Short-chain dehydrogenase/reductase involved in the biosynthesis of abscisic acid (ABA), a phytohormone that acts antagonistically toward salicylic acid (SA), jasmonic acid (JA) and ethylene (ETH) signaling, to impede plant defense responses (PubMed:26648962). During pathogen-host interaction, ABA plays a dual role in disease severity by increasing plant susceptibility and accelerating pathogenesis in the fungus itself (PubMed:26648962). The first step of the pathway catalyzes the reaction from farnesyl diphosphate to alpha-ionylideneethane performed by the alpha-ionylideneethane synthase ABA3 via a three-step reaction mechanism involving 2 neutral intermediates, beta-farnesene and allofarnesene (By similarity). The cytochrome P450 monooxygenase ABA1 might then be involved in the conversion of alpha-ionylideneethane to alpha-ionylideneacetic acid (By similarity). Alpha-ionylideneacetic acid is further converted to abscisic acid in 2 steps involving the cytochrome P450 monooxygenase ABA2 and the short-chain dehydrogenase/reductase ABA4, via the intermediates 1'-deoxy-ABA or 1',4'-trans-diol-ABA, depending on the order of action of these 2 enzymes (By similarity). ABA2 is responsible for the hydroxylation of carbon atom C-1' and ABA4 might be involved in the oxidation of the C-4' carbon atom (By similarity). Hormone biosynthesis. Expression is up-regulated in spores. Leads to slower vegetative growth and dark pigmentation of the mycelia (PubMed:26648962). Leads also to the secretion of a very dark pigment (PubMed:26648962). Affects sporulation and appressoria formation (PubMed:26648962). Shows hyper-branching of the germ tubes, as well as unusual bulges along the hyphae with less melainized appressoria (PubMed:26648962). Significantly reduces the production of abscisic acid (ABA) (PubMed:26648962). Highly reduces virulence (PubMed:26648962). Belongs to the short-chain dehydrogenases/reductases (SDR) family.