Journal of Energy Bioscience 2024, Vol.15, No.6, 358-367 http://bioscipublisher.com/index.php/jeb 360 more less favorable land and further expands its planting range as a bioenergy crop (Huang, 2018). Under these difficult circumstances, sorghum can still have a decent yield. Therefore, in some areas with relatively poor conditions, it is also a reliable source of biomass (Spindel et al., 2018). 3 Sorghum Biomass Composition and Energy Potential 3.1 Structural components: cellulose, hemicellulose, and lignin There are three main components in sorghum biomass: cellulose, hemicellulose and lignin. These components are very important in the process of turning plants into energy. Cellulose and hemicellulose are polysaccharides that can be decomposed into sugars and then fermented into bioethanol. Although lignin can make plants more sturdy, due to its complex structure and difficulty in decomposition, it will affect this process. Some studies have pointed out that the content of these components varies greatly among different sorghum varieties. For instance, the combined proportion of cellulose and hemicellulose in some varieties can range from 52.7% to 60%, while lignin is between 11.6% and 17.7% (Deshavath et al., 2018). There are also studies that have found that these lignocellulose materials of sorghum are effective for ethanol production, especially varieties like Sorghum 506 (Batog et al., 2020). If the lignin content in sorghum is reduced through mutations, such as turning the midvein “brown”, the recovery rate of glucose can be increased and the yield of ethanol can also be enhanced (Rivera-Burgos et al., 2019). 3.2 Energy yield comparison with other bioenergy crops The energy output of sorghum can be compared with that of major bioenergy crops such as corn and sugarcane, and its performance is also quite good. Because it is a C4 plant, its photosynthetic efficiency is high and it produces a large amount of biomass. Even if the environment is not ideal, it can still grow well. Some studies have made comparisons and found that sorghum can produce considerable biomass. For instance, the sweet sorghum grown in Queensland, Australia, can produce 46.9 to 82.3 tons of biomass per hectare, generate 3 059.18 Nm³ of methane, and the total energy value reaches 761.74 MWh per year (Mathias et al., 2023). Although corn and sugarcane are also famous for their high yields, sorghum is more drought-resistant and can be grown on less favorable land. These are all its advantages (Carpita and McCann, 2008). The yield and cellulose content of hybrid sorghum are both higher than those of local varieties and old varieties, which also makes it a better choice for biofuel raw materials (Habyarimana et al., 2016). 3.3 Potential for second-generation biofuels Sorghum has great potential in the production of second-generation biofuels. The second-generation fuel uses lignocellulose materials, not food crops. Thus, it will not compete for land with food for human consumption and can also utilize the land that cannot be used for growing grain. The lignocellulose components of sorghum - such as cellulose, hemicellulose and lignin - can be converted into bioethanol through some biotransformation methods. For instance, there is a kind of sorghum called “brown vein”, which has a low lignin content, a high theoretical ethanol yield and a good conversion efficiency. It is regarded as a good material for the second-generation biofuels (Rivera-Burgos et al., 2019). Sorghum can also be grown on marginal land and does not compete with food for resources, which makes it more suitable to be a sustainable energy crop (Tang et al., 2018a). The research also found that the genetic diversity of sorghum can help increase yield and quality, thus making the production efficiency of fuel higher. Nowadays, the development of molecular breeding and genetic technology also makes it easier for us to cultivate sorghum varieties suitable for energy (Yang et al., 2023). 4 Genetic Improvement for Enhanced Bioenergy Traits 4.1 Breeding strategies for high-biomass sorghum varieties In order to breed sorghum varieties with high biomass, the breeding strategies mainly focus on traits that increase yield and enhance stress resistance. Traditional breeding methods have been used to develop some hybrid sorghum varieties. The vegetative growth period of these varieties is longer than that of sorghum used for grain, so they can accumulate more biomass. Their long growth period, high light interception rate and good efficiency in utilizing sunlight all contribute to the continuous increase of biomass. When breeding, introducing germplasm resources from different sources and combining them with multiple tests in a controlled environment throughout
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