Ground-level ozone (O₃), a harmful air pollutant formed from industrial and vehicular emissions, poses a growing threat to global agriculture. In China, the world’s largest wheat producer, ozone pollution has become a critical concern, with studies estimating yield losses of up to 30% in regions like the North China Plain.
A recent study led by researchers at Yangzhou University offers new insights into how decades of wheat breeding have unintentionally shaped the crop’s response to ozone stress.
Published in Frontiers in Plant Science, the research reveals a paradox: modern wheat cultivars are more resilient to ozone-induced yield losses than older varieties, but this progress comes at the cost of declining nutritional and milling quality.
The Experiment: Testing Decades of Wheat Breeding
The study was conducted over two growing seasons at the Yangzhou Rice and Wheat Free-Air Concentration Enrichment (FACE) facility, an open-field system that simulates elevated ozone levels without isolating plants in artificial chambers.
Unlike traditional closed-chamber experiments, the FACE setup mimics real-world farming conditions, allowing researchers to observe how crops interact with natural variables like sunlight, temperature, and wind.
Seventeen wheat cultivars from China’s Yangmai series—bred between the 1970s and 2000s—were exposed to ozone concentrations 1.5 times higher than ambient levels (averaging ~50 parts per billion during daytime).
These cultivars, widely grown in the Yangtze River basin, were selected to represent different eras of breeding priorities, from disease resistance in the 1970s to high yield and nitrogen efficiency in the 2000s.
Yield Resilience: Modern Cultivars Shine
The results showed a clear trend: newer cultivars suffered smaller yield losses under ozone stress compared to older varieties. On average, ozone reduced wheat yields by 18.19%, but this impact varied significantly across generations.
Cultivars from the 1970s, such as Yangmai 1, experienced a 24.9% yield decline, while post-2000 varieties like Yangmai 19 and 20 lost just 14.7%. This improvement suggests that modern breeding efforts, while not explicitly targeting ozone resistance, have inadvertently selected for traits that mitigate damage.
- 1970s cultivars: 24.9% yield loss.
- 1980s cultivars: 23.3%.
- 1990s cultivars: 19.8%.
- Post-2000 cultivars: 14.7%.
For instance, newer cultivars demonstrated greater stability in 1,000-grain weight—a critical yield component—under ozone stress. Older varieties, by contrast, saw sharp drops in both grain weight and the number of grains per spike.
Researchers attribute this resilience to traits like enhanced nitrogen use efficiency and slower plant aging, which may help buffer against ozone’s oxidative damage.
However, this yield resilience comes with a trade-off: a decline in grain quality. Modern cultivars showed significant reductions in starch content (down 3.2%) and milling traits like bulk density (down 3.0%) and hardness (down 7.3%).
Protein content, meanwhile, increased by 7.9% in post-2000 varieties. While higher protein might seem beneficial, it reflects an imbalance caused by shortened grain-filling periods. Ozone accelerates plant senescence, cutting short the time available for carbohydrate synthesis.
- Starch content: Dropped by 3.2% in post-2000 cultivars (vs. 1.5%–2.6% in older varieties).
- Protein content: Increased by 7.9% in post-2000 cultivars, likely due to shortened grain-filling periods limiting carbohydrate accumulation.
- Bulk density and hardness: Reduced by 3.0% and 7.3%, respectively, in newer varieties, affecting milling efficiency and end-use quality.
As a result, grains accumulate less starch and proportionally more protein—a shift that undermines nutritional balance and processing quality. For example, reduced starch affects calorie content and texture, while lower hardness weakens gluten strength, critical for bread and noodle production.
Sedimentation value, a measure of gluten quality, also dropped by 12.1% in modern cultivars, signaling challenges for food manufacturers.
Why Does Ozone Harm Quality?
Ozone’s dual impact on photosynthesis and aging explains these trends:
1. Photosynthetic Damage: Ozone disrupts chlorophyll and stomatal function, reducing the carbon available for starch synthesis.
2. Accelerated Senescence: Plants age faster under ozone stress, cutting short the grain-filling period. Carbohydrate accumulation (starch) is prioritized early, while proteins dominate later stages.
3. Oxidative Stress: Ozone generates reactive oxygen species that alter enzyme activity, affecting starch and protein composition.
Road Ahead: Balancing Yield and Quality
The study highlights a broader dilemma in agricultural innovation. Over decades, breeders have prioritized yield, disease resistance, and adaptability to high-temperature stress—traits that align indirectly with ozone tolerance.
Yet these gains have come at the expense of quality. Older cultivars, though less productive, often maintained better starch-protein balance and milling characteristics.
This disconnect underscores the need for a more holistic approach to crop breeding, one that balances yield stability with nutritional and industrial requirements. The implications of this research extend beyond China.
As ozone levels rise globally, farmers and policymakers must rethink strategies for climate adaptation. The study suggests that future breeding programs should prioritize stabilizing grain weight under stress, possibly through gene editing or marker-assisted selection.
Techniques like CRISPR could target pathways involved in carbohydrate transport and starch synthesis, helping cultivars maintain both yield and quality. Additionally, adjusting nitrogen fertilization during grain filling might counteract protein-starch imbalances. Meanwhile, stabilizing 1,000-grain weight under stress should be a top priority.
Yet technological fixes alone are insufficient. The study underscores the urgency of reducing ozone precursors like nitrogen oxides and volatile organic compounds. While breeding can buy time, long-term food security depends on curbing emissions.
For now, the Yangmai series offers a template for resilience. Its gradual adaptation to rising ozone levels—driven by both natural selection and human ingenuity—demonstrates the potential of crops to evolve under pressure. However, the study’s findings also serve as a caution: in the race to outpace climate change, quality must not be sacrificed for quantity.
Conclusion
In conclusion, the Yangzhou University study reveals a nuanced story of progress and trade-offs. Modern wheat cultivars, shaped by decades of breeding, are better equipped to withstand ozone pollution—a testament to agricultural innovation.
Yet their declining quality highlights the complexity of breeding for a changing climate. As the world grapples with intersecting crises of pollution, population growth, and food security, this research underscores the need for solutions that harmonize yield, nutrition, and sustainability.
The future of wheat lies not just in resisting ozone, but in balancing resilience with the timeless qualities that make food nourishing, versatile, and culturally meaningful.
Reference: Qian, Y., Zhao, Z., Cao, Y., Ma, Q., Zhu, N., Song, L., … & Zhu, X. (2025). Renewal of wheat cultivars enhances ozone resistance in yield but detrimentally impacts quality: a survey of Chinese wheat. Frontiers in Plant Science, 15, 1526846.
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