Genomic analysis for heat and combined heat-drought resilience in bread wheat under field conditions.

KEY MESSAGE: GWAS on a bread wheat panel with high D genome diversity identified novel alleles and QTLs associated with resilience to combined heat and drought stress under natural field conditions. As heat (H) and drought stresses occur concurrently under field conditions, studying them separately offers limited opportunities for wheat improvement. Here, a wheat diversity panel containing Aegilops tauschii introgressions was evaluated under H and combined heat-drought (HD) stresses to identify quantitative trait loci (QTLs) associated with resilience to the stresses, and to assess the practicability of harnessing Ae. tauschii diversity for breeding for combined stress resilience. Using genome-wide analysis, we identified alleles and QTLs on chromosomes 3D, 5D, and 7A controlling grain yield (GY), kernel number per spike, and thousand-kernel weight, and on 3D (521-549 Mbp) controlling GY alone. A strong marker-trait association (MTA) for GY stability on chromosome 3D (508.3 Mbp) explained 20.3% of the variation. Leaf traits-canopy temperature, vegetation index, and carbon isotope composition-were controlled by five QTLs on 2D (23-96, 511-554, and 606-614 Mbp), 3D (155-171 Mbp), and 5D (407-413 Mbp); some of them were pleiotropic for GY and yield-related traits. Further analysis revealed candidate genes, including GA20ox, regulating GY stability, and CaaX prenyl protease 2, regulating canopy temperature at the flowering stage, under H and HD stresses. As genome-wide association studies under HD in field conditions are scarce, our results provide genomic landmarks for wheat breeding to improve adaptation to H and HD conditions under climate change.

Genetic variation in drought resilience-related traits among wheat multiple synthetic derivative lines: insights for climate resilience breeding.

Twenty-four wheat lines, developed by Aegilops tauschii Coss. introgressions and previously selected for heat or salinity stress tolerance, were evaluated under a drought-rewatering-drought cycle for two years. The objective was to select breeding lines that are resilient to more than one abiotic stress. The experiment was designed in alpha lattice with three replications. Drought was imposed by withholding water during flowering. The results revealed considerable genetic variability in physio-agronomic traits, reflecting the variation in the introgressed segments. High heritability estimates (above 47%) were recorded for most traits, including days to 50% heading, plant height, and thousand-grain weight, indicating the genetic control of these traits which may be useful for cultivar development. The trait-trait correlations within and between water regimes highlighted a strong association among the genetic factors controlling these traits. Some lines exhibited superior performance in terms of stress tolerance index and mean productivity compared with their backcross parent and elite cultivars commonly grown in hot and dry areas. Graphical genotyping revealed unique introgressed segments on chromosomes 4B, 6B, 2D, and 3D in some drought-resilient lines which may be linked to drought resilience. Therefore, we recommend these lines for further breeding to develop climate-resilient wheat varieties.

Expression of seed storage proteins responsible for maintaining kernel traits and wheat flour quality in common wheat under heat stress conditions.

Heat stress during grain filling has been documented to decrease wheat grain yield and quality in arid regions worldwide. We studied the effect of heat stress on wheat flour quality in heat tolerant cultivars to define the effects of heat stress on flour quality and to identify germplasm combining traits for heat tolerance and good flour quality. We studied the kernel phenotypic traits, the expression of seed storage proteins (SSPs), and the resulting flour quality under heat and normal conditions. Under heat stress, all cultivars yielded narrow-shaped seeds, and increased protein contents as compared to the control plants grown under normal conditions. The specific sedimentation values used to estimate the gluten quality varied between cultivars. We identified cultivars that could maintain good flour quality under heat stress conditions: 'Imam', which possessed the Glu-D1d allele responsible for the suitable bread-making; 'Bohaine', which displayed high expression level of SSPs; and 'Condor', which possessed slight variations in the ratio of each SSP under heat stress conditions. Combining the desirable traits from these cultivars could yield a wheat cultivar with heat tolerance and good flour quality.

Rising temperatures and increasing demand challenge wheat supply in Sudan.

Climate warming poses challenges for food production at low latitudes, particularly in arid regions. Sudan, where wheat demand could triple by 2050, has the world's hottest wheat-growing environments, and observed yield declines in hot seasons are prompting the national government to prepare for a warming of 1.5-4.2 °C. Using advanced crop modelling under different climate and socioeconomic scenarios, we show that despite the use of adjusted sowing dates and existing heat-tolerant varieties, by 2050, Sudan's domestic production share may decrease from 16.0% to 4.5-12.2%. In the relatively cool northern region, yields will need to increase by 3.1-4.7% per year, at non-compounding rates, to meet demand. In the hot central and eastern regions, improvements in heat tolerance are essential, and yields must increase by 0.2-2.7% per year to keep pace with climate warming. These results indicate the potential contribution of climate change adaptation measures and provide targets for addressing the wheat supply challenge.

DArTseq-based analysis of genomic relationships among species of tribe Triticeae.

Precise utilization of wild genetic resources to improve the resistance of their cultivated relatives to environmental growth limiting factors, such as salinity stress and diseases, requires a clear understanding of their genomic relationships. Although seriously criticized, analyzing these relationships in tribe Triticeae has largely been based on meiotic chromosome pairing in hybrids of wide crosses, a specialized and labourious strategy. In this study, DArTseq, an efficient genotyping-by-sequencing platform, was applied to analyze the genomes of 34 Triticeae species. We reconstructed the phylogenetic relationships among diploid and polyploid Aegilops and Triticum species, including hexaploid wheat. Tentatively, we have identified the diploid genomes that are likely to have been involved in the evolution of five polyploid species of Aegilops, which have remained unresolved for decades. Explanations which cast light on the progenitor of the A genomes and the complex genomic status of the B/G genomes of polyploid Triticum species in the Emmer and Timopheevi lineages of wheat have also been provided. This study has, therefore, demonstrated that DArTseq genotyping can be effectively applied to analyze the genomes of plants, especially where their genome sequence information are not available.

Novel molecular marker-assisted strategy for production of wheat-Leymus mollis chromosome addition lines.

Developing wheat-alien chromosome introgression lines to improve bread wheat's resistance to stresses, such as drought, salinity stress and diseases, requires reliable markers to identify and characterize the alien chromatins. Leymus mollis is a wild relative of bread wheat resistant to salinity and economically important diseases of wheat, but its genome sequence and cytological markers are not available. We devised a molecular marker-assisted strategy for L. mollis chromosome identification and applied it to produce 10 wheat-L. mollis chromosome addition lines. Using 47 L. racemosus genome polymorphic PCR markers and DArTseq genotyping, we distinguished the L. mollis chromosomes and differentiated disomic and monosomic lines by progeny test. DArTseq genotyping generated 14,530 L. mollis SNP markers and the chromosome-specific SNP markers were used to determine the homoeologous groups of L. mollis chromosomes in the addition lines. To validate the marker-based results, genomic in situ hybridization was applied to confirm the presence and cytological status of L. mollis chromosomes in the lines. This study demonstrates that adequate molecular markers allow the production and characterization of wheat-alien addition lines without in situ hybridization, which saves considerable time and effort.

Genetic variation in heat tolerance-related traits in a population of wheat multiple synthetic derivatives.

In wheat (Triticum aestivum L.) high temperature (≥30°C) during grain filling leads to considerable reduction in grain yield. We studied 400 multiple synthetic derivatives (MSD) lines to examine the genetic variability of heat stress-adaptive traits and to identify new sources of heat tolerance to be used in wheat breeding programs. The experiment was arranged in an augmented randomized complete block design in four environments in Sudan. A wide range of genetic variability was found in most of the traits in all environments. For all traits examined, we found MSD lines that showed better performance than their parent 'Norin 61' and two adapted Sudanese cultivars. Using the heat tolerance efficiency, we identified 13 highly heat-tolerant lines and several lines with intermediate heat tolerance and good yield potential. We also identified lines with alleles that can be used to increase wheat yield potential. Our study revealed that the use of the MSD population is an efficient way to explore the genetic variation in Ae. tauschii for wheat breeding and improvement.

Effect of environment and genotypes on the physicochemical quality of the grains of newly developed wheat inbred lines.

To meet the increased demand for wheat consumption, wheat cultivation in Sudan expanded southward to latitudes lower than 15°N, entering a new and warmer environment. Consequently, wheat breeders developed several wheat genotypes with high yields under these environmental conditions; however, the evaluation of the end-use quality of these genotypes is scarce. In this study, we assessed the end-use quality attributes of 20 wheat genotypes grown in three different environments in the Sudan (Wad Medani, Hudeiba, and Dongola). The results showed significant differences (P ≤ 0.01) in all quality tests among environments, genotypes and genotypes Versus environments. The findings obtained, covered wide ranges of test weight (TW, 76.6-85.25 kg/hL), thousand kernel weight (TKW, 28.70-48.48 g), protein (PC, 9.96-14.06%), wet gluten (WG, 28.63-46.53%), gluten index (GI, 36.36-92.77%), water holding capacity (WHC, 168.42-219.32%), falling number (FN, 508.00-974.67 sec), and sedimentation value (SV, 19.00-40.00 mL). Analysis of the traits, genotypes, and traits versus genotypes showed varied correlations in the three growing environments. The genotype G3 grown in either one or all of the three environments exhibits worthy performance and stability for most of the tested quality traits. The crossing of this genotype with high yield genotypes could produce cultivars with sufficient quality and marketability.