Heat Terminal Stress in wheat. More than one-third of the world’s population depends on wheat (Triticum aestivum L.), one of the most widely grown and important cereal crops. Climate change, with its increasing temperatures, is likely to have a significant impact on global food security, as high-temperature stress can cause yield losses in crops such as wheat. Understanding the mechanisms underlying terminal heat stress resistance in wheat is therefore critical for improving the resilience of this crop to future environmental changes.
2. Heat stress in wheat:
Heat stress can occur at any stage of wheat growth, from seedling emergence to the grain filling, and can cause various physiological, biochemical, and morphological changes in the plant, leading to reduced growth and grain yield. The temperature threshold for heat stress in wheat varies depending on the developmental stage, but temperatures above 35 °C can be detrimental to wheat growth and yield.
3. Mechanisms of heat stress tolerance in wheat:
Heat stress tolerance in wheat is a complex trait that is influenced by multiple genetic and environmental factors. The following are some of the main mechanisms involved in heat stress tolerance in wheat:
- Accumulation of compatible solutes: Compatible solutes, such as proline, are small organic molecules that help to maintain cellular osmotic potential and reduce damage from oxidative stress under heat stress conditions.
- Antioxidant defence system: Plants under heat stress experience an increase in oxidative stress, which can harm cellular elements like lipids, proteins, and DNA. Under conditions of heat stress, antioxidant defence mechanisms such as superoxide dismutase, catalase, ascorbate peroxidase, and glutathione are essential for reducing the effects of oxidative stress.
- Stomatal regulation: Stomata are pores on the leaf surface that regulate the exchange of carbon dioxide and water vapour between the plant and the atmosphere. High temperatures can lead to stomatal closure, reducing water loss from the plant and protecting it from heat stress.
- Heat Photoprotection: High temperatures can cause photodamage to chlorophyll, the pigment responsible for capturing light energy for photosynthesis. Photoprotection mechanisms, such as non-photochemical quenching, reduce photodamage to chlorophyll and maintain photosynthetic efficiency under heat-stress conditions.
4. Methods to improve terminal heat stress resistance in wheat:
Some of the most common ones are:
- Crop management: Adequate soil moisture and fertility management can help wheat plants better tolerate heat stress. Additionally, using a crop rotation system, selecting planting dates, and optimizing planting densities can help reduce the impact of heat stress.
- Breeding for heat tolerance: Wheat breeding programs can select heat-tolerant varieties that have genes that confer better tolerance to high-temperature stress.
- Molecular biology approaches: Advances in molecular biology have allowed for the identification of key genes involved in heat stress tolerance. This knowledge can be used to develop genetically modified (GM) crops with enhanced heat tolerance.
- Physiological approaches: Improving the photosynthetic efficiency of wheat plants can help them better tolerate heat stress. This can be achieved by manipulating factors such as leaf area, water use efficiency, and carbon partitioning.
- Antioxidant systems: Heat stress can lead to an increase in reactive oxygen species (ROS) in wheat plants. Antioxidant systems can help mitigate the damage caused by ROS and hence improve heat tolerance. This can be achieved through genetic engineering, or by applying exogenous antioxidants.
- Use of stress-tolerant cultivars: Cultivars that are naturally tolerant to heat stress can be used in regions that experience high temperatures. These cultivars have been developed through traditional breeding methods, and they have a proven track record of tolerance to heat stress.
- Irrigation: Adequate irrigation during periods of heat stress can help improve wheat growth and yield. This is because it helps to maintain soil moisture levels, which is critical for plant survival during high-temperature events.
- Mulching: Applying organic mulches to the soil surface can help reduce soil temperature, which in turn can help improve wheat growth and yield. This is because the mulch helps to regulate soil moisture levels, which is critical for plant survival during high-temperature events.
Heat stress is a major challenge for wheat production worldwide, as it reduces both grain weight and grain number. Breeding, genetics, physiology, and metabolism are important factors in determining the heat stress tolerance of wheat. Developing heat-resistant wheat varieties through breeding and biotechnology, as well as using management strategies, such as irrigation and mulching, can help to reduce the impact of heat stress and secure food production under a changing climate.
Muhammad Tayyab Ayaz
Department: Plant Breeding and Genetics
University of Agriculture, Faisalabad