Climate change is a major threat to most of the agricultural crops grown in tropical and sub-tropical areas globally. Drought stress is one of the consequences of climate change that has a negative impact on crop growth and yield. In the past, many simulation models were proposed to predict climate change and drought occurrences, and it is extremely important to improve essential crops to meet the challenges of drought stress which limits crop productivity and production. Wheat and barley are among the most common and widely used crops due to their economic and social values. Many parts of the world depend on these two crops for food and feed, and both crops are vulnerable to drought stress. Improving drought stress tolerance is a very challenging task for wheat and barley researchers and more research is needed to better understand this stress. The progress made in understanding drought tolerance is due to advances in three main research areas: physiology, breeding, and genetic research. The physiology research focused on the physiological and biochemical metabolic pathways that plants use when exposed to drought stress. New wheat and barley genotypes having a high degree of drought tolerance are produced through breeding by making crosses from promising drought-tolerant genotypes and selecting among their progeny. Also, identifying genes contributing to drought tolerance is very important. Previous studies showed that drought tolerance is a polygenic trait and genetic constitution will help to dissect the gene network(s) controlling drought tolerance. This review explores the recent advances in these three research areas to improve drought tolerance in wheat and barley.

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Synthetic hexaploid wheat (SHW; 2n = 6x = 42, AABBDD, Triticum aestivum L.) is produced from an interspecific cross between durum wheat (2n = 4x = 28, AABB, T. turgidum L.) and goat grass (2n = 2x = 14, DD, Aegilops tauschii Coss.) and is reported to have significant novel alleles-controlling biotic and abiotic stresses resistance. A genome-wide association study (GWAS) was conducted to unravel these loci [marker–trait associations (MTAs)] using 35,648 genotyping-by-sequencing-derived single nucleotide polymorphisms in 123 SHWs. We identified 90 novel MTAs (45, 11, and 34 on the A, B, and D genomes, respectively) and haplotype blocks associated with grain yield and yield-related traits including root traits under drought stress. The phenotypic variance explained by the MTAs ranged from 1.1% to 32.3%. Most of the MTAs (120 out of 194) identified were found in genes, and of these 45 MTAs were in genes annotated as having a potential role in drought stress. This result provides further evidence for the reliability of MTAs identified. The large number of MTAs (53) identified especially on the D-genome demonstrate the potential of SHWs for elucidating the genetic architecture of complex traits and provide an opportunity for further improvement of wheat under rapidly changing climatic conditions.

The confounding effect of wheat (Triticum aestivum L.) genetic background has been addressed as the major factor in inconsistent agronomic performances of 1RS translocation. The objective of this study was to test the effects of centric translocations of chromosome 1 in various rye (Secale cereal L.) sources on agronomic performance of wheat grown in humid southeastern conditions in North America. Various 1R substitution, 1RS translocation, and 1RL translocation lines in ‘Pavon 76’ were evaluated for agronomic performance. The 1RS translocation line was most favorable for agronomic performance when compared with those of substitution, 1RL translocation, and controls. The 1RS significantly increased grain yield. However, the effect of source of rye chromatin was greater than its position effect in wheat genome. Among translocation lines, those with 1RS derived from ‘E12165’ (CIMMYT) and ‘Amigo’ induced higher mean grain yield and T1DL·1RS derived from ‘BH1146/Blanco rye’ had the lowest grain yield. The mean grain yield of 1RL translocation lines was lower than that of 1R substitution. Thus, selection of 1RS source is important in producing constantly higher grain yield in 1RS translocation lines. Genetic recombination among different 1RS may also be used to create more genetic variation.