Molecular Plant Breeding 2025, Vol.16, No.1, 93-104 http://genbreedpublisher.com/index.php/mpb 98 maize yields and protein content. For instance, early quality protein maize (QPM) hybrids have been developed to tolerate combined drought and heat stress, which are anticipated to increase in frequency due to climate change (Bhadmus et al., 2021). Moreover, the variability in gene expression under different environmental conditions can lead to heterogeneity in grain composition. Studies have shown that transcription factor gene expression in maize is highly variable across different genomic and environmental conditions, which can influence the levels of grain components like protein, oil, and amino acids (Harrigan et al., 2009). This variability underscores the importance of understanding and managing environmental impacts to stabilize protein expression in maize. 5.2 Adaptation of high-protein varieties to different regions The adaptation of high-protein maize varieties to different regions is crucial for ensuring food security under changing climatic conditions. Breeding programs have successfully developed stress-tolerant maize cultivars for various regions, including sub-Saharan Africa, Asia, and Latin America, by integrating advanced breeding techniques and extensive on-farm testing (Prasanna et al., 2021). These efforts have led to the deployment of elite climate-resilient maize cultivars that can thrive in stress-prone environments. Furthermore, the potential for crop production adaptation depends on the availability of future varieties that can cope with climate change. Studies suggest that a significant portion of global cropland may require new crop varieties to avoid yield loss due to climate change. Region-specific breeding efforts are essential to develop varieties that can adapt to local climatic conditions and maintain high protein content (Zabel et al., 2021). For example, modern maize hybrids in Northeast China have shown increased yield potential and resource use efficiency despite adverse climate changes, indicating successful adaptation to new conditions (Chen et al., 2013). 5.3 Soil and irrigation requirements Soil and irrigation management play a vital role in the cultivation of high-protein maize varieties. Low soil nitrogen (N) stress can negatively impact grain yield and protein content. Breeding for nitrogen use efficiency (NUE) is essential to address food insecurity and improve grain quality. Studies have shown that low N conditions reduce grain yield, kernel weight, and protein content, while increasing starch content. Therefore, it is feasible to improve both grain yield and quality traits under low-N conditions through targeted breeding programs (Ertiro et al., 2022). Irrigation practices also influence maize protein content. In regions with limited water availability, developing drought-tolerant maize varieties is critical. For instance, early QPM hybrids with tolerance to combined drought and heat stress have been identified as high-yielding and stable under such conditions (Bhadmus et al., 2021). Additionally, the integration of agronomic improvements, such as optimized irrigation schedules, can enhance maize yield and protein content. Research indicates that agronomic practices, along with climate and genetic factors, contribute significantly to yield gains in maize (Rizzo et al., 2022). 6 Challenges in Breeding 6.1 Balancing yield and protein enhancement One of the primary challenges in breeding maize varieties with high protein content is achieving a balance between yield and protein enhancement. High-protein maize varieties often exhibit a trade-off with yield, as the genetic modifications that increase protein content can negatively impact other agronomic traits. For instance, studies have shown that while Quality Protein Maize (QPM) varieties have superior nutritional profiles, they often yield less compared to non-QPM varieties (Bhatnagar et al., 2004; Tandzi et al., 2017). This negative correlation between yield and protein content complicates breeding efforts, as breeders must carefully select for both traits without compromising one for the other. Moreover, the relationship between grain yield and protein content is influenced by environmental factors such as soil nitrogen levels. Research indicates that low soil nitrogen stress can exacerbate the trade-off between yield and protein content, making it even more challenging to develop varieties that perform well under suboptimal
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