球根作物の球形成に及ぼす温度の影響 (第4報)

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When freesia corms are stored at low temperature (13-15°C) after harvest, the corms do not sprout but consume their food material to form new corms above the old ones. This phenomenon is called pupation-pupa formation, and little works have been done in order to estimate the cause of pupation. The present study was designed to clarify the effect of temperature on induction and process of the pupation for cormlets of‘Rijnveld′s Golden Yellow’.The results obtained were summarized as follows:1. When freesia cormlets were stored at different degrees of constant temperature, 13°C was most effective to pupation and the temperatures lower than 2°C or higher than 20°C showed no effect.2. In the second experiment, the cormlets pretreated with various degrees of temperature (2-21°C) and durations of the treatment (10-50 days) were stored under warm conditions. The chilling pretreatment at 5-17°C was always effective to pupation, and the pretreatment at 9-10°C for 30-50 days was also effective highly and produced large pupa.The longer the period of chilling the more effective, and the duration of 10 days was seemed to be the lower limit for pupation even with optimum temperature.The cormlets treated with chilling below 2°C did not form pupa even 50 days treatment. On the contrary, higher temperature than 21°C inhibited the induction of pupation.3. In the third experiment, the cormlets were treated with chilling at 2-9°C for about 1-3 months and were moved into another thermostat of various degrees of temperature and lastly they were stored for about three months.In the lots of storage at warm temperature of 19-21°C, pupation was accelerated and large corms were formed. While the pupation of the cormlets stored at the temperature lower than 15°C were delayed, almost no pupation was seen in the lots of 5°C.4. It seems that there are two thermo-inductive processes (phases) in corm formation of freesia, viz., the process of induction of physiological state for corm formation and the process of development of corm as the thickening growth of stem. It was recognized that the treatment of low temperature especially about 9-10°C was apparently effective for the induction of physiological state for corm formation and warm temperature at about 20°C promoted the development of freesia corm. Consequently the effectiveness of the low temperature for induction of corm formation increased with the duration of treatment within certain limits.5. On the basis of the results mentioned above, it is estimated that the optimum temperature for corm formation is closely related with the climate of native land of the wild Freesia refracta. There is no doubt that“the acquisition or acceleration of the ability to corm- and bulb-formation by a low temperature treatment”is the general characteristics in the tuberous and bulbous plants which produce the corms or bulbs in early summer, and this phenomenon resembles to vernalization in flower formation.