THE INFLUENCE OF TIMING AND DURATION OF PHOTOPERIODIC LIGHTING ON THE WINTER FLOWERING OF CARNATIONS

Transcription

1 THE INFLUENCE OF TIMING AND DURATION OF PHOTOPERIODIC LIGHTING ON THE WINTER FLOWERING OF CARNATIONS E. Kaukovirta Department of Horticulture, University of Helsinki Helsinki 71, Finland Abstract The carnation stands, which bore shoots carrying 3-7 pairs of leaves, were given photoperiodic lighting between 5 August and 8 September in treatments where the starting time and duratin were varied. In addition, in 1974 the stands were given supplementary lighting during the first 2 cropping period (120 W/m ) with high power mercury lamps put on 35 days after the photoperiodic lighting was terminated. Within the first croppin period, the photoperiodic lighting influenced the quantitative distribution of productivity in all treatments by reducing the October production but increasing that of December. This apparent dual effect of photoperiodic lighting on the distribution of flower production is discused. The quantity of blooms produced during November, January or February was, depending on the starting time and duration of the photoperiodic treatment, either increased or influenced insignificantly by it. Both quantitativity and qualitativity, the photoperiodic lighting had adverse effects on the flowering of the subsequent production period (from March to May). The supplementary illumination given during the first cropping period removed most of these detrimental effects. Acta Horticulturae 71, 1977 Carnations 83

2 Introduction It is established that, under conditions of poor natural illumination, photoperiodic lighting up to the threshold for flowering induction causes the stems to draw out (Dahab, 1967). To avoid this trouble Harris S Ashford (1966) recommended a brief long-day treatment lasting 4-6 weeks and timed according to the stage of development of the shoots. Subsequently, attempts have been made in various countries (eg. Jenkins & Bjerggaard, 1970, Zimmer & Hatipoglu, 1972, Konings, 1973, Muench, 1973, Butters, 1974, Seager, 1974) to adjust the imposition of this long-day treatment according to the timing of flowering in carnations. However, the results have not come upto expectations. Depending on the time of year and the growing conditions, a limited photoperiodic treatment has produced variable results (Zimmer & Hatipoglu, 1972, Bunt, 1974, Kaukovirta, 1974 and 1975). It appears that the requirement for the duration of the photoperiodic treatment will vary according to the growing conditions (Cluench, 1973). On the basis of what has been stated above, it is requisite to determine the most favourable time to impose the long-day treatment for inducing winter flowering, and how the duration of the treatment influences flowering performance. In the following, an account will be given of experiments made at the Department of Horticulture, the University of Helsinki, with this purpose in view. Material and methods On the 7 January 1974, rooted carnation cuttings (culti- 2 var 'Scania') were planted at a rate of 44 plants/m in a peat growing medium in deep but moveable boxes measuring 60 x 120 cm. The first cut was gathered from the stands over May and June, and between and 4.6. all stems were stopped which were judged not capable of flowering by At the beginning of July, the stands were thinned to 2 leave shoots/m. In the second year of the experi- 7k

3 ment, similar pretreatments were made on the stands at the same times to ensure an evenly sized set of shoots for the illumination experiments. On the basis of the radiation level, minimum temperatures in the greenhouses were graded as follows: 5 August - 15 September C by day C at night 16 September - 30 September October - 20 February February - 28 February " - - " after 15 March Photoperiodic lighting was provided from sunrise to sun- 2 set, and the output of the lamps was 50 W/brm. In 1974, incandescent lamps were used as the light source and in 1975 HgLX 400 W lamps. In addition, after the 35 day period of photoperiodic lighting, the 1974 stands received 2 supplementary illumination at the rate of 120 W/m for 16 h/day from HgLX 400 W lamps over the entire harvesting In both years, the illumination experiments were run as two parallel experiments in different sections of the greenhouse. The amounts of radiation incident during the experiments are shown in table 1. On the basis of experiments made from period. (Kaukovirta, 1974, 1975), the timing and duration of the photoperiodic treatment were varied as follows: 1974 a 1 treatment began on 5 August and lasted 2 weeks

4 When the photoperiodic lighting was started the stems carried 3-7 pairs of leaves. Each treatment was made in B replicates, and each replicate consisted of 8 plants. The following account presents results clarifying the effects of the treatments on timing and quality of flowering from October to February, and the effects of the photoperiodic treatment on the later development of the stands, as measured by the mean of the parallel experiments. Results 1_974_expérimen^s Flower production and quality Photoperiodic lighting increased the production of blooms from October to February by % depending on the time of photoperiodic lighting. The number of flowers cut over this period was greatest in the treatment started on the 19 August and lasting three weeks (table 2 and 3). Production over the subsequent cropping period (March-May) was not significantly affected by the lighting treatments. The quality of flower measured as the weight of blooms in the first cropping period (October-February) was decreased by the lighting treatments. The weight of blooms was the lower the later the photoperiodic lighting was commenced. In contrast to this, the weight of blooms gathered over March to May was not affected significantly by the lighting treatment (table 2). The monthly distribution of flower production The photoperiodic lighting treatment had the strongest effect on the December production. The number of flowers cut in December was the greater the later the photoperiodic treatment was begun (figure 1). The December production as a proportion of production from October to February was, however, greatest when the treatment was begun on thb 12 August Ctable 3). In addition, the earliest treatment increased production in November, but 86

5 in January and February only very slightly. Whereas the latest treatment did not increase November production, it increased January production considerably. In all the photoperiodic treatments, October production was lower than in the control. 1_97_5_expe_rime_nt_s Flower production and quality The photoperiodic lighting given in the 1975 experiments increased overall production from October to February by % depending on the duration of photoperiodic illumination. The number of blooms cut from October to February was increased most by a 4 week and least by a 5 week period of photoperiodic lighting (tables 2 and 3). Even so, the relative increase during the period was smaller in the 1975 than in the 1974 experiments [table 3), where in addition to photoperiodic lighting supplementary lighting was commenced during the main cropping period. With a 3 or 4 week period of photoperiodic lighting, the production of carnations from March to May was lower than that of the control. Nevertheless, a 5 week period of photoperiodic lighting did not lower production over March to May (table 2). In the 1975 experiments, the weight of flowers from illuminated plants was lower than for the control. For production from October to February, the difference in weight between control blooms and blooms from lighted plants was greater the longer the period of photoperiodic lighting (table 2). The weight of blooms gathered during the second cropping period (March to May) was reduced by the illumination more than during the period from October to February. The monthly distribution of flower production All the photoperiodic lighting treatments increased the number of blooms gathered during November, December and January, while the numerical inciease was greatest in 87

6 December (figure 3). With only a 4 week treatment, February production was higher than in the control. For all the lighting treatments, the number of blooms gathered in October was smaller than from control carnations. Relative to the control. October production diminished with increasing duration of the illumination period (figure 3). Discussions It is clear from the results of these experiments that to induce carnations to flower during November and December under Finnish conditions, photoperiodic lighting must be started in August. This is shown by the fact that the proportion of blooms gathered in November, relative to production from October to February, increased only when the lighting was begun by the 5 August (table 3). In this respect, the result agrees with the results of illumination experiments made earlier at the Department of Horticulture (Kaukovirta, 1974, 1975). Muench (1973), too, arrives at similar results in his experiments, since a period of photoperiodic lighting started on the 2 August gave rise to a productivity peak in November, while a treatment started on the 23 August gave a peak in January. On the other hand, these findings contradict results obtained in England (Bunt, 1974) where only after August did photoperiodic lighting affect the timing rate of flower production. On the basis of the 1975 results, a photoperiodic treatment alone, given in August gave, compared to the control, more abundant flowering from November to February (figure 2), but had negative effect on the flower production and quality at the second cropping period (March to May). It is apparent that in this experiment the temperatures used, which were 6 C higher than normally used under Finnish winter conditions, were a prerequisite for shoots illuminated in August to flower during November. Likewise, the poor quality of the spring performance can be attributed to the too high temperatures in view of the poor light conditions during the 88

7 winter. This is confirmed by the results of the spring experiment of 1974, in which the photoperiodic treatment did not affect adversely the quality of the spring performance because the plants were given additional light during that part of the productive period when temperatures were higher than usual. Konings (1974), too, found that photoperiodic lighting resulted in a reduction in branching. In the treatments which had received photoperiodic lighting, the average weight of blooms gathered during the winter months was smaller than for the controls, although even the lowest weights were higher than the mean weight of g for large-flowered carnations imported to Finland. The reduction in quality, manifested as a lowering in weight of the blooms, was greatest in those photoperiodic treatments which were terminated late in the season. The reason for this is probably that in such treatments a proportion of the blooms cut between November and February had developed from shoots younger than in treatments receiving a shorter or earlier period of illumination. In accordance with this idea, Jensen and Bjerggaard (1970) have found that the quality of flower stems is poorest in the treatments where illumination has induced flowering premature with respect to the natural developmental rhythm of the shoots. The supplementary lighting given during the main cropping period of 1974 did not improve the quality, measured as the weight, if compared the quality of flowers from the experiments in 1975 which received only photoperiodic lighting. The most likely explanation is that in 1974 the radiation received after the period of photoperiodic lighting was considerably less than in In the experiments described, the number of blooms gathered in October was smaller in all the photoperiodic lighting treatments than in the controls. This difference between the controls and illuminated treatments was marked in the 1975 experiments, in which 39,5 % of the control blooms gathered during the winter were taken in October. The 89

8 probable reason for this is that by the beginning of the photoperiodic treatment the flower initiation had already occured in the most advanced shoots, and the supplementary lighting delayed the development of these advanced shoots. Accordning to Cheng and Langhans (1971), by the time the flower initial has developed into a bud, there prevails a negative correlation between the growth rate of the initial and the daylength. Thus a productive peak timed for December can be regarded as on the one hand a delayed effect on the subsequent development of shoots already initiated flowers, and on the other an enforced effect on the flowering of vegetative shoots. This apparent dual effect of photoperiodic lighting has hitherto received insufficient attention in commercial applications of photoperiodic lighting to the timing of carnation flower production. Literature Bunt, A. C., Response of carnation to light and heat. Commercial Grower 40B1: , Butters, R. E., Effects of spacing and dusk-to-dawn lighting on carnation. Grower 81: Dahab, A. M. Abou, Effects of light and temperature on growth and flowering of carnation (Dianthus c a r y o p h y l l u s L.) Pleded. Landb. hogesch. WagBningen 67-13: Gheng, L. H. and Langhans, R. W., Floral initiation, development, and associated phenomena of D i a n t h u s c a r y o p h y l l u s L. Part I - Effect of photoperiod. J. Amer. Soc. Hort. Sci. 96: Harris, G. P. and Ashford, M., Promotion of flower initiation in the glasshouse carnation by continuous light. J. Hort. Sci. 41: Jensen, K. and Bjerggaard, A., Langdagabehandling of neiliker. Tidskr. Planteavl. 74:

9 Kaukovirta, E., Rate of carnation shoot growth as affected by variation in light conditions during the season of high light intensity. Acta Horticulturae 43i Kaukovirta, E., Erilaisten valokäsittelyjen vaikutus neilikan kehitykseen. Puutarha 76: Konings, H., Praktijkproeven met belichten van anjers. Vakblad voor de Blosministerij. 28, 50:12-13,15. Muench, 3., Die Steuerung des Blühtenmins. Erwerbsgärtner 27: Seager, J. C. R., Carnation illumination. Gardeners' Chronicle 175, 12: Zimmer, K.. and Hatipoglu, A., Edelnelken: Einfluss zusätzlicher Belichtung auf die Entwicklungsdauer. GartBnwelt 72: Table 1 - Total radiation during the aain experimental perioc". Ionth August September October November December January February

10 Table - 3ifeot of the illumination treatments on flower production and weight of blooms curing the first (October -February) and the subsequent (March - May) harvest oeriod. Photoperiodic illumination Supple- The first harvest period The subsequent harvest starting mentary light ^ V<eigEt ol welgire ot from Duration Blooms/pl blooms g Blooms/pl blooms g Experiments in 1974 Check a * a a 5 August 2 weeks " 21. r- b o a O 12 " 2 " b 21. Q b a 19 " 3 " b C a Experiments in 1975 Check a 23. o a 5 August 3 weeks - 4. o" 22. o b b I! 4 " " C I C 19. o d c x) tleans not followed by the same letter differ si lificantly at the 5 % level.

11 Table 3 - Monthly distribution of flower production as persentage from the total in the first harvest period (October - February) as affected by the illumination treatments. Photoperiodic illumination Supple- Total yield Monthly yield as % from the total mentary N< Qf Starting light blooms/ from Duration sgm rei Oct Nov Dec Jan Febr Experiments in 1974 Check August 2 weeks " ti " 3 " Experiments in 1975 Check August 3 weeks ! 4 " I 5 " vo

12 > ginning of photoperiodic lighting differ significantly at the 5% levol. Effect of the illumination treatments on the monthly distribution of flower yield. Experiments in 197^-

13 o «6 a 0) <0 o c 0C UJ 0. co (t kj s o 13 -J «u. <0 «u. <U O g % o To 20 LJ b Figure 2 - Effect of the illumination treatments on the monthly distribution of flower yield. Experiments in