Journal of Energy Bioscience 2024, Vol.15, No.6, 349-357 http://bioscipublisher.com/index.php/jeb 351 lead to unsatisfactory breeding results. In Asia and other regions, traditional breeding has successfully improved maize yields and resistance to various stresses, and traditional breeding has been the cornerstone of agricultural development (Prasanna et al., 2010). However, the complexity of fiber traits affected by multiple genes poses a major challenge to traditional breeding methods. 3.2 Applications of molecular breeding techniques Molecular breeding techniques, such as marker-assisted selection (MAS), have revolutionized maize improvement by marking the association between specific genes or genomic regions and target traits, improving breeding efficiency and accuracy. MAS involves the use of molecular markers associated with specific genes of interest, enabling breeders to select progeny lines with the help of molecular markers of target traits, thereby obtaining superior individual plants containing the target gene. This method has been successfully applied to improve various traits of maize, including disease resistance, insect resistance, drought resistance, waterlogging resistance, cold resistance, salinity resistance, and lodging resistance (Guan et al., 2015). For example, MAS has been used to introduce aflatoxin resistance genes into superior tropical maize lines, significantly accelerating the breeding process (Offornedo et al., 2022). Marker-assisted recurrent selection (MARS) has improved maize yield and stress resistance in tropical regions under arid and optimal conditions in sub-Saharan Africa, demonstrating the potential of MAS in improving complex traits such as fiber content (Beyene et al., 2016). 3.3 Role of genetic engineering in targeting fiber biosynthesis pathways Genetic engineering provides a new route for directly changing the genetic composition of maize to increase fiber content. This method involves introducing foreign genes into recipient cells through in vitro recombination, so that the gene can be replicated, transcribed, translated and expressed in the recipient cells. Advances in genetic engineering, such as CRISPR/Cas9, make it possible to target and edit genes with high precision (Zhou and Hong, 2024). For example, the identification and manipulation of functional genes related to agronomic traits have paved the way for improving maize quality and yield (Ma et al., 2019). Genetic engineering can solve the problems encountered by traditional and molecular breeding methods by introducing new traits that are difficult to achieve by traditional means. This integrated approach can significantly improve the efficiency and effectiveness of breeding programs aimed at developing high-fiber maize varieties (Sethi et al., 2023). 4 Mechanisms Linking High Fiber to Bioethanol Production 4.1 Impact of cellulose and hemicellulose on ethanol yield High-fiber maize is rich in cellulose and hemicellulose, but is wrapped in lignin. After pretreatment, the straw needs to be hydrolyzed to convert it into fermentable sugars to increase ethanol production. Cellulose and hemicellulose are key components of maize cell walls, and their decomposition releases fermentable sugars such as glucose, galactose, and xylose. Studies have shown that optimizing the fermentation process, such as through simultaneous saccharification and co-fermentation (SSCF), can increase ethanol titer. For example, by effectively utilizing 86.20% of cellulose and 82.99% of hemicellulose in pretreated maize cobs, Spathaspora passalidarum U1-58 was able to achieve an ethanol yield of 75.35% (Yu et al., 2017). The higher ethanol titer and yield demonstrate the potential of high-fiber maize as an effective raw material for bioethanol production. 4.2 Reduction in processing costs with high-fiber maize The use of high-fiber maize can reduce the feedstock and processing costs associated with bioethanol production. The increase in the cellulose and hemicellulose content of the feedstock means that more fermentable sugars can be obtained per unit of biomass, thereby reducing the need for additional feedstock. Advances in genetic modification and breeding strategies have made it possible to develop maize varieties with improved cell wall characteristics that are easier to process. By modifying maize traits to optimize the pretreatment and hydrolysis processes, the energy and enzyme costs required for the decomposition of lignocellulosic biomass can be reduced (Torres et al., 2015). Therefore, high-fiber maize can not only increase ethanol production, but also make the production process more cost-effective.
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