Studies on the Factors Controlling Flower Formation in Egg Plant

Abstract

The present studies were carried out to ascertain the organ sensitive to daylength condition affecting flower initiation and to clarify the role of the organ in the process of flowering in egg plants.Results were as follows;1. The plants whose cotyledons were removed, as compared with the unremoved control plants, bore the first flower at higher nodes. Defoliation from the first to the fifth node tended to lower the node with the first flower. From these, the cotyledons themselves may be sensitive to inductive conditions.2. The node with the first flower was hightened by removal of a pair of cotyledons and not done by removal of the complementary half or two halves of cotyledons. This indicates that external conditions given to the complementary half or two halves of cotyledons on a plant will have the same effects on flower formation as the entire plant had been accepted.3. The treatment of cotyledon removal on the second and the fifth day after their expansion tended to raise the number of node with the first flowers. The plants whose cotyledons were removed on the tenth day or more after their expansion bore the first flower at the same node as the unremoved plants. The flowering is apparently promoted by the cotyledon under favorable conditions within ten days after their expansion.4. The temperature was set at the night temperature of 20°C (warm), and 17°C (cool). The daylength consisted of two groups, namely, 20-hour (long-day), and 8- hour photoperiod (short-day). To clarify the sequence of flowering processes, plants were transferred from long-day and cool or relatively low temperature condition to short-day and warm temperature condition {(LD+CT)→(SD+WT)}, and vice versa {(SD+WT)→(LD+CT)} at varied dates after expansion of cotyledons. Control plants were grown under the condition of (LD+CT) or (SD+WT) during the period of the experiment. Plants were grown under the condition of {(SD+WT)→(LD+CT)} bore the first flower at higher node than those under the condition of {(LD+CT)→(SD+WT)}. Differences of the nodes with the first flower among plants grown under the former condition were not significant.Floral initiation was delayed by the treatment of long-day and cool temperature condition (LD+CT) for five days after cotyledon expansion. Floral initiation, however, occurred early if plants were grown under this condition for ten days or more after cotyledon expansion.Differences of the node with the first flower among the treatment periods of ten days or more, were not significant.In conclusion, the organ perceiving temperature and light especially the light-responsive organ, is the cotyledon in egg plants. Froral induction occurs under long-day and cool temperature conditions for ten days after cotyledon expansion. Thereafter. the response of plants to their environment may be involved in a photoperiodic “after-effect”, resulting in flower developing.