THE EFFECT OF SILICON FOLIAR APPLICATION ON THE DEVELOPMENT OF SEASON ORNAMENTAL PLANTS . PART II : Argyranthemum frutescens ‘ Blazer Rose ’ , Xerochrysum bracteatum ‘ Gold ’ , Osteospermum ecklonis ‘ Grande Pink Blush ’ AND Gaura lindheimeri ‘ Corinas Choice ’

Recent research has proved that supplementary application of silicon, involved in plant tolerance against many stress factors, positively influences plant development improving the quality of ornamental plants. A two-factorial experiment involved four cultivars of ornamental plants: Argyranthemum frutescens ‘Blazer Rose’, Xerochrysum bracteatum ‘Gold’, Osteospermum ecklonis ‘Grande Pink Blush’, and Gaura lindheimeri ‘Corinas Choice’ The first experimental factor was the concentration of Actisil preparation being an equivalent of 60, 120, and 180 mg Si×dm, applied three times by spraying, while the second one was the type of medium: peat substrate and peat substrate with sand. Actisil had a beneficial effect on the number of lateral shoots in all plants. The highest number of buds and inflorescences was determined in Xerochrysum and Osteospermum plants sprayed with 0.3% Actisil, and 0.2% Actisil in case of Argyranthemum and Gaura. The effect of medium type on plant growth depended on plant species. Argyranthemum and Osteospermum plants cultivated in the medium with sand showed inhibited growth, although medium type did not affect the growth of Xerochrysum.


INTRODUCTION
Silicon, a chemical element commonly occurring in nature, has a positive effect on plant development and resistance.Its properties include the beneficial effect on the ionic balance in plants, reducing toxic effects of manganese and iron excessive amounts, as well as reinforcement of cell walls (M a r s c h n e r et al. 1990).This element is also known for its stimulation of plant resistance to fungal diseases (M c A v o y and B i b l e , 1996; G i l l m a n et al. 2003), insects (R e y n o l d s et al. 2009), and resistance to unfavourable environmental conditions, among others, too low temperature or water deficit.One of the mechanisms for supporting plants under water stress conditions is decreased transpiration resulting in reduction in water loss, but silicon also partakes in osmoregulation, maintaining water status and adequate supply of nutrients (S a c a ł a , 2009).
Both biotic and abiotic stress factors induce physiological disorders leading to loss in yields and, in case of ornamental plants, to loss of decorative value.Although silicon is not an indispensable element for the growth and development of higher plants, according to E p s t e i n (2009), under stress conditions additional treatment with silicon may cause a big difference in their performance.It is particularly important in glasshouse production as it involves cultivation of plants in soiless media which do not contain silicon.Additional treatment with Si does not cause severe injury to plants as its excessive amounts may be secreted.
The main form of silicon, available to plants, is orthosilicic acid, absorbed by plants and precipitated throughout the plant as amorphous silica (R i c h m o n d and S u s s m a n , 2003).In case of ornamental plants, this element is also applied in the form of silicates, e.g.potassium silicate and sodium silicate as drenches or foliar applications, and it can be also added to medium mixtures, e.g. in the form of rice husk ash (F r a n t z et al. 2005; K a m e n i d o u et al. 2008, 2010).
The aim of the research was to assess the effect of orthosilicic acid contained in Actisil preparation as well as two types of soil on growth and flowering of selected decorative plants for balconies and terraces.
Treatments as well as data recording and analysis followed those presented in Part I of the article.

RESULTS AND DISCUSSION
The influence of silicon on plant development depends on, among others, cultivation conditions and plant species.Among higher plants, some monocotyledons, e.g. the Gramineae (Poaceae) which accumulate high amounts of silicon (more than 1% of dry mass) (M a and Y a m a j i 2008), show a good response to silicon treatment, whereas Dicotyledones are believed to be non-accumulators of Si.For this reason, monocots have become the main object of silicon research, with special focus on rice.Apart from these observations, some dicotyledons, like Aster, are beneficially affected by Si treatment (F r a n t z et al. 2005).
One of the criteria of the plant growth rate is their height.It has been assumed that more intensive development produce plants of increased height.Yet, in the case of numerous ornamentals, taller plants are not the most desired ones.Compact plants showing considerable tillering are often regarded as the most attractive.This requirement is especially important in the case of pot-grown ornamentals.According to S t a r t e k et al. ( 2006 Abundant flowering is extremely important for plants with decorative flowers, which results, among others, from the degree of tillering.One of the most significant factors stimulating lateral bud development is the cytokinin level in shoots.It was detected that foliar treatment with silicon could increase the level of cytokinin in wheat plants (H a n a f y A h m e d et al. 2008).In both years of our experiment, we proved the beneficial effect of orthosilicic acid contained in Actisil preparation on the number of lateral shoots in all plant species selected for the experiment.Irrespective of type of medium and year of experiment, the higher was the concentration of Actisil, the better tillering of Argyranthemum (Table 1) and Xerochrysum plants (Table 2) was found.
In Osteospermum, the two highest concentrations proved to be the most desired ones -they strongly affected, in the same way, the number of lateral shoots (Table 3) -while in Gaura the highest number of lateral shoots was produced due to spraying with Actisil of 0.2% concentration (Table 4).As its concentration increased, this preparation more evidently affected lateral shoot elongation in paper daisy and Gaura.In the case of Argyranthemum, longer lateral shoots were recorded in plants sprayed with higher concentrations of Actisil, while in Osteospermum only 0.3% solution of this preparation resulted in shoot elongation (Table 3).
The number of African daisy and paper daisy inflorescences increased according to the increase in concentration of fertilizer solution and it was connected with longer shoots.In the same taxa, Actisil extended the diameter of inflorescences (Fig. 1).This finding confirms the research results obtained so far, as the beneficial effect of silicon on inflorescence diameter has been proved in case of some species of the same family Asteraceae, such as sunflower Helianthus annuus L. ).Regardless of its concentration, this preparation stimulated flowering of Gaura, yet the highest number of flowers was produced by plants treated with 0.2% solution of Actisil (Fig. 2).The preparation at the same concentration had a beneficial effect on the number and diameter of Argyranthemum inflorescences.On the other hand, at a concentration of 0.1% Actisil inhibited flowering of this variety.These two taxa had larger flowers only under the influence of the highest concentration of the preparation (0.3%).
Actisil significantly regulated the height of such plants as Xerochrysum and Gaura.This parameter showed higher values according to the increase in Actisil concentration.Under the influence of Actisil, higher plants were also characterized by a larger plant diameter.Similar results, regarding the application of Actisil, also introduced three times, were obtained for multiflora rose Rosa multiflora Thunb.ex Murray (H e t m a n et al. 2007).Boston daisy sprayed with Actisil at a concentration of 0.3% reached a 1.7 times larger diameter.A similar phenomenon -an increased diameter of plants obtained by treatment with 0.2% Actisil -was observed in garden pansy (W r a g a and D o b r o w o l s k a , 2007).Osteospermum showed only a slight influence of this preparation as far as plant height and diameter were concerned.
Plant growth also depended on the type of medium the plants were grown in.In Argyranthemum and Osteospermum, inhibited growth characterized plants cultivated in medium with the addition of sand.It was manifested in decreased plant height and diameter values; Argyranthemum plants also showed insufficient tillering as well as poorer flowering (Fig. 4).However, the type of medium did not affect vegetative development of paper daisy, except for plant height which increased in plants grown in peat substrate.Since plant height is not a decisive characteristic for the quality of Xerochrysum as a container-grown plant, it can be well cultivated using cheaper medium with the addition of sand.Gaura, growing in a mixture of peat substrate and sand, demonstrated decreased plant diameter and less numerous, but longer lateral shoots.Longer shoots of this taxon produced higher number of flowers (Fig. 4).The type of growing medium did not influence flower and inflorescence diameter (Fig. 3) in none of the examined plant varieties.
), silicon contained in Actisil preparation improves plant habit of pot-grown chrysanthemums, stimulating shoot elongation of varieties characterized by moderate growth and inhibiting excessive extension of shoots in varieties showing such a tendency.It also improves the quality of garden pansy Viola x wittrockiana (W r a g a and D o b r o w o l s k a , 2007).
(K a m e n i d o u et al. 2008; C a r v a l h o et al. 2009), zinnia Zinnia (K a m e n i d o u et al. 2009), and gerbera Gerbera (S a v v a s et al. 2002; K a m en i d o u et al. 2010 = n.s.; r.n.BxC = 1.9 B = 0.6 C = 0.8 AxC = 1.1 BxC = r.n..; n.s.B = 0.4 C = 0.6 AxC = 0.9 BxC = 0.9 * P means peat substrate, PS means peat substrate with sand in 3:1 ratio = n.s.; r.n.* P means peat substrate, PS means peat substrate with sand in 3:1 ratio peat substrate, PS means peat substrate with sand in 3:1 ratio

Table 1 .
Morphological features of Argyranthemum frutescens 'Blazer Rose' depending on Actisil concentration and type of medium

Table 2 .
Morphological features of Xerochrysum bracteatum 'Gold' depending on Actisil concentration and type of medium Height of plants [cm] Diameter of plants [cm] Number of lateral shoots Length of lateral shoots [cm]

Table 3 .
Morphological features of Osteospermum ecklonis 'Grande Pink Blush' depending on Actisil concentration and type of medium

Table 4 .
Morphological features of Gaura lindheimeri 'Corinas Choice' depending on Actisil concentration and type of medium

Table 5 .
Chlorophyll content in leaves of Argyranthemum frutescens 'Blazer Rose', Xerochrysum bracteatum 'Gold', Osteospermum ecklonis 'Grande Pink Blush' and Gaura lindheimeri 'Corinas Choice' depending on Actisil concentration and type of medium, expressed as the sum of chlorophyll a and b [mg×g -1 of fresh weight] * P means peat substrate, PS means peat substrate with sand in 3:1 ratio