The document describes a three line system of hybrid seed production. It involves an A line that is male sterile, a B line that is fertile and maintains the same nucleus as the A line but with different cytoplasm, and an R line that can restore male fertility in the A line. When the A line is crossed with the B line, it produces a first generation hybrid that is heterozygous. The R line is then used to restore male fertility in the A line for large-scale seed production without needing extra parent lines. Key requirements for successful hybrid seed production using this system include selecting appropriate locations, seed fields, isolation, and cultural practices.