Aegilops Accessions Research Articles

VARIATION IN CALLUS GROWTH AND IN VITRO REGENERATION AMONG CULTIVATED AND WILD WHEAT GENOTYPES UNDER INCREASING SALT STRESS CONDITIONS

Wheat is one of the most widely cultivated and important cereal crops globally, serving as a staple food for millions of people worldwide. However, wheat production is increasingly challenged by environmental stresses, particularly soil salinity. Developing salt-tolerant varieties is essential to enhance wheat yields in saline-prone regions, thereby ensuring food security and agricultural sustainability. This study evaluated the variations in salt stress tolerance among eight wheat genotypes, representing common wheat, durum wheat, and wild wheat, under in vitro culture conditions. Wheat calli, induced from immature embryos, were subjected to increasing NaCl concentrations in the culture media (0, 50, 100, 150 mM NaCl). Callogenesis rates, recorded after one month of in vitro culture during the induction phase, varied between 33% and 100%, with a significant effect of genotype. The Aegilops accessions showed the lowest callus weights at the end of the induction phase, while Vaga and Jenah Khotifa genotypes exhibited the highest biomass. Significant variations in callus growth and regeneration rates were observed among the studied genotypes under increasing salt stress levels. The obtained results indicated that the durum wheat variety Om Rabiaa, the common wheat variety Salambo, and the two wild accessions, especially MZ116, exhibited the highest salt stress tolerance potential among the studied wheat genotypes. Further investigations at transcriptomic and genomic levels are required to elucidate the molecular basis of their high tolerance to salt stress. These genotypes could be utilized to develop salt-tolerant cultivars, which is crucial in the context of global climate change, either through wheat breeding as donor parents or through genetic transformation strategies. Keywords:Triticum, Aegilops, Salt stress, Callogenesis, Plant regeneration, Selection

Genomic characterization and gene bank curation of Aegilops: the wild relatives of wheat.

Genetic diversity found in crop wild relatives is critical to preserve and utilize for crop improvement to achieve sustainable food production amid climate change and increased demand. We genetically characterized a large collection of 1,041 Aegilops accessions distributed among 23 different species using more than 45K single nucleotide polymorphisms identified by genotyping-by-sequencing. The Wheat Genetics Resource Center (WGRC) Aegilops germplasm collection was curated through the identification of misclassified and redundant accessions. There were 49 misclassified and 28 sets of redundant accessions within the four diploid species. The curated germplasm sets now have improved utility for genetic studies and wheat improvement. We constructed a phylogenetic tree and principal component analysis cluster for all Aegilops species together, giving one of the most comprehensive views of Aegilops. The Sitopsis section and the U genome Aegilops clade were further scrutinized with in-depth population analysis. The genetic relatedness among the pair of Aegilops species provided strong evidence for the species evolution, speciation, and diversification. We inferred genome symbols for two species Ae. neglecta and Ae. columnaris based on the sequence read mapping and the presence of segregating loci on the pertinent genomes as well as genetic clustering. The high genetic diversity observed among Aegilops species indicated that the genus could play an even greater role in providing the critical need for untapped genetic diversity for future wheat breeding and improvement. To fully characterize these Aegilops species, there is an urgent need to generate reference assemblies for these wild wheats, especially for the polyploid Aegilops.

Investigation of genetic diversity of Iranian wild relatives of bread wheat using ISSR and SSR markers

BackgroundWild relatives of wheat are one of the most important genetic resources to use in wheat breeding programs. Therefore, identifying wild relatives of wheat and being aware of their diversity, is undeniably effective in expanding the richness of the gene pool and the genetic base of new cultivars and can be a useful tool for breeders in the future. The present study was performed to evaluate the molecular diversity among 49 accessions of the genera Aegilops and Triticum in the National Plant Gene Bank of Iran using two DNA-based markers, i.e., SSR and ISSR. Also, the present study aimed to examine the relationships among the accessions studied belonging to different genetic backgrounds. ResultsTen SSR and tan ISSR primers produced 2065 and 1524 polymorphism bands, respectively. The number of Polymorphic Bands (NPB), the Polymorphism Information Content (PIC), Marker Index (MI), and Resolving Power (Rp) in SSR marker was 162 to 317, 0.830 to 0.919, 1.326 to 3.167, and 3.169 to 5.692, respectively, and in the ISSR marker, it was from 103 to 185, 0.377 to 0.441, 0.660 to 1.151, and 3.169 to 5.693, respectively. This indicates the efficiency of both markers in detecting polymorphism among the accessions studied. The ISSR marker had a higher polymorphism rate, MI, and Rp than the SSR marker. Molecular analysis of variance for both DNA-based markers showed that the genetic variation within the species was more than the genetic diversity between them. The high level of genomic diversity discovered in the Aegilops and Triticum species proved to provide an ideal gene pool for discovering genes useful for wheat breeding. The accessions were classified into eight groups based on SSR and ISSR markers using the UPGMA method of cluster analysis. According to the cluster analysis results, despite similarities between the accessions of a given province, in most cases, the geographical pattern was not in accordance with that observed using the molecular clustering. Based on the coordinate analysis, neighboring groups showed the maximum similarities, and distant ones revealed the maximum genetic distance from each other. The genetic structure analysis successfully separated accessions for their ploidy levels. ConclusionsBoth markers provided a comprehensive model of genetic diversity between Iranian accessions of Aegilops and Triticum genera. Primers used in the present study were effective, informative, and genome-specific which could be used in genome explanatory experiments.

Deciphering the level of genetic diversity in some aegilops species using CAAT box-derived polymorphism (CBDP) and start codon target polymorphism (SCoT) markers.

Maintaining genetic diversity is of the most essential principle for a long-term conservation of plant genetic resources and could play a crucial role in their management. The genus Aegilops is one important member of wheat germplasm, and there are evidences that novel genes of this genus' species can be studied/utilized as ideal sources for the wheat cultivar improvement. The objective of this study was to dissect the genetic diversity and population structure among a set of Iranian Aegilops using two gene-based molecular markers. This study investigated the level of genetic diversity among 157 Aegilops accessions consisting of Ae. tauschii Coss. (DD genome), Ae. crassa Boiss. (DDMM genome), and Ae. cylindrica Host. (CCDD genome) belonging to NPGBI using two sets of CBDP and SCoT markers. The SCoT and CBDP primers yielded 171 and 174 fragments, out of which 145 (90.23%) and 167 (97.66%) fragments were polymorphic, respectively. The average of polymorphism information content (PIC)/ marker index (MI)/resolving power (Rp) for SCoT and CBDP markers were 0.32/3.59/16.03 and 0.29/3.01/16.26, respectively. Results of AMOVA revealed the genetic variability within species was greater than the variation observed among them (SCoT: 88% vs. 12%; CBDP: 72% vs. 28%; SCoT + CBDP: 80% vs. 20%). Based on the information obtained from both markers, the higher level of genetic diversity was found in Ae. tauschii as compared to other species. The grouping patterns obtained by Neighbor-joining algorithms, principal coordinate analysis (PCoA), and Bayesian-model-based structure were consistent with each other and resulted in grouping all studied accessions according to their genomic constitutions. The results of this study revealed a high level of genetic diversity among Iranian Aegilops germplasm. Moreover, SCoT and CBDP marker systems were efficient in deciphering DNA polymorphism and classification of Aegilops germplasm.

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.

Genetic diversity of Aegilops tauschii accessions and its relationship with tetraploid and hexaploid wheat using retrotransposon-based molecular markers

Aegilops is known as the ancestor species of wheat and has a major role in the evolution of wheat. Considering the importance of this species and the fact that Iran is the center of the distribution, fifteen IRAP and REMAP markers were used to evaluate the genetic diversity of Ae. tauschii accessions from different regions of Iran and its relationship with Triticum durum and Triticum aestivum. A high level of polymorphism (99%) was observed for both retrotransposon markers. Polymorphism information content, the effective number of alleles (Ne), Nei’s genetic diversity (H), and Shannon’s information index (I) for IRAP markers were more than REMAP markers. The most genetic diversity was detected in Ae. tauschii accessions. The cluster analysis separated the accessions into three distinct groups. Ae. tauschii accessions from Golestan province grouped in the same cluster with T. aestivum genotypes, indicating that these accessions are probably more like to the progenitor of the bread wheat D genome. Our results revealed that retrotransposon-based molecular markers could be used as the appropriate and reliable marker system to evaluate genetic diversity and relationship in Triticum and Aegilops accessions.

Tribenuron-methyl treatment affects glutathione metabolization and other physiological processes in bread wheat

To maximize crop yield, farmers use a wide array of herbicides. These chemicals have different mechanisms of action such as inhibition of photosynthesis and synthesis of aminoacids, lipids, and carotenoids in plant organs. The action of herbicides is often accompanied by the release of ROS (reactive oxygen species) in cells, and under their effect, modification of physiological processes occur in non-target plant organs, leading to the reduction of crop yields. To overcome stress conditions, plants react through the production of specific metabolites in their cell organelles, synthesizing detoxifying metabolites, among which glutathione (γ-glutamylcisteinylglycine, GSH) and its derivates are the most important. The detoxifying ability of crops varies between species and even between cultivars. Glutathione plays a major role in the detoxification pathways, and its quantity indicates the plant’s capability to metabolize herbicide. In wheat cultivation, the tribenuron-methyl herbicide is widely used. A study on short-term effect of tribenuron-methyl different concentrations (0.5 M, 1 M, 1.5 M) in three wheat cultivars (Pobjeda, Adelajde, and Dajti) and two ancestors Aegilops (accessions Ardenica and Borshi), by evaluating the GSH and pigment content was conducted in 2018 in Albania. A difference in both component content between the control and treated plants was observed. Among the cultivars assessed, Dajti showed the best ability to tolerate herbicide-induced stress. Knowledge on the plants’ reaction under herbicide treatments contributes to the identification of tolerance trait, selection of the right treatment formulation, and development of more effective herbicide safeners.

Diversity of Leaf Cuticular Transpiration and Growth Traits in Field-Grown Wheat and Aegilops Genetic Resources

Plants are subjected to unregulated water loss from their surface by cuticular transpiration. Therefore, specific morphophysiological changes may occur during leaf development to eliminate water loss. This study aimed to examine the cuticular transpiration of 23 winter wheat genotypes and their wild-growing predecessors of the genus Aegilops, which were divided into three groups to demonstrate their diversity. The genotypes were sown in autumn and grown in regular field trials at the Research Institute of Plant Production in Piešťany, Slovakia. Cuticular transpiration and growth parameters were analyzed in the postanthesis growth stage. Gravimetric measurement of residual water loss was performed on detached leaves with a precisely measured leaf area. The lowest nonproductive transpiration values were observed in modern wheat genotypes, while higher cuticular transpiration was observed in a group of landraces. Aegilops species generally showed the highest cuticular transpiration with increased water loss, but the total water loss per plot was low due to the low leaf area of the wild wheat relatives. Some of the growth parameters showed a good correlation with cuticular transpiration (e.g., dry mass per plant), but direct relationships between leaf traits and cuticular transpiration were not observed. This study identified a high diversity in cuticular resistance to water loss in wheat and Aegilops accessions of different origins. The potential of identifying and exploiting genetic resources with favorable cuticular transpiration in crop breeding is discussed.

Effective resistance to powdery mildew in Aegilops L. accessions

Background. Powdery mildew (Blumeria graminis (DC.) E.O. Speer f. sp. tritici Em. Marchal) is widespread and harmful in all regions of bread wheat cultivation. Severe development of powdery mildew leads to a decrease in the number and weight of grains. Growing resistant cultivars is the most environmentally friendly and economically profitable method to protect wheat from the disease. Development of such cultivars requires a search for new donors of effective genes controlling the resistance. To expand the genetic diversity of wheat for resistance to B. graminis, wild relatives of Triticum aestivum L., including Aegilops L. spp., are widely used. The aim of this work was to characterize seven Aegilops spp. for effective seedling and adult plant resistance to powdery mildew.Materials and methods. The material of the study consisted of 437 accessions representing 7 Aegilops spp. (Ae. speltoides Tausch, Ae. caudata L., Ae. biuncialis Vis., Ae. tauschii Coss., Ae. cylindrica Host, Ae. crassa Boiss. and Ae. ventricosa Tausch) from the collection of the N.I. Vavilov All-Russian Institute of Plant Genetic Resources (VIR, St. Petersburg). Juvenile resistance was studied when the seedlings were inoculated with the agent of powdery mildew under controlled laboratory conditions; the adult plant resistance, after artificial inoculation of the plants and under natural infection in the fields of Pushkin and Pavlovsk Laboratories of VIR. Complex populations of the B. graminis agent were used for inoculation. The types of response to infection were scored 10 days after inoculation according to a conventional scale.Results and conclusions. As a result of the tests, susceptibility to powdery mildew was shown in all Aegilops accessions of the D-genome group; all the studied representatives of Ae. speltoides, Ae. caudata and Ae. biuncialis were highly resistant to powdery mildew.

Genetic variability of spelt factor gene in Triticum and Aegilops species

BackgroundThreshability, rachis fragility and spike shape are critical traits for the domestication and evolution of wheat, determining the crop yield and efficiency of the harvest. Spelt factor gene Q controls a wide range of domestication-related traits in polyploid wheats, including those mentioned above. The main goal of the present study was to characterise the Q gene for uninvestigated accessions of wheats, including four endemics, and Aegilops accessions, and to analyze the species evolution based on differences in Q gene sequences.ResultsWe have studied the spike morphology for 15 accessions of wheat species, including four endemics, namely Triticum macha, T. tibetanum, T. aestivum ssp. petropavlovskyi and T. spelta ssp. yunnanense, and 24 Aegilops accessions, which are donors of B and D genomes for polyploid wheat. The Q-5A, q-5D and q-5S genes were investigated, and a novel allele of the Q-5A gene was found in accessions of T. tibetanum (KU510 and KU515). This allele was similar to the Q allele of T. aestivum cv. Chinese Spring but had an insertion 161 bp in length within exon 5. This insertion led to a frameshift and premature stop codon formation. Thus, the T. tibetanum have spelt spikes, which is probably determined by the gene Tg, rather than Q. We determined the variability within the q-5D genes among hexaploid wheat and their D genome donor Aegilops tauschii. Moreover, we studied the accessions C21–5129, KU-2074, and K-1100 of Ae. tauschii ssp. strangulata, which could be involved in the origin of hexaploid wheats.ConclusionsThe variability and phylogenetic relationships of the Q gene sequences studied allowed us to clarify the relationships between species of the genus Triticum and to predict the donor of the D genome among the Ae. tauschii accessions. Ae. tauschii ssp. strangulata accessions C21–5129, KU-2074 and K-1100 are the most interesting among the analysed accessions, since their partial sequence of q-5D is identical to the q-5D of T. aestivum cv. Chinese Spring. This result indicates that the donor is Ae. tauschii ssp. strangulata but not Ae. tauschii ssp. tauschii. Our analysis allowed us to clarify the phylogenetic relationships in the genus Triticum.

The use of molecular-genetic and phytopathological methods to identify genes for effective leaf rust resistance in Aegilops accessions

Background. Identification of effective genes for disease resistance in resistant plant samples is the most important step toward recommending them for breeding. There are three main methods for such identification: hybridological analysis, phytopathological test, and DNA marking. The method of PCR markers is widely used in Russia to identify resistance genes in wheat relatives, including the genus Aegi lops L. for resistance to leaf rust. From a theoretical viewpoint, the presence of a certain amplification fragment can hardly be interpreted as a definite proof of the presence of a resistance gene: during the species evolution, recombinations and mutations could occur, resulting in disturbance of the fragment’s presence and phenotypic expression of its connection with resistance. The purpose of this work was a comparison between molecular-genetic and phytopathological methods to identify leaf rust resistance genes Lr9 and Lr41 in three Aegilops species.Materials and methods. We identified leaf rust resistance genes Lr9 and Lr41 in forty Aegilops accessions using PCR with J13 and GDM35 primers, respectively. In the phytopathological test, the seedlings were infected with the pathogen population (avirulent to Lr9 and Lr41 genes) and the fungus clones virulent to the wheat line with the Lr9 gene.Results and conclusions. According to the data of molecular marking, the Lr41 gene was present in twelve Ae. tauschii Coss. accessions; Lr9 in four Ae umbellulata Zhuk. accessions and four of Ae. biuncialis Vis. All accessions of Ae. tauschii, two of Ae. umbellulata, and three of Ae. biuncialis, possessing effective resistance genes according to the molecular testing, were susceptible to the pathogen population. For three Ae. umbellulata accessions resistant to the population, where DNA marking failed to identify an Lr9 gene, the presence of this gene was shown by a phytopathological test. Thus, there were significant differences in the postulation of effective Lr9 and Lr41 leaf rust resistance genes in Aegilops accessions after a phytopatological test and the use of DNA markers.

Genetic diversity analysis using DArTseq and SNP markers in populations of Aegilops species from Azerbaijan

Despite a large number of Aegilops L. species and their diversity in Azerbaijan, a majority of this genetic material has not been characterized at molecular levels. The current study has implemented DArTseq technology to evaluate genetic diversity among 150 accessions of different Aegilops species from Azerbaijan. A total of 61,574 SilicoDArTseq and 30,433 SNP markers were used to assess genetic diversity in Aegilops species. Genetic diversity was measured using Shannon’s genetic diversity index, which was equal to 0.852. Dendrograms were built to establish the relationship among Aegilops species. Both the DArTseq and SNP markers could completely segregate the U genome species from those with D genome with high confidence and allowed assigning most species to separate subclusters. The pattern of clustering within the Aegilops tauschii Coss. to certain extent was related to their geographical regions. Genetic structure among the 150 Aegilops accessions was similar with the cluster analysis. Two groups were identified in the studied population, which were exactly corresponded to two clusters in the dendrogram. Principal coordinate analysis confirmed sub-grouping obtained by cluster analysis. The first two principal coordinates explained 82.34% of the total variation. The study reported a sufficient level of genetic diversity of Aegilops from different eco-geographical regions of Azerbaijan, which can be very useful for their conservation and management, as well as for profitable diversifying the gene pool of hexaploid wheat.

Drought stress affects the protein and dietary fiber content of wholemeal wheat flour in wheat/Aegilops addition lines.

Wild relatives of wheat, such as Aegilops spp. are potential sources of genes conferring tolerance to drought stress. As drought stress affects seed composition, the main goal of the present study was to determine the effects of drought stress on the content and composition of the grain storage protein (gliadin (Gli), glutenin (Glu), unextractable polymeric proteins (UPP%) and dietary fiber (arabinoxylan, β-glucan) components of hexaploid bread wheat (T. aestivum) lines containing added chromosomes from Ae. biuncialis or Ae. geniculata. Both Aegilops parents have higher contents of protein and β-glucan and higher proportions of water-soluble arabinoxylans (determined as pentosans) than wheat when grown under both well-watered and drought stress conditions. In general, drought stress resulted in increased contents of protein and total pentosans in the addition lines, while the β-glucan content decreased in many of the addition lines. The differences found between the wheat/Aegilops addition lines and wheat parents under well-watered conditions were also manifested under drought stress conditions: Namely, elevated β-glucan content was found in addition lines containing chromosomes 5Ug, 7Ug and 7Mb, while chromosomes 1Ub and 1Mg affected the proportion of polymeric proteins (determined as Glu/Gli and UPP%, respectively) under both well-watered and drought stress conditions. Furthermore, the addition of chromosome 6Mg decreased the WE-pentosan content under both conditions. The grain composition of the Aegilops accessions was more stable under drought stress than that of wheat, and wheat lines with the added Aegilops chromosomes 2Mg and 5Mg also had more stable grain protein and pentosan contents. The negative effects of drought stress on both the physical and compositional properties of wheat were also reduced by the addition of these. These results suggest that the stability of the grain composition could be improved under drought stress conditions by the intraspecific hybridization of wheat with its wild relatives.

Genotypic variability for salt stress tolerance among wild and cultivated wheat germplasms at an early development stage

Abstract This study was conducted to evaluate the variability of salt tolerance potentials among nine wheat genotypes representing wild and cultivated species namely Triticum turgidum subsp. durum, Triticum aestivum and Aegilops geniculata. Ionomic and photosynthetic traits were used for the screening of the studied samples when faced with four salinity levels of NaCl (0, 50, 100 and 150 mM) under green house conditions at the seedling stage. The investigated genotypes exhibited different levels of salt stress tolerance. Ionomic and photosynthetic traits underline the distinctiveness of the common wheat varieties which highlighted particular performances under salt stress conditions and showed higher tolerance potentials among the studied genotypes. Interestingly, the Vaga variety showed more ability to maintain higher K+/Na+ ratios and Pq coefficients compared with the control conditions and stable Fv/F0 and Fv/Fm ratios. Stable behaviour was exhibited by wild Aegilops accessions while durum wheat varieties have been shown to be more sensitive to salt stress. Further investigations were required for the common wheat variety Vaga, which could be useful for successful breeding and biotechnological improvement strategies concerning wheat species.

Genetic diversity of Aegilops L. species from Azerbaijan and Georgia using SSR markers

Five microsatellite (SSR) markers were used to evaluate the genetic diversity of six Aegilops species from Azerbaijan and Georgia. A total of 39 alleles were generated with an average of 7.8 alleles per primer. Twenty markers were species-specific and 6 were accession-specific. The transferability of SSR markers across six species was 100%, with exception of gwm210. The mean polymorphism information content (PIC) and expected heterozygosity (He) values for the entire collection were 0.688 and 0.725, respectively. The average PIC value was the highest in Ae. biuncialis accessions (0.55). The genetic distance (GD) indices, based on five SSR markers, ranged from 0 to 0.83, with a mean value of 0.47. The highest genetic similarity was noted between Ae. neglecta and Ae. triuncialis (GD = 0.26), and the lowest between Ae. neglecta and Ae. tauschii (GD = 0.66). The dendrogram created based on SSR data grouped 72 Aegilops accessions into six clusters according to their taxonomic classification. The accessions from the same province were often placed in the same subclusters, indicating that grouping based on genetic parameters was closely related to the geographic region within countries. The PCoA analysis could differentiate Aegilops accessions according to their species and confirmed subgrouping obtained by cluster analysis.

Identification of New Sources of Resistance to Wheat Stem Rust in Aegilops spp. in the Tertiary Genepool of Wheat.

Recent stem rust epidemics in eastern Africa and elsewhere demonstrated that wheat stem rust is a re-emerging disease posing a threat to wheat production worldwide. The cultivated wheat gene pool has a narrow genetic base for resistance to virulent races, such as races in the Ug99 race group. Wild relatives of wheat are a tractable source of stem rust resistance genes. Aegilops species in the tertiary genepool have not been exploited to any great extent as a source of stem rust resistance. We evaluated 1,422 accessions of Aegilops spp. for resistance to three highly virulent races (TTKSK, TRTTF, and TTTTF) of Puccinia graminis f. sp. tritici. Species studied include Ae. biuncialis, Ae. caudata, Ae. comosa, Ae. cylindrica, Ae. geniculata, Ae. neglecta, Ae. peregrina, Ae. triuncialis, and Ae. umbellulata that do not share common genomes with cultivated wheat. High frequencies of resistance were observed as 977 (68.8%), 927 (65.2%), and 850 (59.8%) accessions exhibited low infection types to races TTKSK, TTTTF, and TRTTF, respectively. Contingency table analyses showed strong association for resistance to different races in several Aegilops spp., indicating that for a given species, the resistance genes effective against multiple races. Inheritance studies in selected accessions showed that resistance to race TTKSK is simply inherited.

Physiological responses to drought stress in wild relatives of wheat: implications for wheat improvement

Wild progenitors of common wheat are a potential source of tolerance to biotic and abiotic stresses. We conducted a glasshouse pot experiment to study genotypic differences in response to drought stress in a collection of 180 accessions of Aegilops and Triticum along with one tolerant and one sensitive control variety. Several physiological traits and chlorophyll fluorescence parameters were evaluated. Our findings indicated that drought significantly reduced shoot fresh (59.45%) and dry (50.83%) weights, stomatal conductance (41.52%) and maximum photosynthetic capacity (41.06%), but increased initial fluorescence (28.10%). Drought stress also decreased the chlorophyll content, relative water content and maximum quantum efficiency by 14.90, 12.13 and 11.42%, respectively. Principal component analysis of the 182 individuals identified three components that explained 57.61 and 61.68% of the total variation in physiological and photosynthetic traits under control and stress conditions, respectively. When grouped into the 12 species tested, the three top components explained 78.22% of the total variation under drought. The means comparison, stress tolerance index and biplot analysis identified five accessions with superior tolerance to drought. Remarkably, four species of wild relatives—Ae. cylindrica (DC genome), Ae. crassa (DM genome), Ae. caudata (C genome) and T. urartu (Au genome)—responded well to drought stress with a lower percentage decline for most traits and high values for the first two components. The potential of these species offers further opportunities for analysis at the molecular and cellular levels to confront with drought stress through a physiological mechanism.

Resistance of Aegilops Species from Israel to Widely Virulent African and Israeli Races of the Wheat Stem Rust Pathogen.

Widely virulent races of the stem rust pathogen (Puccinia graminis f. sp. tritici) such as those isolated from Africa (e.g., TTKSK, isolate synonym Ug99) threaten wheat production worldwide. To identify Aegilops accessions with effective resistance to such virulent stem rust races, up to 10 different species from Israel were evaluated against African races TTKSK, TTKST, and TTTSK and the Israeli race TTTTC as seedlings in the greenhouse. A wide diversity of stem rust reactions was observed across the Aegilops spp. and ranged from highly resistant (i.e., infection type 0) to highly susceptible (infection type 4). The frequency of resistance within a species to races TTTTC and TTKSK ranged from 7 and 14%, respectively, in Aegilops searsii to 98 and 100% in AE. speltoides. In all, 346 accessions were found resistant to the three African races and 138 accessions were resistant (or heterogeneous with a resistant component) to all four races. The species with broadly resistant accessions included Ae. longissima (59 accessions), Ae. peregrina (47 accessions), Ae. sharonensis (15 accessions), Ae. geniculata (9 accessions), Ae. kotschyi (5 accessions), and Ae. bicornis (3 accessions). Few geographical trends or correlations with climatic variables were observed with respect to stem rust resistance in the Aegilops spp. The exception was Ae. longissima infected with race TTTTC, where a high frequency of resistance was found in central and northern Israel and a very low frequency in southern Israel (Negev desert region). This geographical trend followed a pattern of annual precipitation in Israel, and a significant correlation was found between this variable and resistance in Ae. longissima. Although difficult, it is feasible to transfer resistance genes from Aegilops spp. into wheat through conventional wide-crossing schemes or, alternatively, a cloning and transformation approach. The broadly resistant accessions identified in this study will be valuable in these research programs.

Utilization of synthetics for drought tolerance in bread wheat (Triticum aestivum L.)

Wheat (Triticum aestivum L.) is the staple food of 36% of world population. One of the wheat ancestors, D genome donor Aegilops taushii is supposed to impart resistance against the biotic and abiotic stresses. At the time of wheat evolution, very few accessions of Aegilops were available so little tolerance was found in wheat varieties prevailing in that era. In hexaploid wheat, there is only 25% polymorphism so Triticum turgidum (4x) was crossed with different accessions of Aegilops taushii, and genetic diversity was enhanced artificially. Because of synthatics production, it became easy to study wheat genome for improving yield under stress condition to ensure food security.

Evolutionary History of Triticum petropavlovskyi Udacz. et Migusch. Inferred from the Sequences of the 3-Phosphoglycerate Kinase Gene

Single- and low-copy genes are less likely to be subject to concerted evolution. Thus, they are appropriate tools to study the origin and evolution of polyploidy plant taxa. The plastid 3-phosphoglycerate kinase gene (Pgk-1) sequences from 44 accessions of Triticum and Aegilops, representing diploid, tetraploid, and hexaploid wheats, were used to estimate the origin of Triticum petropavlovskyi. Our phylogenetic analysis was carried out on exon+intron, exon and intron sequences, using maximum likelihood, Bayesian inference and haplotype networking. We found the D genome sequences of Pgk-1 genes from T. petropavlovskyi are similar to the D genome orthologs in T. aestivum, while their relationship with Ae. tauschii is more distant. The A genome sequences of T. petropavlovskyi group with those of T. polonicum, but its Pgk-1 B genome sequences to some extent diverge from those of other species of Triticum. Our data do not support for the origin of T. petropavlovskyi either as an independent allopolyploidization event between Ae. tauschii and T. polonicum, or as a monomendelian mutation in T. aestivum. We suggest that T. petropavlovskyi originated via spontaneous introgression from T. polonicum into T. aestivum. The dating of this introgression indicates an age of 0.78 million years; a further mutation event concerning the B genome occurred 0.69 million years ago.