Effect of Gibberellic Acid and Putrescine on Growth, Flowering and Vase Life of Lily Cut Flower (ʻLesothoʼ)

 Lilium flower is a perennial herbaceous flowering plant, belonging to the Liliaceae family. Position of lilies as the fourth best-seller cut flower in the world, as well as the increasing trend of demand for this flower in the global market, indicates the importance of improving the quality and solving the sustainability issues of this flower. Gibberellins are one of the most important endogenous plant hormones involved in controlling plant dormancy. Gibberellin is a plant growth regulator that stimulates physiological responses in plants by affecting photosynthesis. Polyamines, including putrescine, spermidine, and spermine, are a group of plant growth regulators that have effects such as increasing cell division, biosynthesis of enzymes, regulating various developmental stages such as differentiation.
 This study was performed to investigate the effect of gibberellic acid and putrescine on growth, flowering and vase life of Lilium cut flowers. Experiment was performed as factorial based on completely randomized design, included 16 treatments with 3 replications and 2 pots in each replication. The culture medium containing mold leaf soil, sand and perlite (1:1:1) and was prepared by disinfection with fungicide. The first treatment consisted of concentrations of 150, 300 and 450 mg/L gibberellic acid and onions were pre-treated by immersing for 24 hours. The second treatment consisted of concentrations of 0.5, 1 and 2 mM putrescine which was sprayed at the beginning of budding and continued every two weeks until the first bud flower coloring. Growth period conditions in green house were controlled. In this study, different parameters such as bud number, flowering stem length, fresh weight of cut flowers, relative fresh weight of cut flowers, water uptake of cut flowers, vase life, leaf chlorophylls a, b and total, petal carotenoid, percentage of petal cell membrane stability and total soluble solids of petals were examined.
 The results showed that the application of gibberellic acid and putrescine improved the number of buds and increased cell membrane stability. Actually, gibberellic acid preserves the cell membrane by preventing the breakdown of proteins and increasing the pH, thus increasing the vase life. Also Putrescine protects cell membranes by removing free radicals. It is also known that gibberellic acid used at all levels in the experiment increased the height of the flower stem due to its role in cell division and elongation. Study of the flower stem water content and cut flower fresh weight, which are factors for longer vase life, showed that gibberellic acid increases the plant's ability to absorb water and increases these two traits. So that the highest cut flower fresh weight with 13 g difference compared to the control level belonged to the treatment level of 450 mg/L gibberellic acid. Also putrescine reduces plant water loss by increasing membrane permeability to calcium and increases the flower stem water content and cut flower fresh weight, which increases vase life. Also, gibberellic acid by creating water potential in the cell and putrescine by strengthening water relations and preventing blockage of water vessels increased the relative water uptake of cut flower. Thus, the greatest effect was observed on the third day post-harvest and the highest amount (2.47 ml. g-1 FW) on the third day belonged to the highest level of both treatments. Results also showed that all the levels of putrescine increased TSS due to its effect on the synthesis of sugars and carbohydrates in compared to control. The results showed that application of gibberellic acid and putrescine respectively at 300 mg/L and 2 mM, significantly increased the vase life compared to the control. The best vase life (15 days) occurred at 300 mg/L gibberellic acid and 2 mM putrescine. Although gibberellic acid increased growth and flowering of Lilium, but putrescine effectiveness on vase life of cut flower was more evident. The highest amount of leaf total chlorophyll (0.514 mg. g-1 FW) belonged to the treatment of 450 mg/L gibberellic acid and 2 mM putrescine and the lowest amount of leaf total chlorophyll (0.085 mg. g-1 FW) belonged to both treatments were at the control level. Also, in the study of petal carotenoid content, the highest amount ​​belonged to the treatment of 450 mg/L gibberellic acid and 2 mM putrescine.
 According to the results obtained from the present research, it can be concluded that use of gibberellic acid and putrescine had great effects on most of traits in compared to control treatment. The use of putrescine and gibberellic acid improves the flowering and vase life conditions by increasing water uptake and consequently increasing the relative fresh weight.