76.08 %). Extensive LD decay (~ 5.59 Mb) across the whole Capsicum population was observed, demonstrating that a lower number of markers would be required for implementing genome wide association studies for different traits in New Mexican type chile peppers. Tajima's D values demonstrated positive selection, population bottleneck, and balancing selection for the New Mexico Capsicum population. Genetic diversity for the New Mexican chile peppers was relatively low, indicating the need to introduce new alleles in the breeding program to broaden the genetic base of current germplasm.

CONCLUSIONS

Genetic diversity among New Mexican chile peppers was evaluated using GBS-derived SNP markers and genetic relatedness on the species level was observed. Introducing novel alleles from other breeding programs or from wild species could help increase diversity in current germplasm. We present valuable information for future association mapping and genomic selection for different traits for New Mexican chile peppers for genetic improvement through marker-assisted breeding.

Variability and Phylogeny of the Pepper Phytoene Synthase Paralogs PSY1 and PSY2 in Species of Various Capsicum Complexes

Genes homologous to PSY1 and PSY2 that encode phytoene synthase isoforms in Capsicum species C. baccatum, C. chinense, C. frutescens, C. tovarii, C. eximium, and C. chacoense were identified. High conservatism of functionally significant sites of phytoene synthases of the analyzed accessions was revealed. It was found that only PSY1-based clustering of pepper species corresponds to the traditional Capsicum phylogeny; C. eximium was a part of the Purple corolla complex, and C. chacoense was equidistant from Annuum and Baccatum clades. The absence of significant differences between PSY1 and PSY2 of yellow-fruited C. chinense and red-fruited pepper accessions was shown. The yellow color of C. chinense fruit may be the result of both decreased PSY1 expression and increased PSY2 transcription. Thus, it was demonstrated that the acquired fruit pigmentation retains strict phylogenetic limitations, which, however, can be overcome using artificial selection for the activity of phytoene synthase PSY1.

Phytochemical Assessment of Native Ecuadorian Peppers (Capsicum spp.) and Correlation Analysis to Fruit Phenomics

In this work, the impact of pepper (Capsicum spp.) fruits morphology on their composition for health-promoting compounds was investigated. For that purpose, pepper accessions from Ecuador, one of the hotspots in Capsicum's origin, were analyzed for ascorbic acid, polyphenols, capsaicinoids, and prevention of cholesterol oxidation. Plant and fruit phenomics were assessed with conventional descriptors and Tomato Analyzer digital traits. Significant differences among accessions and species revealed a large diversity within the collection. The Capsicum frutescens group displayed the highest levels of capsaicinoids, whereas the polyphenols shortly varied among the five domesticated species. Capsicum pubescens exhibited the lowest content of ascorbic acid. The conventional descriptors describing the magnitude of plants and fruits, as well as digital attributes under the categories of size, shape index, and latitudinal section, mostly explained the variance among Capsicum groups. Correlation test revealed that phytochemical components were negatively correlated with the morphometric fruit attributes, suggesting that huge fruits contained lower amounts of nutraceutical compounds. Multivariate analysis showed that parameters related to fruit size, shape, and nutraceutical composition primarily contribute to the arrangement of pepper accessions. Such results suggested that those traits have been subjected to higher selection pressures imposed by humans.

Large scale SNP unearthing and genetic architecture analysis in sea-captured and cultured populations of Cynoglossus semilaevis

Knowledge on population structure and genetic diversity is a focal point for association mapping studies and genomic selection. Genotyping by sequencing (GBS) represents an innovative method for large scale SNP detection and genotyping of genetic resources. Here we used the GBS approach for the genome-wide identification of SNPs in a collection of Cynoglossus semilaevis and for the assessment of the level of genetic diversity in C. semilaevis genotypes. GBS analysis generated a total of 55.12 Gb high-quality sequence data, with an average of 0.63 Gb per sample. The total number of SNP markers was 563, 109. In order to explore the genetic diversity of C. semilaevis and to select a minimal core set representing most of the total genetic variation with minimum redundancy, C. semilaevis sequences were analyzed using high quality SNPs. Based on hierarchical clustering, it was possible to divide the collection into 2 clusters. The marine fishing populations were clustered and clearly separated from the cultured populations, and the cultured populations from Hebei was also distinct from the other two local populations. These analyses showed that genotypes were clustered based on species-related features. Differential significant SNPs were also captured and validated by GBS and SNaPshot, with linkage disequilibrium and haplotype analysis, seven SNPs have been confirmed to have obvious differentiation in two populations, which may be used as the characteristic evaluation sites of sea-captured and cultured Cynoglossus semilaevis populations. And SNP markers and information on population structure developed in this study will undoubtedly support genome-wide association mapping studies and marker-assisted selection programs. These differential SNPs could be also employed as the characteristic evaluation sites of sea-captured and cultured Cynoglossus semilaevis populations in future.

Effect of Grafting on the Production, Physico-Chemical Characteristics and Nutritional Quality of Fruit from Pepper Landraces

Grafting is a widely utilized agronomical technique to improve yield, disease resistance, and quality of fruit and vegetables. This work aims to assess the effect of grafting and fruit ripening on the production, physico-chemical characteristics, and nutritional quality of fruit from Spanish local pepper landraces. Landraces "Cuerno," "Sueca," and "Valencia" were used as scions, and "NIBER^®" as the rootstock. Two ripening stages of the fruits were sampled: green and red. Grafting improved the yield and marketable quality and did not negatively influence the physico-chemical and nutritional characteristics of the fruit. It was noteworthy that the bioactive compound contents and antioxidant capacity were more related to maturity stage and genotype, and red fruit had a higher antioxidant capacity than green fruit. However, in all the scions, grafting significantly enhanced lycopene content in both red and green fruit. Another important effect of grafting was the volatile compound composition evidenced by discriminant analyses, which was characterized for the first time in the fruit of these landraces. The rootstock and scion combination could be a way to improve not only the production, but also the fruit quality of peppers.

Target sequencing reveals genetic diversity, population structure, core-SNP markers, and fruit shape-associated loci in pepper varieties

BACKGROUND

The widely cultivated pepper (Capsicum spp.) is one of the most diverse vegetables; however, little research has focused on characterizing the genetic diversity and relatedness of commercial varieties grown in China. In this study, a panel of 92 perfect single-nucleotide polymorphisms (SNPs) was identified using re-sequencing data from 35 different C. annuum lines. Based on this panel, a Target SNP-seq genotyping method was designed, which combined multiplex amplification of perfect SNPs with Illumina sequencing, to detect polymorphisms across 271 commercial pepper varieties.

RESULTS

The perfect SNPs panel had a high discriminating capacity due to the average value of polymorphism information content, observed heterozygosity, expected heterozygosity, and minor allele frequency, which were 0.31, 0.28, 0.4, and 0.31, respectively. Notably, the studied pepper varieties were morphologically categorized based on fruit shape as blocky-, long horn-, short horn-, and linear-fruited. The long horn-fruited population exhibited the most genetic diversity followed by the short horn-, linear-, and blocky-fruited populations. A set of 35 core SNPs were then used as kompetitive allele-specific PCR (KASPar) markers, another robust genotyping technique for variety identification. Analysis of genetic relatedness using principal component analysis and phylogenetic tree construction indicated that the four fruit shape populations clustered separately with limited overlaps. Based on STRUCTURE clustering, it was possible to divide the varieties into five subpopulations, which correlated with fruit shape. Further, the subpopulations were statistically different according to a randomization test and F_st statistics. Nine loci, located on chromosomes 1, 2, 3, 4, 6, and 12, were identified to be significantly associated with the fruit shape index (p < 0.0001).

CONCLUSIONS

Target SNP-seq developed in this study appears as an efficient power tool to detect the genetic diversity, population relatedness and molecular breeding in pepper. Moreover, this study demonstrates that the genetic structure of Chinese pepper varieties is significantly influenced by breeding programs focused on fruit shape.

Translation initiation codon (ATG) or SCoT markers-based polymorphism study within and across various Capsicum accessions: insight from their amplification, cross-transferability and genetic diversity

Being an economical and nutritional crop, Capsicum appeases people's peppery taste and is found to bewidely distributed all over the world having vast diversity. In the present study, genetic polymorphism, cross transferability (CT) and genetic diversity were examined among the 54 different accessions of Capsicum species including 49 of Capsicum annuum, three of C. baccatum and two of C. frutescens, using a set of 36 start codon targeted (SCoT) primers. Of the total, 35 SCoT markers showed successful amplification profile among chilli germplasms and an average primer polymorphism was reported as 81.52% which ranged from 50% (SCoT-6) to 100% (SCoT-11). A total of 365 amplicons were obtained with an average of 10.43 bands per primer and the length of the bands ranged from 150 bp to 1.2 kb. Further, polymorphic information content value of SCoT markers ranged from 0.42 (for SCoT-25) to 0.86 (SCoT-27) with an average of 0.78. The average value of CT of SCoT markers was 44.08% ranged from 14.25% to 57.26% among different chilli accessions. A dendrogram was constructed and established genetic relationship among 54 capsicum species, with the help of translation initiation codon polymorphisms or SCoT primer amplification. This study suggests the effectiveness of SCoT marker system for characterizing and assessing genetic diversity of Capsicum germplasm, which can be used for evolutionary studies and to identify agronomically important traits.

Genetic diversity and population structure of Ethiopian Capsicum germplasms

We established a collection of 142 Capsicum genotypes from different geographical areas of Ethiopia with the aim of capturing genetic diversity. Morphological traits and high-resolution melting analysis distinguished one Capsicum baccatum, nine Capsicum frutescens and 132 Capsicum annuum accessions in the collection. Measurement of plant growth parameters revealed variation between germplasms in parameters including plant height, stem thickness, internode length, number of side branches, fruit width, and fruit length. Broad-sense heritability was maximum for fruit weight, followed by length and width of leaves. We used genotyping by sequencing (GBS) to identify single-nucleotide polymorphisms (SNPs) in the panel of 142 Capsicum germplasms and found 2,831,791 genome-wide SNP markers. Among these, we selected 53,284 high-quality SNPs and used them to estimate the level of genetic diversity, population structure, and phylogenetic relationships. From model-based ancestry analysis, the phylogenetic tree and principal-coordinate analysis (PCoA), we identified two distinct genetic populations: one comprising 132 C. annuum accessions and the other comprising the nine C. frutescens accessions. GWAS analysis detected 509 SNP markers that were significantly associated with fruit-, stem- and leaf-related traits. This is the first comprehensive report of the analysis of genetic variation in Ethiopian Capsicum species involving a large number of accessions. The results will help breeders utilize the germplasm collection to improve existing commercial cultivars.

Genetic diversity, population structure, and relationships in a collection of pepper (Capsicum spp.) landraces from the Spanish centre of diversity revealed by genotyping-by-sequencing (GBS)

Pepper (Capsicum spp.) is one of the most important vegetable crops; however, pepper genomic studies lag behind those of other important Solanaceae. Here we present the results of a high-throughput genotyping-by-sequencing (GBS) study of a collection of 190 Capsicum spp. accessions, including 183 of five cultivated species (C. annuum, C. chinense, C. frutescens, C. baccatum, and C. pubescens) and seven of the wild form C. annuum var. glabriusculum. Sequencing generated 6,766,231 high-quality read tags, of which 40.7% were successfully aligned to the reference genome. SNP calling yielded 4083 highly informative segregating SNPs. Genetic diversity and relationships of a subset of 148 accessions, of which a complete passport information was available, was studied using principal components analysis (PCA), discriminant analysis of principal components (DAPC), and phylogeny approaches. C. annuum, C. baccatum, and C. chinense were successfully separated by all methods. Our population was divided into seven clusters by DAPC, where C. frutescens accessions were clustered together with C. chinense. C. annuum var. glabriusculum accessions were spread into two distinct genetic pools, while European accessions were admixed and closely related. Separation of accessions was mainly associated to differences in fruit characteristics and origin. Phylogeny studies showed a close relation between Spanish and Mexican accessions, supporting the hypothesis that the first arose from a main genetic flow from the latter. Tajima's D statistic values were consistent with positive selection in the C. annuum clusters, possibly related to domestication or selection towards traits of interest. This work provides comprehensive and relevant information on the origin and relationships of Spanish landraces and for future association mapping studies in pepper.

Response to organic cultivation of heirloom Capsicum peppers: Variation in the level of bioactive compounds and effect of ripening

Peppers (Capsicum spp.) are one of the most important vegetables and their double use (vegetable or spice) and two commercial stages (unripe and fully ripe) contributed to their use in many recipes and fast diffusion from America. Nowadays, Spain is a center of diversity for C. annuum, with many landraces, offering a great opportunity for adaptation to organic cultivation. Furthermore, Capsicum peppers contain many bioactive compounds, essential to provide high added-value to these cultivars, especially for organic markets, although knowledge about the effect of organic cultivation on Capsicum fruit quality is still scarce. Here, 37 accessions of Spanish landraces and foreign materials from C. annuum and other species were grown under organic and conventional conditions and evaluated for ascorbic acid (AAC), total phenolics (TP) and total red and yellow/orange carotenoids, considering both ripening stages. A large genotypic variation was found within each ripening stage and growing condition for the studied traits. Also, both stages showed high levels, although fully ripe fruits were the richest. Organic conditions enabled higher levels in fully ripe fruits of AAC and TP on average (135 vs 117 mg·100 g-1 and 232 vs 206 mg·100 g-1) and in most accessions, although the genotype×growing conditions interaction also contributed, but at lower extent, to the observed variation. Significant genotype×ripening stage and growing conditions×ripening stage interactions were also found, suggesting that the magnitude of the increase with ripening depends on the accession and growing conditions. By contrast, there were no differences between growing conditions for carotenoids and differences were mainly due to the genotype factor. Finally, the large genotypic variation and favourable organic conditions allowed identifying several materials from different types and uses with very high levels of bioactive compounds for organic cultivation, in both ripening stages but particularly at fully ripe stage (>500 mg·100 g-1).

Large Scale Phenotyping Provides Insight into the Diversity of Vegetative and Reproductive Organs in a Wide Collection of Wild and Domesticated Peppers (Capsicum spp.)

In the past years, the diversity of Capsicum has been mainly investigated through genetics and genomics approaches, fewer efforts have been made in the field of plant phenomics. Assessment of crop traits with high-throughput methodologies could enhance the knowledge of the plant phenome, giving at the same time a key contribution to the understanding of the function of many genes. In this study, a wide germplasm collection of 307 accessions retrieved from 48 world regions, and belonging to nine Capsicum species was characterized for 54 plant, leaf, flower and fruit traits. Conventional descriptors and semi-automated tools based on image analysis and colour coordinate detection were used. Significant differences were found among accessions, between species and between sweet and spicy cultivated types, revealing a large diversity. The results highlighted how the domestication process and the continued selection have increased the variability of fruit shape and colour. Hierarchical clustering based on conventional and fruit morphological descriptors reflected the separation of species on the basis of their phylogenetic relationships. These observations suggested that the flow between distinct gene pools could have contributed to determine the similarity of the species on the basis of morphological plant and fruit parameters. The approach used represents the first high-throughput phenotyping effort in Capsicum spp. aimed at broadening the knowledge of the diversity of domesticated and wild peppers. The data could help to select best the candidates for breeding and provide new insight into the understanding of the genetic base of the fruit shape of pepper.

Exploring the genetic variations and population structure of Turkish pepper (Capsicum annuum L.) genotypes based on peroxidase gene markers

Capsicum is thought as one of the most diverse and significant genera due to its varied uses in different parts of the world. In this study, we worked with a total of 71 pepper genotypes from different locations of Turkey to investigate the level of their diversity using the peroxidase gene polymorphism (POGP) markers to reveal their population structure. For this purpose, 14 peroxidase primer pairs were used. They produced 139 bands (mean = 9.9 bands/primer), of which ~ 85.6% were polymorphic in the all germplasm collection. Polymorphism information content (PIC) ranged between 0.48 and 0.97 with an average of 0.75. Range and mean values for gene diversity (h) were 0.09-0.22 and 0.17, respectively. Shannon's information index (I) per POGP marker ranged from 0.18 to 0.35 with a mean of 0.29. Using three clustering methods (unweighted pair-group method with arithmetic means, principal coordinate analysis, and STRUCTURE) revealed a clear separation of all the C. annuum accessions from C. frutescens and C. chinense accessions in our study. Clusters did not establish an association between the accessions and their geographical origin. This is the first study exploring the population structure through the genetic diversity of Turkish peppers from different regions of the country based on the peroxidase gene markers.

Genome-wide SNP discovery and population structure analysis in pepper (Capsicum annuum) using genotyping by sequencing

Background

Knowledge on population structure and genetic diversity in vegetable crops is essential for association mapping studies and genomic selection. Genotyping by sequencing (GBS) represents an innovative method for large scale SNP detection and genotyping of genetic resources. Herein we used the GBS approach for the genome-wide identification of SNPs in a collection of Capsicum spp. accessions and for the assessment of the level of genetic diversity in a subset of 222 cultivated pepper (Capsicum annum) genotypes.

Results

GBS analysis generated a total of 7,568,894 master tags, of which 43.4% uniquely aligned to the reference genome CM334. A total of 108,591 SNP markers were identified, of which 105,184 were in C. annuum accessions. In order to explore the genetic diversity of C. annuum and to select a minimal core set representing most of the total genetic variation with minimum redundancy, a subset of 222 C. annuum accessions were analysed using 32,950 high quality SNPs. Based on Bayesian and Hierarchical clustering it was possible to divide the collection into three clusters. Cluster I had the majority of varieties and landraces mainly from Southern and Northern Italy, and from Eastern Europe, whereas clusters II and III comprised accessions of different geographical origins. Considering the genome-wide genetic variation among the accessions included in cluster I, a second round of Bayesian (K = 3) and Hierarchical (K = 2) clustering was performed. These analysis showed that genotypes were grouped not only based on geographical origin, but also on fruit-related features.

Conclusions

GBS data has proven useful to assess the genetic diversity in a collection of C. annuum accessions. The high number of SNP markers, uniformly distributed on the 12 chromosomes, allowed the accessions to be distinguished according to geographical origin and fruit-related features. SNP markers and information on population structure developed in this study will undoubtedly support genome-wide association mapping studies and marker-assisted selection programs.

Electronic supplementary material

The online version of this article (doi:10.1186/s12864-016-3297-7) contains supplementary material, which is available to authorized users.

Genome-Wide Divergence and Linkage Disequilibrium Analyses for Capsicum baccatum Revealed by Genome-Anchored Single Nucleotide Polymorphisms

Principal component analysis (PCA) with 36,621 polymorphic genome-anchored single nucleotide polymorphisms (SNPs) identified collectively for Capsicum annuum and Capsicum baccatum was used to characterize population structure and species domestication of these two important incompatible cultivated pepper species. Estimated mean nucleotide diversity (π) and Tajima's D across various chromosomes revealed biased distribution toward negative values on all chromosomes (except for chromosome 4) in cultivated C. baccatum, indicating a population bottleneck during domestication of C. baccatum. In contrast, C. annuum chromosomes showed positive π and Tajima's D on all chromosomes except chromosome 8, which may be because of domestication at multiple sites contributing to wider genetic diversity. For C. baccatum, 13,129 SNPs were available, with minor allele frequency (MAF) ≥0.05; PCA of the SNPs revealed 283 C. baccatum accessions grouped into 3 distinct clusters, for strong population structure. The fixation index (F_ST ) between domesticated C. annuum and C. baccatum was 0.78, which indicates genome-wide divergence. We conducted extensive linkage disequilibrium (LD) analysis of C. baccatum var. pendulum cultivars on all adjacent SNP pairs within a chromosome to identify regions of high and low LD interspersed with a genome-wide average LD block size of 99.1 kb. We characterized 1742 haplotypes containing 4420 SNPs (range 9-2 SNPs per haplotype). Genome-wide association study (GWAS) of peduncle length, a trait that differentiates wild and domesticated C. baccatum types, revealed 36 significantly associated genome-wide SNPs. Population structure, identity by state (IBS) and LD patterns across the genome will be of potential use for future GWAS of economically important traits in C. baccatum peppers.