Effect of sowing dates and heat stress Mitigators on growth responses of wheat (Triticum Aestivum L) under terminal heat stress

Introduction

Wheat (Triticum aestivum L.) is one of the most important cereal crops of the world and plays a pivotal role in ensuring food and nutritional security. In India, wheat is predominantly grown during the rabi season, when crop productivity depends strongly on the prevailing temperature during different phenological stages. However, the increasing frequency of temperature extremes associated with climate variability and climate change has emerged as a major constraint to stable wheat production. Among the different climatic stresses, terminal heat stress is particularly important in wheat-growing regions of Madhya Pradesh especially in the gird region (Gwalior) because the crop frequently encounters high temperatures during the reproductive and grain-filling stages. Sowing date also influences the duration and rate of crop growth, canopy development, biomass accumulation and partitioning of assimilates. A suitable sowing window allows the crop to utilize favourable temperature conditions during vegetative growth and maintain a comparatively longer grain-filling period. In contrast, delayed sowing generally accelerates phenological development and reduces the duration available for biomass accumulation and grain development. A recent study in the Indo-Gangetic Plains reported that appropriate adjustment of planting time can help reduce exposure to post-heading heat stress and improve wheat productivity. Similarly, a systematic review of South Asian wheat research found that advancing sowing by approximately 7-10 days was an effective adaptation option under heat-stress conditions. Growth responses provide an important basis for evaluating the Recent research emphasizes that adaptation to terminal heat stress should not rely on a single intervention but should integrate agronomic and physiological approaches. Metaanalysis of South Asian studies indicated that early sowing, heat-tolerant cultivars and conservation-oriented management can substantially reduce heat-associated yield losses. In particular, early sowing has demonstrated considerable potential because it allows the crop to escape the period of severe terminal heat during grain filling. However, the effectiveness of sowing-time adjustment is dependent on the local thermal regime, genotype and crop management conditions. Therefore, there is a need to evaluate the interaction between sowing dates and heat stress mitigation strategies under field conditions, particularly for wheat grown in the semi-arid environment of central India. A systematic assessment of growth responses under contrasting sowing environments can help identify the sowing window that minimizes exposure to terminal heat, while evaluation of exogenous mitigators can provide information on their capacity to sustain crop growth under high-temperature conditions. Such an integrated approach is particularly relevant in the context of climate change, where increasing temperature variability may reduce the reliability of conventional sowing windows. Keeping these considerations in view, the present investigation entitled "Effect of Sowing Dates and Heat Stress Mitigators on Growth Responses of Wheat under Terminal Heat Stress" was undertaken to assess the influence of different sowing dates and exogenous heat stress mitigation treatments on the growth behaviour of wheat. The study aims to understand whether appropriate adjustment of sowing time, either alone or in combination with physiological mitigation strategies, can maintain favourable crop growth and improve the adaptation of wheat to terminal heat stress. The findings are expected to contribute towards developing practical agronomic strategies for sustaining wheat productivity under warming and increasingly variable climatic conditions.

Materials and Methods

A field experiment was conducted during the rabi seasons of 2024-25 and 2025-26 at the Research Farm of KVK, Gwalior, Madhya Pradesh, under RVSKVV, Gwalior, representing the semi-arid agro-climatic conditions of the Gird region. The experiment was laid out in a split-plot design with three replications, comprising three sowing dates as main-plot treatments: D₁ (15 November), D₂ (5 December) and D₃ (25 December), and five heat stress mitigation treatments as sub-plot treatments: H₀ (water spray), H₁ (KNO₃ @ 2.0%), H₂ (melatonin @ 100 µM), H₃ (sodium nitroprusside @ 100 µM) and H₄ (progesterone @ 1 µM). Thus, 15 treatment combinations were evaluated. Wheat was sown manually on the respective dates, and all plots received uniform recommended agronomic practices, including fertilization, irrigation, weed and pest management. Heat stress mitigation treatments were applied as foliar sprays at the booting and anthesis stages, which are critical periods for terminal heat stress. Meteorological observations were recorded to characterize the prevailing weather conditions. The heat stress mitigation treatments were applied as foliar sprays at the booting and anthesis stages of wheat, which are critical developmental stages associated with increasing sensitivity to high temperature and terminal heat stress as detailed below: Progesterone was applied at 1 µM, corresponding to 0.314 mg L⁻¹.The prepared solutions were applied uniformly over the crop canopy at the booting and anthesis stages using a suitable knapsack or hand-operated sprayer, howver the control plots received an equivalent volume of water spray. Care was taken to ensure uniform spray coverage of the foliage and minimize spray drift between adjacent plots. The foliar applications were performed under suitable weather conditions to facilitate effective absorption and minimize losses due to evaporation or rainfall immediately after application. Growth parameters were recorded at 30, 60 and 90 DAS and at harvest following standard agronomic procedures. Plant population was counted per metre row length, plant height measured in cm, leaf area recorded in cm² plant⁻¹, and plant dry weight determined after oven drying to constant weight. Chlorophyll content was measured using a SPAD meter. Terminal heat stress was assessed based on prevailing temperatures during anthesis and grain filling across different sowing dates. Data were analyzed using ANOVA appropriate for split-plot design, with significance tested by F-test and treatment means compared using CD at 5% probability. CV was calculated to assess experimental variability, while pooled analysis across years considered year effects and their interactions with treatments. Particular emphasis was given to sowing date × heat stress mitigation interaction to identify effective treatments under late-sown conditions. [5] . and Lakhani et al. (2025) [4] . Foliar application of KNO₃, melatonin, SNP and progesterone had no significant effect on plant population due to their application at later growth stages. [3] . Heat stress mitigation treatments had no significant effect at 30 and 60 DAS but significantly influenced plant height at 90 DAS and harvest. At 90 DAS, H₄ (progesterone 1 µM) recorded the highest height (92.46 cm), followed by H₂ (melatonin), H₃ (SNP), H₁ (KNO₃) and H₀ (control); a similar trend occurred at harvest, with H₄ recording the maximum height (97.68 cm).

Results and Discussion

Plant population

The positive effects of SNP and KNO₃ under heat stress were also reported by Suryavanshi et al. (2016) [7] . and Zhang et al. (2023) [8,9] . [1] . [1] . and Zhang et al. (2023) [8,9] . Plant population remained unaffected by the mitigation treatments, confirming their limited influence on crop establishment. Overall, D₁ was the most favourable sowing date, while D₃ adversely affected growth. Among the mitigators, H₄ showed the most consistent improvement in growth and physiological attributes under terminal heat stress, likely through better maintenance of photosynthetic activity, antioxidant defence and cellular metabolism.

Leaf area

Plant dry weight

Summary

Conclusion

Pooled analysis over two years revealed that sowing date significantly influenced crop establishment, growth and physiological performance. D₁ (15 November) recorded the highest plant population, plant height, leaf area, dry weight and chlorophyll content, indicating favourable crop establishment and growth under timely sowing. In contrast, delayed sowing, particularly D₃ (25 December), consistently reduced these parameters due to shortened growth duration and greater exposure to terminal heat stress. Heat-stress mitigation treatments had a more pronounced effect during later growth stages. H₄ (progesterone 1 µM) consistently recorded higher plant height, leaf area, dry weight and chlorophyll content at 90 DAS and harvest, followed by H₃ (SNP 100 µM) and H₂ (melatonin 100 µM). However, these treatments did not significantly influence plant population, indicating their primary role in maintaining growth and physiological activity rather than crop establishment.

Overall, D₁ (15 November) was the most suitable sowing date, whereas D₃ (25 December) adversely affected crop performance. Among the mitigators, progesterone 1 µM emerged as the most promising treatment for sustaining growth and physiological performance under terminal heat stress, followed by SNP and melatonin.

References

1. Buttar ZA, Wu SN, Arnao MB, Wang C, Ullah I, Wang C. Melatonin suppressed the heat stress-induced damage in wheat seedlings by modulating the antioxidant machinery. Plants. 2020;9(7):80.
2. Deihimfard R, Rahimi-Moghaddam S, Eyni-Nargeseh H, Collins B. An optimal combination of sowing date and cultivar could mitigate the impact of simultaneous heat and drought on rainfed wheat in arid regions. European Journal of Agronomy. 2023;147:126848.
3. Jat LK, Singh SK, Latare AM, Singh RS, Patel CB. Effect of dates of sowing and fertilizer on growth and yield of wheat (Triticum aestivum) in an Inceptisol of Varanasi. Indian Journal of Agronomy. 2013;58(4):611614.
4. Lakhani SH, Kumawat PD, Muchhadiya RM, Chhodavadia SK. Impact of sowing time and foliar spray of osmoprotectants on growth, yield attributes and yield of wheat (Triticum aestivum L.) against heat stress. Plant Archives. 2025;25(Supplement 1):231-237.
5. Sattar A, Cheema MA, Farooq M, Wahid MA, Wahid A, Babar BH. Evaluating the performance of wheat cultivars under late sown conditions. International Journal of Agriculture and Biology. 2010;12(4):561565.
6. Singh S, Kingra PK, Dhaliwal LK. Management of weather variability and terminal heat stress in wheat by altering sowing time. Annals of Agricultural Research. 2017;37(4).
7. Suryavanshi P, Buttar GS, Brar AS. Effect of osmoprotectants on performance of wheat (Triticum aestivum) under terminal heat stress condition of NorthWest India. Indian Journal of Agricultural Sciences. 2016;86(8):1037-1042.
8. Zhang X, et al. Effects of spraying KH₂PO₄ on flag leaf physiological characteristics and grain yield and quality under heat stress during the filling period in winter wheat. Plants. 2023;12(9):1801.
9. Zhang X, Ma M, Wu C, Huang S, Danish S. Mitigation of heat stress in wheat (Triticum aestivum L.) via regulation of physiological attributes using sodium nitroprusside and gibberellic acid. BMC Plant Biology. 2023;23:302.