Abstract
Carbohydrates stored in vegetative organs, particularly stems, of grasses are a very important source of energy. We examined carbohydrate accumulation in adult sorghum and maize hybrids with distinct phenology and different end uses (grain, silage, sucrose or sweetness in stalk juice, and biomass). Remarkable variation was observed for non-structural carbohydrates and structural polysaccharides during three key developmental stages both between and within hybrids developed for distinct end use in both species. At the onset of the reproductive phase (average 65 days after planting, DAP), a wide range for accumulation of non-structural carbohydrates (free glucose and sucrose combined), was observed in internodes of maize (11–24%) and sorghum (7–36%) indicating substantial variation for transient storage of excess photosynthate during periods of low grain or vegetative sink strength. Remobilization of these reserves for supporting grain fill or vegetative growth was evident from lower amounts in maize (8–19%) and sorghum (9–27%) near the end of the reproductive period (average 95 DAP). At physiological maturity of grain hybrids (average 120 DAP), amounts of these carbohydrates were generally unchanged in maize (9–21%) and sorghum (16–27%) suggesting a loss of photosynthetic assimilation due to weakening sink demand. Nonetheless, high amounts of non-structural carbohydrates at maturity even in grain maize and sorghum (15–18%) highlight the potential for developing dual-purpose (grain/stover) crops. For both species, the amounts of structural polysaccharides in the cell wall, measured as monomeric components (glucose and pentose), decreased during grain fill but remained unchanged thereafter with maize biomass possessing slightly higher amounts than sorghum. Availability of carbohydrates in maize and sorghum highlights the potential for developing energy-rich dedicated biofuel or dual-purpose (grain/stover) crops.
Highlights
Grasses have played a key role in supporting life across the globe by providing calories derived primarily from cereal grains for humans and forages for animal feed
While substantial information has been generated for carbohydrate content in the primary sink for maize and sorghum genotypes developed for a specific end use, availability and genetic variation of carbohydrates in the secondary sinks of those genotypes has not been explored
We examined the accumulation of selected non-structural and structural carbohydrates in stover, both as a primary and a secondary sink, in maize and sorghum hybrids developed for distinct end uses
Summary
Grasses have played a key role in supporting life across the globe by providing calories derived primarily from cereal grains for humans and forages for animal feed. With increasing world population, decreasing arable land and fresh water, and emerging demand for plant-based fuels, grasses are poised for yet another major role in sustaining human life on earth. Grass stems are considered to be transient sinks of non-structural carbohydrates that act as a “buffering system” between the primary source (leaves) and primary (terminal) sink during various developmental and environmental transitions (Schnyder, 1993; Blum, 1998; Ruuska et al, 2006; Mir et al, 2012; Slewinski, 2012). With increased demand for stover as a source of renewable energy, development of dual-purpose crops which, in addition to grain, provide high quality stover need to be developed
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