Availability of Carbohydrates in the Root Stubble of a High-Yielding Rice Cultivar, "Hokuriku 193".

Root stubble represents a "hidden" (unrecovered) biomass in agriculture. This study investigated its potential as a source of fermentable sugars using the high-yielding rice cultivar Hokuriku 193. The ripened whole plant was disassembled into panicle, straw, and root stubble. The root stubble was further divided into the aboveground part (AP), basal part (BP), and root part (RP), with AP and BP together accounting for 81.8 % (w/w) of the root stubble. In comparison with the straw, AP contained more starch- and β-1,3-1,4-glucan; BP had more starch and ash; RP had more lignin and ash. The total amount of glucan and xylan in root stubble is equivalent to 61.8 % of that found in straw. Following gas-phase HCl pretreatment and the subsequent enzymatic saccharification, sugar yields from AP and BP exceeded 70 %. These results demonstrate that root stubble has strong potential as a new feedstock for saccharification substituting straw.