Studies on tuberous root formation in dahlia. I

Periods of tuberous root formation in dahlia

Abstract

The present study has been conducted to investigate the process of tuberous root formation in dahlia, using a single strain and also var. Tensin (medium decorative).
The results of the investigation are summarized as follows:
1. Seedlings of single strain were planted on June 5 and dug out from June to November at ten-day intervals. As the results of observation, it was ascertained that adventitious roots successively appeared from early June to early August. The diameters of the roots increased from the end of June to November, especially after October, then the adventitious roots developed in the tuberous roots.
The similar facts were observed on the plants cultured from tuber.
The adventitious root and tuberous root have similar anatomical structure, and they are distinguished from the normal fibrous roots.
2. In the second experiment, defoliations were made every ten days from June 21 to September to investigate the influence of reduction of photosynthesis upon the number and development of adventitious roots.
The defoliation in June and July reduced the number of roots, while that after September had little influence on the number of roots and the inhibition of the growth of roots.
The shade treatment in October also reduced the diameters of roots.
3. Experiment 3 was performed to investigate the influence of photoperiod on the growth of roots in dahlia seedlings.
The short day treatment (8-hour photoperiod for 20 or 40 days) reduced the number of roots and increased the diameters of roots, while the plants exposed to the long day condition (24-hour photoperiod) did not differ in number and diameters of roots from the plants grown under the natural day length.
In the plants exposed to 24-hour photoperiod, flower buds were not recognized on August 25, but were observed on September 25.