Sesquiterpene synthase involved in the biosynthesis of volatile compounds which contribute to fruit flavor and aroma (PubMed:21818683, PubMed:14617067). Mediates the conversion of (2E,6E)-farnesyl diphosphate (FPP) into (+)-valencene (PubMed:21818683, PubMed:14617067). No activity detected with geranyl diphosphate (GPP) (PubMed:14617067). (2E,6E)-farnesyl diphosphate = (+)-valencene + diphosphate Binds 3 Mg(2+) or Mn(2+) ions per subunit. Secondary metabolite biosynthesis; terpenoid biosynthesis. Accumulates during fruit maturation and ripening. Induced by ethylene. The Asp-Asp-Xaa-Xaa-Asp/Glu (DDXXD/E) motif is important for the catalytic activity, presumably through binding to Mg(2+). Belongs to the terpene synthase family. Tpsa subfamily.