Abstract
This experiment was carried out to investigate the effect of day-length on the flowering of dahlia in 1959. Each one variety was selected from four strains, Single, Decorative, Cactus, and Pompon.
Three different conditions, long, natural and short, day lengths were given to each variety. Plants were illuminated by the incandescent lamp of 100 watt per 6m2 during night in the long day lot, and were covered with black plastic film from 5 p.m. to 9 a.m. in the short day lot. Tubers were planted in pots on April 15. The day-length treatment started on June 1, The plants of Single and Pompon varieties showed flower buds in every lot, while the plants of Cactus and Decorative showed few flower buds in the short day and natural day lot on June 22. On this day, all main and lateral shoots of each plant were curtailed. Then, the conditions of day-length were changed into the following combinations: L→L, L→N, L→S, N→L, N→N, N→S, S→L, S→N, S→S.
After changing the condition, the observation of flowering was done. All plants of Single and Pompon varieties showed the flower buds by August 21. However, normal flowering was seen in Single strain alone.
Among all the lots, the plants which were given short day-length before or after June 22 showed higher flowering percentages, while the plants Which were given N→L or L→L combination showed poor or no flower buds.
