Drought is one of the major abiotic constraints on wheat yields and also for sustainability of production levels around the world. In the near future, the occurrence likelihood of droughts is predicted to become more common, due to changing climatic conditions, thereby posing a serious threat to the food security system. Heterogeneity, in its time of occurrence and severity levels, is likely to further augment the complexity of drought conditions. Although wheat crop growth has progressively risen to good levels, as evident by notable increases in both area and production, the expected wheat demand for the ever-growing population is quite high. Besides crop yield volatility in the era of climate change and dwindling resources, “trait-based” breeding programs are required, so as to develop high yielding, climate resilient and stable genotypes, at a faster pace. For this to happen, a broad genetic base and wider adaptability to suit varied agro-ecologies would provide enough scope for their quicker spread. The current review places emphasis on making distinct categories of the wheat cultivars/advanced breeding lines, as tolerant, moderately tolerant or susceptible to drought stresses, duly supported by an extensive up-to-date literature base and will be useful for wheat researchers, in order to choose the best potential donors as parents, coupled with the associated traits for the development of drought-tolerant wheat varieties, and also to facilitate molecular studies.
Drought and heat are the key environmental stressors significantly decreasing wheat productivity (86 and 69%, respectively) and weakening food security in the major wheat growing regions worldwide. Wheat crops have regularly experienced combined (Heat+Drought) stress in the field and the joint effects are more detrimental to wheat growth than the effects of each stress separately.Drought and heat stress have shown synergistic, antagonistic, or hypo-additive impacts on growth, grain filling, and yield parameters when combined. In order to escape and/or tolerate these unfavorable environmental conditions, wheat has developed advancedresponses at various levels. This review explores how physiological, morphological, biochemical and molecular traits work together to provide tolerance to coupled stresses. Importance of specific traits such as, canopy temperature, assimilate partitioning and water use efficiency along with reproductive traitswhich provide tolerance against these combined stressors has also been explained. This review also highlighted the potential of altered agronomic practices, application of micronutrients, biopriming of seeds (endophytes) against abiotic stresses. Further emphasize has been given to promising novel technologies like, genome editing (CRISPR),identification of novel QTL's and alleles to improve both heat and drought tolerance for sustainable wheat production.
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