Abstract
In the previous paper the present writer reported that there are two thermo-reactive processes in corm formation of freesia, viz., the process of induction of physiological states for corm formation and the process of development of corm shown as the thickening growth of stem, and that the phenomenon in both cases resembles to vernalization in flower formation. This study was carried out to clarify the effect of the heat treatment after the chilling on the pupation of freesia employing cormlets of ‘Rijnveld′s Golden Yellow’.
When the freesia cormlets pretreated at 5° or 9°C for 20 to 40 days were subjected to the heat treatment at 25° to 35°C for 10 to 40 days, the percentage of pupation decreased as shown in Table 1 to 3. Therefore, it is sure that the high temperature above 25°C suppress the low temperature induction for corm formation, and that the higher the temperature and the longer the period of treatment, the more effective it is for the suppression.
When the cormlets were subjected to the chilling at 9° or 5°C for 102 long days, the pupation was scarcely suppressed by the heat treatment at 30°C for 20 to 30 days.
In this experiment the cormlets, pretreated by low temperature and then stored under neutral temperature of 20-21°C for 10 to 30 days, were subjected to the heat treatment at 30°C for 20 to 30 days. In the cormlets mentioned above the suppression for pupation was less than that of cormlets treated with high temperature just after the chilling treatment. Therefore it is sure that the physiological states for corm formation is stabilized under 20-21°C storage for 10 to 30 days.
The heat treatment given prior to the chilling was effective for the pupation and the percentage of pupation decreased according to the degrees of the induction for corm formation.
In the fifth experiment the cormlets, the chilling induction of which was vanished by the heat treatment, were subjected again to low temperature of 9°C for 30 days. It showed that the cormlets subjected again to the chilling treatment formed new corms.
From the results of investigation in these experiments it seems that the physiological states for corm formation which were induced by the chilling and vanished by the heat treatment are only quantitative and reversible within a certain range.
The aforesaid phenomena in corm formation of freesia resemble to vernalization, devernalization and revernalization in flower formation.
