Abstract
In the previous papers, the authors reported the possibility of dahlia culture for the cut flower in winter by controlling the day-length. The young plants must be prepared by the end of autumn for this type of forcing, using cuttings taken from the mother plants or tuberous roots formed newly in autumn. However, the new tuberous root shows dormancy, deepness of which varies depending on the varieties. The present study deals with the dormancy in tubers of dahlia.
1. When crown-tubers normally produced in the field were dug up and planted in greenhouse on October 25, November 4, 14 or 24, some of them did not sprout even if favorable conditions were given. As the planting time was delayed within this period, the sprouting per cent was decreased. The shoots sprouted from the crown-tubers which were planted during the period from early October to mid-December, did not elongate normally. In many cases, their growth stopped at the stage of two leaves. However when crown-tubers were planted in greenhouse after the end of December, they sprouted well and their shoots grew normally.
Dahlia crown-tuber seems to rest from the beginning of October to the middle of December. However, judging by the facts that at least 40per cent of crown-tubers sprouted throughout this period, it seems that early rest is followed directly by after-rest in dahlia crown-tuber.
2. The degree of rest in dahlia crown-tuber varied among the varieties. There were the following three types in regard to the degree of rest. In the first type, all crown-tubers sprouted and their shoots grew comparatively well. In the second type, about half of crown-tubers sprouted, and their sprouted shoots grew little. In the third type, none of crown-tubers sprouted.
3. Crown-tubers obtained from the plants which were propagated from cuttings after June rested weaker than those obtained from the mother plants. However, when cuttings were taken before May, their crown-tubers rested as deep as those produced by the mother plants. The earlier the cutting time, the deeper rest of crown-tuber.
4. The rest of dahlia crown-tuber was broken by low temperature treatments. When dahlia crown-tubers were dug up on November 20 and treated for 40 days at 0°C, they sprouted well, and their shoots grew normally.
