Maize Genomics and Genetics 2025, Vol.16, No.1, 10-19 http://cropscipublisher.com/index.php/mgg 11 2 Current Understanding in Maize Breeding 2.1 Breeding techniques for quality improvement Traditional breeding techniques have long been employed to enhance maize quality by selecting and crossbreeding plants with desirable traits. These methods rely on phenotypic selection and the evaluation of progeny performance under various environmental conditions. For instance, the evaluation of maize inbred lines for drought and heat stress tolerance has identified several lines with superior traits, which are essential for breeding programs aimed at improving yield stability under stress conditions (Chen et al., 2012). Additionally, the use of combining ability and testcross performance has been instrumental in developing multi-nutrient maize hybrids with high yield potential under both stress and non-stress environments (Matongera et al., 2023a). In recent years, genetic editing techniques such as CRISPR/Cas9 have revolutionized maize breeding by enabling precise modifications at the DNA level. These techniques allow for the targeted introduction of beneficial traits, such as enhanced nutritional content or stress resistance, without the need for extensive crossbreeding. For example, molecular characterization of diverse maize inbred lines using SNP markers has facilitated the identification of genetic regions associated with stress tolerance, which can be targeted for genetic editing to develop superior maize lines (Wen et al., 2011). This integration of traditional and modern techniques is crucial for accelerating the development of high-quality maize varieties. 2.2 Traits related to stress resistance Key genetic traits related to stress resistance in maize include drought tolerance, heat tolerance, and resistance to various pests and diseases. Drought tolerance is a critical trait, as it enables maize plants to maintain productivity under water-limited conditions. Studies have shown that maize lines with high leaf relative water content and the ability to maintain vegetative growth under drought stress exhibit superior drought tolerance (Chen et al., 2012). Similarly, heat tolerance is essential for maintaining yield stability in regions experiencing high temperatures. Maize hybrids developed from heat-tolerant inbred lines have demonstrated enhanced tolerance to elevated temperatures (Chen et al., 2012). Pest and disease resistance are also vital for ensuring maize productivity. For instance, the identification of maize inbred lines with multiple disease resistance (MDR) to pathogens such as northern corn leaf blight, southern corn leaf blight, and aflatoxin contamination has been a significant advancement in breeding programs (Bankole et al., 2022). Additionally, genomic studies have identified SNPs associated with resistance to diseases like maize lethal necrosis, providing valuable markers for breeding disease-resistant maize varieties (Sadessa et al., 2022). These traits collectively contribute to the development of resilient maize lines capable of thriving under various stress conditions. 2.3 Knowledge gaps in previous research Despite significant advancements in maize breeding, several knowledge gaps remain that hinder the full realization of superior maize lines with enhanced quality and stress resistance. One major gap is the limited understanding of the genetic basis of combined drought and heat stress tolerance. Research has indicated that tolerance to combined stresses is genetically distinct from tolerance to individual stresses, necessitating further exploration to identify and incorporate these unique genetic traits into breeding programs (Cairns et al., 2013). Another gap is the need for more comprehensive evaluations of introduced trait donors for adaptation to new growing environments. The genotype × environment interaction (GEI) analysis is crucial for assessing the performance of nutrient-dense maize lines across different environments, yet it is often underutilized (Matongera et al., 2023b). Additionally, there is a need for large-scale screening and validation of identified genetic markers to ensure their effectiveness in diverse environmental conditions. For example, while SNP markers have been identified for various stress resistance traits, their practical application in breeding programs requires further validation and refinement (Sadessa et al., 2022).
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