Maize Genomics and Genetics 2024, Vol.15, No.2, 60-69 http://cropscipublisher.com/index.php/mgg 66 transformation efficiency and genotype independence, facilitating the development of genetically modified maize varieties with multiple stacked traits (Bao et al., 2022). These advancements are expected to continue driving innovation in maize biotechnology, allowing for the development of more robust and versatile herbicide-tolerant crops. 6.2 Emerging herbicide tolerance traits and genes The discovery and incorporation of new herbicide tolerance traits and genes are crucial for addressing the evolving challenges in weed management. For instance, the development of maize varieties tolerant to both glyphosate and glufosinate has shown promise in delaying the development of weed resistance (Yu et al., 2023). Additionally, the identification of genes such as ZmGHT1, which confers glufosinate tolerance, provides new avenues for breeding herbicide-resistant maize (Guo et al., 2023). The engineering of enzymes with robust activity against multiple herbicide families, such as aryloxyphenoxypropionate and synthetic auxins, further expands the toolkit available for effective weed control (Larue et al., 2019). 6.3 Integrating herbicide tolerance with other agronomic traits Integrating herbicide tolerance with other agronomic traits, such as insect resistance and improved yield, is essential for developing comprehensive solutions for crop management. Transgenic maize varieties harboring multiple genes, such as cry2Ab, vip3A, and CP4-EPSPS, have demonstrated strong insect resistance and herbicide tolerance, providing valuable germplasm for future breeding programs (Liu et al., 2023). Moreover, the elimination of trade-offs between resistance, tolerance, and growth in certain maize genotypes highlights the potential for breeding varieties that perform well under complex field conditions. This integrated approach ensures that herbicide-tolerant maize varieties also possess other beneficial traits, enhancing their overall utility and performance. 6.4 Addressing challenges and mitigating risks Despite the progress made, several challenges and risks associated with herbicide-tolerant maize need to be addressed. The emergence of herbicide-resistant weeds due to prolonged use of specific herbicides remains a significant concern (Perry et al., 2016). Strategies such as deploying dual herbicide-tolerant crops from the outset and rotating herbicides with different modes of action can help mitigate this risk (Yu et al., 2023). Additionally, ensuring the safety and stability of genetically modified maize through rigorous testing, such as 90-day feeding studies, is crucial for gaining public trust and regulatory approval (Zhu et al., 2013). Ongoing research should also focus on understanding the genetic and environmental factors influencing herbicide tolerance to develop more resilient and sustainable crop management practices. The future of herbicide-tolerant maize lies in leveraging advanced genetic engineering technologies, discovering new tolerance traits, integrating multiple agronomic traits, and addressing the associated challenges and risks. Continued research and innovation in these areas will be pivotal in enhancing the effectiveness and sustainability of herbicide-tolerant maize varieties. 7 Concluding Remarks The adoption of genetically engineered (GE) maize has led to varied changes in herbicide use. While GE glyphosate-tolerant (GT) maize showed a slight reduction in herbicide use compared to non-GE maize, the environmental impact quotient indicated a more significant reduction in herbicide use. Additionally, the development of dual herbicide-tolerant maize, such as those tolerant to both glyphosate and glufosinate, has shown promise in delaying weed resistance. Advances in genetic engineering have enabled the development of maize varieties with robust tolerance to multiple herbicide families, such as aryloxyphenoxypropionate and synthetic auxin herbicides. This diversification in herbicide tolerance traits is crucial for effective weed management and mitigating the risk of herbicide resistance. Studies on the safety of GE herbicide-tolerant maize, such as those involving glyphosate-tolerant maize with the G2-aroAgene, have demonstrated that these crops are as safe and nutritious as their non-GE counterparts. This is supported by comprehensive toxicological assessments in animal models.
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