Rosetting of suckers grown under long day and high temperature conditions, and breaking the rosetting in the autumn-chrysanthemum

Abstract

It is well known to the growers that suckers produced after flowering of chrysanthemums form rosette in autumn under natural conditions. Usually the rosette suckers are taken into the green house in December or January for the purpose of forcing culture by the commercial growers. But those rosette suckers elongate slowly unless they are subjected fully to low temperature. Therefore, the suckers which will be planted early in winter are obtained from high altitude areas where temperature drops earlier. This suggests an effectiveness of the vernalization on chrysanthemum. SCHWABE, who had investigated minutely the vernalization of chrysanthemum, reported that the suckers produced after flowering formed rosette under the short day condition as a result of devernalization, and in consequence the suckers required to be subjected to low temperature before growing. But in Japan the suckers of chrysanthemum developed after the flowering under shade-culture in the early summer months elongate normally, form the flower bud and come into bloom in autumn. In U.S.A., it is said that chrysanthemums can be made to flower all the year round without being subjected to the specific low temperature. These facts gave the author many questions which are briefly explained below. (1) How many times shall we be able to repeat flowering and propagating of suckers in the autumn-chry-santhmum under high temperature condition? (2) When the suckers do not flower in these cases, can these plants be made to form rosette at the apex by subjecting to short day treatment after stem elongation? (3) If the sucker forms rosette, can we derosette or check it? This study was designed to clear up the above questions. All the experiments were carried out in a glass frame maintained over 18°C in 1958 and 1959. The material plant was the early variety “Shin-Toa”. Flowering and rosetting behaviour of suckers were repeatedly examined, and the rosette plants formed in this experiment were tried for the possibility to be derosetted by spraying the gibbe rellic acid (GB) of 50 and 100 ppm, and checking of rosette formation by applying GB (50 ppm) was tried. 1. Most of suckers, developed _??_on the plants which bloomed under high temperature condition, had flowers, but some formed rosette after stem elongation. While the suckers, developed on those flowering plants, formed rosette after stem elongation. 2. The suckers, developed on the plants which were applied pinching of the growing point under short day or long day condition, flowered and formed no rosette, and the suckers of these flowering plants formed rosette when these plants received short day treatment after stem elongation. 3. Stem elongation of suckers, developed on the plants which were flowered or applied pinching of the growing point under short day condition, was slower, even though these suckers were laid under long day condition, than that of suckers which developed on the plants which were applied pinching of the growing point under long day condition. 4. Spraying of GB (50 and 100 ppm) or long day treatment was found to be effective in derosetting of suckers which had been formed rosette under short day after stem elongation. 5. Derosetted plants by long day treatment again formed rosettes slightly at the growing point by short day treatment, but soon these rosette plants elongated and flowered. 6. As the number of times of GB spraying increased, the derosetted plants flowered earlier at the terminal bud, elongated its stem longer and increased the total number of the flower buds. 7. Resetting of suckers, which would be elongated under long day but would form rosette by short day treatment, was inhibited by GB spraying (50, ppm) 5 days before, or at the beginning of short day treatment. But inhibition was seen only slightly, when GB spraying was done 15 days after short day treatment.