Physiological and Yield Responses of Bread Wheat (Triticum aestivum L.) Cultivars to Thermal Stress in a Sequential Cropping System (Summer-Winter) in the Shavor Region, Khuzestan

Document Type : Scientific - Research

Authors

Mohammad Ali Molaee ¹

Seyed Keyvan Marashi ¹

Abdolali Gilani ²

Shahram Lak ¹

Mojtaba Alavi Fazel ³

¹ Department of Agronomy, Ahv. C., Islamic Azad University, Ahvaz, Iran

² Department of seed and plant Improvement Research, Khuzestan Agricultural and Natural Research and Education Center, Agricultural Research, Education and Extension Organization (AREEO), Ahvaz, Iran.

³ Department of Agronomy, SR.C., Islamic Azad University, Tehran, Iran

10.22067/agry.2026.98135.1271

Abstract

Introduction
Wheat (Triticum aestivum L.) is a strategic crop for Iran's food security, but in tropical regions like Khuzestan, terminal heat stress severely limits its production. A sequential double-cropping system (summer-winter) has been proposed to maximize land use efficiency. In this system, the first crop is sown in late summer (September-October), and the second crop is sown immediately after harvest in winter (January-February). The summer crop faces high soil temperature at germination but benefits from rapid early growth, while the winter crop encounters cold stress at early stages followed by terminal heat stress during grain filling. Therefore, the success of this system depends on selecting suitable cultivars and optimal sowing dates to manage temperature stresses in both cycles.

Materials and Methods
This research was conducted over two cropping years (2022-2023 and 2023-2024) as a Randomized Complete Block Design with a split-plot arrangement. The main factor included four sowing dates (September 11, September 21, October 1, and October 11), and the sub-factor included four wheat cultivars (Mehregan, Chamran-2, Ayeeneh, and Sarang). Winter cropping was performed immediately after the summer harvest on four corresponding sowing dates: January 15, January 20, January 30, and February 4. Physiological indices including leaf area index (LAI), total dry weight (TDW), crop growth rate (CGR), net assimilation rate (NAR), and leaf area duration (LAD) were measured, and grain yield was determined for both cropping cycles. Data from both years were combined and subjected to analysis of variance, and mean comparisons were performed using an appropriate statistical test.
Results and Discussion
The results showed that sowing date, cultivar, and their interaction significantly affected all physiological traits and grain yield. The highest total dry weight (795 g.m^-²) and crop growth rate (15.74 g.m^-². day^-1) were observed in the sowing date October 1/January 30 with the Chamran-2 cultivar. The highest net assimilation rate (16.18 g.m^-². day^-1) was also obtained in the same treatment. This superiority can be attributed to the favorable synchronization of the rapid growth phase with moderate temperatures in autumn and early spring, as well as the longer growth duration (135 days) and better heat tolerance of the Chamran-2 cultivar. However, the Mehregan cultivar on the sowing date October 11/February 4 showed a different performance pattern. Despite having moderate or even low values in some physiological indices such as CGR and NAR, it exhibited the highest leaf area index (4.30), the highest leaf area duration (24.55 days), and consequently the highest mean grain yield (1408 kg. ha^-1) compared to other treatments. The superiority of Mehregan can be explained by its high leaf area duration, which reflects sustained photosynthetic activity over a longer period, and its specific adaptation to water-limited and saline conditions, enabling it to maintain green leaf area even under late sowing dates. In contrast, Chamran-2 and Sarang cultivars, despite their superiority in instantaneous physiological indices (CGR and NAR) at specific sowing dates (especially October 1/January 30), showed lower final yields. This was primarily due to their significantly reduced leaf area index (3.96-3.98) and leaf area duration (17.75-19.75 days), indicating greater susceptibility to terminal heat stress and accelerated leaf senescence during the reproductive stages.

Conclusion
Overall, the success of the sequential cropping system in tropical regions depends on selecting tolerant cultivars and optimal sowing dates. Leaf area index and leaf area duration play a more critical role in final yield compared to other physiological indices. The Mehregan cultivar on the sowing date October 11/February 4 is recommended for this system. Furthermore, the results of this study can serve as a practical guideline for farmers and agricultural managers in Khuzestan and similar warm regions to enhance land use efficiency and achieve sustainable wheat production through double-cropping systems.

Keywords

Crop growth rate

Crop management

Leaf area index

Sowing date

Subjects

• Agroecology and Indigenous Knowledge

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Authors retain the copyright. This is an open access article distributed under Creative Commons Attribution 4.0 International License (CC BY 4.0)

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