Harnessing Genetic Diversity in the USDA Pea Germplasm Collection Through Genomic Prediction

Phenotypic evaluation and efficient utilization of germplasm collections can be time-intensive, laborious, and expensive. However, with the plummeting costs of next-generation sequencing and the addition of genomic selection to the plant breeder’s toolbox, we now can more efficiently tap the genetic diversity within large germplasm collections. In this study, we applied and evaluated genomic prediction’s potential to a set of 482 pea (Pisum sativum L.) accessions—genotyped with 30,600 single nucleotide polymorphic (SNP) markers and phenotyped for seed yield and yield-related components—for enhancing selection of accessions from the USDA Pea Germplasm Collection. Genomic prediction models and several factors affecting predictive ability were evaluated in a series of cross-validation schemes across complex traits. Different genomic prediction models gave similar results, with predictive ability across traits ranging from 0.23 to 0.60, with no model working best across all traits. Increasing the training population size improved the predictive ability of most traits, including seed yield. Predictive abilities increased and reached a plateau with increasing number of markers presumably due to extensive linkage disequilibrium in the pea genome. Accounting for population structure effects did not significantly boost predictive ability, but we observed a slight improvement in seed yield. By applying the best genomic prediction model (e.g., RR-BLUP), we then examined the distribution of genotyped but nonphenotyped accessions and the reliability of genomic estimated breeding values (GEBV). The distribution of GEBV suggested that none of the nonphenotyped accessions were expected to perform outside the range of the phenotyped accessions. Desirable breeding values with higher reliability can be used to identify and screen favorable germplasm accessions. Expanding the training set and incorporating additional orthogonal information (e.g., transcriptomics, metabolomics, physiological traits, etc.) into the genomic prediction framework can enhance prediction accuracy.

Complex polyploid and hybrid species in an apomictic and sexual tropical forage grass group: genomic composition and evolution in Urochloa (Brachiaria) species

Background and Aims Diploid and polyploid Urochloa (including Brachiaria, Panicum and Megathyrsus species) C4 tropical forage grasses originating from Africa are important for food security and the environment​, often being planted in marginal lands worldwide. We aimed to characterize the nature of their genomes, the repetitive DNA, and the genome composition of polyploids, leading to a model of the evolutionary pathways within the group including many apomictic species. Methods Some 362 forage grass accessions from international germplasm collections were studied, and ploidy determined using an optimized flow cytometry method. Whole-genome survey sequencing and molecular cytogenetic analysis were used to identify chromosomes and genomes in Urochloa accessions belonging to the 'brizantha' and 'humidicola' agamic complexes and U. maxima. Key Results Genome structures are complex and variable, with multiple ploidies and genome compositions within the species, and no clear geographical patterns. Sequence analysis of nine diploid and polyploid accessions enabled identification of abundant genome-specific repetitive DNA motifs​. In situ hybridization with a combination of repetitive DNA and genomic DNA probes, identified evolutionary divergence and allowed us to discriminate the different genomes present in polyploids. Conclusions We suggest a new coherent nomenclature for the genomes present​. We develop a model of evolution at the whole-genome level in diploid and polyploid accessions showing processes of grass evolution. We support the retention of narrow species concepts for U. brizantha, U. decumbens, and U. ruziziensis, and do not consider diploids and polyploids of single species as cytotypes. The results and model will be valuable in making rational choices of parents for new hybrids, assist in use of the germplasm for breeding and selection of Urochloa with improved sustainability and agronomic potential, and will assist in measuring and conserving biodiversity in grasslands.

COMPLEMENTARY TOOLS UTILIZED IN THE PEA (Pisum sativum L.) BREEDING PROGRAM AT UNIVERSIDAD NACIONAL DE ROSARIO

Conventional breeding can be complemented by different strategies that increase the efficiency of the methodologies and the current rate of increase in yields in order to meet demand. The use of molecular markers with the aim of developing linkage maps of the species, the use of Blup (Best Linear Unbiased Prediction) for an efficient selection of progenitors to hybridize, the use of in vitro culture to artificially increase the number of F1 plants or the use of digital phenotyping for efficient digital characterization that can be performed during the periodic and routine regeneration of accessions in germplasm collections. Key words: Molecular markers, Blup, in vitro culture, digital phenotyping.

Identification and Validation of a Core Single-Nucleotide Polymorphism Marker Set for Genetic Diversity Assessment, Fingerprinting Identification, and Core Collection Development in Bottle Gourd

Germplasm collections are indispensable resources for the mining of important genes and variety improvement. To preserve and utilize germplasm collections in bottle gourd, we identified and validated a highly informative core single-nucleotide polymorphism (SNP) marker set from 1,100 SNPs. This marker set consisted of 22 uniformly distributed core SNPs with abundant polymorphisms, which were established to have strong representativeness and discriminatory power based on analyses of 206 bottle gourd germplasm collections and a multiparent advanced generation inter-cross (MAGIC) population. The core SNP markers were used to assess genetic diversity and population structure, and to fingerprint important accessions, which could provide an optimized procedure for seed authentication. Furthermore, using the core SNP marker set, we developed an accessible core population of 150 accessions that represents 100% of the genetic variation in bottle gourds. This core population will make an important contribution to the preservation and utilization of bottle gourd germplasm collections, cultivar identification, and marker-assisted breeding.

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

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

Targeting the B1 Gene and Analysis of Its Polymorphism Associated with Awned/Awnless Trait in Russian Germplasm Collections of Common Wheat

The presence of awns on the ear is associated with a number of important plant properties, such as drought resistance, quality of the grain mass during processing, etc. The main manifestations of this trait are controlled by the B1 gene, which has recently been identified and encodes the C2H2 zinc finger transcription factor. Based on the previously identified SNPs in the promoter region of this gene, we constructed markers for dominant and recessive alleles which determine awnless and awned phenotypes, respectively. The markers were successful for use in targeting the respective alleles of the B1 gene in 176 varieties of common wheat, accessions of T. spelta L., as well as on F2/F3 hybrids from crosses between awned and awnless forms of T. aestivum. We first identified a new allele, b1mite, which has both an insert of a miniature Stowaway-like transposon, 261 bp in length, and 33 novel SNPs in the promoter region. Despite these changes, this allele had no effect on the awned phenotype. The possible mechanisms of the influence of the analyzed gene on phenotype are discussed.

Genetic resources of narrow-leaved lupine (Lupinus angustifolius L.) and their role in its domestication and breeding

Narrow-leaved lupine (Lupinus angustifolius L.) is a cultivated multipurpose species with a very short history of domestication. It is used as a green manure, and for feed and food. This crop shows good prospects for use in pharmacology and as a source of fish feeds in aquaculture. However, its genetic potential for the development of productive and adaptable cultivars is far from being realized. For crop species, the genetic base of the cultivated gene pool has repeatedly been shown as being much narrower than that of the wild gene pool. Therefore, efficient utilization of a species’ genetic resources is important for the crop’s further improvement. Analyzing the information on the germplasm collections preserved in national gene banks can help perceive the worldwide diversity of L. angustifolius genetic resources and understand how they are studied and used. In this context, the data on the narrow-leaved lupine collection held by VIR are presented: its size and composition, the breeding status of accessions, methods of studying and disclosing intraspecific differentiation, the classifications used, and the comparison of this information with available data on other collections. It appeared that VIR’s collection of narrow-leaved lupine, ranking as the world’s second largest, differed significantly from others by the prevalence of advanced cultivars and breeding material in it, while wild accessions prevailed in most collections. The importance of the wild gene pool for the narrow-leaved lupine breeding in Australia, the world leader in lupine production, is highlighted. The need to get an insight into the species’ ecogeographic diversity in order to develop cultivars adaptable to certain cultivation conditions is shown. The data on the testing of VIR’s collection for main crop characters valuable for breeders are presented. Special attention is paid to the study of accessions with limited branching as a promising gene pool for cultivation in relatively northern regions of Russia. They demonstrate lower but more stable productivity, and suitability for cultivation in planting patterns, which has a number of agronomic advantages. Analyzing the work with narrow-leaved lupine genetic resources in different national gene banks over the world helps shape the prospects of further activities with VIR’s collection as the only source of promising material for domestic breeding.

Grapevine Shoot Tip Cryopreservation and Cryotherapy: Secure Storage of Disease-Free Plants

Grapevine (Vitis spp.) is one of the most economically important temperate fruit crops. Grapevine breeding programs require access to high-quality Vitis cultivars and wild species, which may be maintained within genebanks. Shoot tip cryopreservation is a valuable technique for the safe, long-term conservation of Vitis genetic resources that complements traditional field and in vitro germplasm collections. Vitis is highly susceptible to virus infections. Virus-free plants are required as propagation material for clonally propagated germplasm, and also for the global exchange of grapevine genetic resources. Shoot tip cryotherapy, a method based on cryopreservation, has proven to be effective in eradicating viruses from infected plants, including grapevine. This comprehensive review outlines/documents the advances in Vitis shoot tip cryopreservation and cryotherapy that have resulted in healthy plants with high regrowth levels across diverse Vitis species.

Structural and functional leaf diversity lead to variability in photosynthetic capacity across a range of Juglans regia genotypes

Similar to other cropping systems, few walnut cultivars are used as scion in commercial production. Germplasm collections can be used to diversify cultivar options and hold potential for improving crop productivity, disease resistance and stress tolerance. In this study we explored the anatomical and biochemical bases of photosynthetic capacity in 11 J. regia accessions in the USDA-ARS National Clonal Germplasm Repository. Net assimilation rate (A) differed significantly among accessions and was greater in those from lower latitudes coincident with increases in stomatal and mesophyll conductance, leaf thickness, mesophyll porosity and gas-phase diffusion, and leaf nitrogen, and lower leaf mass and stomatal density. High CO-saturated assimilation rates led to increases in A under limiting conditions. Greater A was found in lower latitude accessions native to climates with more frost-free days, greater precipitation seasonality, and lower temperature seasonality. As expected, water stress consistently impaired photosynthesis with the highest % reductions in three lower latitude accessions (A3, A5, and A9), which had the highest A under well-watered conditions. However, A for A3 and A5 remained amongst the highest under dehydration. J. regia accessions, which have leaf structural traits and biochemistry that enhance photosynthesis, could be used as commercial scions or breeding parents to enhance productivity.