Plant Gene and Traits 2024, Vol.15, No.4, 162-173 http://genbreedpublisher.com/index.php/pgt 169 ‘IR72’, and ‘Koshihikari’ were genetically engineered to express the bar gene, resulting in stable integration and expression of the transgene. Field trials demonstrated that these transgenic lines produced fertile seeds and exhibited resistance to glufosinate, with minimal impact on agronomic performance (Oard et al., 2004). Additionally, the development of dual herbicide-tolerant maize, which expresses both cp4 epsps and bar genes, highlights the potential for creating crops with multiple herbicide resistances to delay the evolution of weed resistance (Yu et al., 2023). 8.2 Field trials and yield performance Field trials have been conducted to evaluate the agronomic performance and yield of glufosinate-tolerant rice hybrids. Studies have shown that F1 hybrids between transgenic glufosinate-resistant rice lines and weedy rice accessions displayed heterosis in traits such as height, flag leaf area, and number of spikelets per panicle. These hybrids maintained similar agronomic performance to their weedy rice parents across multiple generations, indicating the potential for gene flow from transgenic rice to weedy rice under natural conditions (Song et al., 2011). Another study conducted field trials in Louisiana and Arkansas to assess the genetic and agronomic consequences of transferring glufosinate resistance from transgenic rice to “red rice”. The results indicated that transgenic populations exhibited similar plant vigor and density to non-transgenic populations, with no significant differences in seed dormancy and production (Oard et al., 2000). 8.3 Adoption by farmers and agronomic benefits The adoption of glufosinate-tolerant rice by farmers can offer several agronomic benefits, including improved weed control and reduced crop losses due to weed competition. The successful integration of the bar gene into commercial rice cultivars has demonstrated the effectiveness of glufosinate in controlling weedy rice and other competitive weeds (Oard et al., 2004). However, the potential for gene flow from transgenic rice to weedy rice poses a significant challenge. Studies have shown that gene flow frequencies can vary based on environmental conditions and the genetic background of the rice varieties involved. For example, gene flow from glufosinate-resistant japonica rice to weedy rice was found to be higher than to improved rice cultivars, emphasizing the need for effective management strategies to prevent the evolution of resistant weedy rice populations (Lu et al., 2014; Nadir et al., 2017). In conclusion, while the development and adoption of glufosinate-tolerant rice varieties offer promising agronomic benefits, careful consideration of gene flow risks and the implementation of robust management practices are essential to ensure the long-term sustainability of these technologies. 9 Future Directions and Research Opportunities 9.1 Emerging trends and innovations The development of glufosinate-tolerant rice cultivars presents both opportunities and challenges in agricultural biotechnology. One emerging trend is the creation of dual herbicide-tolerant crops, which can significantly enhance weed management strategies. For instance, transgenic rice plants tolerant to both bensulfuron methyl and glufosinate have been developed, showing promising results in terms of herbicide tolerance without significant growth or yield penalties (Fartyal et al., 2018). This dual tolerance approach could be extended to other herbicides, providing a more robust solution to weed resistance. Another innovation is the high-efficiency transformation techniques for U.S. rice lines, which have shown stable integration and expression of glufosinate resistance under field conditions (Jiang et al., 2000). These advancements in genetic transformation could facilitate the rapid development and deployment of herbicide-resistant rice varieties, thereby improving weed control and crop productivity. 9.2 Addressing current research gaps Despite the progress made, several research gaps need to be addressed to fully harness the potential of glufosinate-tolerant rice. One critical area is the understanding of gene flow dynamics between transgenic rice and weedy rice. Studies have shown that gene flow can occur at varying frequencies, with weedy rice often exhibiting higher rates of transgene acquisition compared to cultivated rice (Chen et al., 2004; Lu et al., 2014; Nadir et al., 2017; Zhang et al., 2018). Further research is needed to quantify these rates under different environmental conditions and to develop strategies to mitigate unintended gene flow.
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