Dehydrogenase; part of the gene cluster that mediates the biosynthesis of the selective antifungal agent ascochitine, an o-quinone methide that plays a possible protective role against other microbial competitors in nature and is considered to be important for pathogenicity of legume-associated Didymella species (PubMed:31554725). The pathway probably begins with the synthesis of a keto-aldehyde intermediate by the ascochitine non-reducing polyketide synthase pksAC from successive condensations of 4 malonyl-CoA units, presumably with a simple acetyl-CoA starter unit (Probable). Release of the keto-aldehyde intermediate is consistent with the presence of the C-terminal reductive release domain (Probable). The HR-PKS (orf7) probably makes a diketide starter unit which is passed to the non-reducing polyketide synthase pksAC for further extension, producing ascochital and ascochitine (Probable). The aldehyde dehydrogenase (orf1), the 2-oxoglutarate-dependent dioxygenase (orf3) and the dehydrogenase (orf9) are probably involved in subsequent oxidations of methyl groups to the carboxylic acid of the heterocyclic ring (Probable). The ascochitine gene cluster also includes a gene encoding a short peptide with a cupin domain (orf2) that is often found in secondary metabolite gene clusters and which function has still to be determined (Probable). Mycotoxin biosynthesis. Homodimer. Belongs to the GMC oxidoreductase family.