S u m m a r yGrowth retardants are applied in order to obtain short and well compact plants. They usually inhibit stem elongation, but also can infl uence the fl owering of plants. The aim of cytokinin application is to obtain well branched plants without removing the apical meristem. Cytokinins usually increase the number of axillary shoots but also can infl uence fl owering. Growth retardants and cytokinins can affect fl ower size, pedicel length, number of fl owers, fl ower longevity, abortion of fl ower buds and number of days from potting plants to the fi rst open fl ower. Flowering of growth retardant and cytokinin treated plants might depend on the method of growth regulator used (foliar spray or soil drench), plant species or even a plant cultivar, but in the highest degree it depends on the growth regulator rate used. These growth regulators, when are applied at rates appropriate for height and habit control, very seldom infl uence fl owering of ornamental plants, but applied at high rates can delay fl owering, diminish fl ower diameter or fl ower pedicel length and also can decrease the number of fl owers per plant. In cultivation of bulb plants, growth retardants, used at very high rates, also cause abortion of fl ower buds. Key words: growth retardants, cytokinins, ornamental plants, fl oweringGrowth retardants, applied in order to obtain short and well compact plants, inhibit stem elongation but also can infl uence fl ower size, pedicel length, number of fl owers, fl ower longevity, abortion of fl ower buds and number of days from potting plants to their fl owering. Cytokinins are used in order to obtain well branched plants without removing the apical meristem. They usually increase the number of axillary shoots but also can affect number of fl owers, fl ower diameter, fl ower longevity and number of days to fl owering. Number of fl owers
The experiment was conducted to inhibit the growth of dwarf alstroemeria cultivars 'Rosalina' and 'Dorotea' using flurprimidol and daminozide. Additionally, the effect of these retardants on days to anthesis, flowering shoots number, diameter and longevity of florets was evaluated. In vitro propagated plants, grown in 12 cm pots were treated with single sprays of flurprimidol (7,5, 15, 22,5 mg l<sup>-1</sup>) and daminozide (2500, 3500, 4500 mg 1<sup>-1</sup>) following second pruning, when shoots were 9-12 cm long. Well retarded plants of both dwarf alstroemeria cultivars were obtained when plants were sprayed with flurprimidol at 22.5 mg 1<sup>-1</sup>. Plants treated with daminozide at all tested concentrations were to tall to be grown in 12 cm pots. Flurprimidol significantly reduced the canopy diameter, number of flowering shoots of alstroemeria cultivars 'Rosalina' and 'Dorotea' and floret size of cultivar 'Rosalina'. Daminozide had no effect on the number of days to flower but flurprimidol delayed flowering of tested cultivars only at concentration of22.5 mg 1<sup>-1</sup>. Intensified green leaf colour was observed on flurprimidol treated plants. The chemical names used: a-(1-methylethyl)-a-[4-(trifluoromethyloxy)-phenyl]-5-pyrimidine-methanol (flurprimidol), butanedioic acid mono (2,2-dimethylhydrazide) (daminozide).
A b s t r a c tThis study was undertaken to evaluate the influence of single foliar flurprimidol treatment on morphology and transpiration of 'Roman' and 'Freedom Red' poinsettias. The growth retardant flurprimidol (Topflor 015 SL) was applied once as a foliar spray at concentrations of 5, 10 or 15 mg × dm -3 when lateral shoots were about 5 cm in length. Single foliar flurprimidol treatment was sufficient to inhibit stem elongation of both poinsettia cultivars. The degree of growth inhibition depended on cultivar and growth retardant concentration. As compared to the control, the shoots of flurprimidol treated 'Roman' and 'Freedom Red' plants were up to 44% and 37% shorter, respectively. The desirable plant heights for 'Roman' and 'Freedom Red' poinsettias were obtained with flurprimidol at concentrations of 5 and 10 mg × dm -3 , respectively. The shoots of flurprimidol sprayed poinsettia were also more rigid and aligned relative to each other and thus the bracts on the plant were placed on the same level. The diameters of growth retardant treated poinsettias were up to 13% narrower. The leaf areas, petiole lengths, fresh and dry weights of 'Roman' and 'Freedom Red' poinsettias treated with flurprimidol were substantially smaller as compared to the control. The bract diameters of both poinsettia cultivars were only slightly affected by growth retardant application. Plants exposed to flurprimidol had also intensified green leaf pigmentation. There was almost no abscission of the oldest leaves in the low portions of growth retardant treated plants, compared to those of the control ones. Flurprimidol had no effect on transpiration rate per unit leaf area and stomatal conductance in both poinsettia cultivars. No phytotoxicity was observed in flurprimidol treated plants. Chemical name used: -(1-methylethyl)--[4-(trifluromethoxy)phenyl]-5-pyrimidinemethanol (flurprimidol).
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