Maize Genomics and Genetics 2025, Vol.16, No.4, 167-181 http://cropscipublisher.com/index.php/mgg 175 7 Genetic and Breeding Approaches for Improving Maize Growth 7.1 Developing maize varieties resistant to environmental stresses Developing maize varieties that resist environmental stresses such as drought, heat, and salinity is critical for maintaining yields amid climate change. Traditional breeding programs have emphasized selecting genotypes resilient to water scarcity and nitrogen deficiency, two major stressors in maize cultivation. These programs rely on germplasm banks to identify and select genotypes with specific traits for drought and heat tolerance. Testing in managed-stress environments allows for the accurate assessment of how well these varieties perform under simulated stress conditions, ensuring that selected genotypes are effective in real-world conditions (Loro et al., 2023). Programs led by institutions like CIMMYT have been instrumental in developing maize varieties suited for tropical regions, where drought and extreme heat are common. These varieties are now widely used across Sub-Saharan Africa and Asia, where they play a crucial role in supporting food security for smallholder farmers. CIMMYT’s approach integrates managed-stress screening and on-farm trials to ensure that selected varieties can withstand local environmental stresses (Prasanna et al., 2021). In addition to drought and heat resistance, breeding programs also focus on secondary traits that support stress tolerance, such as root depth and the anthesis-silking interval, which is critical for synchronizing flowering and pollination during drought conditions. Secondary traits are often inherited alongside primary traits, helping breeders select for complex resilience characteristics in a single breeding cycle. By optimizing these secondary traits, researchers can produce maize varieties that are well-suited for resource-limited and variable environments (Nepolean et al., 2018). 7.2 Role of genetic engineering in maize stress tolerance Genetic engineering has provided maize breeding with advanced tools to improve stress tolerance traits more precisely and efficiently. CRISPR/Cas9, a powerful gene-editing tool, has allowed scientists to target specific genes associated with drought and heat tolerance (Wu and Li, 2024). For instance, the BREEDIT approach combines CRISPR-based multiplex gene editing with conventional breeding to tackle complex traits like yield stability and drought resistance, significantly enhancing maize’s adaptability in unpredictable climates. This multiplex approach allows the simultaneous editing of multiple genes involved in stress responses, creating a more robust stress-tolerant maize variety (Lorenzo et al., 2022). Beyond genome editing, transgenic breeding has been effective in introducing traits from non-maize species. Genes encoding heat shock proteins (HSPs) and heat shock factors (HSFs) have been engineered into maize to provide enhanced thermal tolerance by stabilizing proteins and cellular structures during high temperatures. These transgenic varieties have shown improved productivity under extreme heat and better resilience during key growth stages like pollination and grain filling. In addition, genetic engineering allows for the enhancement of resource-use efficiency in maize. For instance, genes that increase water-use efficiency and nitrogen uptake have been introduced into maize, allowing plants to thrive in resource-scarce environments. This approach is particularly effective in areas facing water scarcity or degraded soil conditions, providing a means to improve yields without extensive input use (Anwar and Kim, 2020). These genetic engineering advancements complement traditional breeding by offering faster, targeted solutions to enhance stress tolerance in maize. 7.3 Conservation of maize genetic diversity Maintaining maize genetic diversity is essential for breeding programs, providing a foundation for future improvements and adaptability. Genetic diversity offers breeders a vast pool of traits that can be harnessed to enhance stress resilience, pest resistance, and yield stability. Participatory breeding programs in countries like Portugal have successfully retained genetic diversity while improving agronomic performance. By involving local farmers in the selection process, these programs ensure that diverse traits valuable for local environments are preserved.
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