FAD-linked oxidoreductase; part of the gene cluster that mediates the biosynthesis of pyriculol and pyriculariol, two heptaketides that induce lesion formation upon application on rice leaves but are dispensable for pathogenicity (PubMed:27902426). The highly reducing polyketide synthase synthesizes the heptaketide backbone of pyriculol and pyriculariol (PubMed:27902426). Pyriculol and pyriculariol contain several hydroxyl moieties and double bonds, so it can be assumed that several reduction steps occur during biosynthesis. These reactions could be executed by PKS19 itself or partly by the tailoring enzymes OXR1, OXR2, RED1, RED2 or RED3, identified within the cluster (Probable). The FAD-linked oxidoreductase OXR1 is the only tailoring enzyme for which the function has been determined yet, and is involved in the oxidation of dihydropyriculol and dihydropyriculariol into pyriculol and pyriculariol, respectively (PubMed:27902426). A + dihydropyriculol = AH2 + pyriculol A + dihydropyriculariol = AH2 + pyriculariol Polyketide biosynthesis. Expression is increased in rice-extract medium (REM) and is correlated with the production of pyriculol. Impairs the production of pyriculol and pyriculariol, but accumulates their reduced forms dihydropyriculol and dihydropyriculariol. Belongs to the oxygen-dependent FAD-linked oxidoreductase family.