COMPARISON OF VARIOUS METHODS OF APPLICATION OF GROWTH REGULATORS IN THE CULTIVATION OF TAGETES PATULA L. ‘BOY GOLDEN’

Anita Schroeter-Zakrzewska, Beata Janowska
Department of Ornamental Plants, University of Life Sciences in Poznań, Poland

ABSTRACT

Three methods of application of growth inhibitors were tested in the cultivation of the French marigold: the soaking of seeds, spraying the medium a few days after seed sowing, and spraying the seedlings. Use was made of daminozide contained in the preparation B-Nine 85 SP at concentrations of 2550 and 4250 mg·dm^-3 (0.3 and 0.5%), and metconazole contained in the preparation Caramba 60 SL at 300 and 600 mg·dm^-3 (0.05 and 0.1%). The response of the plants depended on the kind, concentration and mode of application of the retardant. The soaking of seeds of the French marigold in solutions of the retardants, had an adverse effect on their germination. Soaking seeds in metconazole, spraying the medium with daminozide at a concentration of 2550 mg·dm^-3 and with metconazole at 600 mg·dm^-3, as well as spraying the seedlings with the retardants had an adverse effect on the flowering of the plants.

Key words: daminozide, metconazole, seedlings.

INTRODUCTION

Restricting the growth of bedding plants is commonly practised by producers of seedlings. In some species propagated from seeds, e.g. French marigolds or bedding geraniums, a problem encountered in their production is an early streatching of seedlings, especially in the period of light deficiency. The use of growth retardants at the stage of leaves proper is ineffective then because the hypocotyl is too elongated, and it is well known that a retardant has no effect on an already existing part [5,6]. It should be remember, however, that the response of individual species, or even cultivars, to retardants can vary [4].

The most popular methods of applying growth-inhibiting substances are the spraying and soil drench of plants. A little-known method is that of seed soaking. It is very simple and greatly reduces the amount of the active substance used and then released into the environment, which is of no little significance in the light of today's ecological restrictions [7]. In the experiment reported, a comparison was made of various methods of retardant application, including seed soaking, spraying the medium a few days after seed sowing, and spraying the plants.

MATERIAL AND METHODS

In 2007 an experiment was conducted in which three methods of application of growth regulators were tested in the cultivation of the French marigold (Tagetes patula L.) 'Boy Golden': the soaking of seeds, spraying the medium a few days after seed sowing, and spraying the seedlings.

Marigold seeds were soaked in aqueous solutions of retardants: daminozide at concentrations of 2550 and 4250 mg·dm^-3 (B-Nine 85 SP at the concentration of 0.3 and 0.5%), and metconazole at the concentrations 300 and 600 mg·dm^-3 (Caramba 60 SL at the concentrations 0.05 and 0.1%). The control combination was soaked in water. After 24 hours from the start of soaking, the seeds were sown in multi-pot pallets. The sowing medium was limed highmoor peat mixed with sand (2:1) and brown Superba at 0.5 g per 1 l of substrate.

On the fifth day after sowing, the medium was sprayed with the retardants at the same concentrations as for seed soaking at 10 ml aqueous solutions of retardants per multi-pot pallets. Then a systematic count was made of the number of germinating seeds.

A month after sowing, marigold seedings were planted into 9-cm pots. The planting medium was limed highmoor peat with an addition of a slow-release fertiliser Osmocote 3-4M at 3 g·l^-1 of substrate. As top dressing, every week 0.1% solutions of mixed fertilisers were applied. The plants were first fed with white Kristalon (15-5-30) and then with blue Kristalon (19-6-20) at 100 ml per pot.

A week after potting, the plants were sprayed with the retardants. Again, plants were treated of the same preparations at the same concentrations as for seed soaking and medium spraying.

The parameters measured included the height of plants, number of buds and flowers, and flower diameter. Also, an N-Tester apparatus was used to determine the index of leaf greenness.

The experiment consisted of 8 combinations with 20 replications in each, on plant being a replication.

The results were subjected to a bivariate analysis of variance, and the means were grouped using Duncan's test at the α = 0.05 significance level.

RESULTS AND DISCUSSION

On the basis of the experiment performed, it was found that the response of plants to the retardants used depended on the concentration and kind of the retardant as well as the mode of its application.

The germination of seeds of the French marigold was significantly retarded by the soaking of seeds in a solution of metconazole. Its use at the higer concentration, 600 mg·dm^-3 resulted in a germination rate of a mere 25.7%, and at the lower one, 300 mg·dm^-3, in 37.1%. The germination rate was the highest in the combination where the medium was sprayed with solutions of daminozide at concentrations of 2550 and 4250 mg·dm-3, and metconazole at 600 mg·dm^-3 (Table 1). Similar results were obtained by [6] when they had soaked the seeds of the French marigold and geranium (Pelargonium) in a solution of paclobutrazol for 24 hours. Seed soaking in a paclobutrazol solution also inhibited their germination in vervain, while having no significant effect on germination in celosia (Celosia) and pansy (Viola × wittrockiana) [5].

An efficient and widely used method of growth retardation is the spraying of plants. The most popular preparation employed in the culture of many species of bedding plants is B-Nine. In the present experiment it inhibited the growth of French marigold seedlings. The plants were 15-23% shorter than the control. The retardant was found to have a weak effect when the seeds had been soaked and the medium sprayed a few days after sowing.

Irrespective of the mode of application, metconazole turned out to have a strong effect. The most dwarfed plants were those that developed from seeds soaked in its solution. Depending on the concentration applied, they were as much as 63–67% shorter than the control. A strong effect of metconazole has also been corroborated by the studies of Ueber [11] and Hetz [2].

As a result of soaking the seeds of vervain (Verbena) and marigold (Tagetes) in paclobutrazol, Passian and Bennet [6] as well as Magnitskiy et al. [5] also obtained shorter seedlings.

The present experiment showed that the retardants under study restricted the branching of the French marigold (Tagetes patula). An exception was the combination in which the medium was sprayed with a metconazole solution at 300 mg·dm^-3. The plants did not differ from the control. With soil-applied B-Nine, Schroeter and Janowska [8] also obtained lesser-branched plants of the French marigold. Different results are presented by Krause et al. [3] as well as Szczepaniak and Burda [10]. Those authors showed that B-Nine stimulated the branching of bedding and balcony plants.

When analysing the effect of the retardants on the flowering of the French marigold plants, it can be stated that they affected this feature in different ways. A significant weakening of flowering was visible in plants which had grown from seeds soaked in metconazole, as a result of spraying the medium with daminozide at 2550 mg·dm^-3 and metconazole at 600 mg·dm^-3, and of spraying the seedlings with both, daminozide and metconazole. Also Schroeter and Janowska [8] obtained weaker flowering in the French marigold treated with B-Nine.

The use of metconazole brought about the development of smaller flowers in the French marigold. An exception was the combination in which the medium was sprayed with a metconazole solution at 300 mg·dm^-3. In turn, daminozide had no significant effect on this feature. In the literature one can find information that retardants can cause the development of smaller or larger flowers depending on their kind, concentration, and the plant species.

As a rule, retardants cause a darker colouring of leaves. Ueber [11] as well as Schroeter-Zakrzewska and Janowska [9] obtained a darker colour of the leaves of twinspur (Diascia barberae) when they used metconazole. Using other retardants on various ornamental species, many authors have also reported this effect [12,1]. In the present experiment, however, irrespective of their concentration and mode of application, daminozide and metconazole did not affect the index of leaf greenness (Table 2).

CONCLUSIONS

1. The response of the plants depended on the kind, concentration and mode of application of the growth regulators.

2. The soaking of seeds of the French marigold in solutions of the retardants, especially metconazole, had an adverse effect on their germination.

3. Under the effect of the retardants, lesser-branched plants were obtained.

4. Soaking seeds in metconazole, spraying the medium with daminozide at a concentration of 2550 mg·dm^-3 and with metconazole at 600 mg·dm^-3, as well as spraying the seedlings with the retardants had an adverse effect on the flowering of the plants.

5. The use of metconazole, with the exception of the combination in which the medium was sprayed with its solution at 300 mg·dm^-3, brought about the development of smaller flowers.

6. The retardants employed had no effect on the index of leaf greenness.

REFERENCES

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Accepted for print: 26.08.2009

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