Effects of Seed Vernalization and Photoperiod on Flower Bud Initiation of Summer, Spring, and Winter Flowering Types of Sweet Pea (Lathyrus odoratus L.)

Abstract

The effects of seed vernalization durations for 0, 10, 20, 30, 40 and 60 days at 1°C combined with subsequent 8-, 10-, 12-, 14-, 16- and 24-hr photoperiods at 15°C on the flowering time and the number of nodes to the first inflorescence of a summer, a spring and a winter flowering sweet pea were investigated. The first inflorescence of all flowering types occurred at the highest node and the number of days from sowing to first flower budding was longest in the 8-hr photoperiod with 0 day of seed vernalization. The number of nodes to the first inflorescence in this regime were 54.5, 43.8, and 27.8, respectively, for the summer, spring, and winter flowering types. After a 30-day vernalization, the first flower bud formation was promoted by 14 to 24-hr, 12 to 24-hr, and 8 to 24-hr photoperiods, respectively, for the summer, spring and winter flowering types. Plants of all flowering types produced their first inflorescence with the fewest nodes and shortest time under constant light and 60-day vernalization. The response to photoperid after a 60-day vernalization treatment was markedly smaller in the spring flowering type than in the summer flowering type, and did not exist in the winter flowering type. No statistical difference between the number of the first nodes to flowering and first inflorescence was observed among the seed vernalization treatments combined with the 16 to 24-hr, 12 to 24-hr, and 8 to 24-hr photoperiods, respectively, for the summer, spring and winter flowering types. After a few days of vernalization and short daylengths, the number of nodes to the first inflorescence was higher than the number of the first nodes to flower bud formed in the summer and spring flowering types on account of flower bud drop and vegetative bud formation. In conclusion, flowering of sweet pea seedling is markedly promoted by vernaling seeds for more than 30 days and exposing them to 16 to 24-hr, and 12 to 24-hr, and 8 to 24-hr photoperiods for summer, spring, and winter flowering types, respectively.