Growth Responses to two Commercial Plant Growth Retardants with Different Concentration in Potted Geranium

Background and objective: The aim of this study was to elucidate the effect of varying treatment concentrations of two different plant growth retardants, acting at different inhibition positions during the biosynthetic process, on the growth characteristics of geranium (Pelargonium × hortorum) and then to provide essential data to improve the quality of pot plant production.Methods: Aqueous solutions of diniconazole (Binnari) and daminozide (B-9) at concentrations of 0 (distilled water), 50, 100, 200, and 400 mg⋅L^-1 were prepared for the geranium 'Ringo 2000TM Deep Red'. These solutions were applied by foliar spraying twice at 10-day intervals. Growth characteristics such as plant height, leaf size and relative chlorophyll content (SPAD) were then assessed.Results: When Binnari was applied at concentrations of 0, 50, 100, 200, and 400 mg⋅L^-1 , the corresponding plant heights were 29.5, 23.8, 24.1, 23.0, and 18.4 cm, respectively. There was a statistically significant decrease in plant height with increasing concentration. Conversely, for B-9, plant height was significantly reduced to 26.7 cm only at the 400 mg⋅L^-1 concentration, indicating a less pronounced inhibitory effect compared to Binnari. Leaf width showed a significant decreasing trend with increasing Binnari application concentrations and was 4.6, 4.7, 4.1, 4.2, and 3.9 cm respectively. However, there was no significant difference due to the B-9 treatment. Chlorophyll content increased with increasing concentrations of both retardants.Conclusion: In conclusion, Binnari showed a greater inhibitory effect on geranium growth compared to B-9. The application of Binnari at 400 mg⋅L^-1 resulted in the greatest increase in the ornamental value of the geranium. Furthermore, diniconazole acts during the early stage before the splitting of the GA₁ and GA₄ pathways, thus inhibiting the biosynthesis of both active gibberellins. In contrast, daminozide inhibits the step just before GA₁ biosynthesis. It is concluded that GA₄ serves as the dominant active gibberellin in geranium plants.