Effect of terminal heat stress on wheat and mustard crops in Northern States of India: A review

Introduction

Wheat is the second most important cereal crop globally and plays a crucial role in ensuring food security in India. The Indo-Gangetic plains account for a major share of national wheat production and represent one of the most productive agricultural regions in the world (Ortiz et al., 2008) [19] . Mustard is also an important oilseed crop widely cultivated in northern India due to its adaptability to cool winter conditions (Chauhan et al., 2011) [6] . However, climate change has significantly altered temperature patterns in these regions. Rising global temperatures and frequent heat waves have increased the incidence of heat stress during critical crop growth stages (IPCC, 2021). Terminal heat stress occurs when crops experience elevated temperatures during flowering, grain filling or seed development stages (Farooq et al., 2011 and Megha et al., 2024) [9,4] . These high temperatures accelerate crop maturity, shorten grain filling duration and ultimately reduce crop yield (Asseng et al., 2015) [3] . Heat stress during flowering in wheat causes pollen sterility, reduced grain number and decreased kernel weight (Prasad et al., 2008) [21] . In mustard, high temperature stress during flowering in mustard causes reduced fertility, flower and fruit abortion with loss in seed yield (Young et al., 2004; Singh et al., 2014) [30,25] . Similarly, high temperatures reduce siliqua formation and seed development, leading to significant yield losses (Angadi et al., 2000) [2] . Terminal heat stress caused significant reduction in seed yield/plant (Sharma et al., 2022) [26] . Therefore, understanding the impact of terminal heat stress on wheat and mustard crops is critical for developing effective adaptation strategies.

Climate Change and Occurrence of Terminal Heat Stress

Recent climate studies indicate that average temperatures in the Indo-Gangetic plains have increased significantly over the last few decades (Lobell et al., 2011) [14] . Climate projections suggest further warming of 1.5-2.0 °C by mid-century, which could severely affect crop productivity (IPCC, 2021). Terminal heat stress has become more frequent due to delayed sowing in rice-wheat cropping systems and shortened winter seasons (Aggarwal et al., 2006) [1] . Simulation studies using crop models have predicted wheat yield reductions of 10-18% under future climate scenarios in South Asia (Asseng et al., 2015; Zhao et al., 2017) [3,31] .

Effect of Terminal Heat Stress on Wheat Physiological Effects

High temperature stress significantly affects physiological processes in wheat plants. It reduces photosynthetic efficiency by damaging chloroplast structures and inhibiting photosystem II activity (Mathur et al., 2014) [15] . Heat stress also accelerates leaf senescence, resulting in reduced chlorophyll content and decreased photosynthetic rate (Farooq et al., 2011) [9] . Studies have shown that high temperature during grain filling reduces starch accumulation in wheat grains by inhibiting key enzymes involved in carbohydrate metabolism (Nandan et al., 2020) [17] . Additionally, heat stress increases respiration rate and reactive oxygen species (ROS) production, leading to oxidative damage in plant cells (Mittler, 2006) [16] .

Effects on Grain Development and Yield

Grain development in wheat is highly sensitive to temperature during the reproductive stage. Elevated temperatures reduce grain filling duration and decrease grain weight (Reynolds et al., 2010) [22] . Experiments have shown that wheat yield declines significantly when temperatures exceed 30-32 °C during grain filling (Prasad et al., 2008) [21] . Climate change due to elevated CO 2 concentration in the atmosphere would stimulate biomass production in crops particularly C3 crops like wheat. But simultaneously increasing heat stress due to elevated temperature and resulted moisture stress will reduce yield of crops. Sensitivity of wheat towards variations in temperature gets established by Info-Crop wheat model. It confirmed that rise in temperature reduces growth and negatively impacts yield determining parameters in wheat crop (Dubey et al., 2020) [7] . Delayed planting might have exposed the crop to higher temperatures during reproductive stages, causing reduction in duration of grain filling phase, kernel size, biomass, tiller number, etc. During the lowering and grain-filling stages, high temperatures can adversely affect wheat yield and quality, primarily through the phenomenon known as 'terminal heat stress. This stress disrupts pollination, reduces grain number, and lowers grain size and protein content by shortening the grain filling period (Yadav et al., 2025) [9] . Terminal heat stress reduced mustard yields by 10-18% in several regions of northern India. (Bal, S.K., et al., 2022) [5] Field studies in north-western India have reported yield losses of 20-35% under severe terminal heat stress conditions (Lobell et al., 2011; Asseng et al., 2015) [14,3] . Such reductions pose a serious threat to food security in the region. [3,14] .

Wheat Yield Losses Due to Heat Stress in Northern India

Physiological Mechanism of Heat Stress in Wheat and Mustard

High Temperature Stress ↓ Membrane instability ↓ Chlorophyll degradation ↓ Reduced photosynthesis ↓ Short grain/seed filling period ↓ Lower yield Heat stress disrupts photosynthesis and metabolic processes, leading to reduced grain filling and yield losses in wheat and mustard (Farooq et al., 2011; Hasanuzzaman et al., 2013) [9,11] . Studies revealed that high-temperature stress caused some level of injuries at the seedling stage. Based on the analysis of variances, the main effect of individual cultivars with biochemical parameters such as chlorophyll content, catalase, peroxidase, superoxide dismutase activity and proline content were significantly influenced in mustrad (Sakpal et al. 2023) [23] .

Effect of Terminal Heat Stress on Mustard Physiological Responses

Mustard crops are sensitive to high temperatures during flowering and seed development stages. Heat stress reduces chlorophyll content, disrupts membrane stability and decreases photosynthetic efficiency (Angadi et al., 2000) [2] . These physiological changes reduce biomass accumulation and reproductive success. Survival percentage differed with the application of heat/temperature treatments. It was found that the highest survival percentage (32.3-75.1%) was recorded at 30 °C, while it was found lowest (15.2-48.3%) at 40 °C (Sakpal et al. 2023) [23] .

Growth and Yield Effects

High temperature stress reduces the number of siliqua per plant, seed size and oil content in mustard crops (Chauhan et al., 2011) [6] . Experimental studies have reported yield reductions of 20-30% under late sowing and heat stress conditions (Kumar et al., 2016) [13] .

Impact of Terminal Heat Stress on Wheat Growth Stages

Vegetative → Booting → Flowering → Grain filling ↑ Terminal heat stress Wheat is most sensitive to heat stress during flowering and grain filling stages when high temperature reduces pollen viability and grain weight (Prasad et al., 2008; Reynolds et al., 2010) [21,22] .

Physiological Mechanisms of Heat Stress

Heat stress affects plants through several physiological and biochemical mechanisms including:

Heat stress increases the accumulation of reactive oxygen species such as hydrogen peroxide and superoxide radicals, which damage cellular components (Mittler, 2006) [16] . Plants respond by activating antioxidant defense systems including superoxide dismutase and catalase enzymes (Hasanuzzaman et al., 2013) [11] .

Biochemical Responses of Crops to Heat Stress

Heat stress ↓ ROS production ↓ Protein denaturation ↓ Enzyme inhibition ↓ Reduced carbohydrate synthesis High temperature induces oxidative stress in plants, increasing reactive oxygen species (ROS) that damage cellular structures and reduce crop productivity (Mittler, 2006; Hasanuzzaman et al., 2013) [16,11] .

Adaptation Strategies

To mitigate these effects, it is crucial for farmers to adapt their agricultural practices based on accurate weather forecasts, enabling timely and effective management of crops. Additionally, the strategic use of certain chemicals, such as growth regulators and antioxidants, can help alleviate the negative impact of elevated temperatures on the wheat crop during critical growth stages (Yadav et al., 2025) [9] . Several strategies can reduce the impact of terminal heat stress on crop productivity.

Adaptation Strategies for Terminal Heat Stress Agronomical practices

Agronomic and breeding strategies can mitigate terminal heat stress impacts and improve crop resilience (Reynolds et al., 2010; Aggarwal et al., 2006) [22,1] . Agronomic practices, including nutrient management and the use of beneficial microbes, play a critical role in boosting plant resilience to heat stress (Pillai and Walia 2024) [20] .

Early sowing

Early sowing allows crops to escape high temperatures during reproductive stages (Aggarwal et al., 2006) [1] .

Heat-tolerant varieties

Breeding programs aim to develop wheat varieties with improved heat tolerance and stable yield under stress conditions (Reynolds et al., 2010) [22] .

Improved irrigation and nutrient management

Proper irrigation and balanced fertilization enhance plant growth and reduce heat stress damage (Farooq et al., 2011) [9] .

Conclusion

Terminal heat stress is an increasingly significant challenge for wheat and mustard production in northern India. Rising temperatures during reproductive stages disrupt physiological processes, reduce grain filling duration and significantly decrease crop yield. Studies indicate that wheat yields may decline by up to 35% under severe heat stress conditions, while mustard productivity also decreases due to impaired seed development. Developing heat-tolerant cultivars, adjusting sowing dates and adopting climate-smart agronomic practices will be essential for sustaining crop productivity under future climate scenarios.

References

1. Aggarwal PK, Kalra N, Chander S, Pathak H. INFOCROP: A dynamic simulation model for the assessment of crop yields, losses due to pests, and environmental impact of agro-ecosystems in tropical environments. Agricultural Systems. 2006;89(1):1-25. doi:10.1016/j.agsy.2005.08.001.
2. Angadi SV, Cutforth HW, Miller PR, McConkey BG, Entz MH, Brandt SA, et al. Response of three Brassica species to high temperature stress during reproductive growth. Field Crops Research. 2000;67(1):59-69. doi:10.1016/S03784290(00)00089-1.
3. Asseng S, Ewert F, Martre P, Rötter RP, Lobell DB, Cammarano D, et al. Rising temperatures reduce global wheat production. Nature Climate Change. 2015;5(2):143147. doi:10.1038/nclimate2470.
4. Megha B, Macha SI, Shakuntala NM, Hiremath U, Meena MK. Studies on effect of terminal heat stress on seed quality and its mitigation in chickpea (Cicer arietinum L.). International Journal of Environment and Climate Change. 2024;14(10):317-344. doi:10.9734/ijecc/2024/v14i104489.
5. Bal SK, Prasad JVNS, Singh VK. Heat wave 2022: Causes, impacts and way forward for Indian agriculture. Technical Bulletin No. ICAR/CRIDA/TB/01/2022. Hyderabad (India): ICAR-Central Research Institute for Dryland Agriculture; 2022.
6. Chauhan JS, Singh KH, Singh VV, Kumar S. Hundred years of rapeseed-mustard breeding in India: Achievements and future strategies. Indian Journal of Agricultural Sciences. 2011;81(12):1093-1109.
7. Dubey R, Pathak H, Chakrabarti B, Singh S, Gupta DK, Harit RC. Impact of terminal heat stress on wheat yield in India and options for adaptation. Agricultural Systems. 2020;181:102826. doi:10.1016/j.agsy.2020.102826.
8. Namitha E, Gawande VL, Bharad SG. Effects of terminal heat stress on yield and physiological traits of bread wheat genotypes (Triticum aestivum L.). International Journal of Advanced Biochemistry Research. 2024;8(11):110-118. doi:10.33545/26174693.2024.v8.i11b.2816.
9. Farooq M, Bramley H, Palta JA, Siddique KHM. Heat stress in wheat during reproductive and grain-filling phases. Crop Science. 2011;51(2):647-658. doi:10.2135/cropsci2010.09.0486.
10. Gbegbelegbe S, Chung U, Shiferaw B, Msangi S, Tesfaye K. Quantifying the impact of weather extremes on global food security: A spatial bio-economic approach. Global Change Biology. 2014;20(4):1258-1273. doi:10.1111/gcb.12484.
11. Hasanuzzaman M, Nahar K, Alam MM, Roychowdhury R, Fujita M. Physiological, biochemical, and molecular mechanisms of heat stress tolerance in plants. Plant Physiology and Biochemistry. 2013;64:30-44. doi:10.1016/j.plaphy.2013.01.010.
12. Intergovernmental Panel on Climate Change. Climate change 2021: The physical science basis. Contribution of Working Group I to the Sixth Assessment Report of the Intergovernmental Panel on Climate Change. Cambridge (UK): Cambridge University Press; 2021.
13. Kumar S, Singh VV, Chauhan JS, Yadav SK. Genetic variability and heat stress tolerance in Indian mustard (Brassica juncea L.). Journal of Oilseed Brassica. 2016;7(1):35-40.
14. Lobell DB, Schlenker W, Costa-Roberts J. Climate trends and global crop production since 1980. Science. 2011;333(6042):616-620. doi:10.1126/science.1204531.
15. Mathur S, Agrawal D, Jajoo A. Photosynthesis: Response to high temperature stress. Plant Biology. 2014;16(1):1-10. doi:10.1111/plb.12005.
16. Mittler R. Abiotic stress, the field environment and stress combination. Trends in Plant Science. 2006;11(1):15-19. doi:10.1016/j.tplants.2005.11.002.
17. Nandan G, Dubey RB, GP. Effect of heat stress on wheat grain quality and yield components. Indian Journal of Agricultural Sciences. 2020;90(4):765-770.
18. Narendra MC, Roy C, Kumar S, Virk P, De N. Effect of terminal heat stress on physiological traits, grain zinc and iron content in wheat (Triticum aestivum L.). Czech Journal of Genetics and Plant Breeding. 2021;57:43-50. doi:10.17221/63/2020-CJGPB.
19. Ortiz R, Sayre KD, Govaerts B, Gupta R, Subbarao GV, Ban T, et al. Climate change: Can wheat beat the heat? Agriculture, Ecosystems and Environment. 2008;126(12):46-58. doi:10.1016/j.agee.2008.01.019.
20. Pillai, Walia. Heat stress in Indian mustard (Brassica juncea L.): A critical review of impacts and adaptation strategies. Plant Cell Biotechnology and Molecular Biology. 2024;25(5-6):1-11. doi:10.56557/PCBMB/2024/v25i568673.
21. Prasad PVV, Pisipati SR, Momčilović I, Ristic Z. Independent and combined effects of high temperature and drought stress during grain filling in cereals. Environmental and Experimental Botany. 2008;61(3):263-273. doi:10.1016/j.envexpbot.2007.07.004.
22. Reynolds MP, Pierre CS, Saad AS, Vargas M, Condon AG. Evaluating potential genetic gains in wheat associated with stress-adaptive traits. Journal of Experimental Botany. 2010;61(12):3531-3545. doi:10.1093/jxb/erq166.
23. Sakpal A, Yadav S, Choudhary R, Saini N, Vasudev S, Yadava DK, et al. Heat-stress-induced changes in physiobiochemical parameters of mustard cultivars and their role in heat stress tolerance at the seedling stage. Plants. 2023;12(6):1400. doi:10.3390/plants12061400.
24. Semenov MA, Shewry PR. Modeling predicts that heat stress, not drought, will increase vulnerability of wheat in Europe. Global Change Biology. 2011;17(1):590-605. doi:10.1111/j.1365-2486.2010.02234.x.
25. Singh MP, Lallu, Singh NB. Thermal requirement of Indian mustard (Brassica juncea) at different phenological stages under late sown condition. Indian Journal of Plant Physiology. 2014;19:238-243.
26. Sharma HK, Singh VV, Kumar A, Meena HS, Meena BL, Sharma P, Rai PK. Genetic study of terminal heat stress in indigenous collections of Indian mustard (Brassica juncea L.) germplasm. Journal of Environmental Biology. 2022;43:161-169.
27. Tiwari R, Kumar N, Sharma I. Evaluation of wheat genotypes for terminal heat tolerance in North-Western Plains of India. Plant Physiology Reports. 2013;18(2):151158.
28. Tyagi P, Dhillon SK, Kumar S. Effect of heat stress on growth and productivity of Indian mustard. Indian Journal of Plant Physiology. 2015;20(3):238-243.
29. Yadav A, Nalia M, Kumar Y. Terminal heat stress in wheat: Impacts and solutions. Agriculture Association of Textile Chemical and Critical Reviews Journal. 2025;13(2):204212. doi:10.21276/AATCCReview.2025.13.02.204.
30. Young LW, Wilen RW, Bonham-Smith PC. High temperature stress of Brassica napus during flowering reduces micro-and megagametophyte fertility, induces fruit abortion, and disrupts seed production. Journal of Experimental Botany. 2004;55:485-495.
31. Zhao C, Liu B, Piao S, Wang X, Lobell DB, Huang Y, et al. Temperature increase reduces global yields of major crops in four independent estimates. Proceedings of the National Academy of Sciences of the United States of America. 2017;114(35):9326-9331. doi:10.1073/pnas.1701762114.