Under current technological limitations, the US Department of Agriculture (USDA) in collaboration with the University of

California at Berkeley are trying to develop a genetically engineered switchgrass variety that contains up to 250% more starch than conventional varieties [12] and [13]. This would allow for increasing the economic efficiency of sugar yields and minimizing the final switchgrass-based biofuels costs. If combined with the enzymatic modifications as described above, the production costs of cellulosic ethanol could be reduced substantially. Linsitinib Another feedstock to be potentially used for cellulosic ethanol production in the future is elephant grass (napiergrass) (Pennisetum purpureum) that was introduced to the US from Africa in 1913. This tropical plant is fairly drought-tolerant, grows well on marginal lands and filters nutrients out of runoff in riparian areas. In addition, it does not require irrigation and is capable of producing biomass until the first frost. The main technological requirement and challenge to make napiergrass an efficient and competitive feedstock is to

improve its yields and increase disease resistance [14] and [15]. Poplar has been considered for a long time as a viable Alpelisib in vivo and prospective feedstock for cellulosic ethanol production in the US. Poplar is drought-tolerant and capable of growing on marginal lands. If indeed grown on abundant or marginal land, it does not compete with other crops for food and animal feed. If cultivated on a biofuel farm, poplar trees create favorable wildlife habitats and provide recreational services. By removing

contaminants from soil, poplar has a valuable potential of soil remediation (phytoremediation) [16], which clearly benefits other parts of the ecosystem chain. Growing poplar trees is said to be more fuel efficient and generates a lower carbon footprint Rebamipide than other annual food crops. Its growth rate is considerably slower than that of biofuels oil crops (e.g., crambe and camelina) [17]. However, this problem could be mitigated by applying biochemical modifications, as discussed in the previous section, or nocturnal photosynthesis that allows poplar to absorb carbon dioxide also at night. This feature allows the plants to reach a higher growth rate with lower water requirements (8–16 inches = 203–406 mm) of precipitation annually) as compared with traditional biofuel crops that require 20–40 inches/year (508–1,016 mm/year) [17]. Another possibility to increase poplar growth rates, which also constitutes a major challenge nowadays, is growing genetically modified poplar species that would hold the nocturnal photosynthesis mechanism and thus constitute a feedstock even more tolerant to drought than the conventional poplar species [18]. One of the possible limitations could be harvesting, transport and storage costs. Another feedstock theoretically considered for ethanol production is orange (citrus fruit) peels. Global agriculture produces about 15.