Maize Genomics and Genetics 2024, Vol.15, No.4, 171-181 http://cropscipublisher.com/index.php/mgg 177 developing broad-spectrum and durable disease resistance but also enhances our understanding of the molecular mechanisms underlying MDR (Wanng et al., 2021). 6.3 Yield improvement Teosinte has contributed to yield improvement in maize, particularly under high-density planting conditions. The identification and introgression of the UPA2 allele from teosinte, which regulates upright plant architecture, have been shown to enhance maize yields in densely planted fields. This allele, which was lost during maize domestication, has been reintroduced to modern hybrids, resulting in improved agronomic characteristics and higher yields under high-density planting conditions (Tian et al., 2019). Additionally, the identification of a new QTL underlying seminal root number in a maize-teosinte population has provided insights into improving root architecture, which is crucial for water and nutrient acquisition, ultimately contributing to yield improvement (Wanng et al., 2023). 6.4 Nutritional quality enhancement Teosinte has also been explored for its potential to enhance the nutritional quality of maize. Although specific studies on nutritional quality enhancement were not directly cited in the provided data, the overall genetic diversity and unique traits of teosinte, such as its ability to form aerenchyma under flooding conditions, suggest that it holds promise for improving various agronomic traits, including nutritional quality. The introgression of beneficial alleles from teosinte into maize can potentially lead to the development of maize varieties with enhanced nutritional profiles, thereby addressing both yield and quality aspects of maize production (Mano et al., 2006; Mano and Omori, 2007; 2013). In summary, teosinte has played a crucial role in maize genetic enhancement, contributing to improved drought tolerance, disease resistance, yield, and potentially nutritional quality. The utilization of teosinte-derived alleles and genetic resources continues to offer valuable opportunities for advancing maize breeding programs and addressing global agricultural challenges. 7 Challenges and Limitations The integration of teosinte into maize genetic enhancement presents several challenges and limitations. These can be broadly categorized into genetic barriers, breeding difficulties, and regulatory and ethical issues. 7.1 Genetic barriers One of the primary challenges in utilizing teosinte for maize improvement is the genetic incompatibility between the two species. The presence of specific loci such as Teosinte crossing barrier1 (Tcb1) restricts hybridization with maize, making it difficult to crossbreed the two species effectively (Evans et al., 2001). Additionally, the extensive genomic and transcriptomic variation between maize and teosinte further complicates the integration of beneficial traits from teosinte into maize (Li et al., 2021). The genetic architecture of teosinte, which includes a high degree of genetic diversity and unique alleles, poses significant barriers to the straightforward transfer of traits (Karn et al., 2017; Yang et al., 2019). 7.2 Breeding difficulties Breeding teosinte with modern maize varieties is fraught with practical difficulties. The differences in plant and inflorescence architecture between maize and teosinte, controlled by loci such as teosinte branched1 (tb1), result in phenotypic traits that are not always desirable in modern agricultural contexts. Moreover, the genetic background of teosinte can affect the expression of these traits, making it challenging to predict and control the outcomes of breeding programs. The process of backcrossing and selecting for desirable traits is labor-intensive and time-consuming, often requiring multiple generations to achieve stable and beneficial hybrids (Karn et al., 2017). 7.3 Regulatory and Ethical Issues The use of wild relatives like teosinte in crop improvement also raises several regulatory and ethical concerns. The introduction of wild alleles into commercial maize varieties may be subject to stringent regulatory scrutiny to
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