Which technique is used to detect auxotrophic mutants?

A strain is said to be auxotrophic if it carries a mutation that renders it unable to synthesize an essential compound. This technique distinguishes between mutants and the wild type strain based on their ability to grow in the absence of a particular biosynthetic end product. For example a lysine auxotroph will grow on lysine supplemented media but not on a medium lacking an adequate supply of lysine because it cannot synthesize this amino acid.