Genetic diversity of ribosomal loci (5S and 45S rDNA) and pSc119.2 repetitive DNA sequence among four species of Aegilops (Poaceae) from Algeria

In continuation of our previous research we carried out the karyological investigation of 53 populations of four Aegilops species (A. geniculata, A. triuncialis, A. ventricosa, and A. neglecta) sampled in different eco-geographical habitats in Algeria. The genetic variability of the chromosomal DNA loci of the same collection of Aegilops is highlighted by the Fluorescence In Situ Hybridization technique (FISH) using three probes: 5S rDNA, 45S rDNA, and repetitive DNA (pSc119.2). We found that the two rDNA loci (5S and 45S) hybridized with some chromosomes and showed a large genetic polymorphism within and between the four Aegilops species, while the repetitive DNA sequences (pSc119.2) hybridized with all chromosomes and differentiated the populations of the mountains with a humid bioclimate from the populations of the steppe regions with an arid bioclimate. However, the transposition of the physical maps of the studied loci (5S rDNA, 45S rDNA, and pSc119.2) with those of other collections revealed the existence of new loci in Aegilops from Algeria.

Variability in Physiological Traits Reveals Boron Toxicity Tolerance in Aegilops Species

Boron (B) is an important micronutrient required for the normal growth and development of plants. However, its excess in the soil causes severe damage to plant tissues, which affects the final yield. Wheat, one of the main staple crops, has been reported to be largely affected by B toxicity stress in arid and semi-arid regions of the world. The prevalence of B toxicity stress can be addressed by utilizing wild wheat genotypes with a variant level of stress tolerance. Wild wheat relatives have been identified as a prominent source of several abiotic stress-tolerant genes. However, Aegilops species in the tertiary gene pool of wheat have not been well exploited as a source of B toxicity tolerance. This study explores the root and shoot growth, proline induction, and extent of lipid peroxidation in 19 Aegilops accessions comprising 6 different species and the B-tolerant check wheat cultivar Bolal 2973 grown under Control (3.1 μM B), toxic (1 mM B), and highly toxic (10 mM B) B stress treatment. B toxicity stress had a more decisive impact on growth parameters as compared to the malondialdehyde (MDA) and proline content. The obtained results suggested that even the genotypes with high shoot B (SB) accumulation can be tolerant to B toxicity stress, and the mechanism of B redistribution in leaves should be studied in detail. It has been proposed that the studied Aegilops accessions can be potentially used for genetically improving the B toxicity-tolerance trait due to a high level of variation in the response toward high B toxicity. Though a number of accessions showed suppression in the root and shoot growth, very few accessions with stress adaptive plasticity to B toxicity stress leading to an improvement of shoot growth parameters could be determined. The two accessions, Aegilops biuncialis accession TGB 026219 and Aegilops columnaris accession TGB 000107, were identified as the potential genotypes with B toxicity stress tolerance and can be utilized for developing a pre-breeding material in B tolerance-based breeding programs.

Genome sequences of Aegilops species of section Sitopsis reveal phylogenetic relationships and provide resources for wheat improvement

Aegilops is a close relative of wheat (Triticum spp.), and Aegilops species in the section Sitopsis represent a rich reservoir of genetic diversity for improvement of wheat. To understand their diversity and advance their utilization, we produced whole-genome assemblies of Ae. longissima and Ae. speltoides. Whole-genome comparative analysis, along with the recently sequenced Ae. sharonensis genome, showed that the Ae. longissima and Ae. sharonensis genomes are highly simiar and most closely related to the wheat D subgenome. By contrast, the Ae. speltoides genome is more closely related to the B subgenome. Haplotype block analysis supported the idea that Ae. speltoides is the closest ancestor of the wheat B subgenome and highlighted variable and similar genomic regions between the three Aegilops species and wheat. Genome-wide analysis of nucleotide-binding site leucine rich repeat (NLR) genes revealed species-specific and lineage-specific NLR genes and variants, demonstrating the potential of Aegilops genomes for wheat improvement.

Assessment of morphological and anatomical variability in Triticum species, Aegilops species, interspecific and intergeneric hybrids

Wheat species and wild relatives offer promising resources for wheat improvement and research in the current period of the genetic narrowing of modern wheat cultivars. The present study was performed to evaluate the morphological and anatomical traits of 20 diverse genotypes including Triticum and Aegilops species with intergeneric and interspecific wheat hybrids, which were compared with modern bread and durum wheat cultivars locally adapted to rainfed and irrigated conditions. The study showed that stomata density and size ranged from 55.3 to 108.6 stomata/mm2 and 401.4 to 1296 µm2, respectively, in the selected genotypes. Moving tetraploid to hexaploid genotypes, increased chromosome numbers yielded lower densities of large stomata in wheat species and hybrids. In this regard, the stomatal patterns of two hexaploid wheat hybrids and a wheat species including ‘Agrotriticum’, ‘Aegilotriticum’, and T. compactum, were of low density and large size stomata compared to T. durum cv. ‘Kunduru 1149’ with high density and small size stomata. Interestingly, the wild progenitor of the bread wheat D genome, Ae. tauschii, had a high density of the smallest stomata among the studied genotypes. The study further indicated that morphological parameters decreased under rainfed conditions compared to those under irrigated conditions, with levels varying among the genotypes. The rainfed flag leaf area and 1000-grain weight varied from 0.9 to 23.7 cm2 and from 7.3 to 61.9 g, respectively under rainfed conditions, while they ranged from 1.2 to 35.7 cm2 and 11.5 to 69.9 g under irrigated conditions. The flag leaf area had a significant and strong association with 1000-grain weight under rainfed (r2= 0.79) and irrigated (r2 = 0.77) conditions. T. turanicum and T. polonicum were characterized by the significantly highest 1000-grain weight in both rainfed and irrigated conditions. This study suggests that these wheat species with high 1000-grain weight might have promising alleles to be transferred into durum wheat to increase grain yield.

Aegilops Species for the Improvement of the Leaf and Stripe Rust Resistance in Cultivated Triticale (×Triticosecale Wittmack)

Hexaploid triticale (×Triticosecale Wittmack, 2n = 6x = 42 chromosomes, AABBRR) is a cultivated hybrid, which combines wheat (Triticum aestivum L.) and rye (Secale cereale L.) properties. It has a better ability to be grown on poor soils, compared to wheat. Mainly, triticale is produced for forage feed and bioethanol. Considering the limited diversity of this human-made crop, there is a need to widen its genetic variability, especially to introduce new genes, responsible for agronomic traits, such as resistance to biotic stresses. Leaf rust caused by Puccinia triticina Eriks. and stripe rust caused by Puccinia striiformis Westend are the most destructive foliar diseases of triticale and related cereals. Developing resistant triticale varieties is an important strategy for the control of these diseases. A number of leaf and stripe rust resistance genes have been already introduced into bread wheat from related species using chromosome manipulations. Exploitation of related species conferring desirable loci is the most effective non-GMO way of improving the rust resistance of triticale. The procedure encompasses chromosome doubling of obtained hybrids followed by a number of backcrosses to eliminate unnecessary alien chromatin and to reduce the linkage drag. In this review, we show the recent status of pre-breeding studies, which are focused on transfer of leaf and stripe rust resistance genes from Aegilops species into cultivated triticale using distant crossing and chromosome engineering.

Molecular diversity analysis of genotypes from four Aegilops species based on retrotransposon–microsatellite amplified polymorphism (REMAP) markers

Genetic diversity analysis is an important tool in crop improvement. Species with high genetic diversity are a valuable source of variation used in breeding programs. The aim of this study was to assess the genetic diversity of four species belonging to the genus Aegilops, which are often used to expand the genetic variability of wheat and triticale. Forty-five genotypes belonging to the genus Aegilops were investigated. Within- and among-species genetic diversity was calculated based on REMAP (retrotransposon–microsatellite amplified polymorphism) molecular markers. Obtained results showed that REMAP markers are a powerful method for genetic diversity analysis, which produces a high number of polymorphic bands (96.09% of total bands were polymorphic). Among tested genotypes, Ae. crassa and Ae. vavilovii showed the highest genetic diversity and should be chosen as a valuable source of genetic variation.