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A THESIS FOR THE DEGREE OF MASTER OF SCIENCE
Effect of Pre-cooling for the Forcing
and Flowering of Paeonia lactiflora ‘Taebaek’
‘태백’ 작약의 촉성 재배와 개화를 위한 예냉 처리의 효과
BY
JU HYUN PARK
FEBRUARY, 2013
MAJOR IN FLORICULTURE AND LANDSCAPE PLANTS DEPARTMENT OF PLANT SCIENCE
Effect of Pre-cooling for the Forcing and Flowering of
Paeonia lactiflora ‘Taebaek’
UNDER THE DIRECTION OF DR. KI SUN KIM
SUBMITTED TO THE FACULTY OF THE GRADUATE SCHOOL OF SEOUL NATIONAL UNIVERSITY
BY JU HYUN PARK
MAJOR IN FLORICULTURE AND LANDSCAPE PLANTS DEPARTMENT OF PLANT SCIENCE
THE GRAUATE SCHOOL OF SEOUL NATIONAL UNIVERSITY
JANUARY, 2013
APPROVED AS A QUALIFIED THESIS OF JU HYUN PARK
FOR THE DEGREE OF MASTER OF SCIENCE BY THE COMMITTEE MEMBERS
FEBRUARY, 2013 CHAIRMAN Changhoo Chun, Ph.D. VICE-CHAIRMAN Ki Sun Kim, Ph.D. MEMBER
i
Effect of Pre-cooling for the Forcing
and Flowering of Paeonia lactiflora ‘Taebaek’
Ju Hyun Park
Department of Plant Science, Seoul National University
ABSTRACT
These studies were conducted to investigate the effect of pre-cooling
temperature on the flowering and cut flower quality of Paeonia lactiflora ‘Taebaek’ for forcing culture. Crowns of P. lactiflora ‘Taebaek’ were placed into five temperature regimes in mid September and October, 0 °C for 2 weeks (C0,
non pre-cooling, control); open field for 2 weeks (NT); pre-cooling at 15 °C for 2
weeks (P15); 15 °C for 1 week → 10 °C for 1 week (P15→10); 10 °C for 2 weeks
(P10) to determine the optimum pre-cooling temperature for winter flowering.
Crowns were also placed into three pre-cooling regimes in early July, C0, NT, and
P10 to determine the optimum pre-cooling temperature for autumn flowering.
After pre-cooling treatment, all plants were subjected to a temperature of 0 °C for
6 weeks for dormancy breaking. Plants which had been subjected to each chilling
treatment were maintained in a temperature controlled greenhouse or open field.
ii
increased the number of floral organs. At the end of the pre-cooling period,
stamen primordia were formed in some plant of P15→10 and P10 in October
pre-cooling treatment, while no difference was observed in renewal bud
differentiation in C0, and NT. Almost all flower buds were aborted from their
stems in C0, and NT. On the other hand, pre-cooling treatment promoted
flowering percentage more than the base limit, 80% for commercial production.
Pre-cooling at 10 °C was the most effective in promoting flower percentage. The
flowering time of P10 was earliest (January 13, 26 and November 6, respectively).
Also, pre-cooling increased the cut-flower quality. From these results, pre-cooling
at 10 °C for 2 weeks was recommended as the optimal treatment to promote
flowering percentage with improving the cut-flower quality in forcing culture for
winter or autumn flowering
Key words: cold treatment, dormancy breaking, flower bud abortion, herbaceous
peony, renewal bud development
iii
CONTENTS
ABSTRACT ··· i CONTENTS ··· iii LIST OF TABLES ··· iv LIST OF FIGURES ··· v INTRODUCTION ··· 1 LITERATURE REVIEW ··· 3MATERIALS AND METHODS ··· 7
RESULTS ··· 18
DISCUSSION ··· 35
LITERATURE CITED ··· 38
iv
LIST OF TABLES
Table 1. Experimental layout of P. lactiflora ‘Taebaek’ for winter forcing culture
··· 14
Table 2.Experimental layout of P. lactiflora ‘Taebaek’ for autumn forcing culture
··· 15
Table 3.Effect of pre-cooling on the flowering of P. lactiflora ‘Taebaek’ in winter
forcing culture ··· 24
Table 4. Effect of pre-cooling on the flower quality of P. lactiflora ‘Taebaek’ in
winter forcing culture ··· 27
Table 5. Effect of pre-cooling on the flowering of P. lactiflora ‘Taebaek’ in
v
LIST OF FIGURES
Fig. 1. Dormant crowns of P. lactiflora ‘Taebaek’ with renewal buds (A) and the
growth in a plastic box (B) of ··· 10
Fig. 2. Soil temperature during the experimental period at the open field in 2011
··· 11
Fig. 3. Havesting on March 14, 2012 by forcing culture (A) and the growth in an
open field (B) of P. lactiflora ‘Taebaek’ ··· 12
Fig. 4. Soil temperature during the experimental period at the open field in 2012
··· 13
Fig. 5. Effect of pre-cooling on the growth of renewal buds of P. lactiflora ‘Taebaek’ in winter forcing culture ··· 19 Fig. 6. Effect of September pre-cooling on the development of renewal buds of P.
lactiflora ‘Taebaek’ in winter forcing culture ··· 20
Fig. 7. Effect of October pre-cooling on the development of renewal buds of P.
lactiflora ‘Taebaek’ in winter forcing culture ··· 21
Fig. 8.Flower development of P. lactiflora ‘Taebaek’ in winter forcing culture · 25
Fig. 9. Effect of pre-cooling on the proportions of floral development of P.
lactiflora ‘Taebaek’ in winter forcing culture ··· 26
Fig. 10. Flowering of P. lactiflora ‘Taebaek’ on January 13, 63 days after
treatment ··· 28
Fig. 11. Flowering of P. lactiflora ‘Taebaek’ on January 28, 50 days after
treatment ··· 29
vi
‘Taebaek’ in autumn forcing culture ··· 31 Fig. 13.Effect of pre-cooling on the abortion of P. lactiflora ‘Taebaek’ in autumn
forcing culture ··· 33
Fig. 14. Flowering of P. lactiflora ‘Taebaek’ on November 9, 68 days after
1
INTRODUCTION
Peonies are common herbaceous perennials that have been used as garden or
medicinal plants (Barzilay et al., 2002). Although cut peony flowers are highly
valued in the market, its natural flowering period is relatively short from May to
June in temperate regions of the northern hemisphere. Therefore, cut peony
flowers are imported from Australia and the South America at high prices, except
during the natural flowering season (Bae et al., 2008). Extending the flowering
time of herbaceous peony is critical for cut flower supply to the markets during
off-season.
Flower buds of peony are initiated after the old flowers senesce in early
summer, continue to develop until they enter the endodormancy in late autumn
(Byrne and Halevy, 1986). During the winter, they require low temperature and
prolonged period (2 to 3 months) of chilling under natural field condition to break
their bud dormancy for shoot growth and flower development (Evans et al., 1990).
Forcing culture for cut peony flower production has been established by natural
low temperature or artificial cold storage (Bae et al., 2008; Byrne and Halevy,
1986; Cheng et al., 2009; Evans et al., 1990; Fulton et al., 2001; Halevy et al.,
2002; Kamenetsky et al., 2003). However, this system has several problems.
Firstly, chilling treatment does not accelerate the differentiation, growth and
development of flower bud (Namikawa, 1988). Secondly, flower bud of some
peonies aborted at a high rate (Cheng et al., 2009; Evans et al., 1990). Thirdly,
GA3 treatment tended to lighten the flower color (Aoki, 2009). Therefore, these treatments for forcing are not always economically advantageous.
2
The environmental requirements for flowering of many herbaceous perennials
have been evaluated under controlled conditions owing to their economic value in
horticulture (Cameron et al., 2007). Gradually decreasing temperature appears to
be the main environmental signal impacting endodormancy induction and release
in crown buds (Foley at el., 2009). In addition, endodormancy is also a
prerequisite for fulfillment of floral competence in response to floral-inducing. In
forcing tree peony or tulip, pre-cooling temperature prior to the cold treatment
promoted flower bud differentiation, accelerating the sprouting and flowering
(Aoki, 1992 a, b; Aoki and Yoshino, 1984; Hosoki et al., 1984).
In herbaceous peonies, however effects of pre-cooling temperature on forcing
culture are unknown yet. Therefore, the objectives of the present study were (1) to
investigate the optimum time of pre-cooling treatment, (2) to determine the
optimum temperature of pre-cooling treatment on the flower bud growth and
development, and (3) ultimately to prolong the marketing periods by extending
3
LITERATURE REVIEW
Characteristics of P. lactiflora
The genus Paeonia belongs to the family Paeonaceae and consists of 33
species. Species are divided into tree and herbaceous peonies. Herbaceous peonies
are derived primarily from P. officinialis and P. lactiflora (Huxley et al., 1992). P.
officinialis is native to southern Italy and France, while P. lactiflora is native to
China, Tibet, and Siberia. Most modern ornamental and cut flower species are
derived from P. lactiflora (Rogers, 1995), which is cold hardy and long-lived
perennial. The species commonly grow well in a wide range of soil types and
climates (Kapinos and Dubrov, 1993). Their bushy green, pink, or red stems grow
80-100 cm tall and each cultivar has leaves of a particular shade of green and a
shape ranging from broad to grass-like. Flowers colors are white, yellow, pale
yellow, pink, vivid purplish red, and deep red, thought red colors have
occasionally been seen in the wild. The types of flowers are divided according to
the petal shape: single, Japanese, anemone, semi-double, semi-rose, crown, bomb,
and double. Various peonies have widely been grown in temperate climate regions,
and bloom from late April until early June (Kamenetsky et al., 2003).
Peonies are propagated by root divisions with two to five buds (eyes) and one
to two large roots per unit (Rogers, 1995). In herbaceous peony, flower bud
initiation begins in the perennial ‘crown’ in late summer, as the leaves begin to
senesce, then flower bud development continues until the plant enters dormancy
4
temperatures (chilling) has been experienced. Once sufficient cold temperature
has been accumulated to break dormancy, the buds grow out produce shoots and
flowers during the warmer temperatures of spring (Barzilay et al., 2002; Byrne
and Halevy, 1986; Halevy et al., 2002; Wilkins and Halevy, 1985). P. lactiflora, a
common and popular garden plant, was a highly valued cut flower in the USA and
Asia. Peonies also have been used as a medicinal plant for many years. Recently
the demand for their cut flowers has increased due to their beauty.
Forcing Culture for Cut Flower Production
Cut flower peonies are highly valued in the market, but they are available for
only a short period (2-3 weeks) in late spring and early summer. Forcing cultures
for breaking bud were dormancy attempted to prolong the marketing period by
advancing the flowering time. Peonies have been reported to flower successfully
in areas with at least 2 to 3 months of freezing temperatures (Post, 1952). Chilling
saturation was achieved at 42 chill units for ‘Sarah Bernhardt’ and at 36 chill units
for ‘Duchesse de Nemours’ (Fulton et el, 2001). Byrne and Halevy (1986) found
that dormancy of two cut flower cultivars of containerized herbaceous peony
(‘Festiva Maxima’ and ‘Sara Bernhardt’) was broken after 8 weeks of storage at 1
or 5 °C, and upon transfer to a greenhouse heated to 17 °C, they bloomed in 6 to
10 weeks. However, many of the flowering shoots did not reach anthesis and most
flower buds aborted. Evans et al. (1990) advanced shoot emergence of non-chilled
crowns by drenching them with 2000 mg∙L-1 GA3, but all flower buds again aborted. GA3 is known to partially and sometimes even completely replace the
5
cold requirement for breaking dormancy and for flower initiation (Metzger, 1995).
Although these treatments enabled to flower in winter, the flowering rate was still
lower than 80%, the base limit for commercial production
Pre-cooling Treatment for Forcing Culture
One major problem associated with forcing P. lactiflora has been flower
abortion. Flower abortion commonly refers to the arrest of perfect flower
development and is an important yield-limiting factors in many crops (Kawakatsu
et al., 2012). Flower abortion of flower buds and flowers occurs in early forcing
culture.
As a model perennial, leafy spurge plants in nature enter the endodormancy
when the average daily soil temperature ranges from 15 to 10 °C to prevent crown
buds during the transition from autumn to winter. And then, cold temperature (5 to
0 °C) associated with the transition from endodormany to ecodormancy
(Anderson et al., 2005). Therefore, cold treatment alone has no effect on regrowth
and flowering. Plants required decreasing temperature followed by cold treatment
for rapid growth and flowering (Foley et al., 2009).
Flower bud differentiation and development vary remarkably from year to year
and consequently the flowering percentage and cut-flower conditions were
presumed to be responsible for the variation. Under natural condition, floral
initiation of peony starts in early- September in temperate regions. Sepals, petals,
and stamens differentiate sequentially, and pistil primordia are initiated in next
6
pre-cooling and chilling treatment was effective for tree peonies rapid forcing.
They also found that flower bud differentiation was promoted by pre-cooling at
15 °C for 10 days. Therefore, pre-cooling temperature appears to be the most
important climatic variable to which peonies flowering response (Byrne and
Halevy, 1986). Thus, the objectives of this study were to investigate the effect of
pre-cooling temperature on the flowering and cut flower quality of Paeonia
7
MATERIALS AND METHODS
Plant Materials
Dormant crowns of P. lactiflora ‘Taebaek’ were purchased from a private farm
in Jinju, Korea (35˚ 82' S, 130˚ 85' E) on November 6, 2009. Each crown was
divided into two, each with 4-5 buds, and the two divisions were planted in a
separate plastic box (60 × 39 × 23 cm), filled with coarse peatmoss ‘Tref Go N1’
(Jiffy Products International, Moerdijk, Netherlands). The dormant crowns were
20-27 cm in average (Fig. 1). Each box received 500 mL (pH 6.0, EC 1.6 dS∙m-1) of a water soluble fertilizer Technigro® 16N-17P-17K (Sungro Ltd., Vancouver, British Columbia, Canada) weekly after planting. The plants were watered when
the surface of the potting medium showed dryness and was monitored until the
plants had finished.
Experiment 1. Optimum pre-cooling timing and temperature of Paeonia lactiflora for winter flowering
These experiments were conducted in a greenhouse located at the Experimental Farm of Seoul National University, Suwon, Korea (37˚ 27' S, 126˚ 99 'E) from September 10, 2011 to February 28, 2012. Before the experiment started, the
plants were grown in containers for 3 years in an open filed in Suwon, Korea. The
daily average soil temperatures were received from the Suwon Meteorological
Station located near to the open field (Fig. 2).
Experiment 2. Optimum pre-cooling timing and temperature of Paeonia lactiflora for autumn flowering
8
Farm of Seoul National University, Suwon, Korea (37˚ 27' S, 126˚ 99 'E) from July 4 to November 9, 2012. The plants in containers where cut flowers were
harvest during the previous forcing culture (Fig. 3A). The dormant crowns were
grown in a greenhouse before treatment. The daily average soil temperature was
monitored at 30 min intervals using a data logger (Watch Dog Model 450,
Spectrum Technologies, Inc., Plainfield, IL, USA).
Pre-cooling Treatment
Experiment 1. To determine the optimum pre-cooling time and temperature of
P. lactiflora ‘Taebaek’ for winter forcing culture, the crowns, planted in bulb boxes with media, were randomly allocated into treatments on September 16 and
October 14, 2011. Layout for winter flowering is shown in Table 1. The
treatments were as follows: chilling at 0 °C for 2 weeks (C0, non pre-cooling,
control); open field for 2 weeks (NT); pre-cooling at 15 °C for 2 weeks (P15);
15 °C for 1 week followed by 10 °C for 1 week (P15→10); and 10 °C for 2 weeks
(P10). After pre-cooling treatment, all plants were chilled at 0°C for 6 weeks for
breaking dormancy, and then were grown in the greenhouse under natural light
conditions. Each treatment contained eight plants. The media were watered as
needed to keep them moist. During the experiment, maximum and minimum day
lengths were 11.5 and 9.7 h, respectively. The air temperature within the
greenhouse was monitored at 30 min intervals using a data logger (Watch Dog
Model 450, Spectrum Technologies, Inc., Plainfield, IL, USA). The maximum
(day) and minimum (night) temperatures of the greenhouse were maintained at 23
9
Experiment 2. To determine the optimum pre-cooling time and temperature of
P. lactiflora ‘Taebaek,’ for autumn forcing culture, the crowns, planted in bulb
boxes with media, were randomly allocated into treatments in July 7, 2012. The
layout for autumn flowering is shown in Table 2. The treatments were as follows:
chilling at 0 °C for 2 weeks (C0, no pre-cooling, control); open field for 2 weeks
(NT); and 10 °C for 2 weeks (P10). After pre-cooling treatment, all plants were
chilled at 0°C for 6 weeks for dormancy breaking, and then were grown in the
open field (Fig. 3B). Each treatment contained sixteen plants. The media were
watered as needed to keep them moist. The daily average air temperature was
received from the Suwon Meteorological Station located near to the open field
10
Fig. 1. Dormant crowns of P. lactiflora ‘Taebaek’ with renewal buds (A) and the
growth in a plastic box (B). Arrows indicate the renewal buds.
11
Fig. 2. Soil temperature during the experimental period at the open field in 2011. 09/19 09/26 10/03 10/10 10/17 10/24 10/31 Tempe ratur e ( o C) -10 0 10 20 30 40 Average Maximum Minimum
12
Fig. 3. Harvesting on March 14, 2012 by forcing culture (A) and the growth in an
open field (B) of P. lactiflora ‘Taebaek’
13
Fig. 4. Soil temperature during the experimental period at the open field in 2012. 09/03 09/10 09/17 09/24 10/01 10/08 Tem perautre (o C) 5 10 15 20 25 30 35 Average Maximum Minimum
14
Table 1. Experimental layout of P. lactiflora ‘Taebaek’ for winter forcing culture. Treatments Pre-cooling treatment Cold treatment Forcing condition C0 0 ℃ (2 weeks) → 0 ℃ (6 weeks) → 20/15 ℃ (day/night) NT Natural temperature (2 weeks)
P15 15 ℃ (2 weeks)
P15→10 15 ℃ (1 week) →10 ℃ (1 week)
15
Table 2. Experimental layout of P. lactiflora ‘Taebaek’ for autumn forcing culture.
Treatments Pre-cooling treatment Cold treatment Forcing condition C0 0 ℃ (2 weeks) → 0 ℃ (6 weeks) → 20/15 ℃ (day/night) NT Natural temperature (2 weeks)
16
Measurements and Data Collection
Experiment 1. Renewal bud length was measured and flower bud
differentiation and development were monitored using a stereomicroscope (Carl
Zeiss, Jena, Germany). Four flower buds of P. lactiflora ‘Taebaek’ were sampled
every 2 weeks, from the starting of pre-cooling until the end of cold treatment.
The number of days to bud sprouting (DTS), bursting (DTB) harvesting (DTH),
and flowering (DTF) from the date of transfer to the greenhouse were measured.
Percent flowering, abortion, plant height, stem diameter, and flower diameter
were also measured. The number of shoots and cut flowers per plant, petal
number, and vase life were counted for each treatment. Bud sprouting was defined
as shoot emerged above-ground. Harvest day was defined as when the petal of a
flower bud was visible. Plant height and flower stem diameter below the flower
bud were measured when the flower buds reached approximately 25 mm. Cut
flower stems were held in a controlled environment room at 20 ± 2 °C, with a
light level at bench height of 20-25 µmolm-2s-1 provided by cool white fluorescent tubes, and a 12-h photoperiod. The end of vase life was defined as the time when
petals became wilted, browned, or had abscised.
Experiment 2. Four flower buds of P. lactiflora ‘Taebaek’ were sampled every
2 weeks, from the starting of pre-cooling until the end of cold treatment. Renewal
bud length was measured. The number of days to bud sprouting (DTS), bursting
(DTB), harvesting (DTH), and flowering (DTF) from the date of transfer to the
greenhouse were measured. Percent flowering and abortion were measured. The
number of shoots and cut flowers per crown were counted for each treatment. Bud
17
as when the petal of a flower bud was visible. Plant height and flower stem
diameter below the flower bud were measured when the flower buds reached
approximately 25 mm.
Experimental Design and Data Analysis
The experiment was conducted as a completely randomized design with eight
(Experiment 1) or sixteen (Experiment 2) replicates per treatment during the
forcing. The SAS version 9.2 (SAS Institute INC., Cary, NC, USA) was used to
perform analysis of variance (ANOVA) and general linear models (GLM). When
significant differences occurred, the means were separated using Duncan’s
multiple range tests at the 5% level. Analysis and graph module were made using
18
RESULTS
Experiment 1. Optimum pre-cooling timing and temperature of Paeonia lactiflora for winter flowering
Growth and Development of the Underground Renewal Bud
Renewal buds on the crown were protected by 4-8 specialized cover leaves
which firmly enveloped the inside of the bud. In September pre-cooling treatment,
the renewal bud length increased by 12.4% in P10, while plants without
pre-chilling (C0 and NT) did not significantly show the increase (Fig. 5A). In
September 16, apical meristem produced sepals (Fig. 6A), indicating that flower
bud initiation had already begun. At the end of pre-cooling treatments (after
2weeks), the differentiation of petals was observed in P10 treatment, while no
difference was observed in renewal bud differentiation among C0, NT, P15, and
P15→10 treatments (Fig. 6B-F).
In October pre-cooling treatment, the renewal bud increased by 17.2% (Fig.
5B) and began to produce stamen in P10 (Fig. 7F) after pre-cooling treatment.
Also, petals or stamens were observed in P15 or P15→10, respectively, at the
same time (Fig. 7D-E). These results indicated that the growth and development
19
Fig. 5. Effect of pre-cooling on the growth of renewal buds of P. lactiflora ‘Taebaek’ in winter forcing culture. September pre-cooling (A) and October cooling (B). Vertical bars are standard errors of the means (n=4). For
pre-cooling treatment, refer to Table 1.
Weeks after treatment
0 2 4 6 8 0 5 10 15 20 25 Bud g row th r ate ( % o f in iti al len gt h) 0 5 10 15 20 25 C0 NT P15 P15→10 P10 A B
20
Fig. 6. Effect of September pre-cooling on the development of renewal buds of P.
lactiflora ‘Taebaek’ in winter forcing culture. These pictures are samples on
September 16 at start (A), on September 30 after pre-cooling, C0 (B), NT (C),
P15 (D), P15→10 (E), and P10 (F), respectively. Se: sepal; Pe: petal. White
bars = 0.5 mm. A B C D E F Se Se Se Se Se Se Pe
21
Fig. 7. Effect of October pre-cooling on the development of renewal buds of P.
lactiflora ‘Taebaek’ in winter forcing culture. These pictures are samples on
October 14 at start (A), on October 28 after pre-cooling, C0 (B), NT (C), P15
(D), P15→10 (E), and P10 (F), respectively. Se: sepal; Pe: petal; St: stamen.
White bars = 0.5 mm. A B C D E F Se Se Se Se Se Se Pe Pe Pe St St
22
Plant Growth and Flowering
Day to sprouting, bursting, harvest, and flowering of forced peony are shown
in Table 3. In September pre-cooling treatments, sprouting or bursting from plants
of P10 were about five days earlier than those of C0 or NT. Plants of P10 were
the earliest in sprouting (12 days) and bursting (20 days). Pre-cooling
temperatures significantly affected the flowering date. Anthesis occurred after
61-65 days,even when the plants were exposed to P15, P15→10, or P10. Flowering
date of P10 was January 11, 13 days earlier than that of C0 (Fig. 10A-D). In
October pre-cooling treatments, pre-cooled plants tended to be slightly earlier in
sprouting and bursting, though no significant difference was found. However,
pre-cooling treatments hastened flowering about two weeks and was very effective.
Plants of P10 were the earliest in flowering (January 26) (Fig. 11A-D).
In recording flower development, we differentiated among fully developed
flowers: Flower buds that were aborted in the early stages during their
development from flower buds that were aborted in the later stages of their
development (Fig. 8A-C). Percent flowering generally increased with pre-cooling
treatments. Among September pre-cooling treatments, maximum flowering was
achieved at P10, where about 3 flowers were obtained per plant (Table 4). Thus,
80.9% of the stem reached anthesis at this treatment, while 19.1% of them aborted
their flowers in the early or late stages of development. On the other hand, only
34.4% of flowers reached anthesis (about 1.25 flowers per plant) in NT (Fig. 9A).
Also, flowering percent of C0 and NT in October were 40% and 48.6%,
respectively, whereas, the highest rate of harvestable flowers of P10 was 89.6%
23
Cut Flower Quality
Table 4 shows the effect of pre-cooling on the cut flower quality. Cut flower
qualities (stem height, diameter, flower diameter, petal number and vase life, etc.)
were affected by pre-cooling treatments. In September pre-cooling, stem height
and diameter at flowering was maximal at P10 (71.0 and 0.5 cm, respectively).
Plants of C0 or NT resulted in significant reduction in stem height and diameter.
Flower diameter and petal number also tended to be higher in pre-cooling
treatments. Vase life was extended from 1 (C0 or NT) to 4 days (P10). However,
there was no significant difference in shoot numbers among treatment significant.
The same tendency has also been observed in October pre-cooling treatments. Cut
flower quality was superior in P10. Stem height and diameter was maximal at P10
(68.3 and 0.48 cm). Also, flower diameter and petal number were the highest at
24
Table 3. Effect of pre-cooling on the flowering of P. lactiflora ‘Taebaek’ in winter forcing culture.
z
Refer to Table 1. y
The number of days from the date of transfer to the greenhouse. x
Mean separation within columns by Duncan’s multiple range test at P = 0.05 NS, *, **, ***
Non-significant or significant at P = 0.05, 0.01 or 0.001, respectively. Transferring date Treatment z Days to
y
sprouting bursting harvest flowering Sep. 16. C0 19.6 a x 27.0 a 69.2 a 74.3 a NT 16.2 ab 25.1 ab 68.0 a 71.7 ab P15 14.3 b 24.0 ab 67.6 a 65.1 ab P15→10 14.5 b 22.8 bc 61.8 a 63.5 bc P10 12.5 b 20.0 cd 55.1 ab 61.1 bc Oct. 14. C0 15.5 b 19.5 d 64.6 a 66.8 ab NT 15.2 b 19.3 d 57.8 ab 61.8 bc P15 14.5 b 19.1 d 47.5 b 51.8 cd P15→10 12.8 b 19.0 d 46.6 b 51.0 cd P10 12.8 b 18.1 d 44.3 b 48.8 d Significance
Transferring date (A) ns *** *** ***
Treatment (B) ** * ** *
25
Fig. 8. Flower development of P. lactiflora ‘Taebaek’ in winter forcing culture.
Flower abortion in earlier (A) and later (B) stages, and normal flower bud (C).
26
Fig. 9. Effect of pre-cooling on the proportions of floral development of P.
lactiflora ‘Taebaek’ in winter forcing culture. September pre-cooling (A) and
October pre-cooling (B). For pre-cooling treatment, refer to Table 1. Treatment C0 NT P15 P15 → 10 P10 0 20 40 60 80 100 120 Proportions of f loral developm ent ( %) 0 20 40 60 80 100 120
Flowers reaching anthesis Flower buds aborted at late stage Flower buds aborted at early stage A
27
Table 4. Effect of pre-cooling on the flower quality of P. lactiflora ‘Taebaek’ in winter forcing culture.
z
Refer to Table 1. y
Mean separation within columns by Duncan’s multiple range test at P = 0.05 NS, *, **, ***
Nonsignificant or significant at P = 0.05, 0.01 or 0.001, respectively. Transferring date Treatment z
Stem height Stem diameter Flower diameter No. of shoots No. of cut flowers No. of petals Vase life (cm) Sep. 16. C0 64.8 bc y 0.392 de 10.43 e 5.37 a 1.87 ab 11.87 d 0.8 e NT 65.9 bc 0.448 bc 10.81 cde 4.50 a 1.25 b 12.12 cd 1.3 e P15 65.4 bc 0.419 cd 11.69 bcd 4.62 a 1.87 ab 12.62 bcd 2.6 cd P15→10 69.8 ab 0.496 ab 11.92 abc 4.25 a 2.75 ab 12.62 bcd 2.8 bcd P10 71.0 a 0.525 a 12.05 ab 4.50 a 2.87 ab 13.50 ab 3.7 abc Oct. 14. C0 65.4 bc 0.373 e 10.76 de 6.00 a 1.62 ab 12.25 cd 0.8 e NT 61.4 c 0.429 c 10.74 de 5.00 a 1.62 ab 12.50 cd 1.7 de P15 65.0 bc 0.448 bc 11.85 bcd 4.62 a 3.00 a 12.75 bcd 2.6 cd P15→10 66.2 bc 0.448 bc 12.28 ab 5.75 a 3.00 a 13.00 bc 3.8 ab P10 68.3 ab 0.489 ab 13.00 a 3.87 a 3.25 a 13.87 a 4.1 a Significance
Transferring date (A) * ns ns ns ns ** ns
Treatment (B) ** *** *** ns ** *** ***
28
Fig. 10. Flowering of P. lactiflora ‘Taebaek’ on January 13, 63 days after
treatment. C0 (A), NT (B), P15→10 (C), and P10 (D).
A
C
B
29
Fig. 11. Flowering of P. lactiflora ‘Taebaek’ on January 28, 50 days after
treatment. C0 (A), NT (B), P15 (C), and P10 (D).
A
C
B
30
Experiment 2. Optimum pre-cooling timing and temperature of Paeonia lactiflora for autumn flowering
Growth and Development of the Underground Renewal Bud
The growth and development of renewal buds were promoted by pre-cooling
treatment. During 2 weeks of pre-cooling period, length of renewal buds increased
by 25.2% in P10. However, renewal buds without pre-chilling (C0 and NT) did
not show significant increase (Fig. 12). At the end of pre-cooling treatment, petal
primordia were visible in some buds of P10, whereas leaf primordia were
observed in C0, or NT plants (data not shown).
Plant Growth and Flowering
In all treatments, 100% of the plants sprouted. The earliest sprouting and
bursting occurred on September 12 and 13 in P10 plants. Sprouting or bursting
were 7 days earlier, respectively, in the P10 compared to those of the C0 or NT
(Table 5). Except for P10 plants, flower buds on almost all the developing stems
were aborted, therefore, did not report the flowering results in C0 and NT. The
flowering date of P10 was November 6, about 67 days after transferring to
greenhouse (Table 5). The number of shoots increased by pre-cooling treatment.
Maximum flower bud abortion percentage was observed at C0 (93%). Without
pre-cooling, after exposure only to ambient temperature for 2 weeks (NT), 88.2%
of stem aborted their flowers. In contrast, in pre-cooling at 10 °C (P10) only 16%
of flowers were aborted, where about 4 flowers were obtained per plants (Figs. 13,
31
Fig. 12. Effect of pre-cooling on the growth of renewal buds of P. lactiflora ‘Taebaek’ in autumn forcing culture. Vertical bars are standard errors of the means (n=4). For pre-cooling treatment, refer to Table 2.
Weeks after treatment
0 2 4 6 8 Bu d gr ow th r at e (% of in it ia l le ng th ) 0 10 20 30 40 50 C0 NT P10
32
Table 5. Effect of pre-cooling on the flowering of P. lactiflora ‘Taebaek’ in autumn forcing culture.
z
Refer to Table 2. y
The number of days from the date of transfer to the greenhouse. x
Mean separation within columns by Duncan’s multiple range test at P = 0.05 **, ***
Significant at P = 0.01 or 0.001, respectively. w
Not detected (not flowering by abortion).
Transferring date Treatment z Days to
y
No. of shoots No, of cut flowers sprouting bursting harvest flowering
July. 7. C0 19.7 a x 23.7 a - w - 4.22 b -
NT 18.8 a 22.7 a - - 5.00 b -
P10 12.4 b 15.7 b 55.5 a 67.7 a 7.11 a 3.72 a
33
Fig. 13. Effect of pre-cooling on the abortion of P. lactiflora ‘Taebaek’ in autumn
forcing culture. Vertical bars are standard errors of the means (n=16). For
pre-cooling treatment, refer to Table 2.
Treatment C0 NT P10 Pe rce nt abortion 0 20 40 60 80 100 120
34
Fig. 14. Flowering of P. lactiflora ‘Taebaek’ on November 9, 68 days after
treatment. C0 (A), P10 (B). For pre-cooling treatment, refer to Table 2.
35
DISCUSSION
Forcing herbaceous peony has been practiced among researchers who have
used chilling treatments to give release from dormancy (Byrne and Halevy, 1986;
Dole and Wilkins, 1999; Evans et al., 1990; Fulton et al., 2001). However,
flowering in early winter (January or February) is unstable and frequently
accompanied by lack of sprouting, or abortion of the flower bud. Although
chilling from September may insure complete release from dormancy, the number
of harvestable flowers is mostly limited to a single stem.
In these experiments, the results show that without pre-cooling treatment only
one bud per plant reached anthesis as in C0, or NT, although additional buds were
present and enlarged before abortion (Tables 4, 5). Bud abortion presents a major
difficulty in forcing culture of peony (Cheng et al., 2001; Evans et al., 1990). As
was often observed by growers, an early start of chilling from September brought
about abortion of flower buds (Hosoki et al,. 1984).
A morphological analysis of the peony ‘Sarah Benhardt’ (Barzily et al., 2002)
revealed its similarity to other geophytes species with annual thermoperiodic life
cycles. A perennial crown serves for the accumulation of the storage products
(Kapinos and Dubrov, 1993) and plant renewal. Byrne and Halevy (1986) found
that, the initiation of flower parts began in the renewal bud in June. Bud
development continued until the onset of dormancy in the autumn. As in the tulip,
hyacinth, crocus, and some Allium species (Hartsema, 1961; Kamenetsky, 2003;
Le Nard and De Hertogh, 1993b), floral initiation and differentiation of peony
36
thus indicating that the flower hasn’t been fully differentiated in the autumn
(Barzilay et al., 2002; Wang and Zhang, 1991). Therefore, temperature regime
during the autumn period may accelerate intrabud florogenesis of peony (Brazilay
et al., 2002).
It has been shown for several peony cultivars that prolonged chilling prior to
forcing at warm temperatures promotes dormancy release and flower stem
elongation (Byrne and Halevy, 1986; Catley et al., 2001; Evans et al., 1990;
Halevy et al., 2002; Wilkins and Halevy, 1985). This life cycle differs
considerably from those of geophytes, in which only low temperatures promotes
flower initiation, such as iris, lily, or onion (Le Nard and De Hertogh. 1993a, b;
Rabinowitch, 1990). The result showed that renewal bud development was
promoted by pre-cooling for 2 weeks (Figs. 6, 7). It is known that pre-cooling
accelerates the flower-bud formation of tree peony or other ornamental trees
(Aoki, 1992b; Aoki and Yoshino, 1984; Goi, 1979; Hosoki et al., 1984). Also,
pre-cooling advanced the sprouting and flowering date, because this treatment
decreased the requirement of cumulative temperature to flower (Tables 3, 5).
Therefore, The chilling treatment is required to release buds from dormancy, and
does not have a specific effect on flower initiation.
An effective forcing protocol includes the fulfillment of physiological
requirements at all developmental stages (De Hertogh, 1996). Abortion may be
induced by insufficient accumulation of nutrients into buds by chilling treatment
time or because the renewal bud is still at too early a stage of development in mid
September or October (beginning of sepal formation stage) to respond to low
37
may also be associated with flower bud abortion, such as smaller amount of
cytokine and larger amount of abscisic acid in Iris (Vonk et al., 1986). Exogenous
gibberellins and cytokinin treatment resulted in the decreased occurrence of
flower bud abortion in tulip and Cymbidium (Demunk and Gijzenberg, 1997;
Ohno, 1991), suggesting that abortion is induced by the factors related to hormone
biosynthesis. Therefore, flower bud abortion might be the result of the
inappropriate endogenous hormone ratio and carbohydrates level.
Pre-cooling affected the growth of vegetative and reproductive organs. The
stem height and diameter were increased by pre-cooling, and the flower size, petal
number and flowering percentage were also increased (Table 4). This
phenomenon could be attributed to the promotion of renewal bud (Aoki and
Yoshino, 1984).
There is no doubt that light intensity has a profound effect on flower
development. However, in these experiments, solar radiation was high enough and
was not a limiting factor for flowering.
In conclusion, it is considered that pre-cooling treatment at 10 °C in September,
October for January harvesting or July for November harvesting is applicable
forcing method for the extending the flowering period and normal flowering of P.
lactiflora ‘Taebaek’. However, optimum pre-cooling temperature and date can be
different among cultivars. Therefore, optimum pre-cooling temperature and
38
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43
ABSTRACT IN KOREAN
최근 작약이 고급 부케 및 꽃꽂이 소재로 사용되고 있어 절화로서의 수요 가 급격히 증가하고 있다. 하지만 이러한 작약은 연중 필요에도 불구하고 개 화시기가 5월부터 6월까지 한정되어 있어 대부분 수입에 의존하고 있다. 작약 의 연중 생산을 위해서 저온, 호르몬 처리 등 다양한 연구가 진행되었지만, 꽃 눈의 퇴화 현상이 나타나 낮은 개화율을 보여 촉성재배에 어려움이 있었다. 따라서, 본 논문은 작약의 연중 생산을 위한 촉성 재배 시, 개화율 및 절화 품 질 향상을 위한 적절한 예냉 처리 방법을 구명하고자 실험을 진행하였다. 겨 울철, 즉 1월과 2월 개화를 위한 예냉 처리 온도와 시기를 검정하기 위하여 ‘태백’ 작약을 9월 중순과 10월 중순에 각각 0℃, 자연 온도, 15℃, 15→10℃, 10℃의 5개 환경에서 2주간 예냉 처리하였으며, 이후 휴면 타파를 위해 0℃에 서 6주간 저온 저장 후, 주간 20℃, 야간 15℃로 유지되는 온실에 입실하여 생육을 관찰하였다. 또한, 가을철 개화를 위해서는 7월 초에 각각 0℃, 자연 온도, 10℃의 3개의 환경에서 처리 후, 휴면 타파를 위해 저온 저장고(0℃)에서 저온 처리한 후, 9월에 외부 포장으로 이동하여 생육을 관찰하였다. 그 결과, 15→10℃와 10℃처리구에서는 지하부 눈의 생장과 발달이 촉진된 반면, 0℃와 자연 온도 처리구에서는 눈의 발달에 큰 변화가 관찰되지 않았다. 또한, 0℃와 자연 온도 처리구에서는 대부분의 화아가 퇴화되어 개화율이 현저히 떨어졌지 만, 10℃ 예냉 처리구에서는 개화율이 80% 이상 향상되어 가장 높은 개화율을 보였다. 개화일도 10℃처리구에서 1월 13일과 26일 그리고 11월 9일로 가장44 빠르게 촉진되었으며, 절화 품질 역시 향상되었다. 절화 작약의 겨울철과 가을 철의 개화를 위해서는 9월과 10월, 그리고 7월에 2주간 10℃에서의 예냉 처리 후에 휴면타파를 위해 0℃에서의 6주간 저온 처리를 실시하면, 고품질 작약의 수확이 가능하였다. 이러한 결과는 작약의 촉성 재배를 목적으로 하는 재배자 들에게 실용적인 자료로 활용될 수 있을 것으로 생각한다.
