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.

Salinity Effects on Morpho-Physiological and Yield Traits of Soybean (Glycine max L.) as Mediated by Foliar Spray with Brassinolide.

Salinity episodes that are common in arid regions, characterized by dryland, are adversely affecting crop production worldwide. This study evaluated the effectiveness of brassinolide (BL) in ameliorating salinity stress imposed on soybean at four levels (control (1.10), 32.40, 60.60 and 86.30 mM/L NaCl) in factorial combination with six BL application frequency (control (BL0), application at seedling (BL1), flowering (BL2), podding (BL3), seedling + flowering (BL4) and seedling + flowering + podding (BL5)) stages. Plant growth attributes, seed yield, and N, P, K, Ca and Mg partitioning to leaves, stems and roots, as well as protein and seed-N concentrations, were significantly (p ≤ 0.05) reduced by salinity stress. These trends were ascribed to considerable impairments in the photosynthetic pigments, photosynthetically active radiation, leaf stomatal conductance and relative water content in the leaves of seedlings under stress. The activity of peroxidase and superoxidase significantly (p ≤ 0.05) increased with salinity. Foliar spray with BL significantly (p ≤ 0.05) improved the photosynthetic attributes, as well as nutrient partitioning, under stress, and alleviated ion toxicity by maintaining a favourable K+/Na+ ratio and decreasing oxidative damage. Foliar spray with brassinolide could sustain soybean growth and seed yield at salt concentrations up to 60.60 mM/L NaCl.

Transpiration response of two bread wheat lines differing in drought resilience and their backcross parent under dry-down conditions.

Improving wheat productivity in drylands largely depends on how plants manage limited water resources. Using fraction of transpirable soil water threshold (FTSWTh) and drought stress response function, we characterized the water conservation traits of two wheat multiple synthetic derivative lines (MSD53 and MSD345) which both contain introgressed segments from Aegilops tauschii but differ in drought resilience. The lines and their backcross parent, 'Norin 61', were subjected to dry-down conditions. MSD53 had a higher FTSWTh for transpiration decrease than 'Norin 61' and MSD345. In terms of drought stress response function, MSD53 had the lowest threshold suction, suggesting a lower drought resilience capacity compared with MSD345. However, MSD53 exhibited an effective-water-use trait whereas MSD345 exhibited a water-saving trait under dry-down conditions. These results are consistent with the reported higher yield of MSD53 in comparison with MSD345 under drought stress in Sudan, and demonstrate that high FTSWTh supports effective water use for improved agricultural productivity in drylands. The differences in water conservation traits between the two MSD lines may be attributed to variation in introgressed segments, which can be further explored for drought resilience breeding.