THE EFFECT OF THE MANNER OF BULB CHILLING ON NARCISSI ANTHESIS

Anita Woźny
Department of Ornamental Plants and Vegetable Crops, Faculty of Agriculture and Biotechnology, University of Science and Technology, Bydgoszcz, Poland

ABSTRACT

The experiment studied the effect of a modified manner of bulb chilling on the flowering of narcissus, 'Dick Wilden' and 'Flower Drift' cultivars belonging to the group of double daffodils, and 'Gigantic Star' from the group of wild daffodils. Four dates of bulb forcing were applied: early, mid-early, late and very late. One group of bulbs was chilled 'dry' at the temperature of +5°C and these were placed loose in boxes, while the other was chilled 'wet', meaning together with the subsoil. The experiment showed that bulb chilling together with the subsoil contributed to a few days' earlier anthesis of all three cultivars, and to an increased yield of flowers of 'Gigantic Star' and 'Flower Drift' only in the mid-early date of forcing.

Key words: narcissi, forcing, wet chilling, dry chilling.

INTRODUCTION

Temperature is the basic external factor affecting the growth and development of ornamental bulb plants. Processes taking place at a given stage of bulb development are a result of the thermal conditions occurring at a given time and earlier [1]. Chilling is a starting signal for a number of processes that cause fast growth of the shoots and the progeny bulbs. Low temperature, through its influence on the production of auxines, is necessary for the proper development of tulip flowers and pollen production [11]. Treating ornamental bulb plants with low temperature according to the recommendations for particular species guarantees uniform flowering, followed by one harvest. When narcissi bulbs are not chilled and they are stored at the temperature of 17°C this leads to considerable weakening of the flowering, lack of shoot elongation, bud decay and other physiological disturbances [7]. In the case of tulips, longer chilling leads to earlier flowering and longer shoots [12]. For a number of years, the horticultural practice makes use of a special method of forcing the narcissi chilled dry, without any subsoil at the temperature of +5°C. In this way, plants flowering very early can be obtained – already at the beginning of December. However, the fault of this method is a big proportion of bulbs that do not flower: 30, or even 50%. A modified manner of bulb chilling is increasingly popular among gardeners. This is wet chilling (together with the subsoil), which hastens the flowering and increases the number of flowering bulbs in comparison to the first method. Experiments on tulips and narcissi conducted earlier pointed to a positive effect of the modified manner of bulb chilling in forcing these plants [2,9,10].

The assortment of narcissi cultivars intended for forcing for cut flowers is extending annually. Very ornamental double cultivars enjoy an increasingly greater popularity.

The purpose of the present experiment was to study the effect of the modified method of chilling bulbs on the anthesis of three narcissi cultivars forced in four dates.

MATERIAL AND METHODS

The experiment used four dates of bulb forcing: early – from 12 November, mid-early – from 4 December, late – from 25 December, 2007, and very late – from 15 January, 2008. Three cultivars: 'Dick Wilden' and 'Flower Drift' from the group of double narcissi, and a cultivar of wild narcissi – 'Gigantic Star' were used. Before forcing, the bulbs were chilled for 10 weeks at the temperature of +5°C. One part of the bulbs was chilled according to the principles of the special method, that is dry – placed loose in boxes, while the other part was chilled wet, together with the subsoil, in pots of the dimensions 7×7×8 cm, filled with deacidified (pH 5.5–5.6) high peat. After finishing the dry chilling, the bulbs were planted into pots, and next together with the bulbs chilled wet, they were forced in a glasshouse. For each cultivar, one experimental combination (manner of bulb chilling × date of forcing) included 30 bulbs – 6 repetitions, 5 bulbs each. The period of forcing was calculated on the basis of the weighed mean date when the plants achieved the stage of commercial maturity. It was marked by the moment when slightly opened buds began to take colour. Besides, the number of losses were counted, i.e. the number of bulbs that did not give flowers or gave flowers with the symptoms of physiological diseases. The obtained data expressed in percents were transformed according to Freeman – Tukey in order to be verified statistically. Results of the measurements were analyzed statistically using program STATISTICA.

RESULTS

The studies showed the effect of the manner of bulb chilling on the number of days of forcing the studied cultivars of narcissi. The bulbs forced wet flowered 3 days earlier as compared to the bulbs chilled without the subsoil (Figs. 1, 2, 3). At the same time it was observed that in all studied cultivars the period of narcissi forcing in a glasshouse got clearly shorter with a later date of forcing. In the case of 'Dick Wilden' (Fig. 4) and 'Flower Drift' (Fig. 5) cultivars, no interaction was shown between the manner of bulb chilling and the date of forcing. On the other hand, the statistical analysis of the obtained results concerning 'Gigantic Star' cv. (Fig. 6) indicated a significant effect of the interaction between the two studied factors. In the early date of forcing, no effect of bulb chilling was observed on anthesis. In the other dates, a positive effect of bulb chilling together with the subsoil was found, which led to earlier anthesis. In the mid-early date of forcing, the bulbs chilled wet flowered 5 days earlier, in the late date they flowered 4 days earlier, and in the very late date – 2 days earlier as compared to the bulbs chilled dry.

In the present experiment, the proportion of flowering plants of 'Dick Wilden' cv. depended on the date of forcing. The smallest number of flowers was obtained from the bulbs forced in the early date. In the other dates, the flowering was better and it was at a similar level (Fig. 7).

With a later date of bulb forcing of 'Flower Drift' cv,. the proportion of flowering plants was greater. In the early and later dates of forcing, no differences in the number of collected flowers were observed depending on the manner of bulb chilling. On the other hand, in the mid-early date, more cut narcissi of 'Flower Drift' cv. were obtained from the bulbs chilled wet. In the case of bulbs chilled in a very late date, a reverse reaction was observed (Fig. 8).

The observations showed that independent of the date of forcing, the bulbs of 'Gigantic Star' cv. chilled wet together with the subsoil flowered better. At the same time it was found out that forcing the bulbs of the same cultivar in the mid-early date was connected with a considerable decrease of the proportion of flowering plants as compared to the other dates. In the above-mentioned date the analysis of interaction showed that a positive effect of wet bulb chilling was marked especially clearly (Fig. 9).

DISCUSSION

Results of the present experiment only partly confirmed earlier reports concerning considerable improvement of the yielding and significant acceleration of narcissi anthesis as a result of wet bulb chilling together with the subsoil.

Estimation of the usefulness of the so modified method was made in earlier years, both while forcing the narcissi in artificial [2,6] and natural light [10]. In all the cultivars examined then, bulb chilling together with the subsoil throughout the 10-weeks' period of treating them with a low temperature led to considerable shortening of the forcing period (as a result of earlier rooting) and better yielding. The developing roots can be the place of gibberellins biosynthesis; possibly they supply the elements necessary to create these regulators [3]. Saniewski [8] showed that gibberellins take part in the processes induced by chilling, for example in elongation of the tulip flower shoot and in anthesis. Earlier results, however, were not confirmed in the studies conducted with 'Dick Wilden', 'Flower Drift' and 'Gigantic Star' cultivars. The effect of wet bulb chilling depended above all on the cultivar as well as on the date of narcissi forcing. Relatively little (maximum, up to 5 days) acceleration of anthesis of bulbs chilled wet is worth noticing. An increase of the proportion of plants flowering as a result of chilling the planted bulbs was observed in cultivars 'Gigantic Star' and 'Flower Drift' only in the mid-early date of forcing. The probable cause of the lack of the same positive reaction for all the studied cultivars is the cultivar specificity, and hence individual requirements as for the length, manner and temperature of bulb chilling. In their studies, Rees and Hanks [7] found out that good quality narcissi to be obtained within 30 days are possible after 12- or 15-days' period of bulb chilling at the temperature of +5°C. According to Woźny and Zalewska [10], for the proper growth and anthesis of narcissi it is enough to chill the bulbs at the temperature of 5°C for only 10 weeks, together with the subsoil. On the other hand, Krause [4] recommends chilling the bulbs for 9–12 weeks, according to the special dry method. In the present experiment, like in previous years, the bulbs were chilled dry or wet for 10 weeks. In her studies, Nitschke-Leszczyńska [5] pointed to the possibility of forcing 'Tête á Tête' cv. of narcissi 10 weeks after bulb chilling without the subsoil at the temperature of +5° as well as together with the subsoil at the temperatures of +5°C and +9°C. At the same time, she observed that a 10-weeks' period of chilling the bulbs of 'Minnow' cv. at the temperature of +5°C was the cause of poor anthesis. Lack of a uniform reaction of the narcissi cultivars chosen for the studies can, therefore, result from the fact that the chilling period was too short. This only confirms the hypothesis that the differences between the cultivars today are so big that their individual treatment is necessary.

CONCLUSIONS

1. Narcissi reaction to wet bulb chilling, together with the subsoil, for 10 weeks at the temperature of +5°C depends on the cultivar and the date of forcing.

2. Wet bulb chilling leads to a few days' acceleration of anthesis of 'Dick Wilden', 'Flower Drift' and 'Gigantic Star' narcissi cultivars.

3. Using a modified manner of bulb chilling increases the flower yield of 'Gigantic Star' and 'Flower Drift' cvs. only in the mid-early date of forcing.

REFERENCES

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Accepted for print: 4.05.2009

Responses to this article, comments are invited and should be submitted within three months of the publication of the article. If accepted for publication, they will be published in the chapter headed 'Discussions' and hyperlinked to the article.