Provided are the DNA of a glycoalkaloid biosynthetic enzyme of solanaceous plants (Solanaceae) such as potato, solanaceous plants producing no glycoalkaloids, and a method of producing a cultivar with a reduced risk of accumulating glycoalkaloids, which involves crossing plants in which the expression of an oxidase gene involved in glycoalkaloid biosynthesis is suppressed or the activity of the enzyme is lowered, as mother plants, and screening progeny resulting from the crossing.