Exoglucanase that plays an important function in biomass degradation by catalyzing the hydrolysis of the non-reducing end beta-1,4-glucosidic linkages in cellulose and cellotetraose to release cellobiose. Shows higher hydrolytic activities on phosphoric acid-swollen cellulose (PSC), beta-glucan, and cellooligosaccharide derivatives than on cellulose, of which the best substrates were cellooligosaccharides. Hydrolysis of (1->4)-beta-D-glucosidic linkages in cellulose and cellotetraose, releasing cellobiose from the non-reducing ends of the chains. Optimum pH is 4.5-9.0. Optimum temperature is 30-50 degrees Celsius. Expression increases during infection of rice. The biological conversion of cellulose to glucose generally requires three types of hydrolytic enzymes: (1) Endoglucanases which cut internal beta-1,4-glucosidic bonds; (2) Exocellobiohydrolases that cut the disaccharide cellobiose from the non-reducing end of the cellulose polymer chain; (3) Beta-1,4-glucosidases which hydrolyze the cellobiose and other short cello-oligosaccharides to glucose. Belongs to the glycosyl hydrolase 6 (cellulase B) family.