Increasing the growth and flowering indices of Polianthes in response to different concentrations of phosphorus and gibberellic acid in hydroponic culture conditions

Proper nutrition in the cultivation of cut flowers, including polianthes is extremely important. It is necessary to achieve quantitative and qualitative standards for the cultivation and production of this flower. It has been shown that, due to the lack of many secondary roots and shallow roots, the bulb plants are more sensitive to the lack of nutrients (such as phosphorus) compared to the other horticultural and agricultural crops. Plant growth regulators are particularly important in increasing the quantity and quality of flowers and ornamental plants, one of the most important of which is the positive effects of gibberellins in ornamental plants. Phosphorus (P) plays a key role in photosynthetic activities, flower formation and production of reproductive organs of greenhouse crops. The present study will examine the effects of gibberellin as a plant growth regulators and different concentrations of phosphorus) on the growth characteristics and flowering indices of marigold under hydroponic conditions.

An experiment was implemented to investigate the effect of gibberellic acid and various concentrations of P in nutrient solution on the growth and flowering of polianthes. The experiment was factorial based on a randomized complete block design with three replicates. The cuttings were immersed in 0 (distilled water), 100 and 200 mg/L of gibberellin concentration for 30 min before cultivation. Four levels of different P concentrations (7.75, 15.5, 31 and 62 mg/L) were prepared by monopotassium phosphate (KH2PO4) fertilizer and their effects were evaluated under different levels of gibberellin. Growth, flowering and physiological indicators were measured and evaluated during and at the end of the growing season. All data were statistically analyzed by analysis of variance (ANOVA) using the SAS 9.1 software (SAS Inc., Cary NC). Duncan’s multiple-range test was performed at p = 0.05 on each of the significant variables measured.

The findings of this research showed that the highest values of fresh and dry weight of leaf and stem, number of bulbs and number of buds were observed in the concentration of 31 mg L-1 of P and the treatment of mg L-1 of gibberellic acid. In the combined treatment of 31 mg L-1of P and 200 mg L-1 of gibberellic acid, in comparison with the control treatment, exhibited the length of flower branches increased by 26.06%, the number of flower branches increased by 99%, and the vase life of polianthes flowers increased by 58.47%. Also, the shortest harvest time (105.74 days) was observed in the treatment with 31 mg L-1 of P and 200 mg L-1 of gibberellic acid compared to the control (122.24 days). One of the important findings of this research is that there is no significant difference in the time required to harvest flowers in the treatments of 15. mg L-1 P and 200 mg L-1 gibberellic acid and the control treatment; In fact, despite a 50% decrease in the concentration of P in the nutrient solution, application of 200 mg L-1 gibberellic acid was able to make a significant contribution to the emergence of the flower buds of polianthes. In fact, in reduced P treatments, the gibberellin hormone had an effective role in stimulating the reproductive phase and improving flowering indicators of polianthes with a synergistic effect. The use of gibberellin may improve growth by increasing endogenous gibberellin content, removing oxidative stress and maintaining cell integrity. Furthermore, applications of GA3 together with P fertilizer lead to more biomass production than fertilizer alone (Ullah et al., 2017).

Application of 31 mg L-1 of P and the impregnation of the bulb with the concentration of 200 mg L-1 of gibberellic acid is recommended to accelerate the harvest elongated branches, to enhance the number of branches and the vase life of polianthes flower under hydroponic cultivation.Keywords: Number of branch, Gibberellin, Phosphorus, Vase life, Nutrient solutions.