Sorghum (Sorghum bicolor L. Moench) grown in semiarid regions is often exposed to short periods of high‐temperature (HT) stress during reproductive development. Objectives of this research were (i) to quantify the effects of short episodes of HT stress during reproductive development on physiological, growth, and yield processes of grain sorghum and (ii) to identify the stage(s) most sensitive during the reproductive development phase to HT stress. Plants of hybrid DK‐28 E were grown in growth chambers at daytime maximum/nighttime minimum optimum temperature (OT) of 32/22°C until 29 d after sowing. Thereafter, plants were exposed to OT or HT (40/30°C) or were reciprocally transferred at 10‐d intervals (10 d before flowering, 0, 10, 20, and 30 d after flowering [DAF]) from OT to HT and vice versa. Transferred plants remained in the new temperature regime for 10 d before being returned to their original temperature regime. Continuous HT stress delayed panicle emergence and decreased plant height, seed set, seed numbers, seed yield, seed size, and harvest indices but did not influence leaf photosynthesis. Exposure to short (10‐d) periods of HT stress at flowering and 10 d before flowering caused maximum decreases in seed set and seed yield, and HT stress during postflowering stages (10, 20, and 30 DAF) decreased seed yield, with a larger reduction at early stages of seed development.

Soybean production is greatly influenced by abiotic stresses imposed by environmental factors such as drought, water submergence, salt, and heavy metals. A thorough understanding of plant response to abiotic stress at the molecular level is a prerequisite for its effective management. The molecular mechanism of stress tolerance is complex and requires information at the omic level to understand it effectively. In this regard, enormous progress has been made in the omics field in the areas of genomics, transcriptomics, and proteomics. The emerging field of ionomics is also being employed for investigating abiotic stress tolerance in soybean. Omic approaches generate a huge amount of data, and adequate advancements in computational tools have been achieved for effective analysis. However, the integration of omic-scale information to address complex genetics and physiological questions is still a challenge. In this review, we have described advances in omic tools in the view of conventional and modern approaches being used to dissect abiotic stress tolerance in soybean. Emphasis was given to approaches such as quantitative trait loci (QTL) mapping, genome-wide association studies (GWAS), and genomic selection (GS). Comparative genomics and candidate gene approaches are also discussed considering identification of potential genomic loci, genes, and biochemical pathways involved in stress tolerance mechanism in soybean. This review also provides a comprehensive catalog of available online omic resources for soybean and its effective utilization. We have also addressed the significance of phenomics in the integrated approaches and recognized high-throughput multi-dimensional phenotyping as a major limiting factor for the improvement of abiotic stress tolerance in soybean.

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HighlightAltering root xylem developmental plasticity by increasing the number of vessels and decreasing their diameter enhances water uptake and reduces yield loss in soybean under water-limited conditions.

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Physiological mechanisms of slow canopy wilting in early maturity group soybeans were identified and the underlying QTLs were mapped and confirmed to protect soybean yield under drought in the field.

Circadian clocks are a great evolutionary innovation and provide competitive advantage during the day/night cycle and under changing environmental conditions. The circadian clock mediates expression of a large proportion of genes in plants, achieving a harmonious relationship between energy metabolism, photosynthesis, and biotic and abiotic stress responses. Here it is shown that multiple paralogues of clock genes are present in soybean (Glycine max) and mediate flooding and drought responses. Differential expression of many clock and SUB1 genes was found under flooding and drought conditions. Furthermore, natural variation in the amplitude and phase shifts in PRR7 and TOC1 genes was also discovered under drought and flooding conditions, respectively. PRR3 exhibited flooding- and drought-specific splicing patterns and may work in concert with PRR7 and TOC1 to achieve energy homeostasis under flooding and drought conditions. Higher expression of TOC1 also coincides with elevated levels of abscisic acid (ABA) and variation in glucose levels in the morning and afternoon, indicating that this response to abiotic stress is mediated by ABA, endogenous sugar levels, and the circadian clock to fine-tune photosynthesis and energy utilization under stress conditions. It is proposed that the presence of multiple clock gene paralogues with variation in DNA sequence, phase, and period could be used to screen exotic germplasm to find sources for drought and flooding tolerance. Furthermore, fine tuning of multiple clock gene paralogues (via a genetic engineering approach) should also facilitate the development of flooding- and drought-tolerant soybean varieties.