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Photoperiodism in Sorghum¹

Three varieties of Sorghum bicolor (L.) Moench (i.e., ‘Early Hegari,’ ‘80-Day Milo,’ and ‘Ryer Milo’) were subjected to different treatments of short (10-hour) and long (17-hour) days in controlled-environment chambers. The number of days from planting to floral initiation was determined for each variety in each treatment. The research was conducted to determine the age at which sorghums become sensitive to photoperiod and to estimate the minimum number of inductive cycles required for floral stimulation.

Short days applied after the plants were 15 days of age hastened floral initiation, while long days when the plants were between 15 and 20 days of age delayed initiation. Thus, photopei iodic sensitivity is attained at about 15 days of age. As these varieties increased in age beyond 15 days, less time was required for floral initiation following stimulation. Five short days were sufficient to stimulate floral initiation of plants older than 15 days. Three short days inconsistently hastened floral initiation. A greater number of leaves than the first five were required for photoperiodic induction.

Key Words: Sorghum bicolor (L.) Moench • Floral initiation • Juvenile stage • Controlled-environment chamber

² Formerly NDEA Fellow (now Assistant Professor of Agronomy and Plant Genetics at University of Minnesota, St. Paul, Minn.) an Professor of Agronomy, Oklahoma State University, Stillwater 74074.

Received for publication November 3, 1971.