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A THESIS FOR THE DEGREE OF MASTER OF SCIENCE

Flowering Response of Eremogone

juncea (M.Bieb.) Fenzl to Photoperiod,

Chilling Treatment, and Cold Storage

일장과 저온 처리 및 저온 저장에 따른

벼룩이울타리의 개화 반응

BY

HYEONJEONG KANG

FEBRUARY, 2020

MAJOR IN HORTICULTURAL SCIENCE AND BIOTECHNOLOGY

DEPARTMENT OF PLANT SCIENCE

THE GRADUATE SCHOOL OF SEOUL NATIONAL UNIVERSITY

i

Flowering Response of Eremogone

juncea (M.Bieb.) Fenzl to Photoperiod,

Chilling Treatment, and Cold Storage

HYEONJEONG KANG

DEPARTMENT OF PLANT SCIENCE

THE GRADUATE SCHOOL OF SEOUL NATIONAL

UNIVERSITY

ABSTRACT

Eremogone juncea (M.Bieb.) Fenzl is a Korean native plant which has attractive

characteristics as a potential new ornamental crop with white flowers and summer

flowering. For the commercialization of E. juncea, manipulation techniques to

control flowering time are required. This study was carried out to examine the

flowering response of E. juncea to photoperiod and chilling treatment to induce

flowering (experiments 1 and 2) and cold storage to extend flowering (experiment

ii

3). In experiment 1, naturally chilled one-year-old E. juncea was acclimated under 9

h photoperiod in a greenhouse for a month. After acclimation, the plants were forced

under five different photoperiod conditions of 9, 12, 14, 16, and 24 h. There was no

difference in percent flowering among photoperiod treatments, showing 57-85%.

Furthermore, these plants did not show any significant difference in flowering

parameters, such as days to visible bud, days to the first open flower, and flower stalk

length, among photoperiod treatments. These results indicated that E. juncea can be

classified as day-neutral plants. In experiment 2, the one-year-old plants were

exposed to natural chilling or artificial chilling at 5°C for 0, 4, 8, or 12 weeks and 0,

4, or 8 weeks, respectively, and then moved into a walk-in chamber. Percent

flowering was less than 30% in the non-chilling treatment. Percent flowering

increased with increasing chilling duration at both natural and artificial chilling

conditions. Days to visible bud and days to the first open flower also decreased as

the chilling duration increased. These results indicated that chilling treatment is

necessary for the flowering of E. juncea. To quantify the chilling requirement, the

chill unit was calculated using modified chilling hours model (MCHM) and modified

Utah model (MUM). Irrespective of chilling methods, the flowering characteristics

were highly correlated with the chill unit (CU). For more than 80% flowering, at

least 1,854 CU in MCHM or 1,889 CU in MUM were required in this experiment.

In experiment 3, the plants which were already exposed to natural chilling during

winter season were stored for 0, 4, 8, or 12 weeks at 0°C. Days to visible bud and

days to the first open flower significantly decreased under cold storage treatment

iii

regardless of durations. Percent flowering also significantly decreased in all cold

storage treatments. These results indicated that although flowering could be delayed

by storing the plants at cold temperature, further studies on the storage timing or

temperature are needed to overcome the decrease in percent flowering by cold

storage. In conclusion, chilling treatment and cold storage can be used to control the

flowering time of E. juncea for year-round cultivation.

Additional key words: chill unit, herbaceous perennials, native plants, vernalization

Student number: 2018-28033

iv

CONTENTS

ABSTRACT‧‧‧‧‧‧‧‧‧‧‧‧‧‧‧‧‧‧‧‧‧‧‧‧‧‧‧‧‧‧‧‧‧‧‧‧‧‧‧‧‧‧‧‧‧‧‧‧‧‧‧‧‧‧‧‧‧‧‧‧‧‧‧‧‧‧‧‧‧‧‧‧‧‧‧‧‧‧‧‧‧‧‧‧‧‧‧‧‧‧‧‧‧‧‧‧‧‧‧‧‧‧‧‧‧‧‧‧‧‧‧‧ⅰ

CONTENTS‧‧‧‧‧‧‧‧‧‧‧‧‧‧‧‧‧‧‧‧‧‧‧‧‧‧‧‧‧‧‧‧‧‧‧‧‧‧‧‧‧‧‧‧‧‧‧‧‧‧‧‧‧‧‧‧‧‧‧‧‧‧‧‧‧‧‧‧‧‧‧‧‧‧‧‧‧‧‧‧‧‧‧‧‧‧‧‧‧‧‧‧‧‧‧‧‧‧‧‧‧‧‧‧‧‧‧‧‧‧ⅳ

LIST OF TABLES‧‧‧‧‧‧‧‧‧‧‧‧‧‧‧‧‧‧‧‧‧‧‧‧‧‧‧‧‧‧‧‧‧‧‧‧‧‧‧‧‧‧‧‧‧‧‧‧‧‧‧‧‧‧‧‧‧‧‧‧‧‧‧‧‧‧‧‧‧‧‧‧‧‧‧‧‧‧‧‧‧‧‧‧‧‧‧‧‧‧‧‧‧‧‧‧‧‧‧‧‧‧ⅴ

LIST OF FIGURES‧‧‧‧‧‧‧‧‧‧‧‧‧‧‧‧‧‧‧‧‧‧‧‧‧‧‧‧‧‧‧‧‧‧‧‧‧‧‧‧‧‧‧‧‧‧‧‧‧‧‧‧‧‧‧‧‧‧‧‧‧‧‧‧‧‧‧‧‧‧‧‧‧‧‧‧‧‧‧‧‧‧‧‧‧‧‧‧‧‧‧‧‧‧‧‧‧‧‧ⅵ

GENERAL INTRODUCTION‧‧‧‧‧‧‧‧‧‧‧‧‧‧‧‧‧‧‧‧‧‧‧‧‧‧‧‧‧‧‧‧‧‧‧‧‧‧‧‧‧‧‧‧‧‧‧‧‧‧‧‧‧‧‧‧‧‧‧‧‧‧‧‧‧‧‧‧‧‧‧‧‧‧‧‧‧‧‧‧‧‧1

LITERATURE REVIEW

Flowering Response to Photoperiod in Caryophyllaceae‧‧‧‧‧‧‧‧‧‧‧‧‧‧‧‧‧‧‧‧‧‧‧‧‧‧‧‧‧‧‧‧‧‧‧‧‧4

Flowering Response to Chilling in Caryophyllaceae‧‧‧‧‧‧‧‧‧‧‧‧‧‧‧‧‧‧‧‧‧‧‧‧‧‧‧‧‧‧‧‧‧‧‧‧‧‧‧‧‧‧‧‧4

Chill Unit Models for Calculating Chilling Hours in Horticultural Crops‧‧‧‧‧‧‧‧‧‧‧‧5

Cold Storage for Delaying Flowering‧‧‧‧‧‧‧‧‧‧‧‧‧‧‧‧‧‧‧‧‧‧‧‧‧‧‧‧‧‧‧‧‧‧‧‧‧‧‧‧‧‧‧‧‧‧‧‧‧‧‧‧‧‧‧‧‧‧‧‧‧‧‧‧‧‧‧7

MATERIALS AND METHODS

Flowering Response to Photoperiod (Experiment 1)‧‧‧‧‧‧‧‧‧‧‧‧‧‧‧‧‧‧‧‧‧‧‧‧‧‧‧‧‧‧‧‧‧‧‧‧‧‧‧‧‧‧‧‧8

Flowering Response to Chilling (Experiment 2)‧‧‧‧‧‧‧‧‧‧‧‧‧‧‧‧‧‧‧‧‧‧‧‧‧‧‧‧‧‧‧‧‧‧‧‧‧‧‧‧‧‧‧‧‧‧‧‧11

Cold Storage for Delaying Flowering (Experiment 3)‧‧‧‧‧‧‧‧‧‧‧‧‧‧‧‧‧‧‧‧‧‧‧‧‧‧‧‧‧‧‧‧‧‧‧‧‧‧‧‧16

RESULTS AND DISCUSSION

Flowering Response to Photoperiod (Experiment 1)‧‧‧‧‧‧‧‧‧‧‧‧‧‧‧‧‧‧‧‧‧‧‧‧‧‧‧‧‧‧‧‧‧‧‧‧‧‧‧‧‧‧19

Flowering Response to Chilling (Experiment 2)‧‧‧‧‧‧‧‧‧‧‧‧‧‧‧‧‧‧‧‧‧‧‧‧‧‧‧‧‧‧‧‧‧‧‧‧‧‧‧‧‧‧‧‧‧‧‧‧22

Cold Storage for Delaying Flowering (Experiment 3)‧‧‧‧‧‧‧‧‧‧‧‧‧‧‧‧‧‧‧‧‧‧‧‧‧‧‧‧‧‧‧‧‧‧‧‧‧‧‧‧29

LITERATURE CITED‧‧‧‧‧‧‧‧‧‧‧‧‧‧‧‧‧‧‧‧‧‧‧‧‧‧‧‧‧‧‧‧‧‧‧‧‧‧‧‧‧‧‧‧‧‧‧‧‧‧‧‧‧‧‧‧‧‧‧‧‧‧‧‧‧‧‧‧‧‧‧‧‧‧‧‧‧‧‧‧‧‧‧‧‧‧‧‧‧‧‧‧‧33

ABSTRACT IN KOREAN‧‧‧‧‧‧‧‧‧‧‧‧‧‧‧‧‧‧‧‧‧‧‧‧‧‧‧‧‧‧‧‧‧‧‧‧‧‧‧‧‧‧‧‧‧‧‧‧‧‧‧‧‧‧‧‧‧‧‧‧‧‧‧‧‧‧‧‧‧‧‧‧‧‧‧‧‧‧‧‧‧‧‧‧‧‧38

v

LIST OF TABLES

Table 1. Temperature ranges for calculating chill unit (CU) in chilling hours model

(CHM), Utah model (UM), modified chilling hours model (MCHM), and

modified Utah model (MUM).‧‧‧‧‧‧‧‧‧‧‧‧‧‧‧‧‧‧‧‧‧‧‧‧‧‧‧‧‧‧‧‧‧‧‧‧‧‧‧‧‧‧‧‧‧‧‧‧‧‧‧‧‧‧‧‧‧‧‧‧‧‧‧‧‧‧‧‧‧‧‧‧‧‧‧15

Table 2. Flowering characteristics of E. juncea under different photoperiod

conditions.‧‧‧‧‧‧‧‧‧‧‧‧‧‧‧‧‧‧‧‧‧‧‧‧‧‧‧‧‧‧‧‧‧‧‧‧‧‧‧‧‧‧‧‧‧‧‧‧‧‧‧‧‧‧‧‧‧‧‧‧‧‧‧‧‧‧‧‧‧‧‧‧‧‧‧‧‧‧‧‧‧‧‧‧‧‧‧‧‧‧‧‧‧‧‧‧‧‧‧‧‧‧‧‧‧‧20

Table 3. Flowering characteristics of E. juncea after 0, 4, 8, or 12 weeks of natural

chilling and 0, 4, or 8 weeks of artificial chilling treatments.‧‧‧‧‧‧‧‧‧‧‧‧‧‧‧‧‧‧‧‧‧‧‧‧‧‧‧‧‧‧24

Table 4. Chill units calculated by modified chilling hours model (MCHM) and

modified Utah model (MUM) under 0, 4, 8, or 12 weeks of natural chilling and

0, 4, or 8 weeks of artificial chilling treatments.‧‧‧‧‧‧‧‧‧‧‧‧‧‧‧‧‧‧‧‧‧‧‧‧‧‧‧‧‧‧‧‧‧‧‧‧‧‧‧‧‧‧‧‧‧‧‧‧‧26

Table 5. Flowering characteristics of E. juncea after 0, 4, 8, or 12 of cold storage

treatment.‧‧‧‧‧‧‧‧‧‧‧‧‧‧‧‧‧‧‧‧‧‧‧‧‧‧‧‧‧‧‧‧‧‧‧‧‧‧‧‧‧‧‧‧‧‧‧‧‧‧‧‧‧‧‧‧‧‧‧‧‧‧‧‧‧‧‧‧‧‧‧‧‧‧‧‧‧‧‧‧‧‧‧‧‧‧‧‧‧‧‧‧‧‧‧‧‧‧‧‧‧‧‧‧‧‧‧30

vi

LIST OF FIGURES

Fig. 1. Daily average, maximum, and minimum air temperatures in a greenhouse

located at the Experimental Farm of Seoul National University during

photoperiod treatment (from 6 May 2018 to 29 June 2018).‧‧‧‧‧‧‧‧‧‧‧‧‧‧‧‧‧‧‧‧‧‧‧‧‧‧‧‧‧‧‧10

Fig. 2. Changes in daily average soil temperature under natural and artificial chilling

treatments from 30 November 2018 to 22 February 2019 and 30 November 2018

to 25 January 2019, respectively.‧‧‧‧‧‧‧‧‧‧‧‧‧‧‧‧‧‧‧‧‧‧‧‧‧‧‧‧‧‧‧‧‧‧‧‧‧‧‧‧‧‧‧‧‧‧‧‧‧‧‧‧‧‧‧‧‧‧‧‧‧‧‧‧‧‧‧‧‧‧‧‧12

Fig. 3. Changes in daily average soil temperature before cold storage treatment from

17 November 2018 to 11 April 2019.‧‧‧‧‧‧‧‧‧‧‧‧‧‧‧‧‧‧‧‧‧‧‧‧‧‧‧‧‧‧‧‧‧‧‧‧‧‧‧‧‧‧‧‧‧‧‧‧‧‧‧‧‧‧‧‧‧‧‧‧‧‧‧‧‧‧17

Fig. 4. Growth and flowering of E. juncea as affected by different photoperiod

conditions.‧‧‧‧‧‧‧‧‧‧‧‧‧‧‧‧‧‧‧‧‧‧‧‧‧‧‧‧‧‧‧‧‧‧‧‧‧‧‧‧‧‧‧‧‧‧‧‧‧‧‧‧‧‧‧‧‧‧‧‧‧‧‧‧‧‧‧‧‧‧‧‧‧‧‧‧‧‧‧‧‧‧‧‧‧‧‧‧‧‧‧‧‧‧‧‧‧‧‧‧‧‧‧‧‧‧21

Fig. 5. Growth and flowering of E. juncea at 12 weeks after 0, 4, 8, or 12 weeks of

natural chilling and 0, 4, or 8 weeks of artificial chilling treatments.‧‧‧‧‧‧‧‧‧‧‧‧‧‧‧‧‧‧23

Fig. 6. Correlation between chill units calculated by modified chilling hours model

(MCHM) and modified Utah model (MUM) and percent flowering.‧‧‧‧‧‧‧‧‧‧‧‧‧‧‧‧‧28

Fig. 7. Growth and flowering of E. juncea at 12 weeks after 0, 4, 8, or 12 weeks of

cold storage treatment.‧‧‧‧‧‧‧‧‧‧‧‧‧‧‧‧‧‧‧‧‧‧‧‧‧‧‧‧‧‧‧‧‧‧‧‧‧‧‧‧‧‧‧‧‧‧‧‧‧‧‧‧‧‧‧‧‧‧‧‧‧‧‧‧‧‧‧‧‧‧‧‧‧‧‧‧‧‧‧‧‧‧‧‧‧‧‧31

１

GENERAL INTRODUCTION

With increasing interest and demand for Korean native plants, flowering control

methods for year-round cultivation of new ornamental crops are needed. Eremogone

juncea (M.Bieb.) Fenzl (벼룩이울타리, rush sandwort) is a herbaceous perennial

plant, growing naturally in mountains, slopes, and arid grasslands of Korea, China,

Mongolia, Japan, and far east Russia (Korea Biodiversity Information System). E.

juncea is regarded as a potential ornamental plant because it blooms in the summer

time with white flowers. It is commonly used for the flower garden, ground cover,

and pot plant. However, flowering is limited to a season between July and August.

Therefore, forcing or retarding methods for flowering season control of E. juncea

are needed for introducing E. juncea as a new ornamental crops.

Environmental factors such as photoperiod and temperature affect flowering in

many herbaceous perennial species (Foley et al., 2009; Runkle et al., 1999; Whitman

et al., 1996). The responses to photoperiod and vernalization can be variable among

species or cultivars and the grower needs to recognize the flowering response of

individual cultivars (Seaton et al., 2014).

Eremogone is a genus of Caryophyllaceae and contains about 71 species

(Rabeler and Wagner, 2015). No previous study for determining flowering response

has been reported on E. juncea. Researches have been conducted to examine the

flowering responses of various Caryophyllaceae plants under different photoperiods

２

and temperatures. Krekule and Hájková (1972) identified that Arenaria serphyllifolia

L. is a vernalization required and quantitative long-day plant. Baskin and Baskin

(1987) found that Arenaria fontinalis is a day-neutral plant and required 2,479 h of

vernalization at 0.5-10°C for 100% flowering. Dianthus gratianopolitanus Vill.

‘Bath's Pink’, a day-neutral plant, required three weeks at 5°C for complete

flowering and no plants flowered after eight weeks at 15°C (Padhye and Cameron,

2008). Dall'Agnese et al. (2014) found that cold treatment did not influence flower

opening time of Dianthus barbatus L, a short-day plant.

Determination of chilling requirements for flowering is difficult. Therefore,

many studies have identified the precise chilling requirements by calculating chill

units to quantify low temperatures. Jung and Kim (2009) found that at least 1,200 h

natural cumulative chilling or 1,008 h cumulative chilling below 10°C are

recommended for dormancy breaking of Adonis amurensis Regel et Radde. At least

492 h natural cumulative chill unit or 672 h cumulative chill unit might be required

for dormancy release of Polygonatum odoratum Druce var. pluriflorum Ohwi for.

variegatum Y.N.Lee (Yun et al., 2011).

Finding ways to delay flowering time allows the flowering season control for

year-round cultivation of E. juncea as a new ornamental crop. Cold storage can

extend the flowering season by delaying growth and development. Seo et al. (2009)

and Lee and Park (2015) found that cold temperature by storing delays the flowering

time of Arabidopsis thaliana. The flowering of saffron (Crocus sativus L.) could be

delayed by storing corms before flower initiation (Molina et al., 2005). Li et al. (2005)

３

identified that the cold storage extended the dormant condition of live black willow

(Salix nigra) cuttings for later planting.

The objectives of this study were to observe flowering responses of E. juncea to

photoperiod (Experiment 1), to verify the chilling requirement for flowering of E.

juncea (Experiment 2), and to investigate flowering responses of E. juncea to cold

storage to extend the flowering season (Experiment 3).

４

LITERATURE REVIEW

Flowering Response to Photoperiod in Caryophyllaceae

Photoperiod is an environmental factor to affect flower induction and

development of many plants (Hopkins and Huner, 2004). Flowering responses to

photoperiod are divided into five groups: short-day plants (SDP), long-day plants

(LDP), day-neutral plants (DNP), intermediate-day plants, and ambiphotoperiodic

plants (Thomas and Vince-Prue, 1997). Many studies have been carried out on the

photoperiodic flowering response of plants belonging to Caryophyllaceae. Krekule

and Hájková (1972) found Arenaria serphyllifolia L., a biennial plant, to be a

facultative LDP. Arenaria fontinalis, a winter annual plant, and Dianthus

gratianopolitanus Vill. ‘Bath's Pink’, a herbaceous perennial plant, were classified

to DNP (Baskin and Baskin, 1987; Padhye and Cameron, 2008). Dall'Agnese et al.

(2014) identified that Dianthus barbatus L., a biennial or short-lived perennial plant,

is a SDP. Plants belonging to Caryophyllaceae were classified differently as long-

day plants, day-neutral plants, and short-day plants.

Flowering Response to Chilling in Caryophyllaceae

The flowering of many plants species is either dependent on or promoted by prior

exposure to the prolonged winter cold (Sung and Amasino, 2005). The process by

which exposure to cold promotes flowering is known as vernalization. The effective

５

temperature range for vernalization of many plant species is 1-7°C, however,

vernalization temperature may vary depending on species (Ha TM, 2014). Many

studies have been conducted on the vernalization requirements of plants belonging

to Caryophyllaceae. Krekule and Hájková (1972) identified that Arenaria

serphyllifolia L. is a vernalization requiring plants. Although Arenaria fontinalis

flowered without vernalization, vernalized plants survive better and are healthier

than non-vernalized plants (Baskin and Baskin, 1987). Dianthus gratianopolitanus

Vill. ‘Bath's Pink’ exhibited a quantitative vernalization requiring response (Padhye

and Cameron, 2008). Dianthus barbatus L. did not show significant differences in

days to the first open flower and days to full bloom under vernalization condition,

and longer vernalization duration reduced the inflorescence size but increased the

stem height (Dall'Agnese et al., 2014).

Chill Unit Models for Calculating Chilling Hours in

Horticultural Crops

Chill unit models have been developed for predicting the chilling requirement of

temperate woody perennial plants and quantifying cold temperature (Darbyshire et

al., 2016). Many models have been proposed with varying rages of temperature for

calculating the chill unit. For example, chilling hours model (CHM) is the oldest

method considering one hour at temperature between 0 and 7°C calculated as 1 chill

unit (CU) (Weinberger, 1950). Utah model (UM) calculated the temperature between

６

2.5 and 9.1°C as the most effective temperature for dormancy breaking, taking into

account the negative effects of high winter temperature (Richardson et al., 1974).

Modified chilling hours model (CHM) is the method considering one hour at

temperature between 5 and 7°C calculated as one chill unit (Yun et al., 2011).

Modified Utah model (UM) calculated the temperature between 1.5 and 9.1°C as the

most effective temperature for dormancy breaking.

At least 1,200 h natural cumulative chilling calculated by modified chilling hour

model or 1,008 h cumulative chilling (= six weeks of cold storage) below 10°C might

satisfy the chilling requirement for dormancy breaking, flower bud development, and

subsequent growth of Adonis amurensis Regel et Radde (Jung and Kim, 2009). Yun

et al. (2011) found that at least 492 h natural cumulative chill unit calculated by

modified chilling hours model in the field or 672 h cumulative chill unit (= four

weeks of cold storage at 0°C) is recommended for dormancy release and normal

growth of Polygonatum odoratum Druce var. pluriflorum Ohwi for. variegatum

Y.N.Lee. At least 1,222 h natural cumulative chill unit calculated by modified

chilling hour model of Fulton et al. (2001) could be recommended as a forcing

method for dormancy release, normal growth, and subsequent flowering of Paeonia

lactiflora ‘Taebaek’ (Yeo et al., 2012). Rhie et al. (2012) reported that 1,008 h chill

unit (= chilling for six weeks at 0°C) or 1,058 h chill unit (= nine weeks at 5°C)

calculated by modified chilling hour model of Fulton et al. were necessary to break

dormancy and to induce flowering in P. lactiflora ‘Taebaek’ and ‘Mulsurae’,

respectively. At least 1,483-1,794 cumulative chill unit calculated as the number of

７

hours when the temperatures was below 5°C might satisfy the chilling requirement

for dormancy breaking of Erythronium japonicum Decne. (Liliaceae) (Kim et al.,

2014).

Cold Storage for Delaying Flowering

In Arabidopsis, 10 d of cold at 4°C slightly delays flowering and 20 d of cold at

4°C delays flowering further, indicating that the flowering is delayed in proportion

to the days of cold treatment (Seo et al., 2009). Seo et al. (2009) explain that short-

term cold delays flowering through FLOWERING LOCUS C (FLC) activity. Lee

and Park (2015) identified that flowering is delayed by intermittent cold temperature

that frequently occurs during early spring in the temperate zones in Arabidopsis.

Exposure to cold temperatures triggers the binding of INDUCER OF CBF

EXPRESSION 1 (ICE1) to FLC gene promoter to induce its expression. Lee and

Park (2015) also described that delayed flowering by short-term cold conditions is

mediated primarily by the floral repressor FLC in Arabidopsis. Molina et al. (2005)

found that the flowering of saffron (Crocus sativus L.) could be delayed by extending

the duration of cold storage. In black willow (Salix nigra) cuttings, a dormancy

extension technique can be possible by cold storing at 4.4°C (Li et al., 2005).

８

MATERIALS AND METHODS

Flowering Response to Photoperiod (Experiment 1)

Plant materials

These experiments were conducted in a greenhouse located at the Experimental

Farm of Seoul National University, Suwon, Korea. Naturally chilled one-year-old E.

juncea were purchased from a commercial farm (Gangwon Plant, Hoengseong,

Korea) on 2 April 2018. The plants have been planted into 7 cm (179 mL) plastic

pots filled with saprolite and then were cut with the above-ground part 1.0-1.5 cm

remaining. These plants were acclimated under 9 h photoperiod condition in the

greenhouse for a month. The plants were irrigated when the surface of the potting

medium showed dryness.

Photoperiod treatments

Twenty plants were randomly selected and placed in each greenhouse bench in a

completely randomized design on 6 May 2018. The photoperiods were 9, 12, 14, 16,

and 24 h of continuous light. A truncated 9 h short-day photoperiod was controlled

by black film. The black plastic film on every bench was rolled up at 09:00 HR and

closed at 18:00 HR. Photoperiods were extended by supplemental lighting with white

LEDs (12V SMD 5050 LED, CamFree Co., Ltd., Seoul, Korea). The light intensity

of the white LED was 3 mol∙m2∙s1 at plant canopy to avoid the effects of daily

９

light integral (DLI). The plants were irrigated as necessary with tap water using a

sprinkler. Once every two weeks each pot received 50 mL of water soluble fertilizer

(EC 0.8 mS∙cm1; HYPONeX professional 20N-20P-20K, HYPONeX Japan Co.,

Ltd., Osaka, Japan). Air temperature within the bench was monitored at 30 min

intervals using a data logger (Watch Dog Model 1000, Spectrum Technologies, Inc.,

Plainfield, IL, USA) from 6 May 2018 to 29 June 2018 (Fig. 1).

Data collection and statistical analysis

Percent flowering was measured for each photoperiod treatment. Days to visible

bud and days to the first open flower from the start of photoperiod treatments were

counted. Flower stalk length from the medium to the top of the stalk at the first open

flower was measured.

The collected data were analyzed using analysis of variance (ANOVA) using the

SAS program (Ver. 9.4, SAS Institute, Inc., Cary, NC, USA). Mean separation by

Tukey’s multiple range test at p < 0.05 was performed for all data.

１０

Fig. 1. Daily average, maximum, and minimum air temperatures in a greenhouse

located at the Experimental Farm of Seoul National University during

photoperiod treatment (from 6 May 2018 to 29 June 2018).

0

5

10

15

20

25

30

35

40

45T

emper

atu

re (

⁰C)

Date

Average

Maximum

Minimum

１１

Flowering Response to Chilling (Experiment 2)

Plant materials

These experiments were conducted in a greenhouse located at the Experimental

Farm of Seoul National University, Suwon, Korea. One-year-old E. juncea were

purchased from a commercial farm (Gosan Plant, Pyeongchang, Korea) on 27

October 2018. E. juncea were planted into 10 cm (461 mL) plastic pots filled with

saprolite. These plants received natural chilling in an open field for a month before

chilling treatments and then were cut with the above-ground part 1.0-1.5 cm

remaining. On 30 November 2018, the plants were moved to a container plot filled

with saprolite in an open field or a cold storage room at 5°C for 0, 4, 8, or 12 weeks

or 0, 4, or 8 weeks, respectively.

Daily average soil temperature at a depth of 3 cm was monitored every 30 min

for calculation of chilling requirement under a natural condition using a thermo data

logger (Watch Dog Model 1000, Spectrum Technologies, Inc., Plainfield, IL, USA)

from 30 November 2018 to 22 February 2019 (Fig. 2). The plants which received

natural chilling in an open field or artificial chilling in a cold storage room at 5°C

were moved to a closed plant production system at the university farm (Seoul

National University, Suwon, Korea). In a closed plant production system conditions,

temperature, relative humidity (RH), photoperiod, and light intensity were

maintained at 20°C, 60%, 12 h, and 200 ± 10 mol∙m2∙s1 [fluorescent lamp (TL-D

32W RS 865, Philips Lighting Co., Ltd., Eindhoven, Netherlands) + white LED

１２

Fig. 2. Changes in daily average soil temperature under natural and artificial chilling

treatments from 30 November 2018 to 22 February 2019 and 30 November 2018

to 25 January 2019, respectively.

-10

-5

0

5

10

15

Dai

ly a

ver

age

soil

tem

per

atu

re (

⁰C)

Date

Natural chilling

Artificial chilling

１３

(LEDT5-9015-DHE, FOCUS lighting Co., Ltd., Bucheon, Korea)], respectively. The

plants were irrigated as necessary with tap water by hand watering. Once every two

weeks each pot received 50 mL of a water soluble fertilizer (EC 0.8 mS∙cm1;

HYPONeX professional 20N-20P-20K, HYPONeX Japan Co., Ltd., Osaka, Japan).

Chilling treatments

For the natural chilling treatment, the plants were transferred from an open field

to a closed plant production system at four different transfer dates (11 November

2018, 28 December 2018, 25 January 2019, and 22 February 2019). For the artificial

chilling treatment, the plants were transferred from a cold storage room at 5°C under

dark conditions to a closed plant production system at three different transfer dates

(11 November 2018, 28 December 2018, and 25 January 2019).

Data collection and statistical analysis

Percent flowering was measured for natural and artificial chilling treatments.

Days to visible bud and days to the first open flower from the transferring date were

counted. Flower stalk length from the medium to the top of the stalk, the number of

visible buds, and flower diameter at the first open flower were measured.

Trials were conducted in a completely randomized design with three replicates

of eight plants per treatment. Statistical analysis was performed using ANOVA in the

SAS system for Windows version 9.4 (SAS Institute Inc., Cary, NC, USA). The

statistical significance of the results was confirmed at the 5% level followed by

１４

Tukey’s multiple range tests. All figures were generated using Sigma Plot software

version 10.0 (Systat Software, Inc., Chicago, IL, USA).

To interpret the results in terms of the chill unit (CU), the amount of chilling

required to flowering was calculated. The chill unit model can be used to quantify

winter chill in hours. We used modified chilling hours model (MCHM) and modified

Utah model (MUM) (Table 1). MCHM and MUM were modified based on chilling

hours model (CHM) (Weinberger, 1950) and Utah model (UM) (Richardson et al.,

1974), respectively.

１５

Table 1. Temperature ranges for calculating chill unit (CU) in chilling hours model

(CHM), Utah model (UM), modified chilling hours model (MCHM), and

modified Utah model (MUM).

Chill unit model Temperature range

CHM 0°C < T < 7.2°C = 1, else: 0

UM T ≤ 1.4°C = 0

1.4°C < T ≤ 2.4°C = 0.5

2.4°C < T ≤ 9.1°C = 1

9.1°C < T ≤ 12.4°C = 0.5

12.4°C < T ≤ 15.9°C = 0

15.9°C < T ≤ 18.0°C = 0.5

T > 18.0°C = 1

MCHM 5°C < T < 7.2°C = 1, else: 0

MUM T ≤ 5°C = 0

5°C < T ≤ 1.4°C = 0.8

1.4°C < T ≤ 2.4°C = 1

2.4°C < T ≤ 9.1°C = 1

9.1°C < T ≤ 12.4°C = 0.5

12.4°C < T ≤ 15.9°C = 0

15.9°C < T ≤ 18.0°C = 0.5

T > 18.0°C = 1

１６

Cold Storage for Delaying Flowering (Experiment 3)

Plant materials

These experiments were conducted in a greenhouse located at the Experimental

Farm of Seoul National University, Suwon, Korea. One-year-old E. juncea were

purchased from a commercial farm (Gosan Plant, Pyeongchang, Korea) on 27

October 2018. E. juncea plants were planted into 10 cm (461 mL) plastic pots filled

with saprolite. These plants received natural chilling in a container plot filled with

saprolite in an open field and then were cut with the above-ground part 1.0-1.5 cm

remaining before cold storage treatment. Daily average soil temperature at a depth

of 3 cm was monitored every 30 min using a thermo data logger (Watch Dog Model

1000, Spectrum Technologies, Inc., Plainfield, IL, USA) from 17 November 2018 to

11 April 2019 (Fig. 3).

On 12 April 2019, the plants were moved to a cold storage room at 0°C for 0, 4,

8, or 12 weeks. After cold storage treatment, the plants were moved to an

environmental-controlled growth chamber (HB-301MP, Hanbaek Scientific CO.,

Bucheon, Korea) at a laboratory (Seoul National University, Seoul, Korea). In an

environmental-controlled growth chamber conditions, temperature, relative

humidity (RH), photoperiod, and light intensity were maintained at 20°C, 60%, 12

h, and 200 ± 10 mol∙m2∙s1 [250 W metal halide lamp (Han Young Electrics Co.,

Gwanju, Korea)], respectively. The plants were irrigated as necessary with tap water

by hand watering. Each pot received 50 mL once every two weeks of a water soluble

１７

Fig. 3. Changes in daily average soil temperature before cold storage treatment from

17 November 2018 to 11 April 2019.

-15

-10

-5

0

5

10

15

20

25

30T

emper

atu

re (

⁰C)

Date

Average

Maximum

Minimum

１８

fertilizer (EC 0.8 mS∙cm1; HYPONeX professional 20N-20P-20K, HYPONeX

Japan Co., Ltd., Osaka, Japan).

Cold storage treatments

For the cold storage treatment, the plants were stored at a cold storage room at

5°C under dark conditions, and then transferred to an environmental-controlled

growth chamber at four different transfer dates (12 April 2019, 10 May 2019, 7 June

2019, and 5 July 2019).

Data collection and statistical analysis

Percent flowering was measured for each treatment. Days to visible bud and days

to the first open flower from the transferring date were counted. Flower stalk length

from the medium to the top of the stalk, the number of visible buds, and flower

diameter at the first open flower were measured.

Experiments were conducted in a completely randomized design with three

replicates of 4 plants per treatment. Statistical analysis was performed using ANOVA

in the SAS system for Windows version 9.4 (SAS Institute Inc., Cary, NC, USA).

The statistical significance of the results was confirmed at the 5% level followed by

Tukey’s multiple range tests. All figures were generated using Sigma Plot software

version 10.0 (Systat Software, Inc., Chicago, IL, USA).

１９

RESULTS AND DISCUSSION

Flowering Response to Photoperiod (Experiment 1)

E. juncea grown under different photoperiod conditions did not show significant

differences in all flowering parameters (Table 2 and Fig. 4). Days to visible bud was

28.8, 26.5, 25.5, 25.0 or 25.6 d and days to the first open flower was 41.3, 42.6, 38.8,

39.6, or 40.8 d under 9, 12, 14, 16, or 24 h, respectively. Flower stalk length was

23.3, 24.6, 25.0, 24.7, or 26.6 under 9, 12, 14, 16, or 24 h, respectively. Flowering

occurred under all photoperiod conditions. Percent flowering was 57, 63, 61, 58, or

85% under 9, 12, 14, 16, or 24 h, respectively. There was no difference in percent

flowering among different photoperiod treatments. LDP only flower or flower most

rapidly when exposed to night durations shorter than a critical photoperiod, whereas

SDP flower when exposed to night period longer than a critical photoperiod (Thomas

and Vince-Prue, 1997). DNP flower regardless of daylength. Many studies have been

conducted on photoperiod response of Caryophyllaceae plants. Arenaria

serphyllifolia L. is LDP, Arenaria fontinalis and Dianthus gratianopolitanus Vill.

‘Bath's Pink’ are DNP, and Dianthus barbatus L. is SDP (Baskin and Baskin, 1987;

Dall'Agnese et al., 2014; Krekule and Hájková, 1972; Padhye and Cameron, 2008).

In this study, the flowering of E. juncea were not influenced by photoperiod. Thus,

E. juncea can be classified as DNP, similar to two previously studied species of

Caryophyllaceae (Baskin and Baskin, 1987; Padhye and Cameron, 2008).

２０

Table 2. Flowering characteristics of E. juncea under different photoperiod

conditions (Tukey's multiple range test, p < 0.05).

Photoperiod (h) Flowering (%) Days to

visible bud

Days to first

open flower

Flower stalk

length (cm)

9/15 57 28.8 41.3 23.3

12/12 63 26.5 42.6 24.6

14/10 61 25.5 38.8 25.0

16/8 58 25.0 39.6 24.7

24/0 85 25.6 40.8 26.6

Significance - NS NS NS

NS Non-significant

２１

Fig. 4.

Fig. 4. Growth and flowering of E. juncea as affected by different photoperiod

conditions.

9 h 12 h 14 h 16 h 24 h

Photoperiod

２２

Flowering Response to Chilling (Experiment 2)

Growth and flowering of E. juncea under 8 or 12 weeks of natural chilling and 8

weeks of artificial chilling were better than 0 and 4 weeks of natural and artificial

chilling (Fig. 5). Without chilling treatment, percent flowering was less than 30%

(Table 3). Percent flowering was 63.9, 82.7, or 81.5% under 4, 8, or 12 weeks of

natural chilling and 43.3 or 62.5 % under 4 or 8 weeks of artificial chilling,

respectively. Percent flowering significantly increased with increasing chilling

duration irrespective of the chilling method. According to results of Padhye and

Cameron (2008), 21% of non-chilled D. gratianopolitanus ‘Bath's Pink’ flowered,

whereas 100% flowering was achieved only after chilling at 0°C. Therefore, D.

gratianopolitanus ‘Bath's Pink’ exhibited a facultative vernalization response.

Days to visible bud and days to the first open flower were significantly decreased

with increasing chilling duration regardless of chilling method. Days to visible bud

and days to the first open flower significantly decreased under natural and artificial

chilling treatments compared with non-chilling treatment. Similar results were

reported in various herbaceous perennial, such as Chinese peony, Solomon’s seal,

Amur Adonis, and Asian fawnlily (Jung and Kim, 2009; Kim et al., 2014; Rhie et al.,

2012; Yeo et al., 2012; Yun et al., 2011). For example, 0% of Paeonia lactiflora

sprouted under non-chilling treatment, whereas more than 70% of the plants sprouted

at 0, 5, or 10°C after 6, 9, or 12 weeks of chilling and 100% sprouting under 12

weeks of chilling regardless of chilling temperature (Rhie et al., 2012). Rhie et al.

(2012) also identified that days to flowering was decreased at 0, 5, or 10°C as the

２３

Fig. 5. Growth and flowering of E. juncea at 12 weeks after 0, 4, 8, or 12 weeks of

natural chilling and 0, 4, or 8 weeks of artificial chilling treatments.

２４

Tab

le 3

. F

low

erin

g c

har

acte

rist

ics

of

E.

junce

a a

fter

0,

4,

8,

or

12 w

eeks

of

nat

ura

l ch

illi

ng a

nd 0

, 4

, o

r 8 w

eeks

of

arti

fici

al

chil

lin

g t

reat

men

ts.

Chil

ling

trea

tmen

t

Ch

illi

ng

du

rati

on

(wee

k)

Flo

wer

ing

(%)

Day

s to

vis

ible

bud

Day

s to

fir

st

open

flo

wer

A

t fi

rst

open

flo

wer

Flo

wer

sta

lk

length

(cm

) N

um

ber

of

vis

ible

bu

d

Flo

wer

dia

met

er

(cm

) N

on

0

23

.7 bz

89.8

a

103.3 a

20.9

6.7

1.6

6

Nat

ura

l 4

63

.9 ab

80.8 ab

95.2 ab

20.0

8.4

1.8

3

8

82

.7 a

67.0 b

79.5 b

20.6

9.4

1.4

6

1

2

81

.5 a

68.4 b

85.2 ab

17.8

7.1

1.4

8

Art

ific

ial

4

43

.3 ab

80.8 ab

90.9 ab

19.5

8.8

1.7

5

8

62

.5 ab

70.9 b

83.1 b

20.2

9.3

1.7

3

Sig

nif

icance

Chil

ling t

reat

men

t (T

) *

*

**

*

N

S

NS

NS

Chil

ling d

ura

tio

n (

D)

**

**

**

N

S

NS

NS

T *

D

NS

NS

NS

N

S

NS

NS

z M

eans

wit

hin

colu

mn

s fo

llo

wed

by d

iffe

rent

lett

ers

are

signif

ican

tly d

iffe

rent

by T

ukey

's m

ult

iple

ran

ge

test

at

p <

0.0

5.

NS

, *,

** N

on

-sig

nif

ican

t o

r si

gn

ific

ant

at p

< 0

.05, 0.0

1, re

spec

tivel

y.

２５

chilling duration was extended from 3 to 12 weeks in Paeonia lactiflora. E. juncea

grown under different chilling conditions did not show significant differences in

flowering parameters including flower stalk length, the number of visible buds, and

flower diameter.

There was a significant difference in percent flowering among chilling

treatments. Even though the chilling duration was the same, percent flowering was

different between natural and artificial chilling. While artificial chilling temperature

was constant at 5°C, the natural chilling temperature has been fluctuated, and the

difference in percent flowering seems to be caused by the temperature difference of

the chilling method (Fig. 2). Outdoor fluctuating temperatures have been accepted

to be more effective in satisfying the chilling requirements than artificial constant

temperatures in many woody plants (Hänninen, 1990; Murray et al., 1989). However,

Myking (1997) found no differences in days to budburst between fluctuating and

constant temperatures in Betula pubescens. In addition, constant temperatures are

more effective in dormancy breaking than fluctuating temperatures in coniferous

species (Lavender and Cleary, 1974).

To quantify the chilling temperature received during chilling treatment, chill unit

was calculated using modified chilling hours model (MCHM) and modified Utah

model (MUM). Choi et al. (1996) reported that root zone temperature is more

important for bud dormancy breaking than air temperature, thus soil temperature at

a depth of 3 cm was measured. Chill unit calculated by MCHM was 562, 1,234, or

1,905 and 675 or 1,347 under natural and artificial chilling, respectively (Table 4).

２６

Table 4. Chill units calculated by modified chilling hours model (MCHM) and

modified Utah model (MUM) under 0, 4, 8, or 12 weeks of natural chilling and

0, 4, or 8 weeks of artificial chilling treatments.

Chilling treatment Chilling duration

(week) MCMM MUM

Non 0 0 0 Natural 4 562 497 8 1,234 1,035 12 1,905 1,579 Artificial 4 675 675 8 1,347 1,347

２７

The chill unit was 497, 1,035, or 1,579 and 675 or 1,347 under natural and artificial

chilling, respectively, using MUM. The correlation between the chill unit and the

percent flowering calculated by the two models showed that the percent flowering

increased as the chill unit increased (Fig. 6). Based on the correlation between the

chill units calculated by the two models and the percent flowering, the results

indicated that 1,854 CU calculated by MCHM or 1,889 CU calculated by MUM

might be required for over 80% flowering. Many researches on relationship between

chill unit and flowering were reported in various herbaceous perennials. Percent

sprouting was increased and days to sprouting was decreased with increasing

cumulative chill unit in E. japonicum (Kim et al., 2014). Bud break percentage and

flowering percentage were increased and days to bud break and days to flowering

were decreased with increasing cumulative chilling hours calculated using by

MCHM in A. amurensis (Jung and Kim, 2009). In P. odoratum, Days to sprouting

was shortened and percent sprouting was increased with increasing cumulative chill

unit calculated by MCHM under both natural and artificial chilling conditions (Yun

et al., 2011).

２８

Chill units

0 500 1000 1500 2000 2500

Flo

wer

ing (

%)

0

20

40

60

80

100

Modified chilling hours model

Modified Utah model

Modified chilling hours model

Modified Utah model

Fig. 6. Correlation between chill units calculated by modified chilling hours model

(MCHM) and modified Utah model (MUM) and percent flowering. The data

shown are the mean ± SE. The lines were fitted to a hyperbola single rectangular

I, 3 Parameter; y = y0 + 𝑎𝑥

𝑏+𝑥.

R2 = 0.7873

R2 = 0.7207

２９

Cold Storage for Delaying Flowering (Experiment 3)

Days to visible bud and days to the first open flower significantly decreased

under all cold storage treatments (Table 5). Although there were significant

differences in days to visible bud and days to the first flowering according to cold

storage duration, the flowering season can be extended by delaying the flowering

time by storing the plants at cold temperature. Gonzalez et al. (1998) reported that

cold storage treatment at 5°C lasting six weeks significantly delayed the time of

sprouting in Gladiolus tristis. There were no significant differences in flower stalk

length, the number of visible buds, and flower diameter according to the cold storage

treatment (Table 5 and Fig. 7).

Percent flowering under non-cold storage treatment showed over 80%, but

percent flowering significantly decreased to 58.3, 55.6, or 50.0 under 4, 8, or 12

weeks of cold storage treatment (Table 5). Several studies have reported the negative

effects of cold storage. Molina et al. (2005) identified that the flowering of saffron

(Crocus sativus L.) could be delayed by extending the duration of cold storage, but

this delayed flowering resulted in a significant reduction in spice saffron yield. The

number of flowers and flower size decreased gradually with increasing cold storage

duration in saffron. Upon transfer to forcing conditions, cold-stored corms of saffron

formed flowers earlier than non-cold storage corms. In black willow (Salix nigra)

cuttings, cold storage method can be used to dormancy extension, but survival rates

were 81.3, 43.6, and 43.8% when they were stored for 3, 7, and 12 weeks (Li et al.,

2005). In P. lactiflora, percent flowering of pre-chilling at 0°C for 2 weeks before

３０

Tab

le 5

. F

low

erin

g c

har

acte

rist

ics

of

E. ju

nce

a a

fter

0, 4,

8,

or

12 o

f co

ld s

tora

ge

trea

tmen

t.

Cold

sto

rage

du

rati

on

(wee

k)

Flo

wer

ing

(%)

Day

s to

vis

ible

bud

Day

s to

fir

st

open

flo

wer

A

t fi

rst

open

flo

wer

Flo

wer

sta

lk

length

(cm

)

Nu

mb

er o

f

vis

ible

bu

d

Flo

wer

dia

met

er

(cm

)

0

83

.3 a

z 47.0

a

56.6

a

18.7

8

.0

1.4

9

4

58

.3 a

b

42.7

ab

53.8

b

21.9

1

0.2

1

.48

8

55

.6 b

41.5

b

51.8

b

21.0

8.3

1

.63

12

5

0.0

ab

41.8

ab

52.0

b

21.4

1

0.0

1

.73

Sig

nif

icance

*

*

***

NS

N

S

NS

z M

eans

wit

hin

colu

mn

s fo

llo

wed

by d

iffe

rent

lett

ers

are

signif

ican

tly d

iffe

rent

by T

ukey

's m

ult

iple

ran

ge

test

at

p <

0.0

5.

NS

, *,

**

* N

on

-sig

nif

ican

t or

sign

ific

ant

at p

< 0

.05

, 0.0

01,

resp

ecti

vel

y.

３１

Fig. 7. Growth and flowering of E. juncea at 12 weeks after 0, 4, 8, or 12 weeks of

cold storage treatment.

３２

chilling at 0°C for 6 weeks was 40%, whereas percent flowering of pre-chilling at

10°C for two weeks was 89.6% (Park et al., 2015). Park et al. (2015) also found that

days to flowering was 66.8 or 48.8 d under pre-chilling at 0 or 10°C, respectively,

for two weeks before chilling at 0°C for six weeks. Therefore, the optimum pre-

chilling temperature might be needed to reduce flower bud abortion. Percent

flowering of E. juncea significantly decreased in all cold storage treatments at 0°C,

thus further studies on the storage timing or temperature are needed.

３３

LITERATURE CITED

Baskin JM, Baskin CC (1987) Seed germination and flowering requirements of the

rare plant Arenaria fontinalis (Caryophyllaceae). Castanea 52:291-299

Choi ST, Ahn HG, Kim KW, Park IH (1996) Influence of planting depth and

duration of cold treatment on growth and flowering of Liatris spicata. J Kor Soc

Hort Sci 37:112-117

Dall'Agnese L, Petry C, Backes FAL, Schwab NT, Girard LB, Bellé RA (2014)

Effects of vernalization on flowering of Dianthus barbatus. XXIX international

horticultural congress on horticulture: sustaining lives, livelihoods and

landscapes (IHC2014): 1104 (pp. 191-196)

Darbyshire R, Pope K, Goodwin I (2016) An evaluation of the chill overlap model

to predict flowering time in apple tree. Sci Hortic 198:142-149

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３８

ABSTRACT IN KOREAN

벼룩이울타리는 한국 자생식물이며 여름에 개화하고 하얀색 꽃이

피는 매력적인 특성을 가지고 있어 새로운 관상식물 대상종으로

선정되었다. 벼룩이울타리의 산업화를 위해서는 개화시기를 제어하는

조절 기술의 개발이 필요하다. 본 연구에서는 개화를 유도하기 위해

일장과 저온 처리에 따른 개화 반응을 살펴본 실험 1과 2가 진행되었고,

개화를 지연시키기 위해 저온 저장에 따른 개화 반응을 살펴본 실험

3이 진행되었다. 실험 1에서는 자연적인 저온을 받은 1년생 묘를

온실에서 약 한 달간 9시간 일장 조건에서 순화시킨 후 9, 12, 14, 16,

24시간의 일장 처리가 진행되었다. 일장 실험 결과, 꽃눈분화소요일수,

개화소요일수, 꽃대길이에서는 일장에 따른 유의미한 차이가 나타나지

않았다. 또한, 일장에 따른 개화율에도 차이가 나타나지 않았다. 따라서

벼룩이울타리는 일장에 따른 개화에 차이가 나타나지 않는 중성식물로

분류될 수 있다는 것을 확인하였다. 실험 2에서는 1년생 묘를 사용하여

３９

0, 4, 8, 12주 동안 야외에서의 자연 저온 처리와 0, 4, 8주 동안 5°C 저온

저장고에서의 인공 저온 처리를 실시하였다. 저온 처리 후에는 20°C 의

생장상에서 처리에 따른 결과를 지켜보았다. 저온 무처리구에서는 30%

이하의 개화율을 보였다. 저온 처리기간이 증가할수록 저온 처리 방법에

상관없이 개화율이 증가했고, 꽃눈분화소요일수, 개화소요일수는

감소했다. 이러한 결과를 통해 벼룩이울타리의 개화를 위해서는 저온

처리가 필요하다는 것을 확인하였다. 저온을 정량화하기 위해 modified

chilling hours model(MCHM)과 modified Utah model(MUM)을 사용하여

chill unit(CU)을 계산하였다. 자연 저온과 인공 저온 처리에서 개화

특성은 chill unit과 밀접한 관련이 있었다. 본 실험 결과를 토대로, 80%

이상의 개화율을 위해서는 MCHM에서는 1,854CU, MUM에서는 1,889CU

이상이 요구되었다. 실험 3에서는 겨울철 자연 저온에 노출된

벼룩이울타리 묘를 대상으로 0°C의 저온 저장고에서 0, 4, 8, 12주 동안

저온 저장 처리를 실시했다. 꽃눈분화소요일수와 개화소요일수에서는

모든 저온 저장 처리에서 유의미하게 감소하였다. 개화율의 경우에는

４０

모든 저온 저장처리구에서 유의미하게 감소했다. 이러한 결과는 저온

저장 방법을 통해 식물의 개화를 지연시킬 수 있지만 저온 저장에 의한

개화율의 감소를 극복하기 위해서는 저온 저장 시기나 저장 온도에 관한

추가적인 실험이 필요할 것으로 확인되었다. 결론적으로, 저온 처리와

저온 저장 방법은 벼룩이울타리의 연중 생산을 위한 개화 시기 조절에

사용될 수 있다.

GENERAL INTRODUCTIONLITERATURE REVIEWFlowering Response to Photoperiod in CaryophyllaceaeFlowering Response to Chilling in CaryophyllaceaeChill Unit Models for Calculating Chilling Hours in Horticultural CropsCold Storage for Delaying Flowering

MATERIALS AND METHODSFlowering Response to Photoperiod (Experiment 1)Flowering Response to Chilling (Experiment 2)Cold Storage for Delaying Flowering (Experiment 3)

RESULTS AND DISCUSSIONFlowering Response to Photoperiod (Experiment 1)Flowering Response to Chilling (Experiment 2)Cold Storage for Delaying Flowering (Experiment 3)

LITERATURE CITEDABSTRACT IN KOREAN

10GENERAL INTRODUCTION 1LITERATURE REVIEW 4 Flowering Response to Photoperiod in Caryophyllaceae 4 Flowering Response to Chilling in Caryophyllaceae 4 Chill Unit Models for Calculating Chilling Hours in Horticultural Crops 5 Cold Storage for Delaying Flowering 7MATERIALS AND METHODS 8 Flowering Response to Photoperiod (Experiment 1) 8 Flowering Response to Chilling (Experiment 2) 11 Cold Storage for Delaying Flowering (Experiment 3) 16RESULTS AND DISCUSSION 19 Flowering Response to Photoperiod (Experiment 1) 19 Flowering Response to Chilling (Experiment 2) 22 Cold Storage for Delaying Flowering (Experiment 3) 29LITERATURE CITED 33ABSTRACT IN KOREAN 38