DArT, SNP, and SSR analyses of genetic diversity in Lolium perenne L. using bulk sampling

Diversity of ecotypes of five species of ryegrass from Northwestern Spain by phenotypic traits and microsatellites

BACKGROUND

The Agricultural Research Centre of Mabegondo (Xunta de Galicia, A Coruña, Spain) conserves one of the most important collections of phytogenetic resources of ecotypes and natural populations of grassland species from northwestern Spain, among them populations of ryegrass (Lolium spp.), one of the most cultivated forage grasses in the world. The objective of the present study was to evaluate the diversity among commercial cultivars and natural ryegrass populations with phenotypic traits and molecular markers.

RESULTS

Eleven polymorphic microsatellites loci were used to analyze 58 ecotypes and 10 cultivars (680 DNA samples in total) differentiating 673 genotypes. Two main groups were detected by the Structure analysis, one related to Lolium perenne and a second to Lolium multiflorum. The first group showed two subgroups and the second three. The cluster of L. multiflorum showed two subgroups not related with the third cluster including commercial varieties, one from the Canary Islands (with Lolium rigidum included) and a second one from northwestern Spain, which presented specific agromorphological characteristics, such as lower FES (number of days from 1 January, when three heads per plant were flowering per plot), CRE (growth in flowering, in g of dry matter), and AIN (number of inflorescences per plant).

CONCLUSIONS

This is the first time that a large amount of data on ryegrass from the Iberian Peninsula has been analyzed, obtaining a clear genetic differentiation of the autochthonous varieties from the commercial varieties analyzed. In addition, the genetic structure found in the ecotypes was related to the phenotypic variation analyzed. Being of interest in the conservation of biodiversity and in obtaining better adapted varieties of ryegrasses, due to their specific phenotypic traits, such as a lower FES, CRE and AIN.

Association Analysis of Tiller-Related Traits with EST-SSR Markers in Psathyrostachys juncea

Psathyrostachys juncea is a long-lived perennial Gramineae grass with dense basal tillers and soft leaves. It is used widely in cold and dry areas of Eurasia and North America to establish grazing pasture and is even used as an ideal plant for revegetation and ecological restoration. Plant architecture, especially tillering traits, is critical for bunch grasses in breeding programs, and these traits in plants are mostly quantitative traits. In this study, the genetic diversity, population structure, and linkage disequilibrium of 480 individual lines were analyzed using 127 pairs of the EST-SSR marker, and a significant association between ten plant-architecture-related traits of P. juncea and molecular markers was found. The results of the genetic diversity analysis showed that the number of observed alleles was 1.957, the number of effective alleles was 1.682, Shannon's information index was 0.554, observed heterozygosity was 0.353, expected heterozygosity was 0.379, and the polymorphism information content was 0.300. A total of 480 individual lines were clustered into five groups based on population genetic structure, principal coordinate analysis, and unweighted pair group method with arithmetic mean analysis (UPGMA). The linkage disequilibrium coefficient (r2) was between 0.00 and 0.68, with an average of 0.04, which indicated a relatively low level of linkage disequilibrium among loci. The results of the association analysis revealed 55 significant marker-trait associations (MTA). Moreover, nine SSR markers were associated with multiple traits. This study provides tools with promising applications in the molecular selection and breeding of P. juncea germplasm.

Genetic variability analysis of Russian cultivars of ryegrass (Lolium) based on SCoT markers

BACKGROUND

Ryegrass is a promising crop for the development of meadow farming in the world. More than 1000 cultivated varieties widely used in feed production have been developed, based on the main species - perennial ryegrass (Lolium perenne L.) and annual one (Lolium multiflorum Lam.). Development and implementation of the modern methods of plant varietal and species identification are of great importance. In recent years, molecular markers have been successfully used for these purposes, which increase the accuracy of the breeding material evaluation at a significant reduction of time and labor costs. The aim of this study was to assess the discriminatory potential of the new SCoT marking technique for the identification of Russian perennial (Lolium perenne L.) and annual (Lolium multiflorum Lam.) ryegrass varieties.

RESULTS

Out of the total number of the tested SCoT-primers, 8 polymorphic ones were selected, which demonstrates the high stability and reproducibly amplified DNA fragments. These primers generated 107 PCR products, where 37 were found to be polymorphic. The average number of amplicons per primer was 13. The size of the PCR products varied from 349 to 2718 bp (see Table 3). The polymorphic ratio of the tested markers was 30.8%. The marker SCoT-06 was characterized by the maximum number of PCR products and the highest level of polymorphism (50%). The effective number of alleles (ne) ranged from 1.35 to 1.58 with a mean of 1.48 per locus. The average value of the PIC and Shannon index (I) were 0.35 and 0.46, respectively. The unique PCR fragments were revealed for the identification of tested varieties. Analysis of molecular variance (AMOVA) showed that the level of genetic diversity between ryegrass species (59%) was more than between varieties within a species (41%). Based on binary matrix data, clustering and PCoA analysis (see Figs. 1 and 2) of the samples were carried out that divided them into two groups according to species.

CONCLUSIONS

We found a set of markers that can be useful tools for ryegrass varieties identification. The level of intravarietal polymorphism turned out to be higher than the differences between varieties because of the possible significant heterogeneity of the varietal material. The information obtained can be used in breeding programs to create improved ryegrass varieties adapted to Russian climatic conditions.

Investigation of genetic polymorphism of Russian rape and turnip rape varieties using SSR and SRAP markers

Rapeseed (Brassica napus L.) and turnip rape (B. rapa L. subsp. campestris (L.)) are important agricultural plants widely used for food, fodder and technical purposes and as green manure. Over the past decades, a large number of perspective varieties that are being currently cultivated in every region of Russia have been developed. To increase the breeding efficiency and facilitate the seed production, modern molecular-genetic techniques should be introduced as means to estimate species and varietal diversity. The objective of the presented research study was to investigate DNA polymorphism of the rapeseed and turnip rape varieties developed at Federal Williams Research Center of Forage Production and Agroecology and detect informative markers for varietal identification and genetic certification. To genotype 18 gDNA samples, 42 and 25 combinations of respective SSR and SRAP primers were used. The results obtained demonstrate that SRAP markers were more effective for polymorphism analysis: 36 % of the tested markers revealed genetic polymorphism compared with only 16.7 % of microsatellite loci. Molecular markers to detect differences at interspecific and intervarietal levels have also been found. For the investigated set, such microsatellite loci as Na12A02, Ni2C12, Ni02-D08a, Ra02-E01, Ni03H07а and SRAP-marker combinations as F13-R9, Me4-R7, F11-Em2, F10-R7, F9-Em2 and F9-R8 proved to be informative. Application of the two marker techniques made it possible to detect a higher level of DNA polymorphism in plants of different types (spring and winter varieties) if compared against the intervarietal differences within a species or a group. According to Nei’s genetic diversity index, in the cluster of winter rapeseed, VIK 2 and Gorizont varieties had the longest genetic distance, and in the spring cluster, these were Novosel and Veles. A high level of similarity was found between Vikros and Bizon winter rapeseed varieties. The results obtained have a high practical value for varietal specification of seed material and genetic certification of rapeseed and turnip rape varieties.

RAD-seq as an effective strategy for heterogenous variety identification in plants-a case study in Italian Ryegrass (Lolium multiflorum)

The primary approach for variety distinction in Italian ryegrass is currently the DUS (distinctness, uniformity and stability) test based on phenotypic traits. Considering the diverse genetic background within the population and the complexity of the environment, however, it is challenging to accurately distinguish varieties based on DUS criteria alone. In this study, we proposed the application of high-throughput RAD-seq to distinguish 11 Italian ryegrass varieties with three bulks of 50 individuals per variety. Our findings revealed significant differences among the 11 tested varieties. The PCA, DAPC and STRUCTURE analysis indicated a heterogeneous genetic background for all of them, and the AMOVA analysis also showed large genetic variance among these varieties (Φ_ST = 0.373), which were clearly distinguished based on phylogenetic analysis. Further nucleotide diversity (Pi) analysis showed that the variety 'Changjiang No.2' had the best intra-variety consistency among 11 tested varieties. Our findings suggest that the RAD-seq could be an effectively alternative method for the variety distinction of Italian ryegrass, as well as a potential tool for open-pollinated varieties (OPVs) of other allogamous species.

A multispecies amplicon sequencing approach for genetic diversity assessments in grassland plant species

Grasslands are widespread and economically relevant ecosystems at the basis of sustainable roughage production. Plant genetic diversity (PGD; i.e., within‐species diversity) is related to many beneficial effects on the ecosystem functioning of grasslands. The monitoring of PGD in temperate grasslands is complicated by the multiplicity of species present and by a shortage of methods for large‐scale assessments. However, the continuous advancement of high‐throughput DNA sequencing approaches has improved the prospects of broad, multispecies PGD monitoring. Among them, amplicon sequencing stands out as a robust and cost‐effective method. Here, we report a set of 12 multispecies primer pairs that can be used for high‐throughput PGD assessments in multiple grassland plant species. The target loci were selected and tested in two phases: a “discovery phase” based on a sequence capture assay (611 nuclear loci assessed in 16 grassland plant species), which resulted in the selection of 11 loci; and a “validation phase”, in which the selected loci were targeted and sequenced using multispecies primers in test populations of Dactylis glomerata L., Lolium perenne L., Festuca pratensis Huds., Trifolium pratense L. and T. repens L. The multispecies amplicons had nucleotide diversities per species from 5.19 × 10⁻³ to 1.29 × 10⁻², which is in the range of flowering‐related genes but slightly lower than pathogen resistance genes. We conclude that the methodology, the DNA sequence resources, and the primer pairs reported in this study provide the basis for large‐scale, multispecies PGD monitoring in grassland plants.

Common Vetch, Valuable Germplasm for Resilient Agriculture: Genetic Characterization and Spanish Core Collection Development

Common vetch (Vicia sativa L.) is a legume used for animal feed because of its high protein content and great capacity for nitrogen fixation, making this crop relevant in sustainable agriculture. The Spanish vetch collection, conserved at the Spanish Plant Genetic Resources Center (CRF), is one of the largest collections of this species worldwide, including landraces, wild relatives mainly collected in Spain, and commercial cultivars, but also accessions of international origin. The analysis of the genetic diversity of this material, whose genome has not been sequenced yet, and the assembly of a representative collection could play a pivotal role in conserving and exploiting these genetic resources in breeding programs mainly in those focused on consequences and demands of climate change. In this work, a set of 14 simple sequence repeat (SSR) reference alleles for genetic diversity analysis of the CRF vetch collection has been developed, used for genotyping more than 545 common vetch accessions from all over the world and validated. All the tested markers were polymorphic for the analyzed accessions. Overall, at least 86 different loci were identified with 2-11 alleles per locus with an average of 6.1 alleles per locus. Also, the analyses of the generated SSR database support that most of these SSR markers are transferable across closely related species of Vicia genus. Analysis of molecular variance revealed that wild relatives have a higher genetic diversity than landraces. However, cultivars have similar diversity than landraces, indicating that genetic variability has been barely lost due to the breeding of this legume. Low differences of genetic variations between Spanish and non-Spanish accessions have been observed, suggesting a high degree of diversity within Spanish genotypes, which provide 95% of the total genetic variation, so we have focused our efforts on characterizing genotypes of Spanish origin that were further studied using storage protein profiles. Based on SSR, seed protein profiles, and agromorphological and passport data, a vetch core collection (VCC) containing 47 V. sativa accessions of Spanish origin has been established. In this collection, the characterization has been expanded using ISSR markers, and it has been reevaluated with new agromorphological data, including drought tolerance characters. This VCC presents a minimum loss of genetic diversity concerning the total collection and constitutes an invaluable material that can be used in future breeding programs for direct use in a resilient agricultural system.

Structural, physiological and genetic diversification of Silene vulgaris ecotypes from heavy metal-contaminated areas and their synchronous in vitro cultivation

Results provide significant comparison of leaf anatomy, pigment content, antioxidant response and phenolic profile between individuals from miscellaneous populations and describe unified cultivation protocols for further research on stress biology. The plant communities growing on heavy metal-polluted areas have attracted considerable attention due to their unique ability to tolerate enormous amounts of toxic ions. Three ecotypes of Silene vulgaris representing calamine (CAL), serpentine (SER) and non-metallicolous (NM) populations were evaluated to reveal specific adaptation traits to harsh environment. CAL leaves presented a distinct anatomical pattern compared to leaves of SER and NM plants, pointing to their xeromorphic adaptation. These differences were accompanied by divergent accumulation and composition of photosynthetic pigments as well as antioxidant enzyme activity. In CAL ecotype, the mechanism of reactive oxygen species scavenging is based on the joint action of superoxide dismutase and catalase, but in SER ecotype on superoxide dismutase and guaiacol-type peroxidase. On the contrary, the concentration of phenylpropanoids and flavonols in the ecotypes was unchanged, implying the existence of similar pathways of their synthesis/degradation functioning in CAL and SER populations. The tested specimens showed genetic variation (atpA/MspI marker). Based on diversification of S. vulgaris populations, we focused on the elaboration of similar in vitro conditions for synchronous cultivation of various ecotypes. The most balanced shoot culture growth was obtained on MS medium containing 0.1 mg l^-1 NAA and 0.25 mg l^-1 BA, while the most abundant callogenesis was observed on MS medium enriched with 0.5 mg l^-1 NAA and 5.0 mg l^-1 BA. For the first time, unified in vitro protocols were described for metallophytes providing the opportunity to conduct basic and applied research on stress biology and tolerance mechanisms under freely controlled conditions.

Assessment of Diversity in the Accessions of Setaria italica L. Based on Phytochemical and Morphological Traits and ISSR Markers

This study was carried out to evaluate genetic diversity, phenolic compound composition, and biological activity of Setaria italica L. collected from different parts of South Korea. Antioxidant potential of seeds was estimated by the 1,1-diphenyl-2-picrylhydrazyl (DPPH) radical scavenging assay, and antimicrobial activity was determined by evaluating the minimum inhibitory concentration (MIC). Eight phenolic acids and 3 flavonoids were identified and quantified, among which myricetin and salicylic acid were the most dominant phytochemical compounds detected in the majority of accessions. The antioxidant potential of the leaf extracts of all the accessions was significantly higher (ranging from 32.33 ± 1.53 µg mL-¹ in SI-03 to 87.87 ± 1.63 µg mL-¹) in SI-10 than that of the root, stem, or seeds. Among the 15 accessions, methanolic extracts of the SI-15 accession strongly suppressed the growth of Escherichia coli (250 µg mL-¹). Accessions SI-14 and SI-15 showed positive antimicrobial activity against all gram-positive bacteria. Interestingly, extracts of all accessions were more sensitive towards E. coli and Staphylococcus aureus, with MICs ranging from 250 to 1000 µg mL-¹. Three phenolic acids, namely chlorogenic acid, catechin, caffeic acid, naringin, hesperetin, and myricetin, were found to be moderately positively correlated with antioxidant activities. A wide range of diversity was observed in morphological traits, namely plant height (99.33 to 201.33 cm), culm length (67.10 to 160.00 cm), spike length (12.80 to 24.00 cm), 1000 seeds weight 1.44 to 2.91 g), bloom beginning (93.67 to 128.00 days), and full bloom (99.67 to 135 days). A dendogram generated from unweighted pair group method with arithmetic mean clustering (UPGMA) cluster analysis based on the morphological traits and inter simple sequence repeat (ISSR) marker data revealed three major groups. However, no clear correlation between these two different approaches was found. The average Shannon's information index value (I) was 0.492, and it ranged from 0 to 0.693. The average expected heterozygosity (He) was 0.335, and it ranged from 0 to 0.499. The substantial variation in the morphological traits, bioactive properties, and genetic diversity among the accessions may provide useful information for breeding programs attempting to obtain S. italica with improved bioactive properties.

Pooled DNA sequencing to identify SNPs associated with a major QTL for bacterial wilt resistance in Italian ryegrass (Lolium multiflorum Lam.)

SNPs and candidate genes associated with bacterial wilt resistance in Italian ryegrass were identified by sequencing the parental plants and pooled F₁ progeny of a segregating population. Italian ryegrass (Lolium multiflorum Lam.) is one of the most important forage grass species in temperate regions. Its yield, quality and persistency can significantly be reduced by bacterial wilt, a serious disease caused by Xanthomonas translucens pv. graminis. Although a major QTL for bacterial wilt resistance has previously been reported, detailed knowledge on underlying genes and DNA markers to allow for efficient resistance breeding strategies is currently not available. We used pooled DNA sequencing to characterize a major QTL for bacterial wilt resistance of Italian ryegrass and to develop inexpensive sequence-based markers to efficiently target resistance alleles for marker-assisted recurrent selection. From the mapping population segregating for the QTL, DNA of 44 of the most resistant and 44 of the most susceptible F₁ individuals was pooled and sequenced using the Illumina HiSeq 2000 platform. Allele frequencies of 18 × 10⁶ single nucleotide polymorphisms (SNP) were determined in the resistant and susceptible pool. A total of 271 SNPs on 140 scaffold sequences of the reference parental genome showed significantly different allele frequencies in both pools. We converted 44 selected SNPs to KASP™ markers, genetically mapped these proximal to the major QTL and thus validated their association with bacterial wilt resistance. This study highlights the power of pooled DNA sequencing to efficiently target binary traits in biparental mapping populations. It delivers genome sequence data, SNP markers and potential candidate genes which will allow to implement marker-assisted strategies to fix bacterial wilt resistance in outcrossing breeding populations of Italian ryegrass.

Diversity in Accessions of Panicum miliaceum L. Based on Agro-Morphological, Antioxidative, and Genetic Traits

The genetic diversity and antioxidant potential of Panicum miliaceum L. accessions collected from different geo-ecological regions of South Korea were evaluated and compared. Antioxidant potential of seeds was estimated by the 1,1-diphenyl-2-picrylhydrazyl (DPPH) and 2,2′-azino-bis-3-ethylbenzthiazoline-6-sulfonic acid (ABTS) radical scavenging assays and total phenolic content was determined by the Folin–Ciocalteu method. Total phenolic content (TPC) in 80% methanolic extracts ranged from 16.24 ± 0.86 to 58.04 ± 1.00 mg gallic acid equivalent (GAE)/g of the sample extracts and total flavonoid content (TFC) varied from 7.19 ± 1.05 to 52.56 ± 1.50 mg quercetin equivalents (QE) mg/g of the sample extracts. DPPH radical scavenging capacity of the extracts from the 15 accessions of P. miliaceum varied from 206.44 ± 7.72 to 2490.24 ± 4.641 mg GAE/g of the sample extracts and ABTS radical scavenging capacity ranged from 624.85 ± 13.1 to 1087. 77 ± 9.58 mg GAE/g of the sample extracts. A wide range of genetic variation was observed as measured by Shannon’s information index (I), number of effective alleles (Ne), number of observed alleles (Na), expected heterozygosity (He), unbiased expected heterozygosity (uHe). The observed variation in the bioactive properties, morphological traits, and genetic diversity among the accessions may provide useful information for breeding programs seeking to improve bioactive properties of P. miliaceum.

De Novo Transcriptomic Analysis and Development of EST–SSRs for Styrax japonicus

Styrax japonicus sieb. et Zucc. is widely distributed in China with ornamental and medicinal values. However, the transcriptome of S. japonicus has not yet been reported. In this study, we carried out the first transcriptome analysis of S. japonicus and developed a set of expressed sequence tag–simple sequence repeats (EST–SSRs). We obtained 338,570,222 clean reads in total, of which the mean GC content was 41.58%. In total, 136,071 unigenes were obtained having an average length of 611 bp and 71,226 unigenes were favorably annotated in the database. In total, we identified 55,977 potential EST–SSRs from 38,611 unigenes, of which there was 1 SSR per 6.73 kb. The di-nucleotide repeats (40.40%) were the most identified SSRs. One set of 60 primer pairs was randomly selected, and the amplified products in S. japonicus were validated; 28 primer pairs successfully produced clear amplicons. A total of 21 (35%) polymorphic genic SSR markers were identified between two populations. In total, 15 alleles were detected and the average number was 6. The average of observed heterozygosity and expected heterozygosity was 0.614 and 0.552, respectively. The polymorphism information content (PIC) value fluctuated between 0.074 and 0.855, with a mean value of 0.504, which was also the middle level. This study provides useful information for diversity studies and resource assessments of S. japonicus.