Plant Gene and Traits 2024, Vol.15, No.4, 162-173 http://genbreedpublisher.com/index.php/pgt 167 5.2 Breeding strategies and approaches Breeding strategies for glufosinate-tolerant rice involve both traditional and modern biotechnological approaches. One effective method is the transformation of elite rice lines using gene transfer techniques, such as particle bombardment, to introduce glufosinate resistance genes like pat or bar (Kim et al., 2007). This approach has been successfully applied to U.S. rice lines and photoperiod-sensitive genic male sterile (PGMS) lines, resulting in high transformation efficiency and stable integration of resistance genes (Jiang et al., 2000; Kim et al., 2007). Another strategy is the hybridization of transgenic glufosinate-resistant rice with weedy rice accessions, which has shown that hybrids can maintain high agronomic performance and herbicide resistance across multiple generations (Chen et al., 2004; Song et al., 2011). Furthermore, genetic analysis and fine mapping of resistance loci, such as ZmGHT1 in maize, provide insights into the genetic mechanisms underlying herbicide tolerance, which can be applied to rice breeding programs (Bao et al., 2022). 5.3 Integration into cultivated rice varieties Integrating glufosinate-tolerant traits into cultivated rice varieties requires careful management to mitigate the risks of gene flow and the evolution of resistant weedy populations. Field evaluations have demonstrated that hybrids between transgenic rice and weedy rice can exhibit traits such as increased height, extended flowering, and high seed shattering, which pose ecological risks (Zhang et al., 2003; Zhang et al., 2018). To address these challenges, breeding programs must incorporate strategies to control gene flow, such as the use of mitigation genes that render hybrids unfit to compete (Gressel and Valverde, 2009). Additionally, the development of dual herbicide-tolerant transgenic rice plants can provide sustainable weed management solutions by reducing the reliance on a single herbicide and preventing the evolution of resistant weeds (Fartyal et al., 2018). Effective integration of these traits into cultivated varieties will require ongoing research and field trials to ensure agronomic performance and environmental safety. 6 Challenges in Breeding Glufosinate-Tolerant Rice 6.1 Gene flow and contamination risks Gene flow from glufosinate-resistant rice to weedy rice is a significant challenge due to the potential for creating herbicide-resistant weedy rice populations. Studies have shown that gene flow can occur at varying frequencies depending on the proximity and reproductive compatibility between transgenic rice and weedy rice. For instance, gene flow frequencies from glufosinate-resistant rice to weedy rice have been observed to range from 0.011% to 0.488% under different experimental conditions (Chen et al., 2004; Song et al., 2009; Lu et al., 2014; Sun et al., 2015; Nadir et al., 2017). The bidirectional gene flow between transgenic cultivated rice and weedy rice further complicates the issue, as it can lead to the introgression of weedy traits into hybrid rice, increasing the agro-ecological risks (Zhang et al., 2018). Additionally, the presence of transgenes in weedy rice populations can persist and spread, posing long-term contamination risks (Cao et al., 2009; Yook et al., 2020). 6.2 Environmental and ecological concerns The environmental and ecological impacts of gene flow from glufosinate-resistant rice to weedy rice are profound. The hybrid progeny resulting from such gene flow often exhibit enhanced fitness and weediness traits, which can lead to more aggressive and resilient weedy rice populations (Olguin et al., 2009; Song et al., 2011; Zhang et al., 2018). These hybrids can outcompete native plant species, disrupt local ecosystems, and reduce biodiversity. Moreover, the increased fitness of hybrids, such as higher germination rates and greater vegetative and reproductive potential, can facilitate their persistence and spread in the environment (Cao et al., 2009; Yook et al., 2020). The potential for these hybrids to become dominant in agricultural fields and natural habitats raises significant ecological concerns. 6.3 Regulatory and biosafety issues Regulatory and biosafety issues are critical challenges in the breeding of glufosinate-tolerant rice. The potential for gene flow and the resulting environmental risks necessitate stringent biosafety assessments and regulatory measures. Current regulations may not fully address the complexities of gene flow and the long-term impacts of transgenic crops on wild relatives and ecosystems (Zhang et al., 2003; Sun et al., 2015). Effective management
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