Seed production of hybrids, unlike that of inbred varieties, involves difficult procedures. In hybrid rice seed production, two parents-a cytoplasmic male sterile (CMS) line (female) and restorer line (male)-are grown in alternate fixed row ratios, one after the other. The female line, which is male sterile, receives pollen from the male, which is fertile and set the seed. Therefore, it is essential that both male and female parents flower at the same time. Techniques such as the leaf count method and growth duration difference method are used for the differential seeding of male and female parents. Flowering in male and female parents often fails to synchronize because of environmental conditions. In China, where hybrid seed is produced on a large scale, several techniques have been adopted to synchronize flowering at the early stages of panicle development.