PROBLEM TO BE SOLVED: To provide a method simply and surely enabling the judgment and purity examination of a hybrid seed. SOLUTION: It is tested whether a recombined mitochondria DNA specifically deleted in a cytoplasmic male sterility system is present in a DNA extracted from a seed of test target or from a seedling originated from the seed or not. Whether the seed is a hybrid seed or not or the purity of the hybrid seed is judged or examined on the presence or absence of the recombined mitochondria DNA or on its presence rate. Thereby, the judgment and purity examination of the hybrid seed are rapidly improved.
