Herbicide resistant grain sorghum: Opportunities and challenges

Focus on impoverished crops for sustainable food and nutritional security, especially sorghum, becomes increasingly important in the changing climate regime. Grain sorghum (Sorghum bicolor L.) is a vital cereal crop that could endure an array of biotic and abiotic stresses and is well-suited to arid ecological zones. Sorghum productivity is hindered by intense competition with weeds. However, conventional herbicide use, particularly Acetolactate Synthase (ALS) and Acetyl CoA Carboxylase (ACCase) inhibitors, has led to the development of herbicide-tolerant weeds. Developing herbicide-tolerant sorghum offers an effective strategy to manage weeds while enhancing crop productivity. Conventional approaches, such as utilising genetic diversity from wild relatives, germplasm screening, and induced mutagenesis, have successfully identified and transferred tolerant traits to cultivated sorghum varieties. These methods have produced hybrids tolerant to Acetolactate Synthase and Acetyl CoA Carboxylase inhibitors, providing new options for weed management. Commercially released herbicide-tolerant sorghum production systems include InzenTM (2016, USA), iGrowth® (2020, Argentina), and Double TeamTM (2021, USA), which benefit sorghum producers globally in many countries. Additionally, molecular mapping techniques, including quantitative trait loci mapping and marker-assisted selection, are critical for identifying genes responsible for herbicide tolerance. Advances in gene-editing technologies, such as Clustered Regularly Interspaced Short Palindromic Repeats, have enabled precise modifications to sorghum's genome, further enhancing the development of herbicide-tolerant varieties. Researchers worldwide are focusing on developing tolerance to 4-hydroxyphenyl pyruvate dioxygenase (HPPD), protoporphyrinogen oxidase (PPO)- inhibiting herbicides, Auxinic inhibitors, and Very Long Chain Fatty Acids Synthase (VLCFA) inhibitors, and this development needs to be accelerated. This review highlights the conventional and biotechnological approaches in developing herbicide-tolerant sorghum, underscoring the importance of integrating these strategies for sustainable sorghum cultivation and improved global food security.