Drought stress memory in orchard grass and the role of marker-based parental selection for physiological and antioxidant responses

Drought stress memory occurring in some plants plays a crucial role in their adaptation to unfavorable conditions. However, in open-pollinated plants, this phenomenon is assumed to be affected by population plasticity resulting from kind and level of diversity and inbreeding depression. Physiological perspectives of drought stress memory in four synthetic poly-crossed populations (groups) of orchard grass (Dactylis glomerata) constructed from parental genotypes with contrasting levels (narrow and wide) of molecular and morphological genetic variation were assessed. Populations of two generations (Syn1 and Syn2) were developed and were subjected to three moisture treatments, including normal irrigation (C), primary mild stress-secondary intense stress (D1D2), and secondary intense stress (D2). Pre-exposure to drought significantly improved the mean values of leaf water, chlorophyll, proline, and ascorbate peroxidase compared to intense stress, leading to more effective memory responses. Superiority of groups with high levels of molecular diversity for most traits, suggesting that the molecular genetic distance among parents is an effective predictor of progeny performance. The results indicated that the fitness of progenies of the four polycross groups declines significantly from Syn1 to Syn2, however the magnitude of observed inbreeding depends on the level of diversity and moisture conditions. We propose a hypothesis that underscores the interplay between genetic diversity among parents and drought stress memory providing valuable insights for developing new synthetic varieties in open-pollinated grasses. Specifically, we posit that higher molecular diversity among parental genotypes enhances the potential for robust drought stress memory, thereby contributing to improved progeny fitness under unfavorable conditions.

Genotyping by Sequencing and Plastome Analysis Finds High Genetic Variability and Geographical Structure in Dactylis glomerata L. in Northwest Europe Despite Lack of Ploidy Variation

Large collections of the forage and bioenergy grass Dactylis glomerata were made in northwest (NW) Europe along east to west and north to south clines for genetic resource conservation and to inform breeding programmes of genetic diversity, genepools, and ploidy. Leaves were sampled for genetic analysis and seed and rhizome for ex-situ conservation. Genotyping by sequencing (GBS) was used to assay nuclear DNA diversity and plastome single nucleotide polymorphism (SNP) discovery was undertaken using a long-read PCR and MiSeq approach. Nuclear and plastid SNPs were analysed by principal component analysis (PCA) to compare genotypes. Flow cytometry revealed that all samples were tetraploid, but some genome size variation was recorded. GBS detected an average of approximately 10,000 to 15,000 SNPs per country sampled. The highest average number of private SNPs was recorded in Poland (median ca. 2000). Plastid DNA variation was also high (1466 SNPs, 17 SNPs/kbp). GBS data, and to a lesser extent plastome data, also show that genetic variation is structured geographically in NW Europe with loose clustering matching the country of plant origin. The results reveal extensive genetic diversity and genetic structuring in this versatile allogamous species despite lack of ploidy variation and high levels of human mediated geneflow via planting.

Hybrid identification and genetic variation of Elymus sibiricus hybrid populations using EST-SSR markers

Background

Elymus sibiricus is an important native grass in Qinghai-Tibetan Plateau. Seed shattering is a serious problem for E. sibiricus, especially at harvest time. Cross breeding is an effective way to create new varieties with beneficial characteristic or improved traits, and to broaden genetic base.

Results

In this study, we created five hybrid populations by crossing seven E. sibiricus genotypes that have seed shattering variation. Then, nine EST-SSR primers were used for hybrid identification based on DNA fingerprinting, and genetic diversity analysis of hybrid populations and their respective parents. A total of 15 hybrids were identified. An analysis of amplified polymorphic bands among genuine hybrids and their respective parents revealed mainly two types of markers: 1) hybrids shared bands exclusively amplified in both parents; 2)hybrids shared bands exclusively amplified in male parents. For each hybrid population, the total number of amplified bands ranged from 37 to 57, the percentage of polymorphism varied from 65.12% to 75.68%, with an average of 70.51%. Novel bands found in each hybrid population varied from 0 to 9 bands, suggesting an occurrence of rearrangements in the hybrid population. The structure analysis revealed that all hybrid populations and parents were assigned to eight groups. The principal coordinate analysis (PCoA) showed similar results.

Conclusions

In general, this study proved EST-SSR markers are efficient for hybrid identification, and suggested more genetic variation could be captured in hybrid populations by crossing breeding.

AFLP assessment of genetic variability and relationships in an Asian wild germplasm collection of Dactylis glomerata L

Orchardgrass (Dactylis glomerata L.), an excellent perennial and cool season forage species distributed in most temperate regions, has been cultivated widely in Western China. Amplified fragment length polymorphism markers were employed to determine the genetic variability and population structure among 41 indigenous orchardgrass accessions from Central Asia and Western China. On the basis of 531 polymorphic fragments resulted from eight primer combinations, polymorphic information content (PIC), marker index (MI) and resolving power (RP) averaged 0.252, 16.34 and 25.27 per primer combination, respectively, demonstrating the high efficiency and reliability of the markers used. We found relatively low differentiation (Fst=0.135) for three geographical groups, where Central Asia (CA) and Southwest China (SWC) group exhibited higher intra-population diversity (He=0.20 and 0.21) than that of the Xinjiang (XJ) group (He=0.14). We also did not detect a clear pattern of isolation by distance with a low value of r=0.301 in the Mantel test. STRUCTURE, FLOCK, UPGMA clustering and PCoA analyses showed that CA group is more related to the SWC Group rather than to the XJ Group. In addition, this study strongly suggests that geographical and ecological environmental factors together could better explain the genetic differentiation between different geographical regions than geographic isolation alone, especially for Xinjiang accessions. The present study also could support that Southwest China might be the internal diversity center of D. glomerata in China. The knowledge about the genetic variability of the Asian accessions examined contributes to rapid characterization, defining gene pools of wild accessions, and selecting appropriate germplasms for plant improvement.

Assessing and Broadening Genetic Diversity of Elymus sibiricus Germplasm for the Improvement of Seed Shattering

Siberian wild rye (Elymus sibiricus L.) is an important native grass in the Qinghai-Tibet Plateau of China. It is difficult to grow for commercial seed production, since seed shattering causes yield losses during harvest. Assessing the genetic diversity and relationships among germplasm from its primary distribution area contributes to evaluating the potential for its utilization as a gene pool to improve the desired agronomic traits. In the study, 40 EST-SSR primers were used to assess the genetic diversity and population structure of 36 E. sibiricus accessions with variation of seed shattering. A total of 380 bands were generated, with an average of 9.5 bands per primer. The polymorphic information content (PIC) ranged from 0.23 to 0.50. The percentage of polymorphic bands (P) for the species was 87.11%, suggesting a high degree of genetic diversity. Based on population structure analysis, four groups were formed, similar to results of principal coordinate analysis (PCoA). The molecular variance analysis (AMOVA) revealed the majority of genetic variation occurred within geographical regions (83.40%). Two genotypes from Y1005 and ZhN06 were used to generate seven F₁ hybrids. The molecular and morphological diversity analysis of F₁ population revealed rich genetic variation and high level of seed shattering variation in F₁ population, resulting in significant improvement of the genetic base and desired agronomic traits.