High biomass yield energy sorghum: developing a genetic model for C4 grass bioenergy crops

Abstract

A first‐generation energy sorghum hybrid with enhanced photoperiod sensitivity and long growth duration accumulated more than twice as much biomass as grain sorghum. The energy sorghum produced more leaves (~45 vs 17–20), longer stems (~4 vs 1.5 meters) and had a higher stem‐to‐leaf biomass ratio than grain sorghum. At the end of the season, energy sorghum stems represented 83% of the plant's shoot biomass. The greater biomass accumulation was due to longer growth duration, a higher leaf area index, greater radiation interception, and higher radiation use efficiency. When grown under dryland or limited irrigation conditions, the rate of biomass accumulation by the energy sorghum hybrid was reduced in mid‐season. This decrease was most apparent in August due to summer water deficit; however plants recovered when rain occurred in September. Crop growth modeling and biomass accumulation rates measured under optimal field conditions show that energy sorghum, like other C4 energy grasses, has excellent biomass yield potential. The greenhouse gas offset values of energy sorghum hybrids, grown in large and small field plots, and under fully irrigated and dryland conditions, ranged from 63–78% for cellulosic ethanol production and 88–95% for power generation. This study shows that drought‐tolerant, annual energy sorghum hybrids have the genetic yield potential to contribute significantly to bioenergy production. Sorghum is a genetically tractable, diverse species with a good genomics platform, making energy sorghum a promising genetic model for the design of C4 grass energy crops. © 2012 Society of Chemical Industry and John Wiley & Sons, Ltd

Harnessing Genetic Variation in Leaf Angle to Increase Productivity of Sorghum bicolor

“…Energy sorghum and grain sorghum canopies close 60-75 days after seedling emergence, approximately when grain sorghum reaches anthesis. In contrast, energy sorghum remains vegetative following canopy closure for an additional 140 days, and plants retain a whorl of developing leaves at the top of the canopy that have very small angles (Olson et al 2012). In grain sorghum, from anthesis through grain maturity, canopies lack the whorl of leaves with small angles.…”

“…For the virtual sorghum and lighting in Figure 2A, the conversion efficiency of the canopy with smaller leaf angles is predicted to be 1.0436 of the conversion efficiency of the canopy with large leaf angles. If we further assume that (1) the 4% gain in conversion efficiency is realized for 4 hr (midday) per 14-hr day and (2) the effect calculated is applicable to the duration of vegetative closedcanopy growth, then given a bioenergy sorghum growing season where 140 days are in the vegetative closed canopy of its 200-day growing season (Olson et al 2012), we predict an overall increase of 3% conversion efficiency over the entire growing season. Thus, under these conditions, the canopy with smaller leaf angles has the potential to accumulate 3% more biomass than the canopy with large leaf angles.…”

“…High-biomass energy sorghum hybrids have long growing seasons and accumulate most of their biomass in tall (4 m) closed canopies (Rooney et al 2007;Olson et al 2012;Mullet et al 2014). Over the long bioenergy growing season, small daily improvements in energy conversion efficiency conferred by more optimal leaf angles could translate into large seasonal increases in biomass accumulation.…”

Transcriptome Profiling of Tiller Buds Provides New Insights into PhyB Regulation of Tillering and Indeterminate Growth in Sorghum

“…Modeling of light interception by crop canopies indicates that current genotypes often intercept an excess of light at the top of the canopy (Zhu et al, 2010;Drewry et al, 2014). Energy sorghum hybrids tiller to a greater extent than grain sorghum genotypes, often producing canopies with excess leaf area index (greater than 7; Olson et al, 2012). A more optimal distribution of light interception could be achieved by growing energy sorghum with reduced propensity for tillering at lower plant density with leaves having reduced leaf angles (Truong et al, 2015).…”

Cytoplasm Has No Effect on the Yield and Quality of Biomass Sorghum Hybrids

“…Each seed parent was hybridized using the pollinator line R07007. R07007 is a photoperiod insensitive breeding line in the Texas AgriLife Research program that when hybridized to standard seed parents (such as Tx378, Tx623 and Tx631) produces a photoperiod sensitive hybrid based on epistatic genetic interactions at specific maturity loci [28,29]. Thus a total of nine hybrids, representing three genetically distinct inbreds and three distinct CMS were included in the agronomic analyses.…”