EFFECT OF BLUE LIGHT ON THE GROWTH OF CHRYSANTHEMUM UNDER LONG AND SHORT DAY

Małgorzata Zalewska¹, Anita Woźny^2
1 Department of Ornamental Plants and Vegetable Crops, University of Technology and Life Sciences in Bydgoszcz, Poland
² Department of Ornamental Plants and Vegetable Crops, Faculty of Agriculture and Biotechnology, University of Science and Technology, Bydgoszcz, Poland

ABSTRACT

In many ornamental plants species the light colour can, more or less considerably, modify growth and flowering. Literature offers information on the growth inhibition of seedlings, transplants and cuttings of ornamental plants exposed to blue light.

In the present experiment Chrysanthemum × grandiflorum (Ramat.) Kitam. ‘Boulou White’ was exposed to blue and day light (control), at 3 quantum irradiance levels: 90, 110 and 140 µmol·m^-2·s^-1. The source of light was made up by 36 W fluorescent lamps.

During the cultivation in controlled climate conditions a long day and a short day, each time 4-week long, were applied.

It was demonstrated that the blue light of the highest quantum irradiance both under long- and short-day conditions inhibited the plant growth. The blue light applied under short-day conditions slightly decreased the number of chrysanthemum leaves.

Key words: Chrysanthemum ?grandiflorum (Ramat.) Kitam., quantum irradiance, blue and day light, fluorescent lamp, long and short day.

INTRODUCTION

Although chemical growth retardants are still widely applied in horticultural production, an increasing pollution of the environment and concern with its state call for new ecological methods of obtaining a desired plant habit. For a few years more and more attention has been paid not only to the role of light intensity but also to its quality in terms of its spectral composition, and results of numerous research clearly point to a possibility of a strong modification of growth and development of plants applying light of a given quality while growing. Growth of many species was inhibited by changing the light quality with filters with aqueous solution of CuSO₄ in e.g. chrysanthemum [11, 12, 15, 16], sage [5] and miniature rose [16]; photoselective film in chrysanthemum growing [3, 8, 9] and zinnia, cosmos, petunia [3] and reflective mulches in pepper [4]. The applicable literature gives no information on the effect of blue light emitted by fluorescent lamps on the ornamental plants growth. The aim of the present experiment was to investigate how fluorescent lamps emitting blue light of varied quantum irradiance affect chrysanthemum growth under long- and short-day conditions.

MATERIAL AND METHODS

The experiment was carried out in growth chamber, exposed to artificial light and under controlled climatic conditions. The light was generated by fluorescent lamps made by Philips – TLD, 36 W, emitting blue light – TLD 36W/18 and daylight – TLD 36W/54 – constituting the control (fig. 1, 2, 3). The experiment involved 3 levels of quantum irradiance: 90,110 and 140 µmol·m^-2·s^-1.

Experiment 1. Rooted cuttings of chrysanthemum (Chrysanthemum × grandiflorum (Ramat.) Kitam.),‘Boulou White’ cultivar, (on average 3.5 cm long) were planted on June 27, 2005 into pots 9 cm in diameter. There was used a specialist medium, applicable to chrysanthemum growing. Each combination involved 20 plants (5 replications 4 plants each).

After a week-long cultivation in the glasshouse (at the air temperature of 21°C, and the medium temperature of 23°C), the plants were placed in the growth chamber and exposed to a long day – 16 hours (20:00-12:00). Throughout the cultivation period the air temperature was maintained at 21°C (switched-on lamps) and 19°C (switched-off lamps), while the temperature of the medium – at 23°C. The relative air humidity was 75%. Chrysanthemums were fertilised once a week, treating the roots with Peter’s 20-10-20 fertilizer (produced by Scotts). Every 4 days plant height was measured from the medium surface to the apex. With the chrysanthemum growth, the lamps were being placed higher to maintain the constant initial quantum irradiance.

The experiment was completed after 4 weeks of growing, on August 1; the plant height was measured, the number of fully-formed leaves and the length of internodes were defined (dividing the height by the number of leaves). There were determined the leaf blade area (by Scandix 1.5) [2] and the share of dry matter in the fresh weight of stems, leaves and the shoot. The statistical analysis was made for a  2-factor experiment in a completely randomised design. The significance was verified with the Tukey test.

Experiment 2. Rooted cuttings of ‘Boulou White’ cultivar were planted on July 25, 2005 and after 7 days of growing in the glasshouse, where the average daily air temperature was 24°C and the medium temperature was 23°C, were transferred to the growth chamber. The experiment involved the same light colours and quantum irradiance as in Experiment 1. Chrysanthemums were grown while exposed to a short day 10 hours long (1:00-11:00). During a 4-week growing the same climatic conditions were maintained as in the first part. Having completed the experiment, the same quality parameters were considered as in Experiment 1.

RESULTS

Experiment 1. Blue light of quantum irradiance of 140 µmol·m^-2·s^-1 inhibited the growth of plants cultivated under long-day conditions. Such a reaction was observed already 4 days after the beginning of growing (fig. 4). The statistical analysis carried out after the completion of growing confirmed that under blue light lower chrysanthemums can be obtained only after the application of the highest quantum irradiance (140 µmol·m^-2·s^-1) (fig. 5) It was observed that chrysanthemums grown under blue light of quantum irradiance of 140 µmol·m^-2·s^-1 demonstrated a higher share of dry matter in the fresh weight of leaves, as compared with plants exposed to daylight. The light colour did not affect the number of leaves and their area and the length of internodes (tab. 1 and 2).

Experiment 2. Chrysanthemums grown under short-day conditions, exposed to the light of quantum irradiance of 140 µmol·m^-2·s^-1 already 4 days after the beginning of the experiment in the growth chamber were growing at a lower rate as compared with the plants under daylight (fig. 6). Similarly as in Experiment 1, this trend remained until the end of growing. There was found no chrysanthemum growth inhibition caused by blue light of lower quantum irradiance (90 and 110 µmol·m^-2·s^-1).

The number of leaves in plants grown while exposed to blue light was lower as compared with chrysanthemums exposed to daylight. Chrysanthemums grown under blue light of the highest quantum irradiance formed leaves of a smaller area than under daylight. There was demonstrated no effect of the light colour on the length of internodes, leaf blade area and the content of dry matter in the fresh weight of stems, leaves and the shoots (tab. 3 and 4).

DISCUSSION

Growing chrysanthemums under fluorescent lamps, emitting blue light, there was observed a growth inhibition at quantum irradiance of 140 µmol·m^-2·s^-1. TLD 36W/18 lamps applied in the experiments emit mostly blue light with almost no red and far red. Results of numerous research demonstrate a potential of inhibiting the shoot elongation in chrysanthemum and in other plants by changing the spectral composition of light. Eliminating red (R) but mostly far red (FR) wavelength from the light, increasing the ratio R:FR and blue (B):R, leads to growth inhibition and shortening the plant internodes [10, 14, 15, 16]. Blue light affects the plant growth with the phytochrome, leading to its photoconversion as well as by the cryptochrome [1, 6, 7, 13].

The growth inhibition effectiveness depends on the plant species, light source and intensity and in the case of plants sensitive to the photoperiod – also on the day length. Khattak and Pearson [6, 7] demonstrated that blue light is more effective in controlling growth of chrysanthemums of ‘Snowdon’ and ‘Bright Golden Ann’ cultivars at lower levels of quantum irradiance (3.05 MJ·m^-2ˇday^-1), as compared with better light conditions (7.4 MJ·m^-2·day^-1). In the present experiment blue light inhibited growth of chrysanthemums of ‘Boulou White’ cultivar only when exposed to the highest level of quantum irradiance used (140 µmol·m^-2·s^-1), which must have been due to the fact that the irradiance used in the experiment was definitely lower than that reported by Khattak and Pearson. McMahon and Kelly [11] demonstrated that the effectiveness of spectral filters with CuSO₄ in growth control of ‘Spears’ chrysanthemums depended on the day length. Under short-day conditions chrysanthemums grown under filters were 59% lower as compared with the control, while at long day – 45% lower. In the present experiment ‘Boulou White’ cultivar chrysanthemums grown at blue light of quantum irradiance of 140 µmol·m^-2·s^-1, were slightly over 11% lower than the control, both at short and long photoperiod.

Literature reports show that filters with a solution of copper sulphate and blue photoselective films decrease the leaf blade area in chrysanthemum and in pepper [8, 13] and reduce the dry matter of stems and leaves. In the present research there was found no negative effect of blue light on such characters as the leaf blade area, length of internodes and the share of dry matter in the fresh weight of leaves, stems and the shoot. It was only shown that under short day conditions the number of leaves in chrysanthemums grown in blue light was lower than in the control, however the difference did not deteriorate the plant quality. The present experiment involved fluorescent lamps, while other authors modified the spectral composition of natural light with filters with colourful solutions [12, 14, 15] and using colourful photoselective films [8]. Differences in the reaction of plants can therefore come not only from other intensity but also from other ratios of light of respective spectrum ranges.

CONCLUSION

1. Blue light of quantum irradiance of 140 µmol·m^-2·s^-1 emitted by fluorescent lamps leads to a production of lower ‘Boulou White’ cultivar chrysanthemums, both at long and short day.

2. Chrysanthemums grown while exposed to blue light and short day demonstrated fewer leaves as compared with plants exposed to daylight.

3. Lamps emitting blue light can be effectively used as an environment-friendly chrysanthemum height control method provided high quantum irradiance is applied.

REFERENCES

1. Batschauer A., 1998. Photoreceptors of higher plants. Planta 206, 479-492.

2. Borkowski W., 2000. SCANDIX 1,5 – packet of automatic biometrics programs, Warsaw University.

3. Cerny T.A., Faust J.E., Layne D.R., Rajapakse N.C., 2003. Influence of photoselective films and growing season on stem growth and flowering of six plant species. J. Am. Soc. Hort. Sci. 128(4), 486-491.

4. Decoteau D.R., Kasperbauer M.J., Hunt P.G., 1990. Bell pepper plant development over mulches of diverse colors. HortScience 25(4), 460-462.

5. Incrocci L., Serra G., Lercari B., 1994. Height control of a bedding plant (Salvia splendens F. Sellow) by copper sulphate filters. Acta Hort. 361 491-494.

6. Khattak A.M., Pearson S., 1997. The effects of light quality and temperature on the growth and development of chrysanthemums cvs, Bright Golden and Snowdon. Acta Hort. 435, 113-122.

7. Khattak A.M., Pearson S., 2006. Spectral filters and temperature effects on the growth and development of chrysanthemums under low light integral. Plant Growth Reg. 49, 61-68.

8. Li S., Rajapakse N.C., Young R.E., Oi R., 2000. Growth responses of chrysanthemum and bell pepper transplants to photoselective plastic films. Sci. Hort. 84, 215-225.

9. Li S., Rajapakse N.C., 2003. Far-red absorbing photoselective plastic films affect growth and flowering of chrysanthemum cultivars. HortScience 38(2), 284-287.

10. McMahon M.J., Kelly J.W., Decoteau D.R., 1991. Growth of Dendranthema × grandiflorum (Ramat.) Kitamura under various spectral filters. J. Am. Soc. Hort. Sci. 116(6), 950-954.

11. McMahon M.J., Kelly J.W., 1999. CuSO₄ filters influence flowering of chrysanthemum cv. Spears. Sci. Hort. 79, 207-215.

12. Mortensen L.M., Strømme E., 1987. Effects of light quality on some greenhouse crops. Sci. Hort. 33, 27-36.

13. Oyaert E., Volckaert E., Debergh P.C., 1999. Growth of chrysanthemum under coloured plastic films with different light qualities and quantities. Sci. Hort. 79, 195-205.

14. Rajapakse N. C., Kelly J.W., 1992. Regulation of chrysanthemum growth by spectral filters. J. Am. Soc. Hort. Sci. 117(3), 481-485.

15. Rajapakse N. C., Pollock R.K., McMahon M.J., Kelly J.W., Young R.E., 1992. Interpretation of light quality measurements and plant responses in spectral filter research. HortScience 27(11), 1208-1211.

16. Rajapakse N. C., Kelly J.W., 1994. Influence of spectral filters on growth and postharvest quality of potted miniature roses. Sci. Hort. 56, 245-255.

Accepted for print: 13.12.2006

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