Characterization of Genetic and Allelic Diversity Amongst Cultivated and Wild Lentil Accessions for Germplasm Enhancement

Genetic structure and ecological niche space of lentil's closest wild relative, Lens orientalis (Boiss.) Schmalh

Crops arose from wild ancestors and to understand their domestication it is essential to compare the cultivated species with their crop wild relatives. These represent an important source of further crop improvement, in particular in relation to climate change. Although there are about 58,000 Lens accessions held in genebanks, only 1% are wild. We examined the geographic distribution and genetic diversity of the lentil's immediate progenitor L. orientalis. We used Genotyping by Sequencing (GBS) to identify and characterize differentiation among accessions held at germplasm collections. We then determined whether genetically distinct clusters of accessions had been collected from climatically distinct locations. Of the 195 genotyped accessions, 124 were genuine L. orientalis with four identified genetic groups. Although an environmental distance matrix was significantly correlated with geographic distance in a Mantel test, the four identified genetic clusters were not found to occupy significantly different environmental space. Maxent modelling gave a distinct predicted distribution pattern centred in the Fertile Crescent, with intermediate probabilities of occurrence in parts of Turkey, Greece, Cyprus, Morocco, and the south of the Iberian Peninsula with NW Africa. Future projections did not show any dramatic alterations in the distribution according to the climate change scenarios tested. We have found considerable diversity in L. orientalis, some of which track climatic variability. The results of the study showed the genetic diversity of wild lentil and indicate the importance of ongoing collections and in situ conservation for our future capacity to harness the genetic variation of the lentil progenitor.

Complete chloroplast genome of Lens lamottei reveals intraspecies variation among with Lens culinaris

Lens lamottei is a member of the Fabaceae family and the second gene pool of the genus Lens. The environmental factors that drove the divergence among wild and cultivated species have been studied extensively. Recent research has focused on genomic signatures associated with various phenotypes with the acceleration of next-generation techniques in molecular profiling. Therefore, in this study, we provide the complete sequence of the chloroplast genome sequence in the wild Lens species L. lamottei with a deep coverage of 713 × next-generation sequencing (NGS) data for the first time. Compared to the cultivated species, Lens culinaris, we identified synonymous, and nonsynonymous changes in the protein-coding regions of the genes ndhB, ndhF, ndhH, petA, rpoA, rpoC2, rps3, and ycf2 in L. lamottei. Phylogenetic analysis of chloroplast genomes of various plants under Leguminosae revealed that L. lamottei and L. culinaris are closest to one another than to other species. The complete chloroplast genome of L. lamottei also allowed us to reanalyze previously published transcriptomic data, which showed high levels of gene expression for ATP-synthase, rubisco, and photosystem genes. Overall, this study provides a deeper insight into the diversity of Lens species and the agricultural importance of these plants through their chloroplast genomes.

An evolutionary look into the history of lentil reveals unexpected diversity

The characterization and preservation of genetic variation in crops is critical to meeting the challenges of breeding in the face of changing climates and markets. In recent years, the use of single nucleotide polymorphisms (SNPs) has become routine, allowing us to understand the population structure, find divergent lines for crosses, and illuminate the origin of crops. However, the focus on SNPs overlooks other forms of variation, such as copy number variation (CNVs). Lentil is the third most important cold‐season legume and was domesticated in the Fertile Crescent. We genotyped 324 accessions that represent its global diversity, and using both SNPs and CNVs, we dissected the population structure and genetic variation, and identified candidate genes. Eight clusters were detected, most of them located in or near the Fertile Crescent, even though different clusters were present in distinct regions. The cluster from South Asia was particularly differentiated and presented low diversity, contrasting with the clusters from the Mediterranean and the northern temperate. Accessions from North America were mainly assigned to one cluster and were highly diverse, reflecting the efforts of breeding programs to integrate variation. Thirty‐three genes were identified as candidates under selection and among their functions were sporopollenin synthesis in pollen, a component of chlorophyll B reductase that partially determines the antenna size, and two genes related to the import system of chloroplasts. Eleven percent of all lentil genes and 21% of lentil disease resistance genes were affected by CNVs. The gene categories overrepresented in these genes were “enzymes,” “Cell Wall Organization,” and “external stimuli response.” All the genes found in the latter were associated with pathogen response. CNVs provided information about population structure and might have played a role in adaptation. The incorporation of CNVs in diversity studies is needed for a broader understanding of how they evolve and contribute to domestication.

Strategies of preserving genetic diversity while maximizing genetic response from implementing genomic selection in pulse breeding programs

Genomic selection maximizes genetic gain by recycling parents to germplasm pool earlier and preserves genetic diversity by restricting the number of fixed alleles and the relationship in pulse breeding programs. Using a stochastic computer simulation, we investigated the benefit of optimization strategies in the context of genomic selection (GS) for pulse breeding programs. We simulated GS for moderately complex to highly complex traits such as disease resistance, grain weight and grain yield in multiple environments with a high level of genotype-by-environment interaction for grain yield. GS led to higher genetic gain per unit of time and higher genetic diversity loss than phenotypic selection by shortening the breeding cycle time. The genetic gain obtained from selecting the segregating parents early in the breeding cycle (at F₁ or F₂ stages) was substantially higher than selecting at later stages even though prediction accuracy was moderate. Increasing the number of F₁ intercross (F_1i) families and keeping the total number of progeny of F_1i families constant, we observed a decrease in genetic gain and increase in genetic diversity, whereas increasing the number of progeny per F_1i family while keeping a constant number of F_1i families increased the rate of genetic gain and had higher genetic diversity loss per unit of time. Adding 50 F₂ family phenotypes to the training population increased the accuracy of genomic breeding values (GEBVs) and genetic gain per year and decreased the rate of genetic diversity loss. Genetic diversity could be preserved by applying a strategy that restricted both the percentage of alleles fixed and the average relationship of the group of selected parents to preserve long-term genetic improvement in the pulse breeding program.

Genetic Variation of a Lentil (Lens culinaris) Landrace during Three Generations of Breeding

Genetic differentiation between 40 lentil genotypes was tested using molecular markers. The genotypes were produced from a Greek landrace of commercial interest via the honeycomb breeding methodology, i.e., single-plant selection in the absence of competition, across three successive pedigree generations. The selected genotypes from each generation were examined for genetic relationships using 15 SSR molecular markers with HRM analysis. As expected, low variation among consecutive generations at the level of 2.5–7.7% was detected. Analysis of molecular variance (AMOVA) revealed that partitioning of this variation was at higher percentage within each generation’s population than between them. Population structure analysis indicated that ongoing selection could effectively shift the allelic composition in each generation. The applied honeycomb breeding methodology that effectively improved progeny yield and seed quality increased the percentage of favorable alleles altering allelic composition but not eliminating genetic variation of the breeding population.

Intelligent Characterization of Lentil Genetic Resources: Evolutionary History, Genetic Diversity of Germplasm, and the Need for Well-Represented Collections

The genetic and phenotypic characterization of crops allows us to elucidate their evolutionary and domestication history, the genetic basis of important traits, and the use of variation present in landraces and wild relatives to enhance resilience. In this context, we aim to provide an overview of the main genetic resources developed for lentil and their main outcomes, and to suggest protocols for continued work on this important crop. Lens culinaris is the third-most-important cool-season grain and its use is increasing as a quick-cooking, nutritious, plant-based source of protein. L. culinaris was domesticated in the Fertile Crescent, and six additional wild taxa (L. orientalis, L. tomentosus, L. odemensis, L. lamottei, L. ervoides, and L. nigricans) are recognized. Numerous genetic diversity studies have shown that wild relatives present high levels of genetic variation and provide a reservoir of alleles that can be used for breeding programs. Furthermore, the integration of genetics/genomics and breeding techniques has resulted in identification of quantitative trait loci and genes related to attributes of interest. Genetic maps, massive genotyping, marker-assisted selection, and genomic selection are some of the genetic resources generated and applied in lentil. In addition, despite its size (∼4 Gbp) and complexity, the L. culinaris genome has been assembled, allowing a deeper understanding of its architecture. Still, major knowledge gaps exist in lentil, and a deeper understanding and characterization of germplasm resources, including wild relatives, is critical to lentil breeding and improvement. © 2021 The Authors. Current Protocols published by Wiley Periodicals LLC. Basic Protocol 1: Recording of lentil seed descriptors Basic Protocol 2: Lentil seed imaging Basic Protocol 3: Lentil seed increase Basic Protocol 4: Recording of primary lentil seed INCREASE descriptors.

Application of Genomics to Understand Salt Tolerance in Lentil

Soil salinity is a major abiotic stress, limiting lentil productivity worldwide. Understanding the genetic basis of salt tolerance is vital to develop tolerant varieties. A diversity panel consisting of 276 lentil accessions was screened in a previous study through traditional and image-based approaches to quantify growth under salt stress. Genotyping was performed using two contrasting methods, targeted (tGBS) and transcriptome (GBS-t) genotyping-by-sequencing, to evaluate the most appropriate methodology. tGBS revealed the highest number of single-base variants (SNPs) (c. 56,349), and markers were more evenly distributed across the genome compared to GBS-t. A genome-wide association study (GWAS) was conducted using a mixed linear model. Significant marker-trait associations were observed on Chromosome 2 as well as Chromosome 4, and a range of candidate genes was identified from the reference genome, the most plausible being potassium transporters, which are known to be involved in salt tolerance in related species. Detailed mineral composition performed on salt-treated and control plant tissues revealed the salt tolerance mechanism in lentil, in which tolerant accessions do not transport Na⁺ ions around the plant instead localize within the root tissues. The pedigree analysis identified two parental accessions that could have been the key sources of tolerance in this dataset.

The History of Lentil (Lens culinaris subsp. culinaris) Domestication and Spread as Revealed by Genotyping-by-Sequencing of Wild and Landrace Accessions

Protein-rich legumes accompanied carbohydrate-rich cereals since the beginning of agriculture and yet their domestication history is not as well understood. Lentil (Lens culinaris Medik. subsp. culinaris) was first cultivated in Southwest Asia (SWA) 8000-10,000 years ago but archeological evidence is unclear as to how many times it may have been independently domesticated, in which SWA region(s) this may have happened, and whether wild species within the Lens genus have contributed to the cultivated gene pool. In this study, we combined genotyping-by-sequencing (GBS) of 190 accessions from wild (67) and domesticated (123) lentils from the Old World with archeological information to explore the evolutionary history, domestication, and diffusion of lentils to different environments. GBS led to the discovery of 87,647 single-nucleotide polymorphisms (SNPs), which allowed us to infer the phylogeny of genus Lens. We confirmed previous studies proposing four groups within it. The only gene flow detected was between cultivated varieties and their progenitor (L. culinaris subsp. orientalis) albeit at very low levels. Nevertheless, a few putative hybrids or naturalized cultivars were identified. Within cultivated lentil, we found three geographic groups. Phylogenetics, population structure, and archeological data coincide in a scenario of protracted domestication of lentils, with two domesticated gene pools emerging in SWA. Admixed varieties are found throughout their range, suggesting a relaxed selection process. A small number of alleles involved in domestication and adaptation to climatic variables were identified. Both novel mutation and selection on standing variation are presumed to have played a role in adaptation of lentils to different environments. The results presented have implications for understanding the process of plant domestication (past), the distribution of genetic diversity in germplasm collections (present), and targeting genes in breeding programs (future).

Prospects of next generation sequencing in lentil breeding

Lentil is an important food legume crop that has large and complex genome. During past years, considerable attention has been given on the use of next generation sequencing for enriching the genomic resources including identification of SSR and SNP markers, development of unigenes, transcripts, and identification of candidate genes for biotic and abiotic stresses, analysis of genetic diversity and identification of genes/ QTLs for agronomically important traits. However, in other crops including pulses, next generation sequencing has revolutionized the genomic research and helped in genomic assisted breeding rapidly and cost effectively. The present review discuss current status and future prospects of the use NGS based breeding in lentil.