Several problems affect the production of hybrid seed of sorghum (Sorghum bicolor L. Moench) in Mexico. One of this problems consists of the lack of flowering synchronization between parental lines. The objetives of this research were to determine the sowing date to maximize flowering coincidence, and to describe the parental lines of the sorghum hybrid RB‑4000. The experiment was established at "La Laguna" Research Station, Matamoros, Coahuila, of the National Institute of Forestry, Agricultural and Livestock Research (INIFAP), during the summer of 1990. A compite randomized block design with three replications was used with a split plot treatment arregment, the main plots were the Planting dates (June 29, July 16 and August 4) and the subplots were the planting dates of the female line, within the main plot (3 days after the male, simultaneously, 3 and 6 days before the male). The plant and spikelet descriptors were obtained from ten plants from each row. Line SBA‑25 was used as the female parent (cytoplasmic‑genetic male sterile), and line SBR‑24 as the male (fertility restorer). The main results found were the followings:

• The lesser desynchronization was found when the female was planted three days after the male.
• The highest seed production was obtained in the Planting Date of July 16º.
• Completion of the descriptors of both lines was made.