Conventional Alamo switchgrass and its transgenic counterparts with reduced/modified lignin were subjected to dilute sulfuric acid pretreatment for improved sugar production. At 150 degrees C. the effects of acid concentration (0.75%, 1%, 1.25%) and residence time (5, 10, 20, 30 min) on sugar productions in pretreatment and enzymatic hydrolysis were investigated, with the optimal pretreatment conditions determined for each switchgrass genotype based on total sugar yield and the amounts of sugar degradation products generated during the pretreatment. The results show that genetic engineering, although did not cause an appreciable lignin reduction, resulted in a substantial increase in the ratio of acid soluble lignin:acid insoluble lignin, which led to considerably increased sugar productions in both pretreatment and enzymatic hydrolysis. At an elevated threshold concentration of combined 5-hydroxyfuranmethal and furfural (2.0 g/L), the overall carbohydrate conversions of conventional switchgrass and its transgenic counterparts, 10/9-40 and 11/5-47, reached 75.9%, 82.6%, and 82.2%, respectively. (C) 2011 Elsevier Ltd. All rights reserved.