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This is to certify that the

thesis entitled

CONTROLLED ATMOSPHERE STORAGE
OF SPECIAL PRECOOLED TULIP BULBS
‘(TULIBAWQESNERIANA L.,
'KEES NELIS' AND 'PROMINENCE')

presented by
Timothy A. Prince

has been accepted towards fulfillment
Of the requirements for

M. S. #.degree in _Iiorticu1ture

flMCM L

Major professor

April 29, 1989__

' V

iii-M2 9 as a?
I} t ’1 lD/Jéf‘s

 

OVERDUE FINES:
25¢ per day per item

RETUMIMS LIBRARY MATERIAL§:

Place in book return to mo
charge from circulation reco

 

 

CONTROLLED ATMOSPHERE STORAGE
OF SPECIAL PRECOOLED TULIP BULBS
(TULIPA GESNERIANA L.,
'KEES NELIS' AND 'PROMINENCE')

 

by

Timothy A. Prince

A THESIS
Submitted to
Michigan State University
in partial fulfillment of the requirements
for the degree of
MASTER OF SCIENCE
Department of Horticulture

1980

ABSTRACT

CONTROLLED ATMOSPHERE STORAGE
OF SPECIAL PRECOOLED TULIP BULBS
(TULIPA GESNERIANA L.,
'mmumm'MDwmmmmy)
by

Timothy A. Prince

Oxygen levels of 3 and 5%, obtained by blending N2 and air in a

flow-through system, maintained satisfactory flowering ability of
special precooled 'Kees Nelis' tulip bulbs (Tulipa gesneriana L.)
through 4 but not 6 weeks of storage at 17°C. 'Kees Nelis' bulbs

stored in air or 1% 02 for 4 or 6 weeks and 'Prominence' bulbs stored

at any 0 level for 4 or 6 weeks yielded unsatisfactory flowering.

2
Bulbs special precooled late in the forcing season yielded unsatis-

factory flowering after storage at 17°C regardless of cultivar. Low

02 levels reduced the respiration rate and the ethylene production

rate of bulbs during 6 weeks of storage at 17°C as compared to bulbs
stored in air. Storage of 'Kees Nelis' bulbs for 3 weeks in air with
S or 10 ppm ethylene caused flower abortion upon forcing. Ethylene

in the atmosphere during storage at 3 or 5% 02 caused less flower

abortion. Storage in air with 16% CC for 4 weeks caused stem topple

2
upon forcing.

To My Parents

with thanks for their continuing love and support

ii

ACKNOWLEDGMENTS

I thank Dr. R. C. Herner, Dr. A. A. DeHertogh, and Dr. D. R. Dilley
for their assistance, guidance, and support during the course of this
research. The technical assistance of Norm Blakely, Kees Zonneveld,

and Kees Lommersee was greatly appreciated.

Finally, I thank the Netherlands Flower Bulb Institute for the

generous financial support that made this research possible.

iii

TABLE OF CONTENTS

Page

LIST OF TAKIES O O O O O O O O O O O O O O O O O O O O O O O O 0 v

LIST OF FIGURES. O O O O O O O O O O O O O O O O O O O O O O O 0 ix

INTRODUCTION 0 . o . . . . . . o . . . o . . . o o o . o . . . . 1
MATERIALS AND METHODS. . . . . o . . o . . . . . . . . . . . . . 11
RESULTS OF PRELIMINARY EXPERIMENTS (1977-78) . . . . . . . . . . 18
RESULTS OF MAJOR EXPERIMENTS (1978-79) . . . . . . . . . . . . . 31
DISCUSSION . . . . . . . . . . . . . . . . . . . . . . . . . . . 108

CONGJIJSIONS O O O O O O O O O O O O O O O O C O O O O O O O O O O 114

LIST OF HEBREMES O O O O O O O O O O O O O O O O O O O O O O O 115

iv

Table

1.

2.

3.

4.

5.

6.

8.

LIST OF TABLES

Page

Number of 'Prominence' tulip bulbs flowering normally
after special precooling and 3 wks of air or low 02
level storage at 17°C (1977-78). . . . . . . . . . . . . 30
Shoot quality after early season special precooling and

air or low 02 level storage of 'Kees Nelis' and 'Prom-

inence ' tulip bUlbs at 17°C. 0 Q Q Q Q Q Q . . 0 . . . Q Q 70
Shoot quality after late season special precooling and

air or low 02 level storage of 'Kees Nelis' and 'Prom-

inence' tulip bulbs at 17°C. . . . . . . . . . . . . . . 71
Floral organ measurements of 'Prominence' tulip bulbs
after early season special precooling and air or low 02
level storage for 2 or 4 wks at 17°C . . . . . . . . . . 72
Floral organ measurements of 'Kees Nelis' tulip bulbs
after early season special precooling and air or low 02
level storage for 2 or 4 wks at 17°C . . . . . . . . . . 73
Floral organ measurements of 'Kees Nelis' tulip bulbs
after late season special precooling and air or low 02
level storage for 2 or 4 wks at 17°C . . . . . . . . . . 74
Floral organ measurements of 'Prominence' tulip bulbs

after late season special precooling and 2 wks of air

or low 02 level storage at 17°C. . . . . . . . . . . . . 75

Number of 'Kees Nelis' tulip bulbs flowering normally
after early season special precooling and 2, 4, and 6

wks of air or low 02 level storage at 170C . . . . . . . 76

LIST OF TABLES (Cont'd.)

Table

9.

10.

11.

12.

13.

14.

15.

16.

17.

Page

Number of 'Kees Nelis' tulip bulbs flowering normally
after late season special precooling and 2, 4, and 6

wks of air or low 02 level storage at 17°C . . . . . . . . 81

Number of 'Prominence' tulip bulbs flowering normally
after early season special precooling and 2, 4, and 6

wks of air or low 02 level storage at 17°C . . . . . . . . 82

Number of 'Prominence' tulip bulbs flowering normally
after late season special precooling and 2, 4, and 6

wks of air or low 02 level storage at 17°C . . . . . . . . 83

Plant quality of forced 'Kees Nelis' tulip bulbs after
early season special precooling and air or low 02 level
storage for 2, 4, and 6 wks at 17°C. . . . . . . . . . . . 84
Plant quality of forced 'Prominence' tulip bulbs after
early season special precooling and air or low 02 level

storage for 2 and 4 wks at 17°C. . . . . . . . . . . . . . 86

Shoot quality of 'Kees Nelis' and 'Prominence' tulip

bulbs after early season special precooling and 3 wks
of air and low 02 level storage at 17°C with 0 and 5

pmethyleneooooooooooooooooooooooo 90
Shoot quality after late season special precooling and

air or low 02 level storage of 'Kees Nelis' tulip bulbs

at 17°C with O or 10 ppm ethylene. . . . . . . . . . . . . 91
Floral organ measurements of 'Kees Nelis' tulip bulbs

after early season special precooling and air or low 02
level storage for 3 wks at 17°C with O or 5 ppm ethylene . 92
Floral organ measurements of 'Kees Nelis' tulip bulbs
after late season special precooling and air or low 0

2
level storage for 3 wks at 17°C with Ocnr10 ppm ethylene . 93

vi

LIST OF TABLES (cont'd.)

Table

18.

19.

20.

21.

22.

23.

24.

25.

26.

Floral organ measurements of 'Prominence' tulip bulbs
after early season special precooling and air or low 02
level storage for 3 wks at 17°C with O or 5 ppm ethylene
Number of 'Kees Nelis' tulip bulbs flowering normally
after early season special precooling and 3 wks of air

or low 02 level storage at 17°C with O andS_ ppm ethylene

NUmber of 'Kees Nelis' tulip bulbs flowering normally
after late season special precooling and 3 wks of air

or low 02 level storage at 17°C with O and 10 ppm ethylene

NUmber of 'Prominence' tulip bulbs flowering normally
after early season special precooling and 3 wks of air

or low 02 level storage at 17°C with O and 5 ppm ethylene

Plant quality of forced 'Kees Nelis' tulip bulbs after

early season precooling and air or low 0 level storage

2
for 3 wks at 17°C with 0 or 5 ppm ethylene . . . . . . .

Plant quality of forced 'Kees Nelis' tulip bulbs after

late season precooling and air or low 0 level storage

2
for 3 wks at 17°C with O or 10 ppm ethylene. . . . . . .

Shoot quality of 'Kees Nelis' and 'Prominence' tulip
bulbs after special precooling and 4 wks of air or low

02 level storage with 0.4, 10, and 16% CO2 at 17°C . . .

Floral organ measurements of 'Kees Nelis' tulip bulbs

ter special precooling and air or low 0 level storage

2
for 4 wks at 17°C with 0.4, 10, and 16% C02. . . . . . .

Floral organ measurements of 'Prominence' tulip bulbs

after special precooling and air or low 0 level storage

2
for 4 Vlks at 17°C With 0.4, 10, and 16% C020 0 o o o o 0

vii

Page

94

95

96

97

98

100

101

102

103

LIST OF TABLES (cont'd.)

Table Page

27. Number of 'Kees Nelis' tulip bulbs flowering normally
after special precooling and 4 wks of air or low 02
level storage at 17°C with 0.4, 10, and 16% C02. . . . . . 104

28. Number of 'Prominence' tulip bulbs flowering normally
after special precooling and 4 wks of air or low 02
level storage at 17°C with 0.4, 10, and 15% C02. . . . . . 105

29. Plant quality of forced 'Kees Nelis' tulip bulbs after

special precooling and air or low 0 level storage for 4

2
wks at 17°C with 0.4, 10, and 16% C02. . . . . . . . . . . 106

viii

LIST OF FIGURES

Figure Page

1. Respiration rate of 'Prominence' tulip bulbs at 17-20°C
and 5°C during the 1977-78 forcing season. . . . . . . . . 20

2. Ethylene production rate of 'Prominence' tulip bulbs at
17-20°C during the 1977-78 forcing season. . . . . . . . . 22

3. Ethylene production rate of 'Prominence' tulip bulbs at
5°C during the 1977-78 forcing season. . . . . . . . . . . 24

4. Respiration rate of 'Prominence' tulip bulbs at 17°C
after 4, 8, and 12 wks of storage at 5°C during the 1977-

78 season. 0 O O O O O O O O O O O O O C O O O O O O O O O 26

5. Ethylene production rate of 'Prominence' tulip bulbs at
179C after 4, 8, and 12 wks of storage at 5°C during the

1977-7aseasonooooooooooooooooooooco 28

6. Respiration rate of 'Prominence' and 'Kees Nelis' tulip
bulbs at 5°C and 17°C during the 1978-79 forcing season. . 36

7. Ethylene production rate of 'Prominence' and 'Kees Nelis'
tulip bulbs at 17°C during the 1978-79 forcing season. . . 38

8. Ethylene production rate of 'Prominence' tulip bulbs at
5°C during the 1978-79 forcing season. . . . . . . . . . . 4O

9. Ethylene production rate of 'Kees Nelis' tulip bulbs at
5°C duing the 1978-79 forCing season. 0 o g o a Q o g Q . 42

10. Respiration rate of 'Prominence' tulip bulbs at 17°C after
2, 4, 6, and 8 wks of storage at 5°C during the 1978-79

forCing season 0 O O O O O O O O O O O O O O O O O O O O O 44

LIST OF FIGURES (cont'd.)

Figure Page

11. Respiration rate of 'Prominence' tulip bulbs at 17°C
after 10, 12, 14, and 16 wks of storage at 5°C during
the 1978-79 forcing season . . . . . . . . . . . . . . . . 46

12. Shoot length within 'Prominence' tulip bulbs after
storage at 5°C and subsequent storage for 2 wks at 17°C
during the 1978-79 forCing SeaSOn. . o a Q Q Q o g Q Q Q g 48

13. Tepal length within 'Prominence' tulip bulbs after storage
at 5°C and subsequent storage for 2 wks at 17°C during
th61978-79f°rcmgseasonooooooooooooooco so

14. Anther length within 'Prominence' tulip bulbs after
storage at 5°C and subsequent storage for 2 wks at 17°C
during the 1978-79 forcing season. . . . . . . . . . . . . 52

15. Respiration rate of 'Prominence' tulip bulbs during 6 wks

of air or low 02 level storage at 17°C after early season

SpECialpI'ECOOling.................... S4

16. Respiration rate of 'Kees Nelis' tulip bulbs during 6 wks

of air or low 02 level storage at 17°C after early season

SpeCialprECOOlj-ngoooooooooooooooooooo 56

17. Respiration rate of 'Prominence' tulip bulbs during 6 wks

of air or low 02 level storage at 17°C after late season

special precooling . . . . . . . . . . . . . . . . . . . . 58

18. Respiration rate of 'Kees Nelis' tulip bulbs during 6 wks

of air or low 02 level storage at 17°C after late season

SpeCialprECOOlingooooocooooooooooooon 60

19. Ethylene production rate of 'Prominence' tulip bulbs

during 6 wks of air or low 0 level storage at 17°C after

2
early season special precooling. . . . . . . . . . . . . . 62

LIST OF FIGURES (cont'd.)

Figure Page

20. Ethylene production rate of 'Kees Nelis' tulip bulbs

during 6 wks of air or low 0 level storage at 17°C after

2
early season special precooling. . . . . . . . . . . . . . 64
21. Ethylene production rate of 'Prominence' tulip bulbs

during 6 wks of air or low 0 level storage at 17°C after

2
late season special precooling . . . . . . . . . . . . . . 66
22. Ethylene production rate of 'Kees Nelis' tulip bulbs

during 6 wks of air or low 0 level storage at 17°C after

2
late season special precooling . . . . . . . . . . . . . . 68
23. Flowering of 'Kees Nelis' and 'Prominence' tulip bulbs
after early season special precooling and 4 wks of air or

low 02 level storage at 17°C . . . . . . . . . . . . . . . 77

24. Aborted flower after air storage of 'Kees Nelis' tulip
bulbs for 4 wks; stem topple after air + 16% CO2
of 'Kees Nelis' tulip bulbs for 4 weeks. . . . . . . . . . 79

storage

xi

INTRODUCTION

The tulip bulb is composed of concentric scales separated by
short internodes. The outer scale, or tunic, is brown and papery. The
scales are joined at the basal plate from which emerges the flowering
shoot and the roots. Daughter bulbs are initiated in the axils of

the scales.

Bulb Life Cycle

The tulip bulb life cycle is outlined by Rees (1972). Each
mother bulb planted in the autumn dies upon flowering and is replaced
by daughter bulbs. During the spring, the total dry weight of the
daughter bulbs increases rapidly, with the increase peaking at the
time of leaf senescence. The apices within the bulbs are still in the
vegetative state at lifting time in July in the Netherlands.

Flower initiation occurs when the bulbs are in storage or during
shipment. Differentiation progresses from the tepals to the anthers,
being completed at stage G, with formation of the tri-lobed gynoecium

(Beijer, 1952).

Cold Requirement for Development

Once flower differentiation in the tulip bulb has progressed to
stage G, a period of low temperature is necessary for normal flower
stalk development during the spring in natural conditions or during
forcing (Hartsema, 1961; Rees, 1972). Longer outdoor cold treatments
were found to cause faster growth in height, increased length of mature
stems, shorter number of days to flower, more uniform flowering, and
less flower abnormality (Rees, 1969). The cold requirement for adequate

1

2
stem extension has been shown to be greater than the requirement for
good flower quality (Hobson and Davies, 1978). Dickey (1957) first
showed that the cold requirement could be met by artificially cooling
the bulbs before planting in climates where natural cooling was in-
sufficient.

Guidelines have been prepared for use by growers to segregate
cultivars into groups based upon the cold requirement for forcing.
DeHertogh (1977) classified cultivars into seven groups and identi-
fied minimum, optimum, and maximum number of weeks of cold required.
Rees (1977) expressed the cold requirement as the number of days at
9°C required to produce flowers in 21 days at 18°C. 'Prominence'
required 139 while 'Kees Nelis' required 134 days within a range of
99 to 171 days for all cultivars tested. Hobson and Davies (1978)
reported that the number of cold units applied was more important than
a specific temperature and time in determining good flower quality.

Special precooling is defined as storage of tulip bulbs at 5°C
in a dry, unplanted state to satisfy all of the cooling requirement
before planting (DeHertogh, 1977). This method is in contrast to more
standard methods whereby all or part of the cold treatment (generally
9°C) is applied to planted bulbs. The rate of shoot growth and number
.of bulbs flowering increases with duration of 5°C storage, and 12 to 14
weeks of special precooling is optimal (Moe and Wickstrom, 1973).

Early flowering has been interpreted as the result of satisfying
the cold requirement while at the same time allowing some shoot growth
(Rees and Briggs, 1975). The cold requirement has a lower optimum tem-
perature than does shoot growth. Kawata (1975) found that the temper-

ature optimum for early flowering fell from 5°C to 2°C without any

3
reduction in flower size when the duration of cooling and the degree
of flower development was advanced at the start of precooling. In this
case, some of the shoot growth requirement would have been met before
cooling.

An interruption with warm storage after 6 weeks at 9°C and subse-
quent cooling for 108 days did not nullify the precooling effects as has
been reported for lily bulbs (Rees, 1973; Miller and Kiplinger, 1966).
Interruption with warm storage hastened rather than delayed flowering
of tulip bulbs except at 30°C, where all the flowers aborted. This
finding is relevant to the marketing of special precooled bulbs, although
warm storage during a marketing period just prior to bulb forcing would

follow the entire precooling period.

Biochemical Effects

Algera (1936, 1947) first showed that low temperature storage
increased the sugar concentration in the tulip bulb. He emphasized the
role of reducing sugars for flower shoot development in both hyacinth
and tulip. Moe and Wickstrom (1973) demonstrated that sucrose and fruc-
tosyl sucrose substantially increased during the first 2 to 4 weeks of
special precooling as starch decreased. At the end of 12 weeks at 5°C,
the oligosaccharide content decreased. High temperature (20°C) storage
yielded little change in sucrose and fructosyl sucrose.

A decrease in starch level and rise and fall of sucrose and fruc-
tosyl sucrose during special precooling was confirmed by Haaland and
Wickstrom (1975). They also found the incorporation of 14C from sucrose
into starch to be faster at 21°C than at 5°C within the scales or the
shoot. Incorporation of sucrose into fructosyl sucrose by transfructo-

sylases occurred at a higher rate at 5°C than at 21°C. Sucrose content

4

within the shoot predominated over fructosyl sucrose during cooling.
They concluded that possibly starch conversion to sucrose and subse-
quent transferral to the shoot for floral development was enhanced by
cold temperatures.

Thompson and Rutherford (1977) found that alcohol soluble carbo-
hydrates in the scales of planted bulbs increased during an 8 to 18 week
period of 9°C storage. In addition, precooling of planted bulbs at 5°,

0, or 13°C resulted in alcohol soluble sugar increases in the bulbs

9
(Thompson and Rutherford, 1979). Davies and Kempton (1975) found that
the total fructose level of planted bulbs increased throughout a 9°C
storage period while free fructose remained at relatively low levels.

The absence of a decline in alcohol soluble carbohydrates in
these experiments as opposed to the experiments where bulbs were cooled
while dry and unplanted indicates that differences between unplanted and
planted bulbs in response to cold treatment occur. However, precooling
bulbs at 5°C while dry or in moist peat and perlite gave no difference
in subsequent shoot growth or flowering date (Moe and Hagness, 1975).

Investigations of the changes in amino acids and enzyme levels
during precooling have also been reported. Arginine was found to be the
predominant amino acid in the bulb before floral initiation. After
cooling and development of the shoot, glutamine and asparagine levels
within the entire plant structure rose dramatically (Zacharius, 53'3£.,
1957).

Hobson (1975) found only minor changes in activity of phospho-
glucomutase, phosphohexose isomerase, and 6-phosphogluconate dehydro-
genase in the scales due to cold (9°C) treatment. The enzymes usually

associated with starch breakdown, amylase and phosphoryllase, did not

5
show increased activity at 9°C as compared to activity in uncooled bulbs.
The author concluded that changes in activity resulting from cold treat-
ment were not sufficient to account for the gross changes in composition

that occurred.

Hormonal Effects

Aung and DeHertogh (1968) and Aung, 33.3i' (1969, 1971) exten-
sively investigated the role of gibberellic acid (GA) in the tulip bulb.
Concentration of free GAplike substances increased in planted bulbs
after 4 and 8 weeks at 9°C with a maximum at 13 weeks. Bound GA-like
substances decreased slightly after 4 weeks and rose after 8 and 13
weeks. Release of bound GA and some new syntheses during cold treat-
ment was suggested. Applied gibberellins substituted for the first 6
weeks of precooling but only partially for the second 6 weeks (Bragt and
ZyIstra, 1971). Flowering of isolated buds of 'Apeldorn' was obtained
from explants from bulbs treated at 5°C for 6 weeks and cultivated in
light on a medium containing sucrose and 6A3 (Bragt, 1971).

Hanks and Rees (1977) suggested that two hormonal mechanisms con-
trol extension growth of the tulip stem. Auxin, produced in the gynoe-
cium, regulates growth of the top internode. A GA system, inhibited by

ancymidol, regulates the growth of the lower internodes.

Respiration Rate and Mitochondrial Activity

Few studies of the respiration of tulip bulbs have been reported.
Algera (1936, 1947) found that after a minimum was reached in mid-August,
C02 produced by tulip bulbs slowly increased. Low temperatures reduced

respiration and a return to 20°C increased respiration. Removal of the

6
tunic increased respiration two- to three-fold. Rees (1972) found that

after lifting, 0 consumption was maximal (30-35/ul/g fr. wt./hr) and

2
then decreased to a relatively steady state (10-12‘pl/g fr. wt./hr)

through October. Tunic removal doubled respiration and scale removal
gave clear wound effects with a four-fold increase in respiration. Nezu
and Obata (1964) reported a rate of 4-6 mg COZ/g fr. wt./hr at 30°C in
August. A study of respiration rates of onions (Allium ggpg_L.), a
similar bulb structure to the tulip, showed that the previous storage
temperature was an influential factor on the respiration rate at 10°C
(Adamicki, 1977). Storage at 1°C yielded a higher respiration rate when
transferred to 10°C than storage at 5°C.

Some studies with mitochondria isolated from tulip bulb scales
have been reported. Hobson and Davies (1977) stored bulbs at 9°C or 18°C
for 6 weeks, then planted and grew them to anthesis at the same tempera-
tures. A minimum activity of the mitochondria as measured by the ability
to oxidize succinate, malate, or 2-oxoglutarate was recorded after 10
weeks at either temperature. The activity rose through the 26th week.
Cooled bulbs showed more active mitochondria than uncooled bulbs. High
mitochondrial activity was correlated with low levels of alcohol soluble
carbohydrates and sucrose in cooled bulbs. No relationship was found
in uncooled bulbs.

Arrhenius plots of succinate and NADH oxidation by mitochondria
from bulbs kept in the dark at 20 or 18°C were made by Hobson (1979).

In the range of 0-36OC, mitochondria from uncooled bulbs showed a single
transition point but bulbs cooled for 8 weeks or longer showed indica-
tions of two discontinuities in the diagrams. The author suggested that

tulip bulbs are chilling sensitive, with changes in the activation

7
energy suggesting a phase change in the lipid bilayer. However, direct
analysis of lipid fractions from cooled and uncooled bulbs measuring the
degree of unsaturation and chain length would be desirable before drawing

any conclusions from this work.

Ethylene Effects

A review by Kamerbeek and Munk (1976) lists the major effects of
ethylene on the tulip as gummosis of the bulb scales, bud necrosis,
flower bud blasting, and morphological changes resembling those caused
by unfavorable temperatures.

Kamerbeek,'gt‘gl. (1971) concluded that ethylene can cause gum-
mosis. Only certain cultivars were affected, and a threshold value of
0.1 ppm for bulbs in a highly responsive stage was determined. The
process appeared to be inhibited by low temperature (5°C). Ethylene
production by bulbs infected with Fusarium oxyspgrum tulipae was shown
to cause gummosis. Fusarium was found to produce ethylene abundantly
EEHXEEES (Swart and Kamerbeek, 1977). Infection of young growing bulbs
has been shown to occur mainly during the last few weeks before harvest.
Harvesting too early, before the tunic is sufficiently hardened, was
implicated in high occurrences of Fusarium infection (Bergman and
Beijerbergen, 1970).

Bud necrosis, a storage disorder of tulip bulbs, was extensively
researched by Munk and Beijer (1971) and Munk (1971a, 1971b, 1972, 1973a,
1973b). They found that it is caused by mites that penetrate open buds
during storage. Open buds resulted from greater inhibition of the young
leaves than of the stamens by ethylene exposure as low as 0.1 ppm,

causing the stamens to grow out of the bud. The first symptom‘of bud

8
necrosis is stamen decay, leading to flower necrosis, shoot necrosis,
and finally bulb necrosis, where scales become necrotic. These symptoms
obviously lead to inferior flowering after the bulbs are planted.

Bulbs infected with Fusarium can also cause problems in the
greenhouse after precooling and planting. Schenk and Bergman (1969)
noted growth retardation and yellowing of the leaves, often resulting
in death of the plant before flowering. Munk and Roay (1971) measured
ethylene up to 10 ppm in the soil atmosphere surrounding bulbs infected
with Fusarium. They postulated that this could account for the observed

growth inhibition of shoots and roots and blasting of the flower buds.

Ethylene Production

The production of ethylene by healty tulip bulbs was reported as
too low for detection in samples of surrounding air by Munk (1972). How-
ever, Noe, gt al. (1978b) found that endogenous ethylene production of
'Paul Richter' and 'Apeldorn' bulbs reached a peak 3-4 days after removal
from 5°C to 21°C. One week later, a second peak related to flower blas-
ting was observed. Increasing the duration of storage at 5°C increased
the ethylene production. The authors compared the ethylene production
to that which results from postharvest cold stress in pears (Sfakiotakis

and Dilley, 1974).

Controlled Atmosphere Storage

The use of low pressure storage and the storage of tulip bulbs
in various packages or closed systems has had limited study.

DeHertogh, 33 El. (1978) found that storage of tulip bulbs for
14 days in August in 76- or 150 mm-Hg before any precooling was applied

suppressed leaf growth and floral development. The treatments delayed

9
flowering after subsequent planting of most cultivars. The authors
concluded that low pressure storage offered no advantage over ventilated,
temperature controlled units now being used for shipping. The use of
this technique during other phases of the tulip bulb forcing season
has not been investigated.

Various storage methods for bulbs removed from special precooling
at 5°C have been studied. Hoe and Hagness (1975) found that bulbs held
in poorly ventilated cardboard boxes for more than 4-8 days at warm
temperatures formed many blasted or poor quality flowers upon forcing.
Bulbs kept in closed desiccators at warm temperatures accumulated
ethylene (1.0 - 1.8 ppm) after 5-6 days (Moe, EE.2$" 1978b). Visual
symptoms of floral bud injury within the bulbs were present at 8 days
after removal from 5°C and increased when temperature, ethylene concen-
tration, and/or duration of storage increased. Addition of 4.5% CO did

2

not prevent the injury. Bulbs kept in desiccators where the 02 content

decreased to 1% and CO2 increased to 16% did not show symptoms of
floral bud injury after 8 days (Moe, 25 gl., 1978a). The authors con-
cluded that after special precooling has been concluded, tulip bulbs

i must be held at 15°C or cooler, maximum ventilation should be provided,

and the shipping period should not exceed 8 days.

Storage in Polymeric Films

The use of polymeric films for controlled atmosphere storage
has been investigated for vegetables and fruits, but not for tulip
bulbs. Henig (1975) describes a package as a dynamic system in which
respiration and permeation are occurring simultaneously. There is

uptake of 02 by the produce and evolution of CO , ethylene, water,

2

10
and other volatiles. At the same time, specific restricted permeation
of these gases through the packaging film is occurring. After a short

period of adjustment, steady-state conditions are established within

the intact packaging system, wherein equilibrium concentrations of CO2

and O2 prevail and the respiration rate is equal to the permeation rate
(Tomkins, 1962). The use of two films having different permeabilities

to O2 and CO2 for controlling the concentrations of these two gases
independently has also been investigated (veeraju and Karel, 1966).

Jurin and Karel (1963) described a method involving plotting the rate

of respiration and permeation at different 02 concentrations on the

same set of coordinates. From the intersection of these two curves,

the equilibrium concentration could be determined as well as the decrease

in respiration rate.

Statement of the Problem

It would be desirable to market special precooled tulip bulbs
without a refrigeration requirement. A marketing period exceeding the 8
days now recommended and near perfect flowering would be required. The
objectives of this research were to provide preliminary information
for the development of a controlled atmosphere market package for
special precooled tulip bulbs. This information includes:

1. Effects of precooling duration on subsequent respiration and
ethylene production rates of tulip bulbs at warm temperatures.

2. Possible use of low 0 levels to maintain the flowering
ability of tulip bulbs for various durations of warm storage
after precooling.

3. Respiration and ethylene production rates of precooled bulbs

stored in low 02 at warm temperatures.

4. Effects of high CO and ethylene levels during low 0 storage
on the flowering agility of precooled tulip bulbs.

MATERIALS AND METHODS

The-experiments reported here were performed over two bulb forcing
seasons, 1977-78, and 1978-79. A general description of procedures
applicable to both seasons is followed by specific procedures of each

experiment.

‘Bulb’fiandling

Bulbs of Tuilpa gesneriana L. 'Prominence', and 'Prominence' and
'Kees Nelis', were shipped from the Netherlands and arrived in East Lan-
sing, Michigan, on August 1, 1977, and September 7, 1978, respectively.
They were stored at 17-2o°c (1977) and 17 i o.s°c (1978) in open tray
cases until precooling. The flowering shoot within the bulbs had

reached stage G on August 23, 1977, and by the arrival date in 1978.

Bulb Dissection

At various stages of the research, bulbs were dissected and
examined. The length of the shoot, anthers, and tepals within the bulb
was measured. The ratio of tepals/anthers was calculated. The shoots
were rated as normal, anthers abnormal, entire perianth abnormal, or
entire shoot abnormal. This rating was a modification of the method

used by Moe EE.E£‘ (1978a).

Treatment Application

Treatments were applied and CO and ethylene production were

2
monitored in flow-through systems with either 1 pint (473 ml) or
2 quart (1.89 1) Mason jars, or 10 liter plastic buckets as replica-

tions within treatments in dark, temperature-controlled rooms. All

11

12

treatment chambers were equipped with inlet and outlet ports. Air, NZ,
and CO2 were blended by the use of capilary flow boards to yield con-
stant known flow rates of the desired atmospheres. Ethylene, when applied,
was diffused through short lengths of Tygon tubing into the atmosphere
stream from reservoirs of pure ethylene, to yield the desired concen-
tration (Saltveit, 1978).

Gas sampling was at the exit ports for determination of C02, 02,
and ethylene levels. The atmosphere stream was also sampled before
entering the chambers for determination of CO2 and trace amounts of
ethylene. These levels were subtracted from the exit port determina-
tions to yield production rates calculated in units of ml COZ/kg fr. wt./hr

and pl C2H4/kg fr. wt./day.

Control Monitoring

Controls for the studies involving CO and ethylene production

2
were monitored for both years. Immediately after arrival, five bulbs of
each cultivar were placed in each of four 1 pint Mason jars, and kept under
a constant stream of air (5-16 ml/min). The temperature regime was 20 :
0.50C from arrival time until November 10, 1977, when it was lowered

to 17 i o.s°c in the 1977-78 season. In 1978-79, the temperature was

maintained at 17 : 0.5°C throughout. The CO and ethylene production

2
was monitored throughout the duration of each year's experiments. In
addition, monitoring of bulbs at 5 : 0.S°C was done in the same manner

with flow rates of 1-2 ml/min. Only 3 replications were used for 'Kees

Nelis' in 1978-79.

13

Gas Determinations

One ml air samples were taken with gas tight syringes for ethylene
determination. A Varian 1700 gas chromatograph employing a flame ioniza-
tion detector and an alumina column was used for analysis.

Two ml (1977-78) or 1 ml (1978-79) samples were taken for CO and

2

O2 determinations. Analysis (1977-78) was on a gas chromatograph employing
a thermal conductivity detector and equipped with two columns in parallel.
One column was of silica gel for the separation of CO2 and another of

molecular sieves for separation of N2 and 02 using helium as the carrier
gas at 70°C (Brenner and Cieplenski, 1958). Analysis for 1978-79 was on

a Carle GC 8700 with the same parameters.

Planting

The tunic was peeled from all bulbs prior to planting to facilitate
rooting (DeHertogh, 1977). In 1977-78, a 20 min dip of 1.1 g ethazol
(35% WP)/gal and 1.1 g benomyl (50% WP)/gal was used before planting.
In 1978-79 a drench of 100 ml of 6.8 g benomyl (50% WP)/gal was used
instead of the dip. All bulbs were planted (5 bulbs/pot) in 15 cm pots
containing peat, bark, perlite, and vermiculite (Metromix 300). The
bulbs were planted with their tops just above the soil surface. The
pots were distributed randomly on the greenhouse bench with minimum night
temperature at 13°C (1977-78) or 17°C (1978-79). The plants were fertil-
ized once with 100 ml of 20-20-20 at 200 ppm N when the roots first showed

at the bottom of the pot.

14
Flowering

A plant was considered in flower when 2/3 of the flower showed the
characteristic color of the cultivar. Upon flowering, quality data was
taken as height of the flower, height of the entire plant (from top of
bulb), bottom internode length, top internode length, and the number of
days from planting to flowering. Aborted petals and stem topple were
noted (DeHertogh, 1977) and these plants were not considered normal in

the analysis.

Preliminary Experiments (1977-78)

The effects of three precooling durations and the ability of low 02

levels to maintain the flowering capabilities of 'Prominence' were studied.
_ Precooling Duration Effects -- Bulbs of 'Prominence' were placed at 5°C

on October 13, 1977, in open tray cases for durations of 4, 8, and 12
weeks. At the end of each duration, 5 bulbs were chosen randomly and
placed in each of four 2 quart Mason jars (4 reps) with a flow rate of

9-11 ml air/min at 17°C. The ethylene and CO production was monitored

2
for 2 weeks.

Oxygen.£gzgl Effects -- Bulbs of 'Prominence' were placed at 9°C on Sep-
tember 26, 1977, and moved to 5°C on November 1, 1977, for 12 weeks.
Immediately after the special precooling, 4 replications of 5 bulbs/pot
were planted as controls and 20 bulbs were randomly chosen for dissec-
tion. Ten bulbs were randomly placed into each of four 2 quart Mason
jars (4 reps) for each treatment. The treatments, obtained by blending
N and air by means of a flow-through system, were 0%, 2-3%, 4-7%, 8-11%,

2

and 15-20% 02 at 17°C. After 3 weeks, 5 bulbs from each jar were

15
randomly chosen for dissection and 5 bulbs were planted for flowering

evaluation.

Major Experiments (1978-79)

Experiments were designed to further study the effects of the dura-
tion of the precooling period, to determine more accurately the 02 level
required to maintain the flowering ability of precooled bulbs, and to

evaluate the response to ethylene and high CO levels during low 0 storage.

2 2
Precooling Duration Effects -- Bulbs of 'Prominence' were placed at 5°C on
September 12, 1978, for durations of 2, 4, 6, 8, 10, 12, 14, and 16 weeks.
At the end of each period, 20 bulbs were selected randomly for dissection.
Five bulbs were placed in each of four 2 quart Mason jars (4 reps) with

a flow rate of 25-30 ml air/min at 17°C. The CO2 production was monitored
for 2 weeks after which the bulbs were dissected.

Oxygen.gszgl Effects -- Bulbs of 'Prominence' and 'Kees Nelis' were placed
at 5°C on September 19, 1978 (early season), or November 2, 1978 (late
season) for 14.5 weeks. At the end of each period, 20 bulbs of each
cultivar were selected randomly and dissected and 20 were selected for
planting as controls. The treatments were applied in a 4 x 3 factorial
arrangement of 1.0 i 0.5%, 3.0 i 0.7%, 5.0 1’ 1.0%, and 20 i 1.0% 02,
each at durations of 2, 4, and 6 weeks at 17°C. All were applied with

a flow-through system by blending N and air as described previously,

2
with a 40-60 ml/min flow rate. Each treatment combination for each cul-
tivar was replicated 4 times in 2 quart Mason jars containing 15 randomly

selected bulbs. The replications within cultivar were randomly placed

within the storage room, but the cultivars were kept separate. The 02,

16

CO and ethylene levels were monitored periodically throughout the 6

2!
week duration. After treatment application, 5 bulbs from each jar were
randomly selected for dissection and 10 bulbs were planted for flowering

evaluation.

Carbon Dioxide Eeysl Effects -- Bulbs of 'Prominence' and 'Kees Nelis'
were placed at 5°C on September 14, 1978, for 13 weeks. Ten bulbs of each
cultivar were then randomly selected for dissection and 20 bulbs for
planting as controls. Twenty-five bulbs of each cultivar were placed

in each of two 10 liter buckets (2 reps) for each treatment combination.
The treatments were applied in a 2 x 3 factorial arrangement with O

2

levels at 3.0 i 0.5%, and 19.0 i 1.6%, and CO levels at 0.4 t 0.1%,

2

10.0 i 1.4%, and 16.0 i 1.5%, obtained by blending air, N and co with

2’ 2

flow rates of 150-200 ml/min. The buckets were randomly arranged in the
storage room at 17°C. The CO2 and 02 levels were monitored periodically
throughout a 4 week duration. Five bulbs of each cultivar were then ran-
domly selected from each bucket for dissection and 20 planted for flowering

evaluation.

Ethylene Effects -- Bulbs of 'Kees Nelis' and 'Prominence' (early season)
or 'Kees Nelis' only (late season) were placed at 5°C on October 17, 1978,
and November 30, 1978, respectively, for 13.5 weeks. Ten bulbs of each
were then randomly selected for dissection and 20 were planted as con-
trols. Fifteen bulbs were placed into each of two 2quart Mason jars (2
reps) for each treatment combination. The treatments were in a 4 x 2 fac-
torial arrangement with 0 and 5 i 1 ppm ethylene (early season) and 0

and 10.0 i 1.5 ppm ethylene (late season), with 0 levels of 1.0 i 0.5%,

2
3.0 i 0.7%, 5.0 f 1.0%, and 20 i 1.0% at flow rates of 40-60 ml/min.

17
All treatment replications within each cultivar were randomly placed in
the storage room at 17°C but the cultivars were separated. The CO2 and

02 levels were monitored throughout a 3 week duration. Five bulbs were
then randomly selected from each jar for dissection and 10 were planted

for flowering evaluation.

Statistical Analysis

All experiments were analyzed as completely randomized designs.
Analysis of variance was conducted for flowering and bulb dissection
data (Steele and Torrie, 1960). Tukey's test (1953) at the 1% and 5%
levels of significance was used for mean separation. Analysis between
cultivars and between early and late season was not permitted by the
design.

Bulbs within chambers were treated as subsamples with average values
entered as replications in the analysis. When enough bulbs did not
flower to give replication for the flower quality data, or when most
shoots were in an aborted stage at the time of bulb dissection, the avail-
able data has been given with standard deviations, if possible. In addi-
tion, a balanced replicated set of data was extracted from the design and
analyzed when possible.

Regression analysis was used for the precooling duration experi-
ment of 1978-79 (Draper and Smith, 1966). T-tests were used for testing
differences between slopes of regression lines (Steele and Torrie, 1960).

The CO and ethylene production curves have been given as means of

2

the replications of each day's samplings : 1 standard deviation.

RESULTS 93 PRELIMINARY EXPERIMENTS (1977-78)

Control Monitoring

The respiration rate of uncooled 'Prominence' bulbs declined when
the temperature was lowered from 20 to 17°C, after first rising from 5
to 10 ml COZ/kg/hr during October. The rate slowly increased until
sharply increasing to 27 ml COz/kg/hr in March. The respiration rate
of bulbs at 5°C remained relatively constant at 5 until peaking at
8 m1 COZ/kg/hr after 12 to 15 weeks from the start of the cooling period
(Figure 1).

The ethylene production of 'Prominence' bulbs at 17-20°C fluctu-
ated within a 0 to 5 pl C2H4/kg/day range, with large standard devia-
tions associated with the highest average values (Figure 2). The ethy-
lene production of bulbs at 5°C was less than.1‘pl/kg/day throughout
the cooling period (Figure 3). Production peaked sharply after 8 weeks
and again during the 10th through the 12th week of cooling. A malfunc-
tion in the system which caused the bulbs to become moist preceded the

peak at 8 weeks.

Precooling Duration Effects

The respiration rates of 'Prominence' bulbs during a 2 week period
at 17°C after 4 and 8 weeks of 5°C storage were similar. After 12 weeks,
the rate at 17°C was about twice that of bulbs after 4 or 8 weeks at
5°C (Figure 4).

The ethylene production rates of bulbs at 17°C after 4 and 8 weeks
of 5°C storage were similar, with the peak occurring 2 days earlier for

the 8 week treatment. Bulbs from both treatments yielded declines in

18

19
ethylene production near the end of the monitoring period. Bulbs from
the 12 week duration yielded a stable production through 8 days at 17°C

followed by increased rates (Figure 5).

Oxygen Level Effects

'Prominence' bulbs dissected after 3 weeks at 17°C showed no
visible signs of shoot abnormality regardless of treatment. Storage

of bulbs at all low 02 levels except 0% O2 yielded more normal flowers

upon forcing in the greenhouse than storage at 15-20% 02. The highest

number of normal flowers was obtained from bulbs stored at 2-7% 02

(Table 1).

20

Figure 1. Respiration rate of 'Prominence' tulip bulbs at 17-20°C and
5°C during the 1977-78 forcing season. (Rates are means of 4 replica-

tions of 5 bulbs : 1 standard deviation.)

21

HOOD..'.'

W

1.. 202

 

'3:- := o:- 3. 00 m

2...! o CON

0

t

 

3
o-Wzo
Wu
.....0
mp. O
m.n
I...)
n...
ON 0
N

mm

22

Figgge . Ethylene production rate of 'Prominence' tulip bulbs at 17-
20°C during the 1977-78 forcing season. (Rates are means of 4 repli-

cations of 5 bulbs : 1 standard deviation.)

23

 

 

 

 

 

 

4. 3 2 1
7:01 ......9- . 1‘

298-39... ezwu

NOV DEC JAN FEB
MONTH

0C!

24

FigEEe . Ethylene production rate of 'Prominence' tulip bulbs at 5°C
during the 1977-78 forcing season. (Rates are means of 4 replications

of 5 bulbs : 1 standard deviation.)

25

7.
0

 

 

 

1.88.5...umnn

 

 

 

 

 

6
Q

 

 

 

 

 

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20303001..

0
r. 3%.? m.— . .1

2
0

e: No

1"
0

0C! NOV DEC JAN
MONTH _

SEPT

26

Figure 4. Respiration rate of 'Prominence' tulip bulbs at 170C after
4, 8, and 12 wks of storage at 5°C during the 1977-78 season. (Rates

are means of 4 replications of 5 bulbs : 1 standard deviation.)

©- 3. N

u0<¢0hm amt: m><o
F or m o v

was)... m. ”Emmi. A

27

i

o
co
.-
a.
co.
— 33.....-
at
n.-
no:

 

_

o-
occa-
.-

!uouucoouuuunua NF

0.0000000. w
,""‘ v

con 2 mos)

 

O C
N 1-

O
(‘0

bur FE). .lw
Houonaoad ‘20:)

O
V

O
In

0
(D

28

Figgge 5. Ethylene production rate of 'Prominence' tulip bulbs at 17°C
after 4, 8, and 12 wks of storage at 5°C during the 1977-78 season.

(Rates are means of 4 replications of 5 bulbs : 1 standard deviation.)

29

or

3

NF

£05.05 m
or m

o

mE< m>¢<o

N

 

   

 

! ........ .33‘ NF
0.0.0.000. m
"‘l‘l v

oon 2 we;

 

VH3:

N
l-‘DP l:6)‘ .Id
NOIiDflOOHd

 

30

Table 1. Number of 'Prominence' tulip bulbs flowering normally after
special precooling and 3 wks of air or low 0 level storage at 17°C

 

 

 

(1977-78). 2
02 level Number normal flowersz’ y, x,
(%)
15-20 1.0 ab
8-11 2.7 b
2-3 3.2 bc
0 0.0 a

 

zBulbs planted immediately after precooling
yielded 4.8 normal flowers.

YData are means of 4 replications of 5 bulbs
pl anth a

xValues followed by same letter are not sig-
nificantly different at the 1% level as
determined by Tukey's HSD method.

RESULTS 25 MAJOR EXPERIMENTS (1978-79)

Control Monitoring

The respiration rates of uncooled 'Prominence' and 'Kees Nelis'
bulbs at 17°C peaked at near 20 ml COZ/kg/hr in September followed by
a minimum of 8 ml C02/kg/hr in late October. The rates slowly increased
through February, then increased rapidly during March. 'Kees Nelis'
bulbs had generally higher rates than 'Prominence' bulbs (Figure 6).
The respiration rate at 5°C of bulbs of both cultivars was fairly con-
stant at 5 ml COZ/kg/hr until increasing slightly in January (Figure 6).

Ethylene production of bulbs of both cultivars at 17°C fluctuated
between 0 and 1 P1 C2H4/kg/day through January after which it reached
S‘pl C2H4/kg/day (Figure 7). The ethylene production of 'Prominence'
and 'Kees Nelis' bulbs at 5°C was below 11ul C2H4/kg/day throughout the
cooling period. Production peaked slightly after 2 weeks of cooling
for 'Prominence' bulbs and after 5 weeks for 'Kees Nelis' bulbs. After
12 weeks of cooling (early December), ethylene production from both
cultivars increased 3- to 6-fold and remained at high levels through

January (Figures 8 and 9).

Precoolinnguration Effects

Cooling 'Prominence' bulbs for 2 through 10 weeks yielded similar
respiratory rate patterns during 2 weeks at 17°C. The pattern changed
after 12 weeks of cooling with higher rates and a greater rate increase
during the days bulbs were monitored. The increase was even greater
after 14 and 16 weeks of cooling (Figures 10 and 11).

The shoot lengths within bulbs cut immediately after each 5°C

31

32

duration and after each subsequent 2 week period at 17°C are depicted

in Figure 12. The slope of the regression line for shoot length after
storage at 17°C (top line) was greater than before monitoring. This
indicates that shoot elongation during the 2 weeks at 17°C increased with
the cooling duration.) A relationship between the cooling duration and
the elongation of the tepals and anthers was not apparent as the slopes
of the regression lines were not.different. However, elongation of the

tepals and anthers did occur during the 17°C storage (Figures 13 and 14).

Oxygen Level Effects

Respiration 5332 -- Storage of precooled bulbs under low oxygen regimes
at 17°C yielded lower bulb respiration rates than air storage through-
out the 6 week duration (Figures 15 and 16). This reduction in respir-
ation rate was not as pronounced when the storage occurred after late

season precooling (Figures 17 and 18).

Ethylene Production.§3£g -- The ethylene production of 'Prominence' bulbs
after early season precooling was much greater and exhibited greater
variability than production by 'Kees Nelis' bulbs regardless of the
treatment (Figures 19 and 20). The low O2 treatments yielded lower
ethylene production rates during the 4 to 6 week period for 'Kees Nelis‘
bulbs with 1 and 3%02 inhibiting most effectively. After late season
precooling, 'Prominence' bulbs displayed even higher ethylene production
rates during 17°C storage than bulbs after early season precooling.
However, the ethylene production rate of bulbs stored in air was greatly
reduced (Figure 21). 'Kees Nelis' bulbs after late season precooling

produced ethylene during 17°C storage in the same range as did 'Prominence'

bulbs after early season precooling. Bulbs stored in 5% 02 produced less

33
ethylene than bulbs in 3% 02 (Figure 22). The bulbs of both cultivars
after late season precooling showed visible signs of drying and hardening

of the bulb scales when stored at high 0 levels. This observation may

2
be related to the changing pattern of ethylene production between early

and late season.

Dissection Results -- Bulbs subjected to 2 weeks of any treatment at 17°C
after early season precooling showed few visible signs of abnormality.
After 4 or 6 weeks nearly all bulbs of both cultivars stored in air

showed dried and papery tepals and anthers. Storage at 3 or 5% 02 for

4 or 6 weeks yielded nearly 100% normal appearing shoots for both cul-
tivars. The damage recorded at 1%02 was visible as a softened appear-
ance of the affected organs (Table 2).

The damaging effects of air storage at 17°C for 4 or 6 weeks were
more severe after late season precooling. The lowO2 treatments were
also slightly less effective in yielding normal appearing shoots. The
'Prominence' bulbs displayed poor quality shoots after late season pre-

cooling and low 0 storage (Table 3).

2

Storage of bulbs of both cultivars at low 02 levels for 2 or 4

weeks after early season precooling resulted in lower shoot, tepal, and
anther lengths than those of bulbs stored in air. Storage of 'Prominence'
bulbs for 4 weeks after early season precooling resulted in greater shoot,
tepal, and anther lengths than after 2 weeks of storage regardless of

the 0 level, while 'Kees Nelis' bulbs displayed the same trend for shoot

2
length only. The 'Kees Nelis' bulbs also showed increased tepal/anther

ratios at 1% O as compared to air storage. An adequate number of

2

measurements could not be made after 6 weeks of storage of either cul-

tivar or from 'Prominence' bulbs stored at 1% 02 (Tables 4 and 5).

34

Low 02 storage of 'Kees Nelis' bulbs for 2 weeks after late season

precooling reduced shoot lengths when compared to bulbs stored in air.

However, 5% 0 storage for 4 weeks did not yield reduced shoot lengths.

2

Four weeks of storage of 'Kees Nelis' bulbs at 1 or 3% 0 yielded lower

2

tepal lengths than storage at 5% O with air storage yielding an inter-

2

mediate value. The lowest tepal/anther ratio was evident after 4 weeks
in air. Shrinkage of the tepals may have occurred here (Table 6).
Reductions in shoot and anther lengths of 'Prominence' bulbs stored in

low 02 after late season precooling were evident (Table 7).

Flowering Ability -- Storage of 'Kees Nelis' bulbs at 3 or 5% 02 for
2 or 4 weeks after early season precooling yielded nearly perfect flow-

ering. Both air and 1%.02 storage yielded inferior flowering after 4

and 6 weeks. Storage at 3 or 5%.02 for 6 weeks was less successful than

for 4 weeks (Table 8; Figures 23 and 24). After late season precooling

of 'Kees Nelis' bulbs, the effects of 5% 0 during 4 weeks were still

2
evident, but no treatment gave satisfactory flowering (Table 9).

'Prominence' bulbs displayed the same trends, but responded much

less successfully to low 0 storage after early and especially after

2
late season precooling (Tables 10 and 11; Figure 23).

,EiéflE Quality -- The quality of 'Kees Nelis' plants after early season
precooling and subsequent storage of the bulbs at 17°C and forcing in
the greenhouse is depicted in Table 12. The days from planting to flow-
ering after 2 weeks of storage were increased by all low 02 treatments

when compared to air storage. The days to flower decreased with in-

creased duration of the low 0 storage. Any subsequent storage after

2
precooling resulted in less days to flower than of bulbs planted

35
immediately after precooling (controls).
Flower size of 'Kees Nelis' plants was reduced by any storage at
17°C after precooling compared to controls. Flower size was acceptable

from bulbs stored through 4 weeks at low O levels, with a noticeable

2
size reduction after 6 weeks.

Storage of 'Kees Nelis' bulbs at 5% 02 for 2 weeks yielded plants
similar in height to the control plants, while all other 2 week treat-
ments yielded decreased plant heights. The 4 week duration of low 02
levels resulted in increased plant height over the 2 week duration with
the 6 week duration displaying a decrease in plant height.

All 2 week low 02 level treatments yielded a similar bottom inter-
node length to the control bulbs while air storage resulted in a decreased
bottom internode length. A decrease in bottom internode length was
noted after 6 weeks. ‘

Storage of 'Kees Nelis' bulbs in 5% Oé for 2 weeks resulted in
plants with a greater top internode length than any other 2 week treat-
ment. Low 02 level storage for 4 weeks resulted in increased top inter-
node lengths with a decrease after 6 weeks.

The quality of 'Prominence' plants obtained after early season
precooling, treatment application, and forcing of the bulbs in the green-
house was similar to 'Kees Nelis' plants (Table 13). However, all treat-
ments for which data was available showed lower bottom internode
lengths than controls and all 2 week treatments yielded lower top
internode lengths than the controls.

The late season poor flowering of both cultivars did not supply

enough data for meaningful interpretation.

36

FiglLre 6. Respiration rate of 'Prominence' and 'Kees Nelis' tulip bulbs
at 5°C and 17°C during the 1978-79 forcing season. (Rates are means

of 4 replications of 5 bulbs : 1 standard deviation.)

60

CO2 PRODUCTION
ml
M
O

 

37

Prominence at 17°C
Kees Nelis at 17°C

Prominence at 5°C
KeesNelis at 5°C

00"“.ququ

 

’

fihwniimfigg hfi’

 

 

sm'oa'uov' DEC ' JAN' FEB TMARj
MONTH

38

Figgge 7. Ethylene production rate of 'Prominence' and 'Kees Nelis'
tulip bulbs at 17°C during the 1978-79 forcing season. (Rates are means

of 4 replications of S bulbs : 1 standard deviation.)

39

Prominence m
ms "0' la Ouuouuuuno

C2H4 Pnooucnon

 

 

 

 

 

 

 

 

MONTH

40

Figgge 8. Ethylene production rate of 'Prominence' tulip bulbs at 5°C
during the 1978-79 forcing season. (Rates are means of 4 replications

of 5 bulbs i 1 standard deviation.)

41

 

 

 

 

 

5 4 i- m. 2
ElfiiJT.HlMU—.-s‘
zozuaooE ezuo

DEC JAN

Nov
MON TH

OCT

SEPT

42

Figgge 9. Ethylene production rate of 'Kees Nelis' tulip bulbs at 5°C
during the 1978-79 forcing season. (Rates are means of 3 replications

of 5 bulbs : 1 standard deviation.)

43

7.
O

6 _
Q

 

 

 

 

 

 

e . m. a m
703.3

0
Thu-1 .
zozuaooE ezdu

on NOV DEC JAN
MONTH

SEPT

44

Figgge 10. Respiration rate of 'Prominence' tulip bulbs at 17°C after
2, 4, 6, and 8 wks of storage at 5°C during the 1978-79 forcing season.

(Rates are means of 4 replications of 5 bulbs : 1 standard deviation.)

50
45

'40

CIION

ml-Rg - r'
N U
0' O

co2 rnogu
M
O

-L
Di

.5
o

 

45

 

wks of 5°C
2
4 . .............. ..

6 o——---o
8 .—

D
.I" '

a. '
00.q _ "‘3! v ‘ a...) ‘ ‘
“ ""'0000~~

 

 

 

I
I
.i

 

12 34 5 6 7891011121314
DAYS AFTER STORAGE

46

Figgge 11. Respiration rate of 'Prominence' tulip bulbs at 17°C after

10, 12, 14, and 16 wks of storage at 5°C during the 1978-79 forcing

season. (Rates are means of 4 replications of 5 bulbs : 1 standard

deviation.)

50

45

4O

9". “.34 w m
D): O 01

ml- I:
N
0

CO2 PRODUCTION

.5
0'

_L
O

 

47

 

wks at 5°C of]
10 m“ 0'...
12 O nnnnnnnnnnnnnn O ’0
14 ------ ,e
16 000000000. ’0.
.L
:*---------

 

 

1 234 56 78 91011121314
DAYS AFTER STORAGE

48

Figgge 12. Shoot length within 'Prominence' tulip bulbs after storage
at 5°C and subsequent storage for 2 wks at 17°C during the 1978-79

forcing season. (Lengths are means of 4 replications of 5 bulbs.)

49

mm... a... be hzmsmta 555.2205 8.5%
aw>w.. Xv ._.< ~2<U_m.20_m0nc
o Uom .2 can;
_. VF NF Ow w D V N

I
000G "N“ “\l\“\\-
snared-l \\\\_.\1 ..
.I‘\I\\\\|f\ 00000000000 0
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I “\‘.I|\\\D‘ 000000.00‘0000
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0000‘000
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... x-m..+o.9.u>

0.: .a a...“ + 0%

I'l". 00m

 

can": :pOZmd FOO-.3

2 a a 2
lmwl
HlDNa‘l 100HS

O
1.0

00

50

Figgge 13. Tepal length within 'Prominence' tulip bulbs after storage
at 5°C and subsequent storage for 2 wks at 17°C during the 1978-79

forcing season. (Lengths are means of 4 replications of S bulbs.)

51

Emerita 3240.220; 52 meson n
was... 2 55:.sz:
Uom ._.< aim;
we 3. NF 0.. w o 0 N

000...... UON— .0 'J’N+ 0°“

U'-"' 0.“

cut: :nQZua asap

‘0
l\\\\ I
\
3.: a .\\\
00 I" “
\
\
I. \
53:61» \n .
N “ 0...
0000
\\\“ 00000
“ . .... .
\\\ 000000
. \\ 00000
‘ I 0000
. “ 0.. .
.\ o...
0
000000
0000

 

V

0

0..

NF

lulu!)
HiDNa‘l “Wail

52

Figgge 14. Anther length within 'Prominence' tulip bulbs after storage
at 5°C and subsequent storage for 2 wks at 17°C during the 1978-79

forcing season. (Lengths are means of 4 replications of S bulbs.)

53

hzmmmta >:z<o:_zo.m 52 3.63
was .2 Z. 55:203.”
om _—< mv—ums)
0.. S. N F 0.. m w v N

000000000 UON——. 0J3N+U0n
ll'I'. U0“

cur: :uOZud murhz<

\‘\\\\.1
00“”. "N“ “I‘“‘
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\‘\\\ 0 0000000000000
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~0—.0+ON H»

 

or

NF

[WWI
H19N31 HiHlNV

54

Figure 15. Respiration rate of 'Prominence' tulip bulbs during 6 wks
of air or low 02 level storage at 17°C after early season special pre-

cooling. (Rates are means of 4 replications of 15 bulbs : 1 standard

deviation.)

Production Rate
kg" - hr'|

(302
ml-

100'

90"

80

7O

60

.h
0

01
0

N
O

 

 

IO

55

AIR

 

.5%0,
- 3% 02
1% 02
‘r’.
i 1 l L 4_____J
I 2 3 4 5 6

Weeks of Storage

56

Figgge 16. Respiration rate of 'Kees Nelis' tulip bulbs during 6 wks
of air or low 02 level storage at 17°C after early season special pre-

cooling. (Rates are means of 4 replications of 15 bulbs : 1 standard

deviation.)

Production Rate
ml- kg"- hr"

CO2

IOO

 

 

57

MR

°5%02

.3%O

1%0

p

i l. L

2 3 4 5
Weeks of Storage

01L.

S8

Figgge 17. Respiration rate of 'Prominence' tulip bulbs during 6 wks

of air or low 02 level storage at 17°C after late season special pre-

cooling. (Rates are means of 4 replications of 15 bulbs : 1 standard

deviation.)

IOOF

90

80

70

CO2 Production Rate
ml kg" hr"
at 0)
o o

A
O

01
O

20

 

 

S9

 

 

AIR
5% 02
‘ 30/0 02
|°/o 02
L 1 i l L '
l 2 3 4 5 6

Weeks of Storage

6O

Figgge 18. Respiration rate of 'Kees Nelis' tulip bulbs during 6 wks
of air or low 02 level storage at 17°C after late season special pre-

cooling. (Rates are means of 4 replications of 15 bulbs : 1 standard

deviation.)

002' Production Rate

kg"- hr"

ml-

l20

IIO

 

 

61

AIR

5 °/0 02

0
3/o O2

l°/o 02

C.

1 1 1 l

l 2 3 4 5 6

Wee ks of Storage

62

Figgge 19. Ethylene production rate of 'Prominence' tulip bulbs during
6 wks of air or low 02 level storage at 17°C after early season special

precooling. (Rates are means of 4 replications of 15 bulbs : 1 standard

deviation.)

63

bootsm co 9.32,

 

 

 

 

 

 

Om

‘bH'ZO

)t-l'TV

IJiop I_6
3:03 uouonpmd

64

Figure 20. Ethylene production rate of 'Kees Nelis' tulip bulbs during

6 wks of air or low 02 level storage at 17°C after early season special

precooling. (Rates are means of 4 replications of 15 bulbs 1' 1 standard

deviation.)

65

322m co 9.32,

 

 

m_<

 

 

._fi).|.|11/
I I 3
H3

“flop
aioa uouonpmd

66

Figgge 21. Ethylene production rate of 'Prominence' tulip bulbs during

6 wks of air or low 02 level storage at 17°C after late season special

precooling. (Rates are means of 4 replications of 15 bulbs 1: 1 standard

deviation.)

24
,ul

C H Production Rate

. kq"- day"

67

‘30P Tan/.02
IZO'
IIO"
I00"

90"

5‘
O
T

O)
O
I

(I
O
I

A
C
I

0‘
O
I

H9602

20» I
I0.— 14,4!

)AIR

 

I 2 3
Weeks of Storage

 

0
r
‘
.

I
. 5 6

68

Figgge 22. Ethylene production rate of 'Kees Nelis' tulip bulbs during

6 wks of air or low 02 level storage at 17°C after late season special

precooling. (Rates are means of 4 replications of 15 bulbs 1' 1 standard

deviation.)

69

322m co 9.82,

 

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m2
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muacuc< w manaaa auaucm muoocm muorac< a madame auaucm mucosa ARV Amxzv
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71

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o 0 00w 0 o o 006 o a m
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muonuc< w manage ouaucm muoocm mumruc< w magmas ouducm muoorn ARV Amxsv
ARV muoocn Hmsuocn< Hmeuoz Aflv muoocm Hmsuocn< Hmsuoz Ho>MH No coaumusa
.aucocasowm. .nHHoz hoax.

 

 

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hoax. mo ammuoum Hm>aH No 30H no mam ocm ocaaoouaud Hmfiuodm common mama wavmm >pHHmoU Doorm .m canoe

 

72
Table 4. Floral organ measurements of 'Prominence' tulip bulbs after

early season special precooling and air or low 02 level storage for 2
or 4 wks at 17°c.z’ Y

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

Shoot length (mm) Tepal length (mm)
02 level Duration (wks) Duration (wks)
(%) 2 4 mean 2 4 mean
20 39.7 41.3 40.5 b 11.4 11.7 11.5 b
5 33.9 39.0 36.5 b 10.7 11.7 11.2 ab
3 29.3 33.7 31.5 a 10.0 11.0 10.5 a
mean 34.3 a 38.0 b 10.7 a 11.5 b
Bulbs cut at
start of treatments 33.4 10.3
Anther length (mm) Tepal/Anther (ratio)
02 level Duration (wks) Duration (wks)
(%) 2 4 mean 2 4
20 10.3 10.4 10.4 b 1.09 a 1.13 a
5 9.8 10.6 10.2 b 1.10 a 1.09 a
3 9.2 9.8 9.5 a 1.10 a 1.12 a
mean 9.7 a 10.3 b
Bulbs cut at
start of treatments 9.2 v 1.12

 

zValues within 1- or 2-way tables of means followed by same letter are
not significantly different at the 5% level as determined by Tukey's
I'ISD teSt0

yValues within 2-way tables are means of 4 replications of no more than
.5 dissected bulbs.

73
Table 5. Floral organ measurements of 'Kees Nelis' tulip bulbs after

early season special precooling and air or low 0 level storage for 2

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

2
or 4 wks at 17°C.z’ Y
Shoot length (mm) Tepal length (mm)
02 level Duration (wks) Duration (wks)
(%) 2 4 mean 2 4 mean
20 48.1 48.2 48.2 c 12.5 14.5 14.5 b
5 39.1 43.6 41.4 b 12.8 13.9 13.3 ab
35.9 39.0 37.4 a 12.6 12.8 12.7 a
1 34.7 35.7 35.2 a 12.5 12.7 12.6 a
mean 39.5 a 41.6 b 12.6 a 13.5 a
Bulbs cut at
start of treatments 33.9 11.7
Anther length (mm) Tepal/Anther (ratio)
02 level Duration (wks) Duration (wks)
(%) 2 4 mean 2 4 mean
20 15.0 14.9 14.9 c 0.96 0.98 0.97 b
5 13.0 13.7 13.4 b 0.98 1.01 1.00 ab
12.6 13.2 12.9 ab 1.00 0.97 0.98 ab
1 12.2 12.2 12.2 a 1.03 1.04 1.03 a
mean 13.2 a 13.5 a 0.99 a 1.00 a
Bulbs cut at
start of treatments 11.7 1.00

 

zValues within 1- or 2-way tables of means followed by same letter are
not significantly different at the 1% level as determined by Tukey's
HSD test.

yValues within 2-way tables are means of 4 replications of no more than
5 dissected bulbs.

74
Table 6. Floral organ measurements of 'Kees Nelis' tulip bulbs after

late season special precooling and air or low 0 level storage for 2 or

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

2
4 wks at 17°c.z’ Y
Shoot length (mm)‘ Tepal length (mm)"
02 level Duration (wks) Duration (wks)
(%) 2 4 2 4
20 52.7 c 54.6 c 17.2 bc 16.1 abc
5 46.1 b 54.2 c 15.6 ab 17.6 c
3 43.2 ab 46.5 b 15.0 a 15.7 ab
1 41.1 a 44.9 ab 14.7 a 15.4 a
Bulbs cut at
start of treatments 41.7 14.3
Anther length (mm) Tepal/Anther (ratio)‘
02 level Duration (wks) Duration (wks)
(%) 2 4 mean 2 4'
20 18.5 19.3 18.9 c 0.93 b 0.83 a
5 15.2 16.9 16.1 b 1.03 bc 1.03 be
14.9 15.1 15.0 a 1.01 be 1.04 bc
1 13.8 15.1 14.5 a 1.06 c 1.01 bc
mean 15.6 a 16.7 b
Bulbs cut at
start of treatments 14.0 1.02

 

zValues within 1- or 2-way tables of means followed by same letter are
not significantly different at the 5% level as determined by Tukey's
HSD test.

yValues within 2-way tables are means of 4 replications of no more than
S dissected bulbs.

‘9 "02 level x duration interaction significant at the 1% (“), and

5% (') levels.

75

Table 7. Floral organ measurements of 'Prominence'

late season special precooling and 2 wks of air or low 0

at 17°c.z’ Y

tulip bulbs after

2

level storage

 

 

 

02 level Shoot Tepal Anther Tepal/Anther
length length length
(%) (mm) (mm) (mm) (ratio)
20 47.9 c 13.6 a 12.5 b 1.09 a
5 42.4 b 12.8 a 11.3 ab 1.14 a
3 39.1 ab 12.3 a 10.9 ab 1.13 a
1 37.9 a 11.5 a 9.9 a 1.18 a
Bulbs cut
at start of
treatments 35.2 11.4 10.6 1.07

 

zValues within columns followed by same letter are not significantly
different at the 5% level as determined by Tukey's HSD test.

yValues are means of 4 replications of no more than 5 dissected bulbs.

76
Table 8. Number of 'Kees Nelis' tulip bulbs flowering normally after

early season special precooling and 2, 4, and 6 wks of air or low 02

level storage at 17°C.

 

 

 

 

 

 

Number normal flowersz’ y, x
02 level Duration (wks)
(%) 2 4 6
20 7.5 cd 0.0 a 0.0 a
5 9.7 d 9.8 d 3.2 b
3 10.0 d 10.0 d 5.8 bc
1 8.7 d 4.5 b 0.0 a

Bulbs planted immediately
after special precooling 10.0

 

zValues within rows and columns followed by same
letter are not significantly different at the
1% level as determined by Tukey's HSD test.

yData are means of 4 replications of 10 bulbs
planted.

xO2 level x duration interaction significant at

the 1% level.

77

Figgge 23. Flowering of 'Kees Nelis' (top) and 'Prominence' (bottom)
tulip bulbs after early season special precooling and 4 wks of air or

low 02 level storage at 17°C.

78

 

79

Figge 24. Aborted flower (top) after air storage of 'Kees Nelis' tulip

bulbs for 4 wks; stem topple (bottom) after air + 16% CO2 storage of

'Kees Nelis' tulip bulbs for'4 wks.

80

 

81
Table 9. Number of 'Kees Nelis' tulip bulbs flowering normally after

late season special precooling and 2, 4, and 6 wks of air or low 02

level storage at 17°C.

 

 

Number normal flowersz’ y, x

 

 

 

 

02 level Duration (wks)
(%) 2 4 6
20 6.5 cd 0.0 a 0.0 a
5 7.5 d 3.0 ab 0.0 a
3 7.8 d 3.5 bc 0.5 ab
1 2.3 ab 0.0 a 0.0 a

Bulbs planted immediately
after special precooling 10.0

 

zValues within rows and columns followed by same
letter are not significantly different at the
1% level as determined by Tukey's HSD test.

yData are means of 4 replications of 10 bulbs
plantEd0

x02 level x duration interaction significant at

the 1% level.

82
Table 10. Number of 'Prominence' tulip bulbs flowering normally after
early season special precooling and 2, 4, and 6 wks of air or low 0

2
level storage at 17°C.

 

 

 

 

 

 

Number normal flowersz’ y, x
02 level Duration (wks)
(%) 2 4 6
20 2.0 ab 0.0 a 0.0 a
5 6.2 c 4.8 bc 0.0 a
3 4.0 be 2.2 ab 0.0 a
1 1.5 ab 0.3 a 0.0 a

Bulbs planted immediately
after special precooling 10.0

 

zValues within rows and columns followed by same
letter are not significantly different at the
1% level as determined by Tukey's HSD test.

yData are means of 4 replications of 10 bulbs
planted.

x02 level x duration interaction significant at

the 1% level.

83
Table 11. Number of 'Prominence' tulip bulbs flowering normally after
late season special precooling and 2, 4, and 6 wks of air or low 0

2
level storage at 17°C.

 

 

 

 

 

 

Number normal flowersz’ y, x
02 level Duration (wks)
(%) 2 4 6
20 0.5 ab 0.0 a 0.0 a
5 2.5 b 0.0 a 0.0 a
3 2.8 c 0.0 a 0.0 a
1 0.0 a 0.0 a I 0.0 a

Bulbs planted immediately
after special precooling 9.2

 

zValues within rows and columns followed by same
letter are not significantly different at the
1% level as determined by Tukey's HSD test.

yData are means of 4 replications of 10 bulbs
planted.

xO2 level x duration interaction significant at

the 1% level.

84

 

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No 30H no

 

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85

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86

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87

Effects 2: Ethylene

Dissection Results -- Bulbs of both cultivars contained nearly 100%
normal appearing shoots after early season precooling and 3 weeks in
air (Table 14). The addition of 5 ppm ethylene to the air led to a
majority of dried and brown tepals and anthers. This damage was not
evident in 'Kees Nelis' bulbs after 3 weeks of storage in 3 or 5% 02
with 5 ppm ethylene. Slight damage was recorded for 'Prominence'
bulbs after 3 and 5% O2 storage. A softened appearance of the organs
was recorded at 1% 02 for both cultivars, but the addition of ethylene
led to more normal appearing shoots within 'Kees Nelis' bulbs. The
quality of shoots within 'Kees Nelis' bulbs after late season pre-

cooling and storage in low 0 with and without 10 ppm ethylene were

2
similar to early season results (Table 15). The addition of 10 ppm
ethylene to the air after late season precooling of the bulbs resulted
in more visible damage than with 5 ppm ethylene after early season
precooling. A

The application of 5 ppm ethylene to 'Kees Nelis' bulbs after
early season precooling reduced shoot and anther length regardless of
the 02 level during the 3 week duration (Table 16). Low 02 levels also
reduced the shoot and anther length compared to air storage. The re-
duction in shoot length due to ethylene was not significant after
late season precooling (Table 17). The anther length within 'Kees
Nelis' bulbs kept in air after late season precooling was greater than
in bulbs subjected to low 02 treatments. However, with the addition
of 10 ppm ethylene, the anther length of bulbs in air was the same as
in bulbs stored at low 02 levels. No effect of ethylene upon organ

lengths was significant for 'Prominence' bulbs (Table 18).

88

Flowering Ability -- Ethylene reduced the number of normal flowers ob-
tained from 'Kees Nelis' bulbs after early season precooling and air
storage (Table 19). Abnormal flowers were dried and papery. However,
bulbs held in 3 or 5% 02 did not show a decrease in normal flowers
after ethylene addition. Similar results were obtained with 'Kees
Nelis' bulbs after late season precooling and subsequent storage with
or without 10 ppm ethylene (Table 20). The flowering of 'Prominence'

bulbs after 3 weeks of storage was low for all treatments (Table 21).

Plant Quality -- No effect of ethylene upon any of the plant quality
parameters after early season precooling of 'Kees Nelis' bulbs and

storage at any 0 level was significant (Table 22). The addition of

2
10 ppm ethylene to 'Kees Nelis' bulbs during storage after late season

precooling yielded an increase in the length of the top internode at

flowering regardless of the 0 level during storage (Table 23).

2
'Prominence' bulbs did not yield enough flowers for meaningful plant

quality conclusions.

Carbon Dioxide Level Effects

Dissection Results -- All 'Kees Nelis' shoots appeared normal upon dis-

section regardless of the CO2 or 02 level during the 4 weeks of treat-

ment. 'Prominence' bulbs showed slight abnormalities after air (19% 02)

storage (Table 24). Addition of CO2 yielded increased shoot lengths

within bulbs of both cultivars in air but not within bulbs stored in

3% 02 (Tables 25 and 26). Anther and tepal length was reduced by 3% O2

storage regardless of the CO2 level.

89

Flowering Ability -- No significant effect of CO level upon flowering

2
of 'Kees Nelis' bulbs was evident (Table 27). The flowering of 'Prom-

inence' bulbs showed that without additions of C02, 3% 0 storage

2

increased the number of normal flowers over air storage. With addi-
tional C02, the differences were no longer visible (Table 28). Additions

of C02 did not increase the flowering ability of bulbs held in 3% 02 for

either cultivar.

Plant Quality -- Storage of bulbs in air with addition of 16% CO2 led

to a large number of 'Kees Nelis' stems that toppled at or before

flowering (Table 29 and Figure 24). The level of CO2 did not change

significantly the other quality parameters. Regardless of CO level,

2

storage of bulbs at 3% O for 4 weeks increased all parameters except

2
flower size when compared to air storage. Stem topple was not evi-
dent upon forcing 'Prominence' bulbs. Replication was not adequate

to allow for analysis of the quality parameters of 'Prominence' bulbs.

90

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on o o om o o 6 con o om
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.oucocaeonm. .nHHoZ woox.

 

 

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N
Iona Hmwuoom common >Hnmo noumo unasn odds» .oucocaeonm. poo .mHHoz moox. mo xudaooo noorm .vw pooa

 

91

Table 15. Shoot quality after late season special precooling and air

or low 02 level storage of 'Kees Nelis' tulip bulbs at 17°C with 0 or

10 ppm ethylene.z

 

 

 

 

02 level C2}!4 level Normal Abnormal shoots (%)
%) (%) shoots Entire Tepals & Anthers
(%) shoot anthers only

20 0 100 0 0 0
20 10 0 0 100 0
5 0 90 0 10 0
5 10 100 0 0 0
3 0 100 0 0 0
3 10 90 0 10 0
1 0 90 0 10 0
1 10 100 0 0 0

Bulbs cut at
start of treatments 100 0 0 0

 

zTen bulbs from each treatment were examined.

92

Table 16. Floral organ measurements of 'Kees Nelis' tulip bulbs after
early season special precooling and air or low 02 level storage for 3
wks at 17°C with 0 or 5 ppm ethylene.z’ y

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

Shoot length (mm) Tepal length (mm)

02 level C2H4 level (ppm) C2H4 level (ppm)

(%) 0 5 mean 0 S

20 52.2 47.2 49.7 b 15.3 a 14.0 a

5 44.7 38.4 41.5 a 13.6 a 12.8 a

43.3 42.0 42.6 a 14.8 a 14.5 a
1 4201 4109 4200 a 1406 a 1309 a
mean 45.6 b 42.4 a
Bulbs cut at
start of treatments 41.2 14.1
Anther length (mm) Tepal/Anther (ratio)

02 level C2H4 level (ppm) C2H4 level (ppm)

(%) 0 5 mean 0 5

20 17.4 13.5 15.5 b 0.88 a 1.04 a

5 13.2 13.4 13.3 ab 1.03 a 0.95 a

14.2 13.8 14.0 ab 1.04 a 1.05 a
1 13.8 12.2 12.9 a 1.06 a 1.16 a
mean 14.6 b 13.2 a

Bulbs cut at
start of treatments 14.0 1.01

 

zValues within 1- or 2-way tables of means followed by same letter are
not significantly different at the 5% level as determined by Tukey's
HSD teSto

yValues within 2-way tables are means of 2 replications of no more than
5 dissected bulbs.

93

Table 17. Floral organ measurements of 'Kees Nelis' tulip bulbs after
late season special precooling and air or low 0
wks at 17°C with 0 or 10 ppm ethylene.z’ y

2 level storage for 3

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

Shoot length (mm) Tepal length (mm)
02 level C2H4 level (ppm) C2H4 level (ppm)
(%) 0 10 mean 0 10
20 57.5 52.9 55.2 b 19.3 a 18.3 a
5 46.2 49.1 47.6 a 17.7 a 17.9 a
1 47.5 46.0 46.7 a 17.8 a 17.7 a
mean 50.0 a 49.3 a
Bulbs cut at
start of treatments 45.4 16.5
Anther length (nm0" Tepal/Anther (ratio)
02 level C2H4 level (ppm) C2H4 level (ppm)
(%) 0 10 0 10
20 22.0 b 18.0 a 0.88 a 0.96 a
5 16.9 a 18.6 a 1.05 a 0.98 a
3 18.5 a 18.8 a 1.01 a 0.96 a
1 17.5 a 18.3 a 1.01 a 0.96 a
Bulbs cut at
start of treatments 16.3 1.01

 

zValues within 1- or 2-way tables of means followed by same letter are
not significantly different at the 5% level as determined by Tukey's
HSD test.

yValues within 2-way tables are means of 2 replications of no more than
5 dissected bulbs.

”02 levelx C2114 level interaction significant at the 1% level.

94
Table 18. Floral organ measurements of 'Prominence' tulip bulbs after
early season special precooling and air or low 02 level storage for 3
wks at 17°C with 0 or 5 ppm ethylene.z’ y

 

 

 

 

 

 

 

 

 

Shoot length (mm) Tepal length (mm)

02 level C2H4 level (ppm) CZH4 level (ppm)

(%) 0 5 mean , 0 5

20 50.0 45.6 47.8 b ' 13.6 a 13.2 a

5 41.5 38.1 39.8 a 11.4 a 11.0 a

3 35.6 38.5 37.5 a 11.1 a 11.2 a

mean 42.4 a 40.7 a

Bulbs cut at
start of treatments 36.3 11.9

 

zValues within 1- or 2-way tables of means followed by same letter are
not significantly different at the 5% level as determined by Tukey's
FED tESto

YValues within 2-way tables are means of 2 replications of no more than
5 dissected bulbs.

95
Table 19. Number of 'Kees Nelis' tulip bulbs flowering normally after
early season special precooling and 3 wks of air or low 0
at 17°C with 0 and 5 ppm ethylene.

2 level storage

 

 

 

 

 

 

Number normal flowersz’ y, x
02 level C2H4 level (ppm)
(%) 0 5
20 6.0 b 2.5 a
5 9.5 C 1000 C
3 8.0 be 7.0 bc
1 0.0 a 0.0 a

Bulbs planted immediately
after special precooling 10.0

 

zValues within rows and columns followed by same
letter are not significantly different at the
5% level as determined by Tukey's HSD test.

yData are means of 2 replications of 10 bulbs
planted.

x02 level x duration interaction significant at

the 5% level.

96
Table 20. Number of 'Kees Nelis' tulip bulbs flowering normally after

late season special precooling and 3 wks of air or low 0 level storage

 

 

 

 

 

 

2
at 17°C with 0 and 10 ppm ethylene.
Number normal flowersz’ y, x
02 level CZH4 level (ppm)
(%) 0 10
20 6.5 be 0.0 a
5 10.0 c 8.0 bc
3 6.0 be 5.5 bc
1 4.5 ab 4.0 ab

Bulbs planted immediately
after special precooling 10.0

 

zValues within rows and columns followed by same
letter are not significantly different at the
5% level as determined by Tukey's HSD test.

YData are means of 2 replications of 10 bulbs
planted.

xO2 level x C2H4 level interaction significant

at the 5% level.

Table 21. Number of 'Prominence' tulip bulbs flowering normally after

early season special precooling and 3 wks of air or low 0

97

at 17qC with 0 and 5 ppm ethylene.

2

 

 

02 level

(%)

 

20

5

3

1

mean

Number normal flowersz’ y

 

C H level (ppm)

 

 

Bulbs planted immediately
after special precooling

2 4

0 5 mean
1.0 0.0 0.5 a
3.5 3.5 3.5 b
1.0 1.5 1.2 ab
0.0 0.0 0.0 a
1.6 a 2.5 a

9.5

 

zVaules within 1-way table of means followed by
same letter are not significantly different at
the 5% level as determined by Tukey's HSD test.

yValues within 2-way table are means of 2 repli-

cations of 10 bulbs planted.

level storage

 

98
Table 22. Plant quality of forced 'Kees Nelis' tulip bulbs after early

season precooling and aircurlow 0 level storage for 3 wks at 17°C with

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

2
0 or 5 ppm ethylene.z’ y
Days to flower Flower size (cm)
02 level C2114 level (ppm) C2H4 level (ppm)
(%) 0 5 0 5 mean
20 22.7 a 22.2 a 4.3 4.6 4.4 b
5 22.6 a 23.3 a 5.1 5.0 5.0 a
3 22.9 a 24.2 a 4.9 5.0 5.0 a
mean 4.8 a 4.9 a
Bulbs planted immediately
after special precooling 28.5 5.4
Plant height (cm) Bottom internode length (cm)
O2 level C2H4 level (ppm) C2H4_level (ppm)
(%) 0 5 mean 0 5 mean
20 27.8 28.6 28.2 b 5.9 5.0 5.4 b
5 36.3 35.3 35.8 a 9.2 9.3 9.2 a
3 35.7 35.5 35.6 a 9.9 9.6 9.7 a
mean 33.3 a 33.1 a 8.3 a 7.9 a

Bulbs planted immediately
after special precooling 30.0 9.3

99
Table 22 (cont'd.).

Top internode length (cm)

 

 

 

 

02 level C2H4 level (ppm)
(%) 0 S
20 8.5 a 10.4 a
5 11.1 a 10.3 a
3 9.4 a 10.8 a
Bulbs planted immediately
after special precooling 6.0

 

zValues within 1- or 2-way tables of means followed by same letter are
not significantly different at the 1% level as determined by Tukey's
HSD test.

yValues within 2-way tables are means of 2 replications of no more than
10 flowering plants.

100
Table 23. Plant quality of forced 'Kees Nelis' tulip bulbs after late

season precooling and aircnrlow 0 level storage for 3 wks at 17°C with

 

 

 

2
0 or 10 ppm ethylene.z’ y, x
02 level C2H4 level Days Flower Plant Bottom
to size height internode
flower length
(%) (ppm) (cm) (cm) (cm)
20 0 15.3 4.8 30.4 7.3
20 10 21.0 5.0 31.0 ' 5.0
Standard deviation 2.1 0.1 0.4 0.4
5 0 19.7 a 5.2 b 36.7 a 9.4 a
5 10 21.6 a 5.0 ab 39.1 a 8.4 a
3 0 23.1 a 4.8 ab 35.9 a 9.5 a
3 10 22.2 a 5.0 ab 37.9 a 9.8 a
1 0 19.9 a 4.9 ab 34.3 a 9.6 a
1 10 21.8 a 4.7 a 34.0 a 9.0 a
Bulbs planted immediately
after special precooling 19.3 5.3 32.5 9.3

Top internode length

 

0 level C H level (ppm)

 

 

 

2 2 4
(%) 0 10 mean
20 8.3 10.0 9.1
5 10.3 12.6 11.5 b
3 10.7 12.2 11.5 b
1 8.9 10.1 9.5 a
mean 9.9 a 11.6 b
Bulbs planted immediately
after special precooling 7.0

 

zValues within columns or 1-way tables of means followed by same letter
are not significantly different at the 5% level as determined by
Tukey's HSD test.

yData are means of 2 replications of no more than 10 flowering plants.

xBulbs stored in air did not yield enough flowers for proper replica-
tion, so the data were excluded from the analysis of variance.

101

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102

Table 25. Floral organ measurements of 'Kees Nelis' tulip bulbs after

special precooling and air or low 0 level storage for 4 wks at 17°C

with 0.4, 10, and 16% c02.z’ Y

2

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

Shoot length (mm)‘ Tepal length (mm)
CO2 level 02 level (%) 02 level (%)
(%) 19 3 19 3 mean
0.4 48.3 b 35.2 a 14.6 12.0 13.3 a
10 54.5 bc 36.3 a 15.0 12.7 13.8 a
16 61.3 c 34.9 a 16.0 12.8 14.4 a
mean 15.2 b 12.5 a
Bulbs cut at .
start of treatments 32.0 4.8
Anther length (mm) Tepal/Anther (ratio)
CO2 level 02 level (%) 02 level (%)
(%) 19 3 mean 19 3
0.4 14.7 12.0 13.3 a 0.99 a 1.00 a
10 15.3 12.4 13.9 a 0.98 a 1.02 a
16 15.6 12.5 14.0 a 1.02 a 1.03 a
mean 15.2 b 12.3 a
Bulbs cut at
start of treatments 3.6 1.33

 

zValues within 1- or 2-way tables of means followed by same letter are
not significantly different at the 5% level as determined by Tukey's
HSD test.

yValues within 2-way tables are means of 2 replications of no more than
5 dissected bulbs.

’COZ level x 02 level interaction significant at the 5% level.

 

103

Table 26. Floral organ measurements of 'Prominence' tulip bulbs after
special precooling and air or low 0 level storage for 4 wks at 17°C

2
with 0.4, 10, and 16% c02.z’ y

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

Shoot length (mm)“ Tepal length (mm)
CO2 level 02 level (%) 02 level (%)
(%) 19 3 . 19 3 mean
004 3708 a 3009 a ‘ 1100 1003 1006 a
10 6003 b 2907 a 1203 904 1009 a
16 84.7 c 33.2 a 13.2 10.9 12.0 a
mean 12.2 b 10.2 a
Bulbs cut at
start of treatments 28.0 9.9
Anther length (mm) Tepal/Anther (ratio)
CO2 level 02 level (%) 02 level (%)
(%) 19 3 mean 19 3
0.4 9.9 9.3 9.6 a 1.11 a 1.11 a
10 11.6 9.0 10.3 a 1.06 a 1.04 a
16 11.9 9.5 10.7 a 1.10 a 1.15 a
mean 11.1 b 9.3 a
Bulbs cut at
start of treatments 9.1 1.09

 

2values within 1- or 2-way tables of means followed by same letter are
not significantly different at the 5% level as determined by Tukey's
HSD test.

yValues within 2-way tables are means of 2 replications of no more than
5 dissected bulbs.

“C02 level x 02 level interaction significant at the 1% level.

104
Table 27. Number of 'Kees Nelis' tulip bulbs flowering normally after
special precooling and 4 wks of air or low 0 level storage at 17°C with

2
0.4, 10, and 16% 002.

 

 

Number normal flowersz’ y

 

 

 

 

02 level CO2 level (%)
(%) 0.4 10 16 mean
19 6.5 20.0 9.5 12.0 a
3 20.0 18.5 16.5 18.3 b
mean 13.2 a 19.2 a 13.0 a

Bulbs planted immediately
after special precooling 20.0

 

zValues within 1-way table of means followed by same letter
are not significantly different at the 5% level as deter-
mined by Tukey's HSD test. .

yValues within 2-way table are means of 2 replications of
20 bulbs planted.

 

105
Table 28. Number of 'Prominence' tulip bulbs flowering normally after
special precooling and 4 wks of aircn:low 0 level storage at 17°C with

0.4, 10, and 16% CO

2
20

 

 

 

 

 

 

 

Number normal flowersz’ y, x
02 level CO2 level (%)
(%) 0.4 10 16
I:
19 1.0 a 5.0 ab 7.5 ab 3
3 10.0 b 8.0 ab 7.0 ab
Bulbs planted immediately
after special precooling 19.5
!

 

zValues within rows and columns followed by same
letter are not significantly different at the
5% level as determined by Tukey's HSD test.

yData are means of 2 replications of 20 bulbs
planted.

xO2 level x CO2 level interaction significant at

the 5% level.

106
Table 29. Plant quality of forced 'Kees Nelis' tulip bulbs after special

precooling and air or low 0 level storage for 4 wks at 17°C with 0.4,

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

2
10, and 16% c02.z’ y
Days to flower Flower size (cm)
CO2 level 02 level (%) 02 level (%)
(%) 19 3 mean 19 3
0.4 27.4 27.9 27.6 a 5.1 a 5.0 a
10 23.0 27.8 25.4 a 5.2 a 5.1 a
16 22.2 27.1 24.7 a 4.9 a 4.8 a
mean 24.2 a 27.6 b
Bulbs planted immediately
after special precooling 35.5 5.3
Plant height (cm) Bottom internode length (cm)
CO2 level 02 level (%) 02 level (%)
(%) 19 3 mean 19 3 mean
0.4 31.9 34.0 32.9 a 5.9 8.7 7.3 a
10 32.5 35.4 33.9 a 6.1 9.2 7.6 a
16 30.6 35.4 33.0 a 5.7 9.3 7.5 a
mean 31.7 a 34.9 b 5.9 a 9.0 b

Bulbs planted immediately
after special precooling 37.7 8.9

 

 

 

 

 

 

 

 

 

 

107
Table 29 (cont'd.).
Top internode length (cm) Toppled stems.
CO2 level 02 level (%) 02 level (%)
(%) 19 3 mean 19 3
0.4 10.0 11.5 10.8 a 0.0 a 0.0 a
10 10.0 10.4 10.2 a 0.0 a 0.5 a "
16 9.2 10.7 9.9 a 7.5 b 0.5 a '
mean 9.8 a 10.9 b
Bulbs planted immediately
after special precooling 11.2 0.0
, I.
I

zValues within 1- or 2-way tables of means followed by same letter are
not significantly different at the 5% level as determined by Tukey's
HSD test.

yValues within 2-way tables are means of 2 replications of no more than
20 flowering plants.

'COZ level x 02 level interaction significant at the 5% level.

DISCUSSION

Control Monitoring

The respiration pattern of uncooled tulip bulbs displayed an ini-
tial peak in early autumn which was likely associated with completion
of floral initiation. The final respiration peak of bulbs at room
temperature could have been caused by shoot or bulb senescence, flower
abortion, and/or invasion of the bulb tissue by other organisms. When
the bulbs were moved to 5°C, the respiration lowered to a steady state.
A slight increase in the rate at 5°C occurred during January, regardless
of when the cooling period began. This suggested that the increase in
respiration rate was not the result of satisfaction of a cold require-
ment for normal flowering since the increase occurred after different
durations of cold treatment. The cause of the increased rate was not
determined.

The ethylene production rate of uncooled bulbs was low and vari-
able. The rise in production during February and March was probably due
to flower abortion. Placing the bulbs at 5°C resulted in lower ethylene
production rates. The increase in ethylene production after 12 weeks
at 5°C could have resulted from a change in membrane permeability leading
to greater ethylene liberation or from an increase in actual ethylene
production. (An earlier, additional peak in ethylene production at 5°C
during the 1977-78 season closely followed a malfunction in the system
which caused the bulbs to become moist.) A relationship between increased
ethylene production and satisfaction of the bulb cold requirement was
suggested since the increase occurred after 12 weeks and was not the
result of a change in temperature. However, this work did not elucidate

whether the increase was a chilling sensitivity reaction, or the result

108

 

109

of some hormonal mechanism for controlling shoot growth or scale tissue
senescence. It was not determined whether the scales, the floral shoot,

or both were the source of increased ethylene production.

Precooling Duration Effects

A relationship between satisfaction of the cold requirement and
increased bulb respiration rate was also suggested. After 12 weeks at
5°C, the respiration pattern during the subsequent 2 weeks at 17°C dis- I?
played increased rates as compared to the rates of bulbs cooled for .

shorter periods. This suggested that cold treatment did not have a

 

cumulative effect upon bulb respiration rate, but that a requirement H;
was satisfied which yielded increased rates. The increase may have been

a necessary event in the processes leading to stem elongation and floral

development or could have been the result of decreased respiratory effi-

ciency.

Bulb ethylene production subsequent to the cold treatment increased
after 12 weeks at 5°C during the 1977-78 season. However, the results
were not confirmed since data were not available during the 1978-79 sea-
son due to increased air flow rates.

A surge of shoot growth did not occur to correspond with the res-
piration increase after 12 weeks at 5°C when the bulbs were moved to
17°C. However, the bulbs were not planted so the moisture level may
have been limiting. This lack of shoot elongation may prove to be a
desirable bulb characteristic in designing a packaging system, since

excessive shoot growth could lead to damage during shipping and handling.

110
Ogygen Level Effects
The respiration of early season special precooled 'Prominence' and
'Kees Nelis' bulbs in response to the treatments at 17°C were very simi-‘
lar. Low 02 levels resulted in decreased bulb respiration rates. This

decrease was less pronounced after late season special precooling and

corresponded to a lesser ability of low 0 levels to reduce shoot growth

2
at 17°C. The low 0 levels also reduced ethylene production of bulbs

2
after early season special precooling. 'Prominence' bulbs consistently
produced more ethylene than 'Kees Nelis' bulbs. The drying of the bulbs
reported later in the season was the most likely reason for the decrease

in bulb ethylene production at the higher 0 levels.

2

Storage of special precooled bulbs in 1% 02 at 17°C was unsuccess-
ful as indicated by the appearance of the dissected shoots and the poor
flowering that resulted. Anaerobic respiration probably occurred in these
bulbs.

Storage of early season special precooled 'Kees Nelis' bulbs in 3
or 5% 02 at 17°C for 4 weeks was successful in obtaining satisfactory
flowering. 'Prominence' bulbs and bulbs of both cultivars precooled later
in the forcing season yielded unsatisfactory flowering regardless of the
treatment.

The problems with'Prominence' bulbs could have been related to their
greater ethylene production or the loose and damaged tunics which they
commonly display. Loose tunics could have led to drying of the root
plate during any phase of storage. This could have led to poor growth
upon forcing due to inadequate rooting, even if the shoots were in good
condition as was indicated by the dissection data.

The poor flowering after late season special precooling could have

111

been due to the increased respiration rates which led to increased water
loss and a decreased carbohydrate supply. These factors would not neces-
sarily have been displayed in dissected bulbs. The increase in green-
house daytime temperatures during the late season forcing could not be
overlooked as a possible cause of the poor flowering.

No bulbs had shoots displaying visible symptoms of damage upon dis-
section after treatment during the 1977-78 season, nor did any show symp-
toms after the CO2 level experiment in 1978-79. These two experiments
involved lower flow rate/chamber volume ratios which obviously led to
higher relative humidities in the chambers. This emphasized that rela-
tive humidity must be investigated when designing a package with poly-
meric films to obtain low 02 atmospheres. The proper humidity level
may extend the successful storage period.

Any storage at 17°C subsequent to cooling shortened the days from
planting to flowering. This was related to the shoot growth that occurred

even during the low 0 level storage. Flower size was acceptable from

2
'Kees Nelis' bulbs after early season special precooling and 4 weeks of

storage at 3 to 5% O The reduction after 6 weeks could have been due

20
to water or carbohydrate loss. The same effect could have reduced the
bottom and top internodes of bulbs stored in air.

The effects of temperature during low 0 level storage upon res-

2
piration rate, ethylene production rate, and diffusion rate were not
investigated. Temperature is expected to be a critical factor in the

success of a polymeric film package system.

Ethylene Effects

When ethylene was added to the air stream, bulbs displayed damaged

anthers and tepals upon dissection and aborted flowers after forcing

112
similar to that reported by 1030: and Beijer (1971). Storage at 3 or

5% O2 reduced this damage. This finding supports the theory of an O2
requirement for ethylene action (Burg and Burg, 1967a). This reduction
in damage could prove valuable in a polymeric film package where ethy-
lene may accumulate.

Ethylene addition reduced shoot and anther growth during storage
at 17°C. This was similar to the reduced growth reported in bulbs
before cold treatment (Munk, 1973a). An increase in the length of
the top internode at flowering was observed after the addition of 10 ppm
ethylene during storage. This suggested some auxin-ethylene inter-
action with ethylene possibly limiting the ability of polar auxin
transport to occur, causing a build-up in the top internode. This
effect was observed at low 02 levels where the effects of ethylene are
generally not as evident. There is disagreement as to whether this

auxin-ethylene interaction actually occurs in other plant tissues

(Burg and Burg, 1967b; Morgan and Gausman, 1966).

Carbon Dioxide Level Effects

The increased Shoat lengths within bulbs treated with 10 and 16%

CO2 suggested that CO may have acted as a competitive inhibitor of the

2
action of ethylene in inhibiting shoot growth (Burg and Burg, 1972a).

High CO2 levels in combination with low 02

no visual beneficial effects on flowering. The experimental design was

levels during storage had

very weak in elucidating treatment effects. The increase in the number
of stems which toppled at or before flowering after the addition of 16%

CO indicates that this level of CO may not be tolerated in a poly-

2 2
meric film package although the damage was not as evident at low 02

113
levels. DeHertogh (1977) suggests that low Ca levels in the top inter-

node are responsible for stem topple. A lowering of the pH in the stem

tissue by high CO2 levels could have lowered the Ca deposited in the

cell walls leading to stem topple.

1.

3.

4.

5.

6.

CONCLUSIONS

The satisfaction of the bulb cold requirement corresponded to
increased ethylene production at 5°C and increased respiration
rates at 17°C subsequent to cold treatment.

Low 02 level (3 to 5%) storage of special precooled 'Kees Nelis'

tulip bulbs in a flow-through system at 17°C was succesful in
maintaining satisfactory flowering ability through 4 weeks.

The response of cultivars to low 0 level storage differed. 'Prom-

2

inence' bulbs responded much less successfully than 'Kees Nelis'
bulbs in yielding satisfactory flowering.

Bulbs that were special precooled earlier in the season responded
much more successfully than late season special precooled bulbs.

Low 02 levels in a flow-through system reduced the detrimental

effects of ethylene (5 or 10 ppm) in aborting the flowers of 'Kees
Nelis' bulbs during the storage period subsequent to cold treatment.

The effects of high CO levels during storage of bulbs were unclear,

2

although 16%.CO in an air flow-through system led to stem topple

2

upon forcing.

114

 

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