Triticeae Genomics and Genetics, 2025, Vol.16, No.4, 166-174 http://cropscipublisher.com/index.php/tgg 167 POD, CAT and GR, to reduce oxidative damage (Ahmad et al., 2018). When drought and high temperature occur together, these reactions are usually more intense, and sometimes the combined effects of the two stresses are more serious than either alone (Ru et al., 2022). 2.2 Molecular mechanisms involved At the molecular level, wheat activates some stress-related genes. These genes allow it to synthesize some special proteins, such as dehydrins (DHNs) and heat shock factors (TaHSF1a), as well as some transcription factors (such as TaWRKY-33, TaNAC2L) and genes related to abscisic acid signaling (Rampino et al., 2006). Dehydrins are activated when wheat is short of water, which can help plants retain water and protect tissues (Vukovic et al., 2022). In addition, wheat also strengthens antioxidant pathways, such as the ascorbic acid-glutathione cycle, to remove harmful reactive oxygen species in the body (Itam et al., 2020). These genes and pathways are more obviously expressed in wheat varieties with strong drought and heat resistance, indicating that they have genetic advantages in stress resistance. In wheat, some metabolites will also change, such as proline, GABA, sugars and organic acids, and their increase also helps to improve the ability to resist stress. 2.3 Impact on growth and yield components Sometimes, wheat grows short, does not tiller much, and has a small flag leaf area. This is not necessarily due to improper management. Drought and high temperature are often the "masterminds" behind the scenes. These stresses are bad enough when they occur alone. When they occur together, the impact is even more obvious - short spikes, fewer grains, and reduced thousand-grain weight (Alsamadany et al., 2023). Especially if the stress happens to occur during the reproductive period of wheat, it will be even more troublesome. The grains will not be fully filled, and the yield will naturally fall (Qaseem et al., 2019). However, not all varieties will "fall down". Some wheat can mature early or allocate resources better in the face of adversity. In this case, their performance is usually okay. On the other hand, those varieties that are sensitive to adversity often cannot resist, and their growth and yield will be greatly affected (Sareen et al., 2023b). Of course, the final result also depends on how long the stress lasts and how severe it is, and it cannot be generalized. 3 Genetic Strategies for Enhancing Stress Resistance 3.1 Conventional breeding and landrace utilization Traditional breeding has been used for many years. Breeders select drought-resistant or heat-resistant individuals from existing germplasm resources and local varieties, and then crossbreed and improve them (Trono and Pecchioni, 2022). However, because many modern wheat varieties have undergone long-term repeated selection, their genetic diversity has decreased. This also makes the number of stress resistance genes available for breeding even smaller (Mao et al., 2023). To increase the source of stress resistance genes, researchers will introduce some wild relatives or traditional local varieties. For example, Haynaldia villosa is a very useful resource (Xing et al., 2017). In addition, synthetic hexaploid wheat and diversified germplasm banks can also help expand the genetic base, allowing wheat to have multiple resistances at the same time. 3.2 Marker-assisted and genomic selection In the past, we relied on experience, but now many breeding works have been promoted by "looking at genes". Technologies such as MAS, MABC, and GS actually use molecular information to pick out genes or QTLs related to drought and heat resistance, and then introduce them into new varieties. It is not to say that every QTL is reliable, but some "meta-QTL" (MQTL) have repeatedly appeared in different experiments, indicating that they are still quite stable (Tanin et al., 2022). Some have been verified by GWAS studies and can be used. However, it is interesting that in addition to these phenotype-related genes, breeders are now paying more and more attention to the integration of traits such as root structure, antioxidant function, and even osmotic regulation. Putting these favorable factors together is indeed helpful to accelerate variety improvement (Pn and Patil, 2024). Research on synthetic hexaploid wheat has also found many potential stress resistance genes, which can be regarded as a foundation for subsequent improvement work (Bhatta et al., 2019).
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