AFLP-based genetic diversity of wild orchardgrass germplasm collections from Central Asia and Western China, and the relation to environmental factors

Genetic diversity of a Silybum marianum (L.) Gaertn. germplasm collection revealed by DNA Diversity Array Technology (DArTseq)

Silybum marianum (L.) Gaertn. is a multipurpose crop native to the Mediterranean and middle east regions and mainly known for the hepatoprotective properties of fruit-derived silymarin. Despite growing interest in milk thistle as a versatile crop with medicinal value, its potential in agroindustry is hindered by incomplete domestication and limited genomic knowledge, impeding the development of competitive breeding programs. The present study aimed to evaluate genetic diversity in a panel of S. marianum accessions (n = 31), previously characterized for morphological and phytochemical traits, using 5,178 polymorphic DArTseq SNP markers. The genetic structure investigated using both parametric and non-parametric approaches (e.g. PCA, AWclust, Admixture), revealed three distinctive groups reflecting geographical origins. Indeed, Pop1 grouped accessions from Central Europe and UK, Pop3 consisted mainly of accessions of Italian origin, and Pop2 included accessions from different geographical areas. Interestingly, Italian genotypes showed a divergent phenotypic distribution, particularly in fruit oleic and linoleic acid content, compared to the other two groups. Genetic differentiation among the three groups, investigated by computing pairwise fixation index (FST), confirmed a greater differentiation of Pop3 compared to other subpopulations, also based on other diversity indices (e.g. private alleles, heterozygosity). Finally, 22 markers were declared as putatively under natural selection, of which seven significantly affected some important phenotypic traits such as oleic, arachidonic, behenic and linoleic acid content. These findings suggest that these markers, and overall, the seven SNP markers identified within Pop3, could be exploited in specific breeding programs, potentially aimed at diversifying the use of milk thistle. Indeed, incorporating genetic material from Pop3 haplotypes carrying the selected loci into milk thistle breeding populations might be the basis for developing milk thistle lines with higher levels of oleic, arachidonic, and behenic acids, and lower levels of linoleic acid, paving new avenues for enhancing the nutritional and agronomic characteristics of milk thistle.

Environmental Niche Dynamics of Blue Grama (Bouteloua gracilis) Ecotypes in Northern Mexico: Genetic Structure and Implications for Restoration Management

Understanding the genetic structure adopted by natural populations and its relation to environmental adaptation is critical for the success of restoration programs. We evaluated the genetic structure and temporal environmental niche dynamics of blue grama (Bouteloua gracilis) in 48 populations. The genetic evaluation was performed through amplified fragment length polymorphism (AFLP) molecular markers. The maximum entropy method was used to model the past, present, and future environmental niches of the three clusters derived from the genetic analysis. The environmental niches of the three genetic clusters showed dynamic overlaps and isolations during the last interglacial and glacial maximum. The paleoclimatic events, which occurred during those periods, may have reinforced genetic exchange among populations and affected their genetic structure. Genetic clusters also presented different environmental niches in the present. Thus, they can be considered as three distinct ecotypes and restoration programs must be carried out using local germplasm from each environmental niche to increase their chance of success. Based on the environmental niches of the genetic clusters, changes are expected in the near and mid-century future. Therefore, climate change must be considered for species conservation management and future restoration programs.

EST-SSR Primer Development and Genetic Structure Analysis of Psathyrostachys juncea Nevski

Psathyrostachys juncea is a perennial forage grass which plays an important role in soil and water conservation and ecological maintenance in cold and dry areas of temperate regions. In P. juncea, a variety of biotic and abiotic stress related genes have been used in crop improvement, indicating its agronomic, economic, forage, and breeding value. To date, there have been few studies on the genetic structure of P. juncea. Here, the genetic diversity and population structure of P. juncea were analyzed by EST-SSR molecular markers to evaluate the genetic differentiation related to tillering traits in P. juncea germplasm resources. The results showed that 400 simple sequence repeat (SSR) loci were detected in 2,020 differentially expressed tillering related genes. A total of 344 scored bands were amplified using 103 primer pairs, out of which 308 (89.53%) were polymorphic. The Nei's gene diversity of 480 individuals was between 0.092 and 0.449, and the genetic similarity coefficient was between 0.5008 and 0.9111, with an average of 0.6618. Analysis of molecular variance analysis showed that 93% of the variance was due to differences within the population, and the remaining 7% was due to differences among populations. Psathyrostachys juncea materials were clustered into five groups based on population genetic structure, principal coordinate analysis and unweighted pair-group method with arithmetic means (UPGMA) analysis. The results were similar between clustering methods, but a few individual plants were distributed differently by the three models. The clustering results, gene diversity and genetic similarity coefficients showed that the overall genetic relationship of P. juncea individuals was relatively close. A Mantel test, UPGMA and structural analysis also showed a significant correlation between genetic relationship and geographical distribution. These results provide references for future breeding programs, genetic improvement and core germplasm collection of P. juncea.

Dissection of the genetic basis of genotype-by-environment interactions for grain yield and main agronomic traits in Iranian bread wheat landraces and cultivars

Understanding the genetic basis of performance stability is essential to maintain productivity, especially under severe conditions. In the present study, 268 Iranian bread wheat landraces and cultivars were evaluated in four well-watered and two rain-fed conditions for different traits. According to breeding programs, cultivars were in a group with a high mean and stability in terms of GY, GN, and SW traits, while in terms of PH, they had a low mean and high stability. The stability of cultivars and landraces was related to dynamic and static stability, respectively. The highest number of marker pairs and lowest LD decay distance in both cultivars and landraces was observed on the B genome. Population structure differentiated indigenous cultivars and landraces, and the GWAS results for each were almost different despite the commonalities. Chromosomes 1B, 3B, 7B, 2A, and 4A had markers with pleiotropic effects on the stability of different traits. Due to two rain-fed environments, the Gene Ontology (GO) confirmed the accuracy of the results. The identified markers in this study can be helpful in breeding high-performance and stable genotypes and future breeding programs such as fine mapping and cloning.

Contrasting effects of local environment and grazing pressure on the genetic diversity and structure of Artemisia frigida

Drylands count among the most globally extensive biomes, and while many desert and dry rangeland ecosystems are under threat, genetic structures of dryland species are still rarely studied. Artemisia frigida is one of the most widely distributed plant species in the temperate rangelands of Eurasia and North America, and it also dominates in many habitats of Mongolia due to its tolerance to low temperatures, drought and disturbance. Local environmental conditions and grazing pressure can influence species performance and affect spatial patterns of genetic diversity in contrasting ways, and our study set out to evaluate such effects on the genetic diversity and structure of A. frigida. We first developed new species-specific Simple Sequence Repeats (SSRs) markers using whole genome sequencing. We then analysed 11 populations of A. frigida that had been sampled along a large climatic gradient in Mongolia, which were sub-structured according to three levels of grazing intensity. Estimates of genetic diversity at the population level were high (HO = 0.56, HE = 0.73) and tended to increase with higher precipitation and soil nutrient availability. Grazing had no effect on genetic diversity, however, a high number of grazing-specific indicator alleles was found at grazed sites. Genetic differentiation among populations was extremely low (global GST = 0.034). Analysis of Molecular Variance revealed 5% variance between populations along the climatic gradient, with 3% of the variance being partitioned among different grazing intensity levels. We found no relationship between geographic and genetic distances, and thus no isolation by distance in this widely distributed species. The relatively low genetic structuring suggests that considerable gene flow exists among A. frigida populations across the rangelands of Mongolia, in spite of the pervasive grazing in the region.

SSR-based evaluation of genetic diversity in populations of Agriophyllum squarrosum L. and Agriophyllum minus Fisch. & Mey. collected in South-East Kazakhstan

The development of informative polymorphic DNA markers for poorly studied genera is an important step in population analyses of living organisms, including those that play very important ecological roles in harsh environments, such as desert and semi-desert area. Examples of those poorly studied desert species are Agriophyllum squarrosum L. and Agriophyllum minus Fisch. & Mey. However, a recent RNA-sequencing project in A. squarrosum has proposed a large set of hypothetical SSR (simple sequence repeat) markers. In this work, 11 novel polymorphic SSRs were found due to the screening of 24 randomly selected SSRs for three populations of A. squarrosum and one population of A. minus. The analysis of 11 SSRs revealed 16 polymorphic loci in two Agriophyllum species, 8 polymorphic loci within three populations of A. squarrosum, and 6 polymorphic loci in the population of A. minus. Statistical analyses showed high interspecific, but relatively low intraspecific genetic diversity. The phylogenetic clusterization and population structure analysis have demonstrated a clear segregation of A. minus from A. squarrosum, as well as the separation of population 1 from populations 2 and 3 of A. squarrosum. Thus, we identified the set of novel and informative SSR markers suitable for the study of genetic diversity in Agriophyllum.

Genetic variability and structure of an important wild steppe grass Psathyrostachys juncea (Triticeae: Poaceae) germplasm collection from north and central Asia

Russian wildrye, Psathyrostachys junceus (Fisch.) Nevski, is an important wild steppe perennial grass, which is characterized by longevity and short robust rhizomes. It also has highly resistance in grazing and abiotic stress. In this study, the genetic diversity of eleven P. juncea wild germplasms from north and central Asia was investigated using AFLP markers. The P. juncea populations were divided into three clades in both UPGMA dendrogram and PCoA clustering corresponding to the three genetic memberships in STRUCTURE analysis. The genetic specificity of Xinjiang (XJ) populations was revealed by the highest N_e (1.5411) and H_j (0.3553) and their dispersion shown in UPGMA. High inbreeding coefficient (Wright’s F statistics, f = 0.496, F_st = 0.128) was observed although a moderate degree of gene flow (N_m = 1.4736) existed, that may ascribe to habitat fragmentation or the low seedling recruitment, which ultimately resulted in decrease of population size and their genetic diversity. The key factors inducing moderate genetic differentiation detected in this study were isolation by distance (IBD), climatic variabilities and geographical barriers. All these results provide insights into the study of genetic status and germplasm collecting of Russian wildrye.

Isolation-by-environment as a driver of genetic differentiation among populations of the only broad-leaved evergreen shrub Ammopiptanthus mongolicus in Asian temperate deserts

Whether the effect of migration-selection-drift equilibrium on population structure is governed by spatial or environmental differences is usually elucidated by isolation-by-distance (IBD), isolation-by-environment (IBE), and isolation-by-resistance (IBR) tests. The population structure of Ammopiptanthus mongolicus, a broad-leaved evergreen psammophyte in eastern Central Asia, was previously thought to follow an isolation by distance pattern. However, recent studies have emphasized the effects of environmental factors on its growth and distribution, suggesting an important influence of local adaptation on the genetic structure of the species. Using inter-simple sequence repeat (ISSR) markers, we verified the previously inferred low intra-population variation and high inter-population differentiation. However, in contrast to previous studies, the results of partial Mantel tests and a maximum likelihood population effects mixed model (MLPE) suggested that local climate differences, rather than geographic distances or resistance distances, are the main factor affecting population differentiation. Further analysis with removal of multicollinear climatic variables and univariate MLPE found that summer and winter precipitation were crucial for shaping the current population genetic structure. Since local precipitation is related to the regeneration, colonization, and overwintering survival of A. mongolicus, its influence on demographic change may explain its effect on the population genetic structure. In addition, precipitation is related to terrain despite westward decreases, which explains the independence of genetic difference and geographic distance. The identified role of IBE suggests that collecting germplasm resources from genetically differentiated populations could be a more effective strategy to preserve the overall genetic diversity of the species than the establishment of corridors to enhance gene flow among populations.