Plant height, width, number of branches and flowering period need to be modified to develop Aster tataricus L. var. minor M. as a potting or a bedding plant. Two experiments were conducted to see the effect of plant growth regulators (PGR) on the growth and flowering of the plants. First, the rates of PGR were tested as follows ; malefic hydrazide (MH) 500, 2000 and 4000 ppm ; dikegulac sodium 500, 2000 and 4000 ppm ; ethephon 100, 500 and 1500 ppm; chlormequat (CCC) 500, 1000 and 3000 ppm; paclobutrazol (PP-333) 50, 100 and 500 ppm ; daminozide (SADH) 500, 2000 and 4000 ppm ; ancymidol 50, 100 and 500 ppm ; 6-benzyl aminopurine (BA) 50, 200 and 1000 ppm ; gibberellic acid (GA) 20, 50 and 200 ppm. Second, PGR were tested as single treatment or mixtures of two. The medium concentration of the first experiment was applied as foliar spray on July 25. Results of the above experiments can be summarized as follow :
1. The experiment testing PGR for a single treatment or mixtures of the two : Control of growth. MH, PP-333, SADH, BA for a single treatment and CCC treated with MH, ancymidol and BA were effective on the reduction of plant height. Plant width was reduced by MH, CCC, ancymidol and GA. The number of branches increased by MH and BA treatment or by the mixtures of BA with either GA, ancymidol or CCC. However, BA combined with MH was not effective.
Control of flowering. Flowering was delayed, and the number of flowers was reduced by the single treatments of BA, SADH, MH, PP-333 and by the mixtures of BA with MH, PP-333, CCC and SADH, and MH with BA, SADH, PP-333, CCC. The plants bloomed 5 days earlier than control when treated with GA only, but 2-3 days later when GA was used with other PGR. Flower width was reduced by MH, BA single treatments and by the mixture of GA and MH. Flower stalk length was reduced by PP-333 and BA single treatments and by the mixtures of BA and CCC.
In conclusion, the single treatments of CCC and ancymidol or the mixtures of ancymidol with GA, BA, MH or CCC were effective. While PP-333 and SADH for a single treatment were effective on the control of plant size, they were not satisfactory since they reduced flower size and the ornamental value.
2. The experiment of PGR concentrations : MH, a growth inhibitor, treatment of 2000 or 4000 ppm resulted in the reduction of plant height, the increase of number of branches, the delay of flowering, and the reduction of flower size, especially at the higher concentration. The plants treated with dikegulac sodium died at 2000 or 4000 ppm, whereas those treated at 500 ppm were shortened without blooming. Growth of plants was not modified by ethephon treatments, but at 500 or 1000 ppm flowering of those was delayed, and at 1500 ppm the length of flower stalk and the number of flower was reduced.
CCC reduced plant height at 500 or 3000 ppm, delayed flowering at 1000 ppm, and reduced the number of flowers at 1000 or 3000 ppm. PP-333 reduced the plant height at all rates, delayed the blooming at 100 or 1000 ppm, and reduced flower size. SADH treatment at 2000 or 4000 ppm was effective on the reduction of plant height, the delay of blooming, and the reduction in the number of flowers. Ancymidol at all concentrations was not effective on the growth but reduced the number of flowers. At 500 ppm blooming was promoted. GA treatment did not affect growth of the plant, but was effective on early blooming and lengthening flowering stalk.
From the above results, it can be concluded that the optimum concentration of each PGR for the control of growth and flowering was 2000 ppm for MH, 1000 ppm for ethephon, 2000 ppm for SADH, 1000 ppm for ancymidol and 50 ppm for BA.
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