Date of Award


Degree Type


Degree Name

Master of Science in Plant and Soil Science


Plant and Soil Science

First Advisor

William R. Krul


Many annual bedding plants are overly tall with sparse, pale foliage. Plant growth retardant chemicals commonly correct these undesirable characteristics. A method of producing dwarf plants by seed treatment with growth retardants could be useful to seed producers, commercial growers and home gardeners.

To determine the feasibility of producing dwarf plants by treating seeds with retardants, seeds were treated directly with aqueous, acetone or talc formulations of retardants, and indirectly by treatment of plants producing seed. The retardants SADH (N,N-dimethylamino succinamic acid), CCC ([2-chloroethyl] trimethylammonium chloride), Amo-1618, (4-hydroxy-5-isopropyl-2-methylphenyl trimethylammonium chloride, 1-piperidine carboxylate), and Ancymidol (a-cyclopropyl-a-(p-methoxyphenyl)-5-pyrimidine methanol) were used to treat seeds of marigold (Tagetes erecta L.), salvia (Salvia splendens Sello ex Nees), and petunia (Petunia hybrida Vilm.). Seeds were germinated and plants were grown to maturity. SADH, CCC and Ancymidol were also applied to marigold, salvia and petunia plants. Since inhibition of internode elongation is the primary effect of retardants, height measurements were taken to evaluate the effectiveness of all treatments.

The results of treatment of over 5,000 plants show that Ancyroidol is clearly more effective than SADH or CCC in inhibiting internode elongation of marigold, salvia and petunia plants. Drench applications retarded growth more than sprays. In some cases retardant treatment stimulated growth.

The inhibitory effect of retardant treatment is present one month after treatment and at flowering. Inhibition is generally maintained in the field. Amendment of Ancymidol mixed with ion exchange resin to the growing medium is also an effective method of controlling height of marigold, silvia and petunia plants in the greenhouse and in the field.

The results of treatment of over 3,000 seeds indicate that although few treatments inhibited internode elongation in plants grown from treated seeds, direct seed treatment with aqueous solutions of Ancymidol may be an effective method of controlling height of some bedding plants. Acetone seed treatments increased lateral branching in plants grown from treated seeds, but did not retard growth. Talc seed treatments did not inhibit growth of plants grown from treated seeds. Germination was delayed and percent germination was reduced by high concentrations of retardants applied to seeds.

With few exceptions, indirect seed treatment by treatment of parent 1plants was an ineffective method of inhibiting growth of second generation plants. However, several treatments with Ancymi dol inhibited growth of the progeny of marigold and petunia plants, indicating that further work with Ancymidol is warranted.

Retardant treatments of plants and seeds inhibited growth more in sununer than in winter, probably because retardant action is dependent on the rate of gibberellin (GA) synthesis, which is higher in summer than in winter. Similarly, retardant treatments were more effective on young plants than on mature plants, and young plants have higher rates of GA synthesis than mature plants.

Since retardant inhibition of growth is influenced by light intensity and duration, there may be an interaction between retardants and phytochrome. Further work on the seasonal effects of retardants on phytochrome levels and activity is indicated.



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