Carbohydrate and Ethanol Production Efficiency of Grain Sorghum.

Grain sorghum (Sorghum bicolor L. Moench) grown often exposed to environmental stress mainly drought and/or high temperature stress during reproductive development. The impact of short episodes of drought or high temperature stress on grain composition and its ethanol production efficiency is not well understood. The objective of this research was to quantify the impact of short episodes of drought and/or high temperature stress during the reproductive development on grain composition and ethanol production efficiency. To understand these responses, two experiments were conducted in controlled environment conditions. In the first experiment, plants were exposed to four water treatments (fully irrigated control; drought stress from boot leaf emergence to flowering; drought stress from flowering to seed-set; and drought stress from seed-set to mid seed fill) during reproductive development. In the second experiment plants were grown at daytime maximum/nighttime minimum temperature of 32/22ºC until 30 days after sowing (DAS) under fully irrigated conditions. Thereafter, plants were exposed to 40/30ºC (high temperature, HT) for 10 d at different stages (10 d prior to flowering, at flowering, 10, 20 and 30 d after flowering). Drought stress significantly decreased sugar contents (glucose + sucrose, mg g^-1) and ethanol production (%, w/w). Ethanol production was lowest when stress occurred at early and mid stages of grain filling, compared to pre-flowering or later stages of grain filling. There were no effects of high temperature stress on carbohydrate composition; where as high temperature stress at 10 and 20 d after flowering resulted in lowest ethanol production. These results suggest that environmental factors during grain growth and development could impact biofuel production efficiency and these factors need critical evaluation.