The in vivo growth and development of micropropagated Elatior begonias ( Begonia x hiemalis )

Micropropagation is an efficient way to produce pathogen-freeElatior begonias. However, certain problems arise when these plants are used in commercial pot plant production. The plants grow too luxuriantly, the root collars remain thin and flowering is delayed. To investigate the impact of the growing method, an experiment with different sources of supplementary light and different substrates was arranged in spring 1987. The following Elatior begonia cultivars were studied: ’Afrodite’, ’Afrodite Special’, 'Afrodite Rosa’, ’Mandela’, ’Barbara’, ’Connie’, ’Marja’ and ’Sirene’. Four different lamp types were used: highpressure sodium lamps (Airam SNaKd 330 W), high-pressure mercury lamps (Airam HgLX 400 W), high-pressure metal halide lamps (Philips HPI/T 375 W) and, as a control treatment, incandescent lamps of 100 W. The plants were potted in 82-peat (Sphagnum peat with moderate fertilization and medium sieving grade), 82-peat (3 parts) plus perlite (1 part) or 82-peat (2 parts) plus perlite (2 parts). The plants lighted with SNaKd or HgLX lamps were the highest, the broadest and the first to reach anthesis and the sale stage. The plants in the control group were the smallest and the last to reach anthesis and the sale stage. The effect of the substrate on the time required to reach anthesis and the sale stage was clear only in the cultivar ’Afrodite Special’; when potted in peat-perlite 2 + 2, its plants flowered 2 weeks later than in other substrate mixtures. The height and the width of the plants were not greatly affected by the substrate. None of the lamp types or substrates clearly increased the number of flower buds or the diameter of the root collar. The proportion of saleable plants varied with the cultivar, lighting and substrate. In most cultivars it was below 50 %. The chief factors reducing saleability were luxuriant growth, weak flowering and oblique growth habit. Index words: Begonia x hiemalis, micropropagation, lighting, substrate.


Introduction
Elatior begonias (Begonia x hiemalis) have become very popular as flowering pot plants.Traditionally, they are propagated by leaf or stem cuttings, depending on the cultivar.With the general development of methods of tissue culture, micropropagation of Elatior begonias has also become possible and has proved to be an efficient means of producing a large number of healthy plants in a short time.In this way it is possible to control the spread of one of the most serious diseases of Elatior begonia, bacterial leaf spot and blight caused by Xanthomonas begoniae.As no efficient chemical control of this disease is available at the moment, it is easily spread with tradition- ally propagated cuttings.
In spite of the superior healthiness of the plants, commercial producers have not been completely satisfied with the micropropagated Elatior begonias.When grown in the same way as traditionally propagated plants, they are said to show luxuriant and elongated growth together with delayed flowering.
Thinness of the root collar has also been re- ported, which poses a special problem in vigorously growing cultivars with a heavy crown.

Materials and methods
The research was done with the commercially micropropagated Elatior begonia 'Afro- dite Limelight'.At the beginning of the ex- periment, the plants were at the growth stage at which the commercial producers receive them, s -l o 5-10 cm high.They were potted on 3. 3. 1987 in 12-cm plastic pots, using a sub- strate with three parts of 82-peat (Sphagnum peat with 0.95 % of 10-11.3-16-fertilizer and 6.2 % of dolomite lime by weight, medium sieving grade) and one part of perlite.After this the plants were transferred to a green- house.
The plants were lighted with incandescent lamps at 04.00-08.00hours and at 16.00 - 20.00 hours for 3 weeks, to maintain the vegetative condition.The plants were then given a short-day treatment of 3 weeks, during which the light-dark cycle was 8 hours light and 16 hours dark.After the short-day treatment, the plants were grown in natural daylength.
Two growth retardants were used, chlorme- quat (CCC 75 %) and ancymidol (Reducymol), both as sprays.One half of the plants was sprayed with chlormequat and the other half with ancymidol.Both halves were divided into three different solution groups: group 1. 500 ppm chlormequat or 37.5 ppm ancymidol group 2. 1000 ppm chlormequat or 50.0 ppm ancymidol group 3. 1500 ppm chlormequat or 62.5 ppm ancymidol Each of these solution groups was divided into three groups according to the number of times that they were sprayed: group 1. Sprayed once, just before the short- day treatment group 2. As for group 1, but sprayed once more after 2 weeks group 3.As for group 2, but sprayed once more after 2 weeks A group of plants receiving no growth retardants were used as controls.The sprays were applied to the point of run-off.The night temperatures were intended to vary with the growing stage, as follows: vegetative period + 17°C, short-day treatment +2O°C and time to flowering +ls°C.In practice, however, these temperatures were difficult to keep and the night temperature range observed was + 14-+ 17°C (veg.), + 16-+ 20°C (short- day) and + 16-+ 18°C (flow.).Fertilizing was begun 3 weeks after potting.A fertilizer with 14 % N, 5 % P, 21 % K plus micro- nutrients was used.Nutrients were applied at every watering at the rate of 112 ppm N, 38 ppm P and 168 ppm K.
A completely randomized design was used with six replications.Height was measured from the pot rim to the highest peak of the plant.Width was determined as the average of two measurements at right angles to each other.The beginning of anthesis was deter- mined as the date when the first open flower was observed and the sale stage was determined as the date when six flowers were open.The number of branches was counted and the diameter of the root collar was measured on the top of the growing substrate.The diameter measurement of the root collar was taken from the first-flowering branch.The length of the flower stalk was measured from the first opened flower.
When a plant had reached the sale stage, the experiment was terminated for its part and the height, width, number of branches, flowers and flower buds, length of the flower stalk, diameter of the root collar and sale- ability were observed.As there are no official requirements concerning the saleability of Elatior begonias, a subjective judgement was used and the results in Figure 2 are thus merely indicative.The whole experiment was termi- nated on 26. 5. 1987, i.e. 12 weeks after pot- ting and 9 weeks after the beginning of the short-day treatment.

Results
The time taken to reach anthesis was significantly longer (1 week) only in the plants treated twice with 1000 ppm chlormequat, compared with the untreated plants.The time taken to reach the sale stage was not significantly affected by either of the retardants.However, the retardants seemed to delay flowering to some extent.Plants treated twice with any concentration were in most cases the last to reach anthesis and the sale stage (Figure 1).
The height of the plants was reduced by every growth regulator treatment.Spraying with ancymidol caused excessive growth retar- dation, especially at the concentration of 62.5 ppm.The increase in width was significantly reduced by ancymidol but not by chlorme- quat.The length of the flower stalk was mar- kedly reduced by all the treatments except spraying once with any concentration of chlormequat.The flower stalks of plants treated with ancymidol were extremely short.No differences were observed in the number of branches, flowers or flower buds, or in the diameter of the root collar (Table 1).
The greatest proportions of saleable plants were obtained by spraying once with 500 or 1000 ppm chlormequat or leaving the plants untreated.None of the plants treated with an- cymidol or twice with 1500 ppm chlormequat were saleable (Figure 2).No leaf damage was observed with any treatment.The leaves of the plants treated with ancymidol were darker green than those of the plants treated with chlormequat or the control plants.

Discussion
Chlormequat and ancymidol did not significantly delay the beginning of flowering or arrival at the sale stage, except in the plants sprayed twice with 1000 ppm chlormequat.Means in the same column differ significantly from the control in the MSD test, 5 °7o level.
Hilding (1975) studied the effect spraying with 0.04-0.1 °7o chlormequat (400 -1000 ppm) and reports that no differences were ob- served in the beginning of anthesis between treated and untreated plants in summer.Late in autumn, treatment with chlormequat caused slight retardation of flowering.
In this experiment strong reduction of height was obtained by using ancymidol.Even the lowest concentration, 37.5 ppm, sprayed only once, caused the plants to become dwar- fed.Krauskopf and Nelson (1976), who investigated the effect of spraying with 16.5 and 33 ppm ancymidol on the cultivar 'Schwaben- land Red', report that these concentrations were ineffective both in autumn (October) and in spring (March).It is likely that differences exist between the cultivars of Elatior begonia in the sensitivity to growth regulators.This conclusion is supported by the report of Hilding (1975).For spraying, Adriansen (1983) recommends ancymidol concentrations of 5 150 ppm, depending on the species.The increase in width was effectively re- duced by ancymidol but not by chlormequat.
It has been shown that the width of Elatior begonias is significantly reduced only when there is excessive reduction of height (Kraus- kopf and Nelson 1976, Will 1977, Schenk  and Brunderi 1980).
The effect of ancymidol on the flower stalks was the same as on the growth in general; ex- cessive reduction, which made the plants treated with ancymidol unsaleable.Chlor- mequat was effective in reducing the length of the flower stalks when used two or three times at any concentration.The effectiveness of chlormequat in reducing the length of the flower stalks was also noted by Sandved  (1972) and Hilding (1975).
Plants of the best quality, and thus the greatest proportions of saleable plants, were obtained by spraying once with 500 or 1000 ppm chlormequat or not using growth retar- dants at all.With the cultivar 'Schwabenland', Hilding (1975) obtained plants of the best quality by spraying once with 0.1 % (1000 ppm) chlormequat.
The reduction in quality and in the propor- tion of saleable plants was mainly due to long Fig. 2. The effect of chlormequat and ancymidol sprays on the proportion (%) of saleable plants in Elatior be- gonia 'Afrodite Limelight'.
flower and leaf stalks and elongated growth (untreated plants) or to short flower and leaf stalks and excessively compact growth (treated plants).There was also the problem of oblique growth, a growth habit which leads to the plant bending to one side and having a front and a back.The bending was independent of the direction of incoming daylight.Oblique growth was noted in all groups, even in plants dwarfed by ancymidol and thus not having a heavy crown.In groups with little or no growth retardation, the oblique growth habit could be overcome by supporting the crown at an early stage with two or three sticks.The oblique growth habit has been observed among other micropropagated Elatior begonia cultivars as well (Roivainen 1987).The reason for such growth is unknown.

Fig
Fig. I.The effect of chlormequat and ancymidol sprays on the time taken to reach anthesis and the sale stage in Elatior begonia 'Afrodite Limelight'.

Table 1 .
The effect of chlormequat and ancymidol on the growth of the Elatior begonia cultivar 'Afrodite Lime- *