Studies on flowering control of dahlia. VIII

Effect of day-length on dormancy in axillary bud

Abstract

Using plants propagated from crown-tubers or cuttings, the authors studied the factors affecting the dormancy of axillary buds of dahlia. After the plants were grown under the photoperiod of 10, 11, 12 or 13 hours for various days after decapitation, their lateral shoots were cut off at the lowest nodes. All the plants were then transferred to 14-hour day-length.
As shown in the previous papers, dahlia is a non-obligate short-day plant. The optimum photoperiod for its flowering is13 to14 hours, and the lower critical photoperiod is about 12 hours. When dahlia plant is grown under photoperiods shorter than the lower critical length, its top growth is much inhibited, and flower buds formed remain blind.
The lower critical photoperiod of the plants propagated from cuttings was about 12 hours. When the plants were grown under a photoperiod of 12 hours or less for 70 to 80 days, their axillary buds became dormant.
The lower critical photoperiod of the plants propagated from crown-tubers was longer than that of the plants propagated from cuttings. And the axillary buds of the former became dormant more easily than those of the latter. When the plants propagated from crown-tubers were grown under 13 hour day-length for 80 days, some of their axillary buds did not sprout.
When all the mature leaves were removed after 60 to 70 days of short-day treatments, the axillary buds sprouted and grew better than those of intact plants. However, if the plants remained under short-day for 80 days, the axillary buds did not sprout either even if all the leaves had been removed These facts suggest that mature leaves exposed to short photoperiods may produce some substance which inhibits sprouting of axillary buds. And it seems that this substance moves from mature leaves to axillary buds or near the buds and accumulates there, causing the buds to rest.