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This is to certify that the

dissertation entitled

Growth and Development of Dicentra spectabilis
in Relation to
Storage Temperature and Harvest Date

 

presented by

Anne Marie Hanchek

has been accepted towards fulfillment
of the requirements for

Ph.D. degree in Horticulture

 

 

ZMM {aim

Major professor

Date June 28, 1989

 

MS U is an Affirmative Action/Eq ual Opportunity Institution 0- 12771

 

 

PLACE IN RETURN BOX to remove this checkout tram your record.
TO AVOID FINES return on or before due due.

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MSU Is An Affirmative AetlorVEquel Opportunity lndltution

 

GROWTH AND DEVELOPMENT OF DIQEEIBA EEEQIABILLQ
IN RELATION To Brannon TEMPERATURE AND nanvrsr DATE

BY
Anne Marie Ranchek

A DISSERTATION

Submitted to
Michigan state University
in partial fulfillment of the requirements
for the degree of

DOCTOR OF PHILOSOPHY

Department at Horticulture

1989

(0035251

ABSTRACT

GROWTH AND DEVELOPMENT OF QLQENIRA SEECTABILIS
IN RELATION TO STORAGE TEMPERATURE AND HARVEST DATE

BY
Anne M. Hanchek

Herbaceous perennials overwinter perennating buds at or
below the soil surface and can exhibit distinct patterns of
seasonal growth. In the fall of 1985 and 1986, field-grown
crowns of seven genera , including Qicentra spectabilis (L.)
Lem. were harvested weekly from western Michigan fields and
stored bare-root in polyethylene-lined crates at oc.
Regrowth after storage was superior at later harvests.

In continued work to characterise the chilling
requirements of Q; spectabilig, four separate regrowth
responses were observed: eye etiolation, budbreak, stem
elongation, and flowering. Unstored crowns harvested in
October took 77 days from potting to break bud. storage at
-2.5, o, 2.5, or so for 2 weeks promoted budbreak. After 8
weeks of chilling, buds broke in 10-20 days. Crowns
required 4 weeks of 55c for stem elongation and 8 weeks for
faster flowering. At gloc, eyes etiolated in storage but
budbreak was not hastened; essentially no stem elongation
was observed after these treatments. ht later harvests,
less chilling was needed to achieve the same response. By
mid-November in 1986, minimum field soil temperatures were

below so, and harvested crowns broke bud in 5-15 days after

only 2 weeks storage at glsc. Constant exposure to 20c
delayed budbreak.

In 1987, Q. spectabilig eyes were excised from October-
harvested crowns stored for o, 4, 8, or 12 weeks at 5, 7.5,
or 1°C. The eye was identified in stained fresh sections as
an overwintering structure of scales enclosing primary and
secondary buds. Btiolation of the eye without budbreak
occurred by cell elongation in the basal region. During
storage, the domed vegetative meristem observed at harvest
lengthened into a spike bearing floral primordia. After 12
weeks at 1°C, eyes were three times their original length
and contained few leaves but many flower buds. rloral
primordia were first observed microscopically in eyes from
crowns held 4 weeks at 100 and 8 weeks at so. Despite more
rapid floral development, crowns held at 10c grew very
slowly when planted and usually failed to produce expanded
flowers. After exposure to so for 8 weeks, most crowns

flowered in 40 days and inflorescence size was larger.

ACRNOWLEDGNENTS

My advisor, Dr. Art Cameron, has been an invaluable
source of ideas and encouragement. Re have shared many
projects, from gardens to posters, and my education here at
Michigan state University has been enriched by that
diversity. My thanks to you, Art, for allowing me to follow
my own path through the Ph.D. program.

Among those who have helped me in my work, I would
especially like to thank my colleagues in Dr. Cameron's lab
for their support and physical labor. My thanks go to Ralph
Meiden, Cindyi Welch, Ahmad Schirazi, Roy Lefevre, Kathy
Gunn, Sharon Schwab, Jane laldron, Diana Dostal, Tammy
O'Connell, Matt Jenks, and Charles Robinson.

I would also like to thank Walters Gardens of Zeeland,
Michigan, for so generously supplying the plant material
used in my research, and for the friendship and assistance
offered by Dennis, Mary, and the entire staff.

Last but not least, I would like to thank my family and
friends for their unfailing love and support during the
course of my graduate studies. I am especially grateful to
my mother, Marjorie, and my husband, Iran, for their active
interest in my work, their pride in my accomplishments, and

their firm belief that I would eventually achieve my goals.

iv

TABLE OE CONTENTS

Page

LiSt 0: Tables. 0 O O O O O O O O O O O O O O I O O O O O O C O O O O O O O O O O O O O O O O O O O OVi
List or rigur.s. O O O O O O I O O O O O O O O O O I O O C O O O O O O O O O O O O O O O O O O O OVii
Intrcductione O O O O O I O O O O O O O O C O O O O O O O O O O O O O O O O O I O O O I O O O O O O O O O 1

Chapter 1. Effect of Harvest Date on storage Quality of
narbaceous PerenniaIBOOOOOOOOOOOOOOOOIOOOOOOOOOOOOOO0.6

Chapter 2. Effect of Harvest Date on Growth Responses of

pigggtra gpggtabilig after Chilling..................49

Chapter 3. Review of Bud Dormancy Literature.............65

Chapter 4. Effect of Temperature and Duration of
Temperature Exposure on Regrowth of Qiggntra
spectabilig after 8torage............................79

Chapter 5. Effect of Temperature on Eye Development of

mm EEBCtabil;aeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeee127

smaIYOOOOOOOOOOOOOCOOOOOOOOOOOOOOOOOOOOOOOOOOOOO0......141

LIST OF TABLES

Table 1.1. Growth form and hardiness of herbaceous
perennials used in harvest date studies...................20

Table 1.2. Season averages for dry weight and moisture
content (w/w) of herbaceous perennial roots and crowns
harvested in the fall of 1985.............................21

Table 2.1. Effect of harvest date and storage duration
on number of Dicentra spectabilig crowns that broke bud
within 180 days of growing conditions.....................54

Table 4.1. Effect of storage duration and temperature
on number of Dicentra spectabilis crowns that broke bud
within 180 days of growing conditions.....................91

Table 4.2. Effect of storage at -2.5C on condition and
regrowth of Dicentra spectabilis crowns. Means

calculated for plants with at least one broken eye........92

Table 4.3. Effect of storage duration and temperature

on mean days from potting to budbreak of Dicentra
spectabilis crowns. Means calculated for crowns with

at least one broken eye...................................93

Table 4.4. Effect of storage duration and temperature

on mean rate of stem elongation in mm/week during the

first week of post-break growth of Dicentra spectabilis
crowns. Means calculated for crowns with at least one
brakan ey.0000000000...0..0.00000000000000000000000.0.0.0094

Table 4.5. Effect of storage duration and temperature

on number of Dicentra spectabilis crowns harvested on
10/9/87 that broke bud within 120 days of growing
conditions.0...OOOOOOOOOOOOOOOOOIOOOOOOOOOOOOOOOOOOOOO0.0095

Table 5.1. Effect of storage temperature and duration on

percent of Dicentra crowns with floral buds as observed in
fresh sections at 7.5 to 64x magnification...............132

vi

LIST OF FIGURES
Page

Figure 1.0 Gross morphology of 219535;; spectabilis
crown showing eyes and tuberous roots......................4

Figure 1.1 Minimum daily soil temperatures at 10 cm

depth at Trevor Nichols Experimental Farm, Fennville,

MI, and average soil temperatures at 10 cm depth at

10:00 am in perennial fields, Eeeland, MI.................23

Figure 1.2 number and average length of crown buds per
plant at weekly harvests from 9/26/85 to 11/28/85.........25

Figure 1.3 Crown bud development of Dicentra
gpgctabilig at weekly harvests from 10/7/86 to 12/2/86....27

Figure 1.4. Effect of harvest date and length of
storage at 0C on condition and regrowth of Aquilggia
‘B.1dam.1.r’00......OOOOOOOOOOOOOOOOOO0.0....00......O0.029

Figure 1.5. Effect of harvest date and length of
storage at 0C on condition and regrowth of Coreopsis

lagggglata ‘8unburst' (1985) or ggzggpgig grandiflora
‘sunr‘Y' (1986’OO0.0.0.0000...00.00.00.000.0.0.0.000...00.31

Figure 1.6. Effect of harvest date and length of
storage at 0C on condition and regrowth of Dicentra
spectgilis in1985.0000000000000000000000.0.00.0.0...0.0.33

Figure 1.7. Effect of harvest date and length of
storage at 0C on regrowth of Dicentra gpectabilis in

1986.00.00...00......OOOOOOOOOOOOOOOOOOO0.0.0....CO0.0.00.35

Figure 1.8. Effect of harvest date and length of
storage at 0C on condition and regrowth of Geum
M‘RSe Bradshaw’OOOOOOOOOOOOOOOOOOOOOOOO0.0.0.00.037

Figure 1.9. Effect of harvest date and length of
storage at 0C on condition and regrowth of Gypsophila
paniculata \8nowflake'....................................39

Figure 1.10. Effect of harvest date and length of

storage at 0C on condition and regrowth of Iberis
ggmpgrgirggg ‘snowflake'..................................41

vii

Figure 1.11. Effect of harvest date and length of
storage at 0C on condition and regrowth of Lupingg
‘Ru38.11 HYDrids’.00.000.000.000...OOOOOOOOOOOOOOOOOO0.0.43

Figure 1.12. Effect of harvest date and length of
storage at 0C on whole plant height of perennials at 3-
"..kg from potting.OI.OO0......OOOOOOOOOOOOOOOOOOO0.00.045

Figure 2.1 Minimum daily soil temperatures at 10 cm

depth at Trevor Nichols Experimental Farm, Fennville,

MI, during the fall of 1986, and average soil

temperature at 10cm depth at 10 am in Dicentra

spectabilis field, Zeeland, MI............................56

Figure 2.2. Effect of harvest date and length of
storage at 0C on mean days from potting to budbreak of

Dicentra gpectabilis crowns...............................57

Figure 2.3. Effect of harvest date and length of
storage at 0C on mean rate of stem elongation during
first week of post-break growth of Dicentra spectabilis

crowns...00.0.0000...OOOOOOOOOOOOOOOCOOO0.00.00.00.000000058

Figure 2.4. Effect of harvest date and length of
storage at 0C on regrowth at 5 weeks post-break of

Dicentra spectabilis crowns...............................60

Figure 2.5. Effect of harvest date and length of
storage at 0C on flowering of Dicentra spectabilis

cronseeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeee62

Figure 4.1 Minimum daily soil temperatures at 10 cm

depth at Trevor Nichols Experimental Farm, Fennville,

MI, and average soil temperature at 10 cm depth at

10:00 am in Dicentra spectabilis fields...................97

Figure 4.2. Effect of storage for 4 or 10 weeks at 0,
2.5, 5, 10, 15 or 20C on mean length of Dicentra

Milli QYQSeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeegg

Figure 4.3. Effect of storage for 4 or 10 weeks at 0,
2.5, 5, 10, 15 or 20C on percent of Dicentra
gpggtabilig eyes that opened in storage..................101

Figure 4.4. Effect of storage temperature and duration
on mean days from potting to budbreak of Dicentra
spectabilis crowns.OOOOOOOOOOOOOOOOOOOOOO0.0.000...I....0103

Figure 4.5. Effect of storage temperature and duration

on mean days from harvest to budbreak of Dicentra
seoggflilis crownsOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOCOO0000105

iix

Figure 4.6. Effect of storage temperature and duration
on mean rate of stem elongation during the first week

of post-break growth of Dicentra gnggtabilig crowns......107

Figure 4.7. Effect of storage temperature and duration
on mean height at 5 weeks post-break of Dicentra

M111 plants................o.....o................109

Figure 4.8. Effect of storage temperature and duration

on flowering of Dicentra spectabilis: percent non-

dormant crowns producing at least one expanded flower
within 220 days after potting............................111

Figure 4.9. Effect of storage temperature and duration

on mean days to flower for 219333;; gpgggabilig: means

calculated for non-dormant crowns producing at least
one expanded flower......................................113

Figure 4.10. Effect of storage temperature and
duration on mean length of Dicentra spectabilig eyes.

Crowns harvested October 9, 1987.........................115

Figure 4.11. Effect of storage temperature and
duration on mean days to budbreak for Dicentra
spectabilig crowns harvested October 9, 1987.............116

Figure 4.12. Effect of storage temperature and
duration on mean rate of stem elongation during the

first week of post-break growth of Dicentra spectabilig
crowns harvested October 9, 1987.........................117

Figure 4.13. Effect of storage temperature and
duration on regrowth of Dicentra spectabilig crowns

h‘nest.d catcher 9' 1987....OOOOOOOOOOOOOOOOOOOO0.0....0119

Figure 4.14. Effect of storage temperature and

duration on flowering of Dicentra spectabilis crowns
hafl.st.d catcher 9' 1987.00.00.000000000000000000000000.121

Figure 4.15. Effect of storage temperature and
duration on days to flower for Dicentra spectabilig

crowns harvested October 9, 1987.........................122

Figure 4.16. Effect of storage temperature and

duration on floral production of Dicentra spectabilis
crowns harvested October 9, 1987.........................123

Figure 5.1. Minimum daily soil temperatures at 10 cm
depth at Trevor Nichols Experimental Farm, Fennville,
MI, and average soil temperature at 10 cm depth at

10:00 am in Dicentra spectabilig field in 1987 in

calona' ”I.0.0..OO...O0.0.00000000000000000000000000....0133

ix

Figure 5.2. Vegetative anatomy of fall-harvested
mm Weeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeee135

figure 5-3- The are of Dicentra Min-.m-u-n-nlas
Figure 5.4. Anatomy of floral eyes of Dicentra

0.0.0....OOOO0.000.000.0000.00.0.0.0...O0.0.0.138

INTRODUCTION

Dormancy in perennials is a familiar phenomenon,
especially in the world's temperate zones, where we most
often associate it with winter survival. A leafless tree,
although very visible, is not the only example of bud
dormancy. Herbaceous perennials also have perennating buds,
not on aerial stems, but on roots, crowns, stolons,
rhizomes, and in bulbs. These buds can exhibit distinct
patterns of dormancy.

The definitions used in the study of dormancy are
subject to discussion and continuing revision (5). Several
systems of terms have been proposed, some for both buds and
seeds, some for a particular organ or tissue only. The
American Society for Horticultural Science at its 1988
annual meeting proposed this general definition of dormancy:
"the suspension of (visible) growth of any plant
structure(s) containing a meristem(s) in response to
external or internal control" (2).

One growth cycle of herbaceous perennials is typified
by Coreopsig lagggolata, which is killed back to a leafy
rosette by cold weather. With protection, it can remain
evergreen all winter. By some definitions, the plant is
quiescent rather than at rest since regrowth can occur in a

1

2
heated greenhouse when crowns are defoliated in the months
of September, October, and November (Chapter 1). Since
growth can resume at any time that temperature and
moisture are favorable, we can also call such goreopsis
ecodormant (5).

On the other hand, many perennials completely lose all
aboveground structures during part of the year. Spring-
flowering bulbs and ephemerals die back early in summer,
apparently in a pre-programmed response to the seasonaly
unfavorable conditions under which they evolved (7). They
are generally described as "summer-dormant" but this refers
more to lack of above-ground parts than to cessation of
growth. In fact, some authors claim there is no true
dormancy in certain bulbs such as tulip and daffodil since
the flowering apex continues to develop during the leafless
period (3,4).

Somewhere between these two extremes is the growth
cycle of fiesta, which emerges from the soil in spring,
attains full growth and flowering during the summer, and
dies back in fall. Defoliation in late summer does not
induce new growth. This basic pattern also describes
Dicentra spectabilis (Lam.) L., the old-fashioned bleeding
heart (6,8). Dicentra has a spreading, tuberous root system
with adventitious crown buds or "eyes" that elongate rapidly
in spring (Figure 1.0: 1).

In a preliminary study in 1985-86, when crowns were

harvested, defoliated, and potted immediately, the eyes did

3
not elongate even after seven months in the greenhouse.
Those same crowns grew well after exposure to cold
temperatures in storage, supporting Lopes and Weiler's (6)
observation that Dicentra requires chilling to overcome bud
dormancy. The first of the following studies was begun to
examine the relationship between harvest date and regrowth
after storage of selected fall-harvested herbaceous
perennials. Further experiments were designed to explore

the relationship between harvest date, storage temperature,

and growth responses of Dicentra gpectabilis.

 

Figure 1.0 Gross morphology of Dicentra spectabilig

crown showing eyes and tuberous roots.

LIST OF REFERENCES

Allenstein, P., A.M. Richards, J.L. Taylor, and A.C.
Cameron. 1987. Growing perennials. Cooperative
Extension Service Bulletin E-1984 (new), Michigan State
University.

ASHS Committee to Evaluate Dormancy Terminology. 1988.
Challenges in dormancy research: Communication of
complex systems. HortScience 23:716-717.

De Hertogh, A.A. 1974. Principles for forcing tulips,
hyacinths, daffodils, Easter lilies and Dutch irises.
Scientia Hort.2:313-355.

Ramerbeek, G.A., J.C.M. Beijersbergen, and 2.x. Schenk.
1970. Dormancy in bulbs and corms. Proc. 18th Int.
Hort.Cong. 5:233-239.

Lang, G.A. 1987. Dormancy: A new universal terminology.
HortScience 22:817-820.

Lopes, L.C. and T.C. leiler. 1977. Light and temperature
effects on the growth and flowering of Dicentra

gpgctabilis (L.) Lem. J. Amer. Soc. Hort. Sci. 102:388-
390.

Rees, A.R. 1981. Concepts of dormancy as illustrated by
the tulip and other bulbs. Ann. Appl. Biol. 98:544-
548.

Stern, A.R. 1961. Revision of Dicentra (Fumariaceae).
Brittonia 13:1-57.

CHAPTER 1

EFFECT OF HARVEST DATE
ON STORAGE QUALITY OF HERBACEOUS PERENNIALS

Many herbaceous perennials are grown commercially in
southwest Michigan fields. The basic production scheme is
to plant seeds or cuttings in the spring, lift and divide
the crowns in the fall, and store them bareroot in
polyethylene-lined crates at -2 to +2C for several months
until shipped (3,7,8).

The recent surge in popularity of herbaceous perennials
has meant an increased demand upon growers by retailers for
quality material. Many of these retailers are located in
warmer areas of the U.S. where fall planting is popular.
Retailers find a definite advantage in having two marketing
seasons, but have difficulty filling fall orders since the
major Michigan producer prefers not to ship at that time.

In the growers' experience, plants harvested before November
in Michigan generally do not store well, often rotting
completely and are of lower overall quality.

USDA recommendations do not address harvest date as a
factor in the storage of herbaceous perennials (11) although
the reader is referred to Mahlstede and Fletcher (12) who
stress the importance of maturity for successful handling of

7
all nursery stock. Certain perennials which are summer-
dormant such as iris and oriental poppy can be lifted early
in the fall. The recommendation for most other herbaceous
perennials is to dig as late as possible in the season. In
an experiment with Alcoa (hollyhock), plants dug before
October 5 and held at 2C regrew poorly (12). Plants
harvested later in the digging season regrew much better.
Langhans and Weiler (9) also emphasized the importance of
maturity in storage of lily bulbs, with late September or
early October harvests for best quality.

Date of harvest can also greatly affect subsequent
regrowth of stored strawberry crowns. Best results were
achieved when harvest was delayed until December in the
northern temperate zone (1,2,5,22,24). Lift date has also
been identified as an important factor in successful storage
and establishment of conifer seedlings. The ability to
survive cold storage and regenerate roots when planted
peaked from October to April in the northern temperate zone
for Douglas-fir and ponderosa pine (19,20) and from December
to February for lodgepole pine and interior spruce (18).
Preliminary experiments by Maqbool (unpubl. data 1983)
indicated that a similar pattern could exist for several
herbaceous perennials.

This study was designed to examine the relationship
between harvest date and regrowth after storage of selected

fall-harvested herbaceous perennials, including Dicentra

switching-

EATEBIALQ AND EEIEQQE

128; g;pg;imgn_g. Seven different species were used:
Aguilggia L. 'Biedermeier', gorggpgig|langgglata L.
'Sunburst', spring-planted niggntra spectabilig (L.) Lem.,
£32! quellygn Sweet 'Mrs. Bradshaw', gypggphila pagicglata
L. 'Snowflake', Iberis semperziggns L. 'Snowflake', and
Lupinus L. 'Russell Hybrids'. Specific information on root
system, storage type, and hardiness is given in Table 1.1.

Each week for twelve weeks, from September 11 to
November 27, plants were lifted from commercial fields in
western Michigan (Walters Gardens, Zeeland, MI). At each
harvest, ten soil temperatures at 10 cm depth were recorded
per species at the harvest site. Weather records from the
Trevor Nichols Experimental Farm, Fennville, MI were also
obtained (15). Soil cores at 5 cm to 10 cm were removed,
and the samples were weighed before and after oven-drying to
determine percent water content (w/w). Plants were
processed by shaking off all loose soil and removing the
green tops. The number and average length of eyes (crown
buds) on each plant of Aguilggia, G o hi1 , Lupinus, and
Dicentra were recorded. Five plants of each of the seven
species were then potted and put in a cool greenhouse (19C
day/12C night). Twenty crowns of each were stored in bulk
at 0C in polyethylene-lined crates to avoid desiccation
stress (3,21,24).

On January 8 and on April 9, ten plants per species

from each harvest were removed from storage and evaluated

9

for mold, using a 1 to 4 scale (1:0-25% surface molded,
2=26-50% surface molded, 3=51-75% surface molded, 4=76-100%
surface molded). The crowns were then potted and their
regrowth was evaluated at 3 and 4 weeks after each potting,
using a 0 to 5 scale (0=dead, 0.5=dormant buds, 1=emergent
growth, ...5=vigorous growth) following Maqbool (13). Whole
plant height was measured and presence of buds or flowers
noted.

At three times during the harvest season, ten extra
plants were dug and processed, then divided into root and
crown. The parts were weighed, oven-dried, and reweighed to

give dry weight and moisture content on a fresh weight

basis.
12§§ egeeeieeeee. Three species were used: tra
metabilis. motile missiles; 'Snowflakc'. and

Cogeopsis ggeegiglege Hogg ex Sweet 'Sunray' (Table 1.1).

Each week for nine weeks from October 7 to December 2, ten
plants of each species were potted immediately, ten were
stored at OC for two months, and ten at 0C for four months.
Gypsopeila and Cogeopsis were held under natural daylength
in the greenhouse. Qicentge alone was regrown under 16
hours of 8.5 mol/day-m2 supplemental light. Regrowth, mold,
and flowering were evaluated as before, but height was not‘
measured.

Development of eyes was monitored for Dicentra only.
At each harvest, ten plants were washed and all visible eyes

(;2 mm) excised from the crowns. Number, length, and dry

10
weight of the eyes were recorded. Root and crown weights
were not measured for any species.

The data for each year were analyzed as a
completely randomized design (14). Least significant
differences between treatment means were calculated at the
0.05 level with n=5 replicates per treatment cell (no
storage) or n=10 (with storage). Standard errors were

calculated for dry weight and water content means.

BBEQLTQ

£911 eeeeieiege. In the sandy loam soil of Ottawa
County, moisture in the upper soil during September,
October, and November varied from 5% to 12% (w/w) in
response to temporary conditions such as rainfall, snow,
cultivation, cloud cover, etc (data not shown). No pattern
was obvious. Soil temperature at 10 cm depth declined from
near 20 to 2C over both harvest seasons (Figure 1.1).

Soil tests by the MSU Soil Testing Lab showed high
levels of phosphorous, calcium, and magnesium, and adequate
nitrogen and potassium in all fields. pH ranged from 6.5 to
6.8, cation exchange capacity from 2 to 4 meq/100g.

21525 QQIELQPEEBE 2212:: AQIZEEE- There '01. 30
significant changes over the 12 week harvest season in dry
weight or moisture content of the root and crown in any of
the seven species harvested in 1985. Average moisture
content of roots was close to 70% for all species except

12egie whose roots were only 55% water. Water content of

11
crowns was generally a little higher than roots (Table 1.2).

Average length of eyes in the four species producing
crown buds was 2 to 4-fold greater at later harvests (Figure
1.2). For nieeeeze, gypeepnile, and Lepieee, eye length was
greatest on the last harvest date. For Ageilegie, length as
measured was highest in mid-November. In contrast, the
number of eyes per stem did not increase over the harvest
season. A sample of 21222£££ on September 11, however, was
completely lacking in visible eyes, suggesting that eye
production was relatively rapid and synchronized between
September 11 and 26.

In 1986, sampling was restricted to Qieeeege and each
eye 2 mm or longer was individually measured. Neither
number of eyes nor length per eye varied significantly
during October or November (Figure 1.3). Length remained at
10-15 mm throughout the season, similar to the initial 1985
length. Dry weight per eye, however, increased in mid-
November.

Poee-gtegage eoeditiee.i Aggilegie. Plants harvested
before November and stored for over 5 months (long storage)
were more than 50% covered with mold (Figure 1.4). In
general, little to no mold growth was associated with later
harvests and shorter storage periods. Neither harvest date
nor storage length appeared to affect survival or regrowth
quality. The best-looking plants were those harvested in
mid-September and immediately potted, or those harvested in

November and stored at least 5 months. The latter generally

12
flowered better as well. None of the plants potted
immediately after harvest or after short storage flowered
within 8 weeks of observation.

Cereensis- gereeeeia lenseglata 'Bunburst' crowns
lifted anytime during the harvest season in 1985 and potted
immediately regrew (Figure 1.5). However, most plants
harvested before October 31 did not survive 2 months
storage: survival rate was even less for longer periods.
All crowns harvested in mid-November or later survived 4
months at 0C. In addition, mold on stored crowns decreased
with later harvests (r=-0.87, e=0.0001) and was barely
detectable for the final three harvest dates. Regrowth
quality of stored crowns followed the same pattern as mold
growth, with the most vigorous plants being those harvested
in late November and stored 1 to 4 months.

Coreopeig qgeggiglege 'Sunray', harvested in 1986, did
not support mold growth in storage and 100% of the crowns
survived. Crowns potted the day of harvest regrew but were
generally of lower and less predictable quality than those
stored 2 or 4 months (Figure 1.5d). For 'Sunray', the best
plants were those harvested in mid-October or later, and
stored 4 months. No plants of either Coeeopsie cultivar
flowered within 8 weeks of observation.

DIQQDSIA- Plants potted the day of harvest survived,
but usually did not regrew, except for a few plants from the
latest harvests in 1986 (Figures 1.6, 1.7). Dormant eyes

were visible on many non-growing plants. Stored plants

13
showed an entirely different regrowth pattern. If harvested
before October 10 in 1985, pieenege crowns came out of
storage heavily molded, rotted, and dead. Those harvested
on or after November 7 showed little mold development in
storage and excellent regrowth. The transition from dead to
vigorous plants took place over four weeks in October.
Results were similar for both storage durations.

In 1986, very little mold developed in storage, even at
early harvest dates, and all plants survived. Regrowth,
however, paralled that of the previous year (Figure 1.7).
In both years, late harvests and long storage at 0C produced
higher quality plants which were also more likely to flower.

gegn. Stored crowns were rarely free of mold (Figure
1.8). Early harvests and long storage periods aggravated
the problem. Survival, however, was excellent despite mold
growth. Death in storage was only notable (z25%) for very
early harvests stored for 5 months.

Crowns potted the day of harvest always showed
excellent regrowth. Stored plants did not regrew as well,
except for late harvests and 1 to 2 month storage. Quality
tended to decrease with storage duration. No plants
flowered within 8 weeks of observation.

gypeeeeile. Mold on Qypeepeile roots increased while
percent survival decreased with storage length of 5 months
or more for early harvests in 1985 (Figure 1.9). In
October, plants were harvested and stored successfully for

short periods: November harvests survived longer storage of

14
4 months. Regrowth quality of October harvests was poor but
increased in November. Unstored plants generally regrew
well, but stored roots produced taller plants (data not
shown).

In 1986, results were quite different. The regrowth
quality of plants harvested in October or November and
stored for 4 months was consistently high. Two months
storage produced good plants only from later harvests, while
unstored roots did not regrow well after mid-October. No
plants flowered within 8 weeks of observation.

IEeeie. Harvest of Ibegis began on October 3 rather
than September 11. Since these plants are sub-shrubs and
were not cut back at harvest or potting, regrowth was
defined as greening of existing foliage and extension of
lateral branches. Height during regrowth was not measured.
Foliage of October-harvested plants was heavily molded after
5 months at 0C (Figure 1.10). Surviving individuals from
these treatments also regrew poorly. Shorter storage
periods and later harvests produced better quality plants
which were free from mold. Unstored Ibegie from all
harvests grew well in the greenhouse but did not flower.
Flowering was best for plants harvested in November and
stored at least 4 months.

Lgpieee. Mold growth was generally greater for early
harvests and longer storage periods (Fig. 1.11). Of the few
plants harvested and stored before mid-October that

survived, some individuals were diagnosed with gythium by

15
the MSU Plant Diagnostic Clinic. However, Lupigus harvested
and potted immediately always regrew fairly well. Regrowth
after storage improved as harvest was delayed. No plants

flowered within 8 weeks of observation.

DISQQQEIQ!

Mold rating was not generally indicative of subsequent
regrowth quality. Harvest date was always more highly
correlated with mold than was subsequent regrowth, with the
exception of Iberis, which was stored as a leafy evergreen.
Its damp, compressed foliage provided an excellent medium
for growth of surface molds in storage and growing points
were often damaged. Yet fungicides such as benomyl can be
phytotoxic (6,13). Unpublished work by Heiden (pers. comm.)
shows that removal of stems and foliage of Ibegis before
storage, rarely done in practice, avoids these problems and
results in a predictably high-quality plant.

Most crowns of any perennial that came out of storage
completely covered with mold regrew poorly, but plants free
of mold did not always regrow well. Also, the mold rating
refers only to eugface mold. In many cases, dead or dying
plants were rotted in storage as opposed to molded. The
possibility of internal pathogens such as bacteria or the
oomycete found in Lupinue cannot be ignored, although the
subject was not part of this study (6).

gegeepeie and gege, plants with fibrous root systems

and stored as trimmed rosettes, grew fairly well despite

16
being cut back when potted immediately after harvest. After
storage, however, plants from early harvests were of very
low quality, especially after long periods. Beginning in
mid-October, regrowth ratings began to equal or surpass
those of unstored plants. Plant height followed the same
pattern, but showed, in addition, an interesting reduction
in height of unstored plants harvested late in November
(Figure 1.12a). Flashy-rooted species (Ageilegie, Diceetra,
gypeeenile, and Lepieee), stored as bare roots with dormant
crown buds, behaved similarly but did not regrow as well
without storage (Figure 1.12b). Additional exposure to OC
not only improved the regrowth rating, but greatly increased
height relative to the control.

Although a tall plant did not always receive a high
regrowth rating, height and regrowth quality were strongly
correlated (r=0.9, a=0.0001) for all the perennials studied
except geem. Mold decreased over as harvest was delayed for
both plant types, but increased with storage duration for
early-harvested fleshy-rooted species.

In 1985, all stored crowns were potted on the same
days, so storage length varied with harvest date, the later
harvests always being stored for shorter periods. This
mimicked the industry practice of harvesting the same
material at several times in the fall, then mixing harvest
dates in the same shipment. Under these conditions,
regrowth quality after storage rose as harvest was delayed.

If regrowth was mainly a response to time in storage, then

17
plants from the first harvest after short storage (a total
of 17 weeks at DC) should have behaved as plants from the
last harvest after long storage (a total of 18 weeks at 0C),
and the two parameters would be well correlated. This was
not the case. Late harvest consistently improved regrowth
quality after storage.

In 1986, the treatments were designed for constant
storage duration. Under those conditions, regrowth was
unchanged with respect to harvest date for sexeepeie (a
different species than in 1985), slightly better at later
dates after short-term storage for Qypeeeeile, and greatly
improved for Qieeeeee. Clearly, both harvest date and
storage duration can affect regrowth.

Over the harvest season, there was a change in the
plant response to storage. Early in the season, the shorter
the time spent at 0C, the better. At some point, though, in
response to field chilling, plants "hardened" and remained
undamaged by long storage. Mahlstede and Fletcher (12)
reported that decreasing moisture content from 80% to 73%
signalled maturity in Lleee. Lily bulb growers recognize
maturity when the old stem pulls easily form the bulb (9).
Researchers have tried to measure the hardening process by
monitoring changes in starch content of roots (2,5) or
electrolyte leakage after freezing tests (4,25). In this
experiment, dry weight of crowns, moisture content, eye
length, and eye number per crown were measured. Only eye

length varied significantly with harvest date, but the

18
relationship was not adequate to predict a complex response
such as storage quality.

Overall, the observed changes in plant response to
storage in 1985, whether in mold rating, regrowth, height,
or crown bud length, occurred in mid-October at the same
time as minimum soil temperatures dropped below 10C.
Similar changes could be seen in October of 1986, but soil
temperatures dropped earlier and stayed low for several
weeks. Chilling has long been assumed to drive the
hardening process (23), but most authors have worked with
woody plants that carry aerial perennating buds (16,17,18).
Logically, herbaceous perennials would respond to the
temperature of the soil surrounding their terrestrial buds.
This may explain why little or no mold was found on stored
crowns harvested in 1986. The change from "unstorable" to
"storable" may have taken place the first week of the
harvest period. This study implies that the critical
temperature was below 10C. However, controlled chilling at
co in storage did not fully replace field chilling for
early-harvested plants. There must be other factors at
work, such as diurnal temperature cycles or photoperiod
effects (9,19,23).

The most striking response, by far, was seen in
Qieee_;e. The drastic changes from dead to living, molded
to non-molded, non-growing to growing, and non-flowering to
flowering suggest a switch turned on by exposure to cold

temperatures, as experienced both in the soil environment

19
and in the storage room. These results further support the
observation that 212225;; requires chilling to overcome
dormancy (10), and that dormancy develops as part of the

hardening process.

 

20

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22

Figure 1.1 Minimum daily soil temperatures at 10 cm
depth at Trevor Nichols Experimental Farm, Fennville,
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10:00 am in perennial fields, Zeeland, MI.

A. 1985. Zeeland standard error of the mean=0.3.

B. 1986. Zeeland standard error of the mean=0.4.

 

SOIL TEMPERATURE (0C)

son. TEMPERATURE (0C)

23

 

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24

Figure 1.2 Number and average length of crown buds per
plant at weekly harvests from 9/26/85 to 11/28/85. At
least 30 plants sampled per mean.

A. Ageilegie \Biedermeier': LSD.05 (number)=0.1,
LSD.05 (length)=0.3.

B. pieeeege specteeilis: LSD.05 (number)=0.1,
LSD.°5 (length)=0.4.

C. Gypsophila paniculata \Snowflake': LSD.os
(number)=0.1, LSD.05 (length)=0.5.

D. Lupinus \Russell Hybrids': LSD.05
(number)=7.5, LSD.05 (length)=2.3.

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26

Figure 1.3 Crown bud development of Dicentra
spectabilis at weekly harvests from 10/7/86 to 12/2/86.
At least 30 plants sampled per mean.

A. Mean number per plant and mean length of crown
buds:no significant differences between means.

B. Mean dry weight in mg per eye: LSD005=20.5.

 

27

DICENTRA 1986

 

143 It

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CROWN BUDS PER STEM (—n—)

 

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DATE OF HARVEST 1986

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28

Figure 1.4 Effect of harvest date and length of
storage at DC on condition and regrowth of Aqeilegie
\Beidermeier'.

A. Percent survival.

B. Mean mold rating at potting where 1=0-25%
surface molded, ...4=76-100% surface molded:
LSD.05=0.7.

C. Mean regrowth quality at 3-4 weeks after
potting where =dead, 0.5=dormant buds, 1=emergent
growth, ...5=vigorous growth: LSD. 5 (no
storage)=1.4, LSD.°5 (with storage?=1.0.

D. Percent plants flowering within 4 weeks after
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30

Figure 1.5. Effect of harvest date and length of
storage at 0C on condition and regrowth of eeeeeeeie

langeqlata ‘sunburst' (1985) or screensis grendiflera
‘Sunray' (1986).

A. Percent survival in 1985.

B. Mean mold rating at potting in 1985 where 1=0-
25% surface molded, ...4=76-100% surface molded:
Lsn.os=o.s.

C. Mean regrowth quality at 3-4 weeks after
potting in 1985 where =dead, 0.5=dormant buds,
1=emergent growth, ...5=vigorous growth: LSD.

(no storage)=1.0, LSD.05 (with storage): .9.

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32

Figure 1.6. Effect of harvest date and length of
storage at OC on condition and regrowth of Qieeeeee

sesstabilis in 1985-

A. Percent survival.

B. Mean mold rating at potting where 1=0-25%
surface molded, ...4=76-100% surface molded:
LSD.°5=0.5.

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potting where 0=dead, 0.5=dormant buds, 1=emergent
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33

 

 

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34

Figure 1.7. Effect of harvest date and length of

storage at 0C on regrowth of Qieentra spectabilis in
1986.

A. Mean regrowth quality at 3-4 weeks after
potting where 0=dead, 0.5=dormant buds, 1=emergent
growth, ...5=vigorous growth: LSD.°5=1.0.

B. Percent crowns flowering within 4 weeks after
potting.

 

7. FLOWERING

REGROWTH RATING >

DICENTRA 1986

 

 

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DATE OF HARVEST 1986

11/21

 

   

 

 

36

Figure 1.8. Effect of harvest date and length of
storage at 0C on condition and regrowth of gee;
geellyon \Mrs. Bradshaw'.

A. Percent survival.

B. Mean mold rating at potting where =0-25%
surface molded, ...4=76-100% surface molded:
LSD.°5=0.4.

C. Mean regrowth quality at 3-4 weeks after
potting where =dead, 0.5=dormant buds, =emergent
growth, ...5=vigorous growth: no significant
differences between no storage means, LSD.05 (with
storage)=0.7.

 

 

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MOLD RATING

REGROWTH RATING 0

 

 

 

 

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9/26 10/10 10/25 11/7 11/21

DATE OF HARVEST 1985

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38

Figure 1.9. Effect of harvest date and length of
storage at ca on condition and regrowth of eyeeepeile
paniculata \Snowflake'.

A. Percent survival in 1985.

B. Mean mold rating at potting in 1985 where =0-
25% surface molded, ...4=76-100% surface molded:
LSD.05=0.9.

C. Mean regrowth quality at 3-4 weeks after
potting in 1985 where 0=dead, 0.5=dormant buds,
1=emergent growth, ... 5=vigorous growth: no
significant differences between no storage means,
LSD.05 (with storage)=0.9.

D. Mean regrowth quality at 3-4 weeks after
potting in 1986 where 0=dead, 0.5=dormant buds,
1=emergent growth, ... 5=vigorous growth:
589.05=°'3°

 

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40

Figure 1.10. Effect of harvest date and length of
storage at oc on condition and regrowth of 122:15
sempezgigege \Snowflake'.

A. Percent survival.

B. Mean mold rating at potting where 1=0-25%
surface molded, ...4=76-100% surface molded:
LSD.05=0.5.

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potting where 0=dead, 0.5=dormant buds, =emergent
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41

 

 

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33.0.8 020.. I 005.05 .59..» 010
35.0.5 Ecru Te 00. a 003.05 02 Te
mom. H822... ...o 33 new. 502.2: .3 mos
_«\.. 2\_. ou\o. o.\o. o~\o ..\o .u\.. 2\.. o~\o. o.\o_ o~\o ..xo
IF > P b P P p I P I b I O h L P L b > I- . E h F b O
33.05 3.01% T. g 02 I
0355 ozS I 85.2» 958.. a To .2
U305 95.0: o are
.1— TON
W” .2
0
TN m YO?
.3
w
.8
I” H...
N” .2
no -8
1
3a
r8.

 

 

 

 

 

mEmm:

0 oNuva HlMOtIOBEl

'IVAIAEIOS 34

4

42

Figure 1.11. Effect of harvest date and length of

storage at 0C on condition and regrowth of Lupine;
\Russell Hybrids'.

A. Percent survival.

B. Mean mold rating at potting where 1=0-25%

surface molded, ...4=76-100% surface molded:
LSD.05=0.7.

C. Mean regrowth quality at 3-4 weeks after
potting where 0=dead, 0.5=dormant buds, 1=emergent
growth, ...5=vigorous growth: no significant

differences between no storage means, LSD.05 (with
storage)=1.0.

 

>

Z SURVIVAL

MOLD RATING

REGROWTH RATING 0

43

LUPINUS

 

 

  
    
 

O-OIKJSHMUBE
IbiISHORTSflNUGE
e—e UJKBSHNUGE

 

 

 

T T T T

- . 1 f ,1
9/26 10/10 10/26 11/7 11/21

DATE OF HARVEST 1985

9/11

 

4..

34

24

1-1

 

 

ere UNIBSRNMOE
TrilSHORTSNNUGE

 

T T ' T r r - T’ 2' T
9/11 9/2: 10/10 10/26 11/7 11/21

DATE OF HARVEST 1985

 

sl
4.
34
2.1

H

 

OJ

e—eIMJSfllUGE
e—etflfllfl’SKlnGE
ewe UNKBSNNMGE

  

 

 

 

9/2: '10/10 ' Io/ze' 11'/7 ' 11721'

DATE OF HARVEST 1985

T T
9/11

44

Figure 1.12. Effect of harvest date and length of
storage at as on whole plant height of perennials at 3-

4 weeks from potting. Data averaged over indicated
cultivars.

A. Fibrous rooted genera: Coreogsig and gggg.

8- Flashy-rooted genera: Maia. 212m.
ngsophi;a, and Luginus.

 

45

FIBROUS ROOTED SPECIES

>

 

20
e—el«)SflNUGE
11r<ISHORTSflflUGE
H LONG STORAGE

15-1 ,. A
- I? ‘T

A
\\
n

PLANT HEIGHT (CM)

 

 

 

 

 

 

DATE OF HARVEST 1985

D r I r l ' I ' l ' l ' 1
9/11 9/26 10/10 10/26 11/7 “/21
DATE OF HARVEST 1985
B FLESHY ROOTED SPECIES
20
H NO STORAGE .
A 4 H SHORT STORAGE -
2 H LONG STORAGE "
8 15-I
+- 4 ‘
LT] 10.. a
I q r.
I—-, " ‘ ,
Z 5" (a .. . P’é ; ; ‘.‘ 3 9
05. '-' / Y °
. d n - a
DJ ' l l ' T ' T ' T ' T
9/11 9/26 10/10 10/26 11/7 11/21

 

 

LIST OF REFERENCES

Anderson, 3.x. and C.G. Guttridge. 1975. Survival and
vigour of cold-stored strawberry runner plants after
different lifting dates, storage temperatures and pre-
storage treatments. Sxpl. Hort. 27:48-57.

Bringhurst, R.S., v. Voth, and D. Vannook. 1960.
Relationship of root starch content and chilling to
performance of California strawberries. Proc. Amer.
Soc. Hort. Sci. 75:373-381.

Cameron, A.C. and u. Maqbool. 1986. Postharvest storage
of bare-root hardy perennials: The relation of water
loss to storage survival. Acta Hort. 181:323-329.

Dexter, S.T., W.B. Tottingham, and L.F. Graber. 1930.
Preliminary results in measuring the hardiness of
plants. Plant Phys. 5:215-223.

Freeman, J.A. and 3.8. Pepin. 1971. Influence of plant
size, date of digging and duration of cold storage on
the growth of strawberry plants. Can. J. Plant Sci.
51:267-274.

Ranchek, A.M., R. Everts, u. Maqbool, and A.C. Cameron.
1989. Storage molds of herbaceous perennials. J.
Environ. Hort. In review.

Heiden, R. and A.C. Cameron. 1986. Bare-root perennials
require cautious handling. Amer. Nurseryman 163(7):7s-
88.

Lake, 3., C. Noble, and D.F. Hamilton. 1982. Growing
herbaceous perennials. Amer. Nurseryman 155(7):81-85.

Langhans, R. and T. Weiler. 1967. Factors affecting
flowering, p. 37-46. In: D. Riplinger and R. Langhans
(eds.). Faster lilies. Prepared for the New York and
Ohio Lily Schools.

10. Lopes, L.C. and T.C. Weiler. 1977. Light and temperature

effects on the growth and flowering of Dicentra
gpectabilis (L.)Lem. J. Amer. Soc. Hort. Sci. 102:388-
390.

46

11.

12.

13.

14.

15.

16.

17.

18.

19.

20.

21.

22.

47

Luts, J.R. and R.E. Hardenburg. 1968. The commercial
storage of fruits, vegetables, and florist and nursery
stocks. USDA Agriculture Handbook No.66., Washington,
D.C.

Mahlstede, J.P. and W.E. Fletcher. 1960. Storage of
nursery stock. Amer. Assoc. of Nurserymen, Washington,
DOC.

Maqbool, n. 1986. Postharvest handling and storage of
bare-root herbaceous perennials, MS Thesis. Michigan
State University, East Lansing, MI.

Nilliken, G.A. and N. D. Remmenga. 1989. Statistical
analyses and the personal computer. EortScience 24:45-
52.

NSU Agricultural Weather Service. 1985,1986. Weather
data listing for Trevor Nichols Experimental Farm,
Fennville, NI. Dept. of Entomology, Michigan State
University, East Lansing, MI

Richardson, E.A., S.D. Seeley, and D.R. Walker. 1974. A
model for estimating the completion of rest for ‘Red
Eaven' and \Elberta' peach trees. nortScience 9:331-
332.

Ritchie, G.A. 1984. Effect of freezer storage on bud
dormancy release in Douglas-fir seedlings. Can J. For.
Res. 14:186-190.

Ritchie, G.A., J.R. Rodin, and N. Kleyn. 1985.
Physiological quality of lodgepole pine and interior
spruce seedlings: effects of lift date and duration of
freezer storage. Can. J. For. Res. 15:636-645.

Stone, E.C., J.L. Jenkinson, and S.L. Krugman. 1962.
Root-regenerating potential of Douglas-fir seedlings
lifted at different times of the year. Forest Science
83288-297.

Stone, E.C. and G.E. Schubert. 1959. Root regeneration
by ponderosa pine seedlings lifted at different times
of the year. Forest Science 5:322-332.

Stuart, N.W. 1954. Noisture content of packing medium,
temperature and duration of storage as factors in
forcing lily bulbs. Proc. Amer. Soc. Hort. Sci.
63:488-494.

Voth, v. and R.S. Bringhurst. 1970. Influence of nursery
harvest date, cold storage, and planting date on
performance of winter planted California strawberries.
J. Amer. Soc. Hort. Sci. 95:496-500.

48

23. Weiser, C.J. 1970. Cold resistance and acclimation in
woody plants. RortScience 5:403-411.

24. WOrthington, J.T. and D.R. Scott. 1970. Successful

response of cold-stored strawberry plants dug in the
fall. J. Amer. Soc. Sort. Sci. 95:262-266.

25. Eehnder, L.R. and F.O. Lanphear. 1966. The influence of

temperature and light on the cold hardiness of Tagug
gggpigatg. Proc. Amer. Soc. Sort. Sci. 89:706-713.

CHAPTER 2

EFFECT OF HARVEST DATE
ON GROWTH RESPONSES OF DICENTBL SEEQIA§;L;§ AFTER CHILLING

In earlier studies (Chapter 1), quality of stored
herbaceous perennials increased with later harvests.

Dicentra gpggtabilig in particular showed a marked change
over the harvest season in its response to chilling. Quality
was much higher for plants lifted in November than in
September. At the whole plant level, storage quality is
measured by overall vigor of subsequent regrowth, usually
rated on a subjective, arbitrary scale. Although such a
rating system is a valid and valuable means of assessment,

it does not distinguish between the various components of
successful regrowth after storage.

In forestry, the ability of a stored seedling to
regenerate roots has been a useful tool in understanding
establishment problems (17). The aboveground portion of a
nursery transplant, however, has generally received greater
attention. Days to budbreak as a measure of bud dormancy
can be used very precisely (5,12,14), especially when stages
of development are clearly defined (13) and the distinction
is made between budbreak itself and subsequent growth of the
bud (4). Overall height has also been widely used to quantify

49

50
regrowth (1,2,7) with the understanding that the results can
be skewed by skinny, tall, low-quality plants (8).

Lopes and Weiler (7) used a variety of measurements to
study the effect of growing conditions on Dicent a,
including shoot number, node number, internode length, leaf
area, plant height, and plant weight. In addition to
examining post-storage growth responses in relation to date
of harvest, this study was also an effort to identify
specific parameters for assessing regrowth in Dicentra

s t s.

EAIEEILLQ AND HE 003

One year old Dicentra spectabilis (L.) Lem. crowns were
harvested weekly in western Michigan fields (Walters
Gardens, Zeeland) in 1986 for nine weeks from October 7 to
December 2. Loose soil was removed by shaking and any green
material was trimmed, leaving the eyes intact. At each
harvest, ten soil temperatures at 10:00 a.m. at 10 cm depth
in the field were measured. Soil temperature records were
also obtained from the Trevor Nichols Experimental Farm,
Fennville, El (10). Crowns were stored in polyethylene-
lined crates to avoid desiccation stress (3) and held at 0C
for 0, 2, or 4 months, with ten plants per treatment. After
treatment, the crowns were potted with eyes exposed and
regrown in a cool greenhouse (19C day/12C night) under 16
hours of 8.5 mol/day-m2 supplemental light.

After potting, all plants were inspected daily for

51
budbreak, defined in this study as the opening of bud scales
and appearance of floral parts or expanding leaf margins
from within the eye. Time to first budbreak was recorded
for each crown. If eyes had not broken after 180 days of
growing conditions, crowns were discarded (Table 2.1). At
time of break, eye length was measured. The eye was
remeasured at 7 days post-break to determine the elongation
rate of that individual eye during the first week post-
break.

At 5 weeks post-break, the regrowth quality of the
entire plant was rated on a 0 to 5 scale (0=dead,
0.5=dormant buds, 1=emergent growth, 2=minimal growth,
3=acceptable growth, 4=better growth, 5: vigorous growth)
following Maqbool (8). Whole plant height to the highest
leaf was measured at the same time. The date at which each
crown first produced an expanded flower was also noted.

Treatment means were calculated on the basis of plants
which survived to that point of development. The data were
analyzed as a completely randomised design (9,11). Standard
errors of interaction means were calculated with n=8
replicates per treatment cell, the smallest n in the

analysis.

EESELIE

Soil temperatures at 10 cm below the surface dropped
sharply in early November from 11C to 2C (Figure 2.1). Days

from potting to budbreak of unstored Dicentra crowns also

52
decreased over the harvest season, with a sharp drop in
mid-November (Figure 2.2). By the last harvest on December
2, unstored crowns broke in 10 days, essentially the same
time as chilled crowns from earlier harvests.

Harvest date also affected time to budbreak following
cold storage, decreasing it in general by 1 day for each
extra week spent in the field. In addition, there was a
small but significant decrease in days to budbreak with 4
months rather than 2 months exposure to 0C. For any given
harvest date, the average difference after 2 or 4 months
storage was 1.3 days. For some individual plants from
November harvests, budbreak after 4 months of chilling was
very rapid, taking place within the first day after potting.
Overall, the difference between the two storage periods was
greatly overshadowed by the difference between chilling for
either duration and no chilling.

Longer chilling affected eye growth, however, in plants
harvested in December. Length of the first eye to break was
18 mm with or without 2 months of chilling, but increased to
29 mm with 4 months of chilling. This growth occurred
without budbreak and was termed "eye etiolation". The same
eyes elongated rapidly after budbreak, up to 30 mm per day
for some individuals. Initial growth rates increased with
chilling duration in all cases (Figure 2.3). Although
unchilled plants never grew quickly despite rapid budbreak,
by late November they achieved a moderate growth rate and

eventually moderate height. Chilled plants regrew well for

53

all harvest dates (Figure 2.4a). Regrowth ratings followed
essentially the same pattern as height, with longer chilling
consistently leading to higher quality plants (Figure 2.4b).

Flowering exceeded 80% in all 4 month treatments
(Figure 2.5), while chilling for 2 months gave variable
results. Among the unchilled plants, only those harvested
on November 18 or later flowered to any extent, but late-
harvest crowns flowered quite well. Time to flower from
potting for chilled Dicentra decreased from nearly 50 days
to 20 days or less over the harvest season (Figure 2.6).
Time to bloom for unchilled plants also decreased with later

harvests.

QIQQESSIQ!

For Dicentra as for other nursery stock, chilling in
storage did not completely replace hardening in the field
(6,15,16). Harvest date still had an effect on chilled
plants. There were significant interactions at the 0.05
level between date of harvest and length of chilling for all
parameters tested. Although decreasing daylength has been
shown to promote dormancy in Dicentra (18), the importance
of diurnal temperature cycles in the hardening process is
unknown.

In earlier studies (Chapter 1), overall plant quality
increased as harvest was delayed. However, distinct events
were obvious in the regrowth process. Budbreak was the

first step, and in chilled plants, was followed by stem

54
elongation. Additional chilling in storage increased the
rate of vegetative growth in the greenhouse. Early-harvest,
non-chilled crowns eventually broke bud but did not grow in
height. Such stunted individuals might even flower by
pushing out a single floret from the open eye, but chilling
improved both the ability and the time to flower.

As expected, since flowering could not occur until the
eye opened, there was a strong overall correlation (r=0.88,
a=0.0001) between days to budbreak and days to flower.
Overall plant quality was closely related to plant height at
5 weeks post-break (r2=0.86, a=0.0001), confirming earlier
work (Chapter 1).

Based on these results, regrowth of Digggtgg
gpggtabilig after storage can be divided into four separate,
albeit related responses: eye etiolation, budbreak, stem

elongation, and flowering.

Table 2.1. Effect of harvest date and storage duration on
number of Dicentra spectabilis crowns that broke bud within
180 days of ggowing conditions (19C day/12C night, 16 hrs
8.5 mol/day-m supplemental light). Ten crowns per

 

 

treatment.
LENGTH OF STORAGE AT 0C

HARVEST DATE ------------------------------------------

1986 0 MONTHS 2 MONTHS 4 MONTHS
October 7 10 10 8
October 14 8 10 8
October 21 9 10 10
October 28 8 9 10
November 4 9 9 10
November 11 10 9 9
November 18 10 10 10
November 25 10 10 8

December 2 10 10 10

 

56

 

24-

224 1986

SOIL TEMPERATURE (OC)

, . r . . . 1 . .
9/9 9/23 10/7 10/21 11/4 11/18 12/2

 

 

 

Figure 2.1. Minimum daily soil temperature at 10 cm
depth at Trevor Nichols Experimental Farm, Fennville,
MI, during the fall of 1986, and average soil
temperature at 10cm depth at 10 am in Dicentra

(spectabilig field, Eeeland, MI. Zeeland standard error
of means=0.7.

57

 

100
e—OTBKISWORAGE

90~ ,, s—e 2 MONTHS STORAGE
b—t 4IMNWDESSWORAGE
801

70-

U

60-
504
40-

9

DAYS TO BUDBREAK

20-

10-1 : “§l>*~‘

   

 

«n-un

-
-
n A -1‘
fi

 

r

1O/21 ' 11% 11718 1272
DATE OF HARVEST 1986

10/7

Figure 2.2. Effect of harvest date and length of
storage at 0C on mean days from potting to budbreak of
Dicentra spectabilig crowns. Means calculated for
crowns with at least one broken bud: standard error of
the interaction means=7.6.

 

58

 

110- e—o NO STORAGE
a—e ZIMNWRRSSWORAGE
100- H 4 MONTHS STORAGE

90-
80-
70--I

50-

 

     

  

STEM ELONGATION (MM/WEEK)
8

 

 

 

 

fir

     

10/7 1O/21 11'/4 11718 ' 1222

DATE OF HARVEST 1986

Figure 2.3. Effect of harvest date and length of
storage at 0C on mean rate of stem elongation during
first week of post-break growth of Dicentra spectabilig
crowns. Means calculated for crowns with at least one
broken bud: standard error of the interaction
means=11.9.

59

Figure 2.4. Effect of harvest date and length of
storage at 0C on regrowth at 5 weeks post-break of
Dicentra gpggtgbilig crowns. Means calculated for

crowns with at least one broken bud.

A. Mean plant height: standard error of the
interaction means=2.8.

8. Mean regrowth quality. Rating scale of 0 to 5
where 0=dead, 0.5=dormant buds, 1=emergent growth,
‘..5=vigorous growth): standard error of the
interaction means=0.4.

 

>

PLANT HEIGHT (CM)

REGROWTH QUALITY

60

 

e—e NO STORAGE
40- a—s 2 MONTHS STORAGE
35 H 4 MONTHS STORAGE

'5 _. - - "' a
25 -

20-
15-

10-1

'I

p

04 9? :A: r t T
10/7 1O/21 11/4 11/13 12/2

DATE OF HARVEST 1985

 

1 |

 

 

 

 

e—e NO STORAGE
H 2 MONTHS STORAGE
5~ H 4 MONTHS STORAGE _ A
A ‘ ‘ - 2 T _
4-I ,_ " = .1 r. 3
- 5 r.
m r.
3-
2" 'l
1- ‘_
c c - c 3 a
O . . . 1 A 1 . r - A
10/7 10/21 11/4 11/18 12/2

DATE OF HARVEST 1986

 

61

Figure 2.5. Effect of harvest date and length of
storage at 0C on flowering of Dicentra spectabilig

crowns .

A. Percent non-dormant crowns producing at least
one expanded flower.

8. Mean days from potting to flowering. Means
calculated for crowns with at least one expanded

flower. Only treatments with.z50% flowering
shown.

 

% CROWNS FLOWERING :9

DAYS TO FLOWER

 

100-
90-
80-
7D-
60-
50-
40-
30-
20-I
ID-

 

v

  
  
  

: a '

e—e NO STORAGE
H 2 MONTHS STORAGE
H 4 MONTHS STORAGE

 

 

10/7

 

 

1

1O/21 11/4 11/18 12/2

DATE OF HARVEST 1986

 

80-
70-
60-1

507

30-
20-
10-

 

0—0 NO STORAGE
H 2 MONTHS STORAGE
H 4 MONTHS STORAGE

 

10/7

T ‘—

10/21 111/4 11718 ‘ 12}2
DATE OF' HARVEST 1986

 

LIST OF REFERENCES

Eryne, T.C. and A.H. Halevy. 1986. Forcing herbaceous
peonies. J. Amer. Soc. Hort. Sci. 111:379-383.

Guttridge, 0.8. 1958. The effects of winter chilling on
the subsequent growth and development of the cultivated
strawberry plant. J. Hort. Sci. 33:119-127.

Heiden, R. and A.C. Cameron. 1986. Bare-root perennials
require cautious handling. Amer. Nurseryman 163(7):75-
88.

Fuchigami, L.H. and C-C. Nee. 1987. Degree growth stage
model and rest-breaking mechanisms in temperate woody
perennials. HortScience 22:836-845.

kobayashi, x.n., L.H. Fuchigami, and M.J. English.
1982. Modeling temperature requirements for rest
development in Corpus gggigga. J. Amer. Soc. Hort. Sci.
107:914-918.

Hronenburg, E.C. and L.M. Wassenaar. 1972. Dormancy and
chilling requirement of strawberry varieties for early
forcing. Euphytica 21:454-459.

Lopes, L.C. and T.C. Weiler. 1977. Light and
temperature effects on the growth and flowering of
Dicentra spectabilis (L.) Lem. J. Amer. Soc. Hort. Soc.
102:388-390.

Maqbool, M. 1986. Postharvest handling and storage of
bare-root herbaceous perennials, MS thesis. Michigan
State University, East Lansing.

Milliken, G.A. and M.D. Remmenga. 1989. Statistical
analyses and the personal computer. HortScience 24:45-
52.

10. MSU Agricultural Weather Service. 1986. Weather data

listing for Trevor Nichols Experimental Farm,
Fennville, MI. Dept. of Entomology, Michigan State
University, East Lansing, MI.

11. Nelson, L.A. 1989. A statistical editor's viewpoint of

statistical usage in horticultural science
publications. HortScience 24:53-57.

63

12.

13.

14.

15.

16.

17.

18.

64

Richardson, E.A., S.D. Seeley, and D.R. Walker. 1974. A
model for estimating the completion of rest for \Red
Haven' and \Elberta' peach trees. HortScience 9:331-
332.

Richardson, E.A., S.D. Seeley, D.R. Walker, J.L.
Anderson, and S.L. Ashcroft. 1975. Pheno-climatography
of spring peach bud development. HortScience 10:236-
237.

Ritchie, G.A. 1984. Effect of freezer storage on bud
dormancy release in Douglas-fir seedlings. Can J. For.
ROS. 14:186-190.

Ritchie, G.A., J.R. Roden, and N. kleyn. 1985.
Physiological quality of lodgepole pine and interior
spruce seedlings: effects of lift date and duration of
freezer storage. Can. J. For. Res. 15:636-645.

Steponkus, P.L. and F.O. Lanphear. 1966. Factors
influencing artificial cold acclimation and artificial
freezing of Hedgra helix ‘Thorndale'. Proc. Amer. Soc.
Hort. Sci. 91:735-741. ‘

Stone, E.C., J.L. Jenkinson, and S.L. Rrugman. 1962.
Root-regenerating potential of Douglas-fir seedlings
lifted at different times of the year. Forest Science
8:288-297.

Weiler, T.C. and L.C. Lopes. 1976. Photoregulated

Dicentra spectgbilis (L.)Lem. as a potential potted
plant. Acta Hort. 64:191-195.

CHAPTER 3

REVIEW OF BUD DORHANCY LITERATURE

In the past 50 years, there have been many extensive
reviews of bud dormancy in the scientific literature
(10,14,15,24,43,46,52,53,57,61,63). Despite research and
discussion, dormancy remains an elusive phenomenon. Several
current reviews have focussed on the search for a "universal
terminology" that will resolve the semantic confusion in
describing types of dormancy (30,31). The definition of
dormancy itself is controversial (see Lang et al. (31) for
an excellent comparison of published definitions). Lack of
growth at the whole organ level, i.e. a bud, is quite
different from the microscopic level, i.e. meristematic
tissue. Due to this dependence on morphology, a definition
of dormancy is often specific to one system.

The American Society for Horticultural Science at its
1988 annual meeting proposed this general definition:
dormancy is "the suspension of (visible) growth of any plant
structure(s) containing a meristem(s) in response to
external or internal control" (3). Under the broad heading
of dormancy, three physiological states are recognized.

Ecodormant/quiescent structures resume growth in a favorable

65

66
environment. Paradormant/correlatively inhibited structures
will not grow in a favorable environment due to the
influence of other plant parts such as bud scales, an apical
bud, leaves, or the seed coat. Endodormant/resting
structures have an internal block which prevents growth,
despite favorable conditions. The block is often overcome
'by chilling.

These terms refer to the status of the plant without
reference to underlying mechanism. The lack of a
physiological understanding of the basic processes of
dormancy induction and release has contributed to the
confusion in terminology. General hormonal models involving
one to several plant growth regulators have been proposed
but have done little to clarify real mechanisms of response
based on experimental evidence (14,44,61). New work using
single-gene AHA-deficient Arabiggpgig mutants holds great
promise for revealing mechanisms of genetic and hormonal
regulation of dormancy in seeds (25).

Dormancy in perennating buds, however, may involve
factors other than, or in addition to, those controlling
growth of seeds. Like a seed, a bud contains a meristem
within a durable outer covering (bud scales), but there are
often several competing meristems in one structure. Unlike
a seed, a bud is physically connected to stem and root with
potential interaction between organs. Also, a dormant bud
is usually well-hydrated in comparison to a seed.

Much of the research on bud dormancy has been based on

67
woody plant systems in which short days and subsequent cool
temperatures promote dormancy and cold acclimation (20,43,
53,63). Endodormancy is broken by further chilling before
environmental conditions actually allow growth. The optimum
chilling temperature is usually given as 5 to 7C with
temperatures at or below 0C considered ineffective
(14,19,43,44). A number of fairly accurate empirical models
predict the end of endodormancy based on "chilling units"
accumulated during exposure to that temperature range
(4,47,54). Foresters working with conifer seedlings,
however, include temperatures 50C when assessing chilling
history and optimum lift date (49,50,51).

Since the buds of woody plants are aerial, generally
only air temperature is considered the driving factor. An
unusual model by Mullin and Parker (41) uses soil
temperature in the root zone at 15 cm depth to calculate
"degree hardening days" for best nursery storage of
seedlings. Root growth potential is strongly correlated
with shoot survival and extension (50), but a direct causal
link is hard to demonstrate (11,22) despite evidence that
hormone synthesis/conversion in roots may promote budbreak
and growth in Douglas-fir (34) and perhaps apple (65). The
role of roots in bud dormancy remains largely unexplored.

A basic problem in the study of dormancy is knowing the
physiological state of the plant at a given time (16). The
same plant may respond differently to chilling at different

seasons, but this inherent dynamic quality is often

68
overlooked in applying treatments. A recent approach to bud
dormancy of woody plants based on physiological status is
the degree growth stage (°gs) model of Fuchigami et al.
(20). Like some earlier phenological descriptions (42), the
°gs model orders growth cycle events, but with precise
definitions and without reference to calendar time. Point
events in the cycle can be determined by tests. For
example, vegetative maturity is reached when leaf removal no
longer stimulates regrowth. A plant moves continuously
through the cycle from maximum growth to maximum rest to
maximum growth.

The model contains some interesting points: 1) The
growth cycle is continuous, implying that growth and
dormancy are quantitative states. 2) Processes such as
development of dormancy and cold acclimation can be
separated physiologically (27,43). 3) Although the model
itself seems applicable to all temperate woody plants, its
relation to real time varies with year, location, species,
and plant age, deriving specific models from the general one
(26,42). In many ways, the °gs model resembles the cellular
life cycle model presented in biology textbooks and
provides a valuable context in which to study dormancy
phenomena.

An entirely different reductionist approach to growth
has been used with bulbs and corms, highly specialized
herbaceous perennials of the Liliaceae and Iridaceae.

Growth and flowering of these small, self-contained units

69
can be precisely controlled by applied temperature
treatments. Bulbs are environmentally programmed or
"forced" to flower at a specific time (12,17,23). Usually a
stepped series of temperatures are applied, with different
levels promoting different processes such as flower
formation or stem elongation. The treatments have been
established through years of trial and error and are
designed for specific cultivars grown under specific
conditions. The goal is flower production, however, so less
attention has been paid to release from vegetative dormancy
than to phenology of floral development (45).

Rapid flowering of tulip, hyacinth, and narcissus
depends on completion of organogenesis at warm temperatures
(20C), promotion of stem elongation by coOl temperatures
(8C), and modification of growth rate by greenhouse
conditions (12,13,23). The effect of cold on days to
budbreak has been largely ignored in the literature.
However, in tulip, rate of stem elongation is greater after
storage at 5C than at 21C and after 12 weeks of 5C than
after 2-10 weeks (39,40). Some additional effect was seen
with -1C in short-term storage.

Unlike tulip and most bulbs and corms, lily requires
vernalization (32). Chilling at 0.5 to 9C induces floral
initiation to occur after storage (12,17,23). For lily, as
for woody plants, chilling hours can be calculated to
predict regrowth responses. Cold treatment also promotes

vegetative growth. Long periods of chilling shorten time to

7O
budbreak for lily but reduce flowering (55,60). However, as
in tulip, some vegetative growth can occur without chilling:
stems simply do not elongate (33). The work of Wang and
Roberts (60) suggests that the primary daughter axis in lily
is paradormant in early spring and summer due to inhibitors
in daughter scales, then becomes ecodormant under cool
temperatures and short days as the mother axis senesces.

Not all bulbs need a cold treatment. Bulbous iris and
ggphyrgnthgg are two examples of strictly ecodormant bulbs,
growing whenever temperature and moisture permit (23,24).

In contrast, bulbs which evolved under a mediterrannean
climate, such as tulip, require cold to stimulate stem
elongation, while lily, a temperate native, requires cold to
induce flowering as well (24,45). The relative effects of
chilling on time to budbreak vs. rate of stem elongation
need to be studied separately.

Forcing schedules for bulbs incorporate many of the
same concepts used in dormancy models for woody plants.
Perhaps the distinction between bud and bulb is not as great
as has been thought, despite obvious physical differences
(32,46). Bulbs and corms in nature respond to the soil
environment: like seeds they can be independent of a root
system during dormancy: and the meristem is deeply embedded
in dense, protective tissue. Non-bulbous herbaceous
perennials combine characteristics of both woody perennials
and bulbs. They carry perennating buds at or below the soil

surface, but not within a bulb or corm. They maintain a

71
full root system during dormancy--in fact, a dormant
herbaceous perennial is often little more than roots and
buds, with highly reduced stems. The physical arrangement
of these organs varies greatly among temperate zone plants
with the herbaceous perennial habit (29).

As small, easily handled plants with exposed buds and
distinct growth cycles, it is surprising that few herbaceous
perennials have been the subject of dormancy studies. The
exception is strawberry, an important semi-evergreen small
fruit. Short days in the fall promote dormancy in
strawberry (8), as in trees, with maximum rest assumed to
develop in mid-November (5). Survival and regrowth after
storage depend greatly upon harvest date and chilling
history (1,5,8,18,58,64 ). Without sufficient chilling, leaf
initiation proceeds slowly (2) and plants are stunted (21).
After storage at -1 to 7C, vegetative regrowth is vigorous
(5,21,28,59). Longer chilling stimulates runner production
(5) but reduces flowering (8,58).

Chilling requirements for vegetative regrowth after
harvest of dormant crowns have been demonstrated for a
number of herbaceous perennials. Rhubarb, a plant with
underground buds, shows release of dormancy in late November
to early December in the northern temperate zone (7,38,56).
Before that time, harvested crowns will not grow under
forcing conditions. By mid-November, forced growth is quite
vigorous. According to Loughton (38) and Tompkins (56),

chilling units accumulate below 10C as in woody systems, and

72

soil temperatures at 10 cm depth can be used to predict the
end of rest and best lift date for forcing (Loug, Tomp) as
in woody plant systems.

Astilbe requires 9-12 weeks at 5C for vigorous growth
(6), peony 9 weeks at 6C (9), American ginseng 50-100 days
at 5C (35), and Dicentra 939211511; 120 days at 0C (48).
These conditions in general have not been optimized for
harvest date and storage temperature, but requirements tend
to decrease with later harvest (9,35). Near 0C or long-term
chilling results in taller plants in many cases (6,9,48).

pigggtra gpggtabilig also requires chilling to overcome
dormancy developed in the field (Chapters 1 and 2) or
induced by short days under greenhouse conditions (36,37).
Fully dormant crowns of greenhouse provenance regrew well
after 8-12 weeks at 5C (37: Hanchek, unpub. data). Field-
harvested crowns required less chilling but were highly
variable in response (62). The following study attempts to

explore dormancy of Dicentra gpectabilis in greater detail.

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78

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Hort. Sci. 110:769-774.

CHAPTER 4

EFFECT OF TEMPERATURE AND DURATION OF TEMPERATURE EXPOSURE
ON REGROUTH OF QLQENIBA SEIQILEILIQ AFTER STORAGE

Earlier studies (Chapters 1,2) made it clear that
Qicentre epeeEeeilie changed physiologically as the harvest
season proceeded, and the evidence pointed to temperature,
both in the field and in storage, as a major factor
controlling subsequent growth. Four separate responses can
be distinguished in the regrowth of 212222;; after storage:
eye etiolation, budbreak, stem elongation, and flowering.
This study was begun to explore the relationship between
these growth responses and storage temperature, and to

examine the chilling requirement in detail.

EAIEEIALQ AND HEIHQQQ

gel; teeperatuge ee;1ee:;2e_. One-year-old Diceetge
epeeeeeilie (L.) Lam. crowns were harvested from commercial
fields in western Michigan (Walters Gardens, Zeeland) on
October 7 and November 18 of 1986. Loose soil was removed
by shaking and any green material was trimmed, leaving the
eyes intact. At each harvest, ten soil temperatures at 10

cm depth in the field were measured. Records of soil

79

80
temperatures were also obtained from the Trevor Nichols
Experimental Farm, Fennville, MI (25). The crowns were
packed in a moistened 1:1 peat:perlite mixture in poly-
ethylene-lined crates to avoid desiccation stress (6) and
simulate 13 gig; chilling, and stored at -2.5, 0, 2.5, 5,
10, 15, or 20C for 0, 2, 4, 6, 8, or 10 weeks. Each
treatment was applied to twenty plants. After treatment,
the crowns were potted with eyes exposed and held in a cool
greenhouse (19C day/12C night) under 16 hours of 8.5
mol/day-m2 supplemental light. At one week after break,
they were moved to benches under natural lighting.

Those crowns which were removed after 0, 4, and 10
weeks were first closely examined and the length of every
visible eye was measured. All plants were inspected daily
after potting for budbreak, defined in this study as the
opening of bud scales and appearance of floral parts or
expanding leaf margins from within the eye. Days to first
budbreak was recorded for each crown. If eyes had not
broken after 180 days in the greenhouse, the crowns were
discarded. At time of break, eye length was measured. It
was remeasured at 7 days post-break to determine the
elongation rate of that individual eye during the first week
post-break.

At 5 weeks post-break, the regrowth quality of the
entire plant was rated on a 0 to 5 scale (0=dead,
0.5=dormant buds, 1=emergent growth, ... 5=vigorous growth)

after Maqbool (23). Whole plant height to the highest leaf

81
was measured at the same time. The date at which each crown
first produced an expanded flower was also noted. An
expanded flower was defined as a well-colored floret with
sepals detached (34). If flowers were not produced,
presence or absence of aborted flower buds was noted.

Ineegeeeieee geepegeeQre eeries-lg z. Crowns were
harvested from southwestern Michigan fields (DeGroot
Nurseries, Coloma) on October 9, 1987. At harvest, ten
field soil temperatures at 10 cm depth were measured.
Records of soil temperatures were also obtained from the
Trevor Nichols Experimental Farm, Fennville, MI (25). The
plants were processed and packed as in 1986, and stored at
5, 7.5, or 10C for 0, 4, 8, or 12 weeks with twenty plants
per treatment.

They were then potted and regrown under 18 hours of 8.3
mol/day-m2 supplemental light, and the same parameters were
measured as in the 1986 temperature series experiments. The
plants were held under lights until flowering peaked with a
maximum number of fully developed, apically reflexed flowers
(34). The inflorescences were then removed. Since the

flowers of D. epectabilis are essentially 2-dimensional,
2

 

floral production was measured in mm by a Delta-T area
measurement system, just as leaf area is measured. All
floral parts contributed to the surface area measurement,
including flowers, axes, and aborted flower buds, but no
subtending leaves.

Treatment means were calculated on the basis of plants

82
which survived to that point of development. Data were
analyzed as a completely randomized design (24,28). Standard
errors of the interaction means were calculated based on the

smallest n (replicates per treatment cell) in that analysis.

EISELIS

£211 eegeieiege. Minimum soil temperatures at 10 cm
depth had not dropped below 10C before the October 7 harvest
in 1986 (Figure 4.1a). By the late harvest on November 18,
temperatures below 10C had been common during the previous
six weeks. In the week preceding harvest in October of
1987, soil temperatures often fell below 10C (Figure 4.1b).

2311 LEEDSIEEEIQ £231£§:12§£- When October crowns were
held at -2.5C, many had frozen, blackened, or rotted eyes
after even 2 weeks. Much less damage was observed on
November plants. Death of apparent growing points at -2.5C
may have been responsible for the high number of crowns
which failed to break bud following that temperature
treatment (Table 4.1). Cold hardiness, however, was
apparently an all-or-nothing situation since plants which
survived -2.5C grew quite vigorously after potting. Due to
overall lower survival and visibly damaged eyes, the -2.5C
treatment was analyzed separately from other data (Table
4.2).

The change in eye length due to chilling was striking,
especially for the early harvest. After 10 weeks in storage

at 10 and 15C, October crowns had eyes whose average length

83
was more than double the length at harvest (Figure 4.2).
eieegege harvested in late November showed less etiolation
at 10 or 15C but had more eyes that opened in storage
by separation of bud scales without the appearance of
expanding leaf margins (Figure 4.3). The distinction
between eye etiolation and stem elongation is important:
the former occurred in dark storage without or without
opening of eyes: the latter took place in the greenhouse
after budbreak and consisted of elongation of the bud axis
from within and protruding out of the eye.

The time from potting to budbreak declined from 77 days
for control plants harvested in early October to 29 days for
November controls (Table 4.3). Time to budbreak decreased
as temperature decreased from 20 to ac (Figure 4.4). 0 and
2.5C were the most effective treatments at 2 and 4 weeks,
but after 8 weeks, all temperatures of 5C and lower caused
eyes on October crowns to break in 10 to 20 days. Crowns
harvested in mid-November broke in 5 to 15 days from potting
after 2 weeks at 15C or lower. Further chilling did not
consistently hasten budbreak, and constant exposure to 20C
delayed it.

Although days to budbreak from peeeieg decreased with
chilling, it is important to distinguish between the effects
of simple aging and true chilling effect. Plotting days to
budbreak from harvest against temperature shows that
exposure to 0C-5C actually did induce earlier budbreak,

especially for the October harvest (Figure 4.5). At 10C or

84
higher, time to budbreak was not reduced even after 10 weeks
of storage. After exposure to low temperatures for about 4
weeks, dormancy release was practically complete, and
further chilling had diminishing promotive effects. This
was even more obvious for the November harvest which
received field chilling.

Highly etiolated eyes on October crowns from 10 and 15C
treatments generally did not break upon transfer to the
greenhouse. The eyes shrivelled and died, while smaller
eyes broke first (Figure 4.2). Moderately etiolated eyes on
November crowns did break but often died later. For both
harvest dates, average eye length upon breaking was greater
after 6 weeks of higher temperatures.

After 1 week in growing conditions, however, crowns
exposed to 5C or less in storage showed rapid rates of stem
elongation, as much as 10 mm per day for some individuals
(Figure 4.6). Growth rate was not substantially affected
until 4 weeks of chilling, although budbreak was promoted
after 2 weeks (Table 4.2). Once again, there was a clear
distinction between the growth responses of budbreak and
stem elongation. For both the October and November-
harvested crowns, 8 weeks of exposure to constant
temperatures depressed the subsequent initial growth rate.
At 10C to 20C, growth in the first week was negligible. In
the case of the mid-November harvest, after 15C or 20C the
rate was even less than for the unstored control.

At 5 weeks post-break, plant height still reflected the

85
initial rate of stem elongation (Figure 4.7). Plants held
at non-chilling temperatures, or for insufficient time at
chilling temperatures, never made up the difference. Either
they continued to grow slowly or they experienced arrested
growth soon after break. Some eyes, particularily etiolated
ones, died in the second or third week post-break.

Regrowth quality of Diceetga crowns closely matched
height measurements, except that shorter, bushier
individuals received high ratings (data not shown). Plants
harvested in mid-November were of better quality overall
than October plants. In general, 5C or lower was required
to produce a vigorous, attractive plant.

In 1986, the only flowering data taken were percent
crowns flowering per treatment and days from potting to
first flower. Many crowns did not successfully expand a
single floret (Figure 4.8), although many produced aborted
flower buds. From the October harvest, 41% of all surviving
crowns flowered, while 25% more showed evidence of aborted
flowering. From the November group, 55% of survivors
flowered while an additional 22% had aborted buds.

Chilling at 0C to SC for 6 or more weeks produced more
flowering plants from the October harvest than other
treatments, while 10C and below encouraged flowering in the
November harvest (Figure 4.8). But even after storage at
10C or warmer, a few October crowns managed to push expanded
flowers from the eyes, often without any accompanying

foliage. In plants that received insufficient chilling, the

86
flowering axis simply did not elongate. The effect of
temperature on days to flower is hard to assess
statistically since so many plants failed to bloom, but it
appears that longer periods at chilling temperatures
hastened flowering for plants from both harvest dates
(Figure 4.9).

IEEQEEQQLESQ teepe;e§e;e eeries—l9e . Eye etiolation
in storage was again measured in 1987, and was definitely
promoted by 10C in darkness (Figure 4.10). Highly etiolated
eyes from 10C storage were less likely to break than
moderately etiolated ones.

As in 1986, eyes broke quickly after chilling at 5C
(Figure 4.11), and growth due to stem elongation was
correspondingly rapid (Figure 4.12). After 10C, budbreak
was much slower and growth rate during the first week did
not change from the control. The "intermediate" temperature
of 7.5C promoted budbreak and growth to about the same
extent as 10C.

The same relationship between the three temperatures
held true in regard to plant height and regrowth quality at
5 weeks post-break (Figure 4.13). Height and overall
quality were best expressed after 8 weeks of exposure to SC.
The warmer temperatures of 7.5C and 10C were both
ineffective in stimulating regrowth.

After 5 weeks of regrowth, most crowns held for 8 weeks
at any of the temperatures showed some evidence of floral

development (Figure 4.14a). However, only plants held at 5C

87

produced expanded flowers with any success, even after 90
days in the greenhouse (Figure 4.14b). Days to flower from
potting appeared to decrease with longer exposure to SC
(Figure 4.15), but the limited number of plants flowering
prevented statistical comparison of means. Most crowns
exposed to 5C for 8 weeks flowered in 40 days.

A single normal 212225;; floret has an average area of
about 40 mmz. Only 9% of all the unchilled crowns in this
experiment flowered, and the average inflorescence area per

plant was about 50 mm2

, hardly more than one blossom. After
chilling at 5C, crowns produced large racemes of 140-200 mm2

average area (Figure 4.16).

Dlflsflfifilgl

Four separate growth responses were observed in 2;
epeeEabilis during the course of this study, each with a
different time/temperature requirement. Eye etiolation,
unaccompanied by meristematic growth of the primary bud
within the eye, was promoted by warm temperatures (10 to
20C). Budbreak, stem elongation, and flowering were promoted
by cold temperatures (-2.5 to 5C). The "intermediate"
temperature of 7.5C did not act as a promoting temperature
for any of these responses.

After chilling at 0 to 2.5C, early-harvest Dicentga
required only 2 weeks of exposure to break bud quickly, but
4 weeks were required to induce stem elongation, and 8 weeks

to hasten flowering. As the harvest season progressed and

88
soil temperatures dropped in the field, chilling in storage
had much less effect. However, storage at warm temperatures
late in the season seriously reduced regrowth.

Optimum temperatures for dormancy release in Dicentra
were lower than the 4 to 7C range cited for woody plants
(10,13,29,30), but were similar to those given for greatest
stem elongation in tulip (9,26,27), lily (8,11,15), and
strawberry (3,14,17,35). Increased elongation with longer
periods of chilling was also reported for tulip (26) and
Qieeeege eucullaria (33).

Stunted growth of incompletely chilled plants has been
reported for peach seedlings (12), strawberry (14), lily
(19). Mamas (22). admmc a a
(33), indicating quanitatively different requirements for
budbreak and elongation of the meristematic axis. One
physiological explanation for a differential response was
put forward by zigas and Coombe (36) who suggested that cold
promotes germination of peach seedlings by reducing ABA
levels, and elongation by increasing GA levels. This
hormonal model for the breaking of dormancy could possibly
be extended to buds. Exogenous GA has been shown to
partially substitute for the cold requirement for elongation
in many plants (7) including DISEASES speetabilie (21).

Flowering is a complex response incorporating several
steps: initiation of floral buds, differentiation of the
flowering axis, and maturation and expansion of florets

(18). Since storage temperature affects bud axis

89
elongation, it was not surprising that days to flower
decreased with chilling of crowns while incidence of
flowering increased. However, production of visible flower
buds was much less affected by temperature. Expanded
flowers were occasionally produced even by stunted crowns
from 20C treatments (Figure 4.7).

A causal relationship between temperature and flowering
in pieegege remains to be seen. Many spring-flowering
perennials such as tulip, iris, and strawberry do not
require vernalization (1,15,17) although chilling may
enhance organogenesis (2,4,8,26,27,31,32). Buds on Dicentra
crowns may have aborted due to storage conditions (16) or,
as Lopes and Weiler (22) observed, to low light in growing
conditions. There was complete loss of flower buds with 6.9
mol/day-m2 total light. In these present studies, expansion
of florets and number per panicle was always greater on
212225;; flowered under supplemental light, indicating the
importance of total light in the growing environment on
floral production.

Response of 212222;; epeetebilie to storage temperature
seems consistent with dormancy patterns observed in woody
plants and bulbs, with optimum chilling for dormancy release
at 0 to 2.5C. Growth responses are distinct and easily
observed. In addition, 2; epeeeeeilie can be readily
propagated by tissue culture (20) or stem cuttings and is
easily handled in the field, the storage room, and the

greenhouse, allowing statistically valid numbers of

90
replicates. Dicegtga seems an excellent system for the
further study of bud dormancy and the effects of storage

environment on vegetative regrowth.

91

Table 4.1. Effect of storage duration and temperature on
number of Dicentra spectabilie crowns that broke bud within
180 days of ggowing conditions (19C day/12C night, 16 hrs
8.5 mol/day-m supplemental light). Twenty crowns per
treatment.

 

OCTOBER 7, 1986 HARVEST

 

 

STORAGE STORAGE DURATION IN WEEKS
TEMPERATURE 2 4 6 8 10
-2.5 C 11 7 12 18 13
0 ‘ 19 15 17 20 13
2.5 20 15 2O 2O 16
5 17 19 2O 20 20
10 20 19 18 2O 19
15 18 20 19 2O 19
2O 19 18 15 19 17

CONTROL: 20

 

 

NOVEMBER 18, 1986 HARVEST

 

 

STORAGE STORAGE DURATION IN WEEKS
TEMPERATURE 2 4 6 8 10
-2.5 C 20 15 18 18 18
0 20 20 20 2O 19
2.5 20 2O 20 20 19
5 20 19 19 2O 18
10 20 18 19 20 2O
15 20 20 2O 20 20
2O 20 2O 19 16 19

CONTROL: 18

 

 

 

 

 

 

 

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93

Table 4.3. Effect of storage duration and temperature on
mean days from potting to budbreak of Dicentra spectabilis
crowns. Means calculated for crowns with at least one

broken eye: SEM = standard error of the interaction means.

 

OCTOBER 7, 1986 HARVEST

 

 

STORAGE STORAGE DURATION IN wzsxs
TEMPERATURE 2 4 6 s 10
o c 43 27 19 10 24
2.5 47 29 15 16 23
s 63 36 27 12 9
10 73 82 46 47 so
15 as as 72 58 75
20 74 83 66 63 7S
CONTROL: 77 days ssxn=13=9.4

 

 

NOVEMBER 18, 1986 HARVEST

 

 

STORAGE STORAGE DURATION IN WEEKS

TEMPERATURE 2 4 6 8 10
O 9 8 7 6 6

2.5 10 10 10 5 8

5 11 1O 9 6 4

10 16 12 5 6 4

15 15 16 12 9 6

2O 18 37 26 34 41

CONTROL: 29 days SEMn=16=3.5

 

94

Table 4.4. Effect of storage duration and temperature on
mean rate of stem elongation in mm/week during the first
week of post-break growth of Dicentre spectabilis crowns.
Means calculated for crowns with at least one broken eye:
SEM = standard error of the interaction means.

 

OCTOBER 7, 1986 HARVEST

 

 

STORAGE STORAGE DURATION IN WEEKS
TEMPERATURE 2 4 6 8 10
0 C 0.6 37.1 34.7 28.8 49.6
2.5 1.0 26.9 35.7 25.3 43.9
5 1.2 8.8 28.8 24.2 20.2
10 0.9 1.3 1.1 1.1 2.3
15 0.9 1.4 1.1 0.9 2.7
20 1.3 0.3 1.7 0.8 0.8
CONTROL: 0.6 mm/week SEMn=13=3.8

 

 

NOVEMBER 18, 1986 HARVEST

 

 

STORAGE STORAGE DURATION IN WEEKS
TEMPERATURE 2 4 6 8 10

0 20.3 23.8 33.6 18.9 42.7
2.5 21.7 33.6 37.1 15.4 44.8

5 18.2 28.0 35.7 19.6 46.2
10 15.4 17.5 18.2 16.1 37.1
15 7.7 9.8 7.0 4.2 19.6
20 2.8 4.2 5.6 1.4 1.4

CONTROL: 18.2 mm/week

ssun=16=4.7

 

95

Table 4.5. Effect of storage duration and temperature on

number of Dicentra spectabilis crowns harvested on 10/9/87
that broke bud within 120 days of giowing conditions (19C

day/12C night, 16 hrs 8.3 mol/day-m supplemental light).

Twenty crowns per treatment.

 

 

STORAGE STORAGE DURATION IN WEEKS
TEMPERATURE 0 4 8 12
5 C 16 19 20 20
7.5 19 20 18 20

10 14 17 20 18

 

Figure 4.1 Minimum daily soil temperatures at 10 cm
depth at Trevor Nichols Experimental Farm, Fennville,
MI, and average soil temperature at 10 cm depth at
10:00 am in QIQSREIE 52222321115 fields.

A. 1986: Zeeland, MI. Eeeland standard error of
means=0.7.

B. 1987: Coloma, MI. Coloma standard error=0.1.

SOIL TEMPERATURE (0C)

SOIL TEMPERATURE (OC)

 

24+

A 1986

m ZEELAND

 

 

 

— FENNVILLE

. . A , . .
10/21 11/4 11/18 12/2

 

 

m COLOMA
— FENNVILLE

B 1987

 

. t r , . .
10/23 11/6 11/20

 

Figure 4.2. Effect of storage for 4 or 10 weeks at 0,
2.5, 5, 10, 15 or 20C on mean length of Diceetge

spectabilis eyes.

A. Mean eye length at potting for crowns
harvested on October 7, 1986: standard error of
the interaction means (n=62) = 2.5 mm.

B. Mean length at budbreak of first eye to break
on crowns harvested on October 7, 1986: standard
error of the interaction means (n=13) = 4.7 mm.

C. Mean eye length at potting for crowns
harvested on November 18, 1986: standard error of
the interaction means (n=63) = 2.5 mm.

D. Mean length at budbreak of first eye to break
on crowns harvested on November 18, 1986: standard
error of the interaction means (n=18) = 3.5 mm.

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100

Figure 4.3. Effect of storage for 4 or 10 weeks at 0,
2.5, 5, 10, 15 or 20C on percent of Dicentga

spectebilis eyes open in storage.

A. Crowns harvested October 7, 1986.

B. Crowns harvested November 18, 1986.

7. EYES OPENED IN STORAGE

% EYES OPENED IN STORAGE

101

 

100-
90-
80-
7D-
60-
50-
40-
30-
20-
10-

al.

 

o—o 4 WEEKS STORAGE
H 10 WEEKS STORAGE

A 10/7/86 HARVEST

 

a $ $—
5 10 15 20

TEMPERATURE IN STORAGE (0C)

 

100-
90-
80-
70-
60-
50H

20%

 

  

0—04$“EEKSSUORMME
a—B "DWEEKSENORNME

8 11/18/86 HARVEST

 

 

 

 

5 10 15 20
TEMPERATURE IN STORAGE (OG)

102

Figure 4.4. Effect of storage temperature and duration
on mean days from potting to budbreak of Dicentra
spectabilis crowns. Means calculated for crowns with
at least one broken eye.

A. Crowns harvested October 7, 1986: standard
error of the interactions means (n=13) = 9.4 days.

B. Crowns harvested November 18, 1986: standard
error of the interaction means (n=16) = 3.5 days.

DAYS TO BUDBREAK

DAYS TO BUDBREAK

103

 

100-
90-
80
70-
60-
50-
40-
30-
20-
10-

0°C

 

A 10/7/86 HARVEST

 

 

 

111:

l ' I ' l ' l

4 6 8 10

WEEKS IN STORAGE

 

100-
90-

3111

0°C
5°C
10°C
20°C

8 11/18/86 HARVEST

 

 

 

WEEKS IN STORAGE

 

 

104

Figure 4.5. Effect of storage temperature and duration
on mean days from harvest to budbreak of Dieeeege

spectegilis crowns. Means calculated for crowns with
at least one broken eye.

A. Crowns harvested October 7, 1986: standard
error of the interactions means (n=13) = 9.6 days.

B. Crowns harvested November 18, 1986: standard
error of the interaction means (n=16) = 3.4 days.

 

DAYS FROM HARVEST TO BUDBREAK

DAYS FROM HARVEST TO BUDBREAK

105

 

140-

 

 

 

A 10/7/86 HARVEST
120- = .
100‘ 1
80
«I
60-
40-
: H 20°C c
201 H 10°C : e
‘ H 5°C ;
o—o 0°C
0 ' r I r I I r I
0 2 4 6 8 10
WEEKS IN STORAGE
140 ‘ a—o 20°C
‘ H 10°C 8 11/18/86' HARVEST
III—I 5°C
120- e—e 0%
1004

 

 

 

 

 

WEEKS IN STORAGE

 

 

106

Figure 4.6. Effect of storage temperature and duration
on mean rate of stem elongation during the first week

of post-break growth of Diceetre spectabilis crowns.
Means calculated for crowns with at least one broken

eye.

A. Crowns harvested October 7, 1986: standard
error of the interactions means (n=13) = 3.8
mm/week.

B. Crowns harvested November 18, 1986: standard
error of the interaction means (n=16) = 4.7
mm/week.

STEM ELONGATION (MM/WEEK)

STEM ELONGATION (MM/WEEK)

107

 

50 'I 0°C

10°C 10/7/86 HARVEST
20°C

3111

U
U
L

U

 

 

 

WEEKS IN STORAGE

 

 

0°C

5°C

10°C 11/18/86 HARVEST

20°C e

3111

 

 

 

 

 

 

o
1
N- (I
A
1
.

.
007E

I
81”

WEEKS IN STORAGE

108

Figure 4.7. Effect of storage temperature and duration
on mean height at 5 weeks post-break of D1eee§ge

spectabilie plants. Means calculated for crowns with
at least one broken eye.

A. Crowns harvested October 7, 1986: standard
error of the interactions means (n=13) = 1.4 cm.

8. Crowns harvested November 18, 1986: standard
error of the interaction means (n=16) = 1.6 cm.

 

>

PLANT HEIGHT (GM)

PLANT HEIGHT (CM)

109

 

 

 

 

 

 

 

 

 

.35
H 0°C
I—I soc 10/7/86 HARVEST
30" H 10°C
H 20°C 2\
25- \a
20-
15-
10-
5..
O . —-—--.‘f ——-—_:_—-_—____r__\ .. 1,
° 2 4 6 a 10
WEEKS IN STORAGE
.35
11/18/86 HARVEST
30-
3
25- 4“
20-I
15-1
o-o 0°C
101 H 5°C
H 10°C
5" a—a 20°C
0 1* 4:1
0 1o

 

WEEKS IN STORAGE

 

 

110

Figure 4.8. Effect of storage temperature and duration
on flowering of Dicentra spectabilis: percent non-

dormant crowns producing at least one expanded flower
within 220 days after potting.

A. Crowns harvested October 7, 1986; 20%
flowering without storage.

B. Crowns harvested Hovenber 18, 1986; 39%
flowering without storage.

73 CROWNS FLOWERING >

% CROWNS FLOWERING In

111

 

 

 

 

1001 I A
6 T H 6 WEEK STORAGE
90.; ; 10/7/8 HARVES H 4 WEEK STORAGE
H 2 WEEK STORAGE
801
70 ~
60-
505 a
40" g
30-
20-4 = =
10-1 5 e
O I '- ‘.‘.
O 5 1O 15 20

TEMPERATURE IN STORAGE (°C)

 

100 ‘

10-4

 

  
     

11/18/86 HARVEST

H 6 WEEK STORAGE

e—e 4 WEEK STORAGE

e—o 2 WEEK STORAGE
r

 

5 1'0 15
TEMPERATURE IN STORAGE (°C) ‘

 

 

112

Figure 4.9. Effect of storage temperature and duration

on mean days to flower for Dicentra spectabilis: means
calculated for non-dormant crowns producing at least
one expanded flower.

1. Crowns harvested October 7, 1986; 139 days to
flower without storage.

3. Crowns harvested November 18, 1986: 79 days to
flower without storage.

 

b

DAYS TO FLOWER

DAYS TO FLOWER

113

 

220-
200+
1804
160-
1401

 

12°T

100 ‘

 

e—e 2 WEEKS STORAGE
H 4 WEEKS STORAGE
H 6 WEEKS STORAGE

 

10/7/86 HARVEST

 

I

20

I l

5 10 13
TEMPERATURE IN STORAGE (00)

 

220.
200-
1804
1601
1404
1201
100i

804

 

e—o 2 WEEKS STORAGE
H 4 WEEKS STORAGE
H 6 WEEKS STORAGE

11/18/86 HARVEST

 

 

0 r—* T u

r
5 1O 15 20

TEMPERATURE IN STORAGE (0C)

 

 

114

Figure 4.10. Effect of storage temperature and

duration on mean length of Qicentra gpectabilig eyes.
Crowns harvested October 9, 1987.

A. Mean eye length at potting: standard error of
the interaction means (n=58)=2.l mm.

B. Mean length at budbreak of first eye to break:

standard error of the interaction means (n=14):
4.3 mm.

EYE LENGTH AT POTTING (MM)

BE LENGTH AT BREAK (MM)

115

70

 

60.. A 10/9/87 HARVEST A

50-
40A 5

.30-

H

H

10- H TO'C
B-EI 7.5‘C

0H5”; 1 , .

 

 

 

O 4 8 12
WEEKS IN STORAGE

 

60~

3 10/9/87 HARVEST

SO-

40-

30-

     
 

H 10°C
H 7.5‘C
H 5°C

 

 

 

O 4 8 12
WEEKS IN STORAGE

116

 

50 .k " 10/9/87 HARVEST

 

 

 

 

E‘ I: ‘7'
:5 V
o: “ a
2%
3 40d
CD A
O ..
.— \‘
‘9
< 20- I
D

. a—a 10°C 9

a—a 7.5°C
O o—o 5°C '
T T r
O 4 8 12

WEEKS IN TREATMENT

Figure 4.11. Effect of storage temperature and
duration on mean days to budbreak for Dicentra
sgectabilis crowns harvested October 9, 1987. Means
calculated for crowns with at least one broken eye;
standard error of the interaction means (n=14) = 7.3
days.

117

 

o—o 5°C

4OJ a—a 7.5“C
a—a 10°C
35~

30-
254

 

10/9/87 HARVEST

 
     

20-
15-
10d

Ln
L

 

STEM ELONGATION (MM/WEEK)

F1

 

-cL

 

 

 

fl.—

0 4 8 12
WEEKS IN STORAGE

Figure 4.12. Effect of storage temperature and
duration on mean rate of stem elongation during the
first week of post-break growth of Dicentra spectabilis
crowns harvested October 9, 1987. neans calculated for
crowns with at least one broken eye; standard error of
the interaction means (n=14) = 3.3 mm/week.

118

Figure 4.13. Effect of storage temperature and
duration on regrowth of Qigggtgg spectabilis crowns
harvested October 9, 1987. neans calculated for crowns
with at least one broken eye.

A. Mean plant height at 5 weeks post-break;
standard error of the interaction means (n=14) =
1.9 cm.

3. Mean regrowth quality at 5 weeks post-break
where 0=dead, 0.5=dormant buds, 1=emergent growth,

..5=vigorous growth; standard error of the
interaction means (n=14)=o.l.

D

PLANT HEIGHT (CM)

REGROWTH RATING

10~

119

 

o—o 5°C
J a—a 7.5°C
e—e 10°C

 

 

10/9/87 HARVEST

 

 

 

 

 

WEEKS IN STORAGE

 

    

 

 

 

 

 

 

o—o 5°C
5" a—a 7.5’C

H 10’C
41
3-1
2. 10/9/87 HARVEST
1 45—-=: :2
0 a r I

WEEKS IN STORAGE

120

Figure 4.14. Effect of storage temperature and
duration on flowering of Dicentra spectgbilig crowns
harvested October 9, 1987. Percentages based on crowns
with at least one broken eye.

A. Percent crowns with visible flower buds by 5
weeks post-break.

8. Percent crowns with at least one expanded
flower within 180 days of potting.

 

% CROWNS WITH FLOWER BUDS

% CROWNS FLOWERING

121

 

100-
90d
80d
704

1O-I

 

 

10/9/87 HARVEST

' a—a 10°C
_ a—a 7.5°C

o—o 5‘C

 

I r

a 12
WEEKS IN STORAGE

 

100-
90-4
80-I
704

 

o—o 5‘C
e—a 7.5’C
H 10°C '-

10/9/87 HARVEST

 

 

 

 

 

 

4 12
WEEKS IN STORAGE

122

 

1 4O
' E. 10/9/87 HARVEST
1 20

1001]

 

BO-

60-

40- 9
I \

20- s—a 10°C

‘ a—a 7.5°C

e—o 5°C

 

DAYS TO FLOWER

 

 

 

O T TT r

O 4- 8 12
WEEKS IN STORAGE

Figure 4.15. affect of storage temperature and

duration on days to flower for giggntgg spectabilis
crowns harvested October 9, 1987. Means calculated for

crowns with at least one broken eye.

123

 

 

 

 

 

 

e—o 5°C
200‘ e a—a 7.5°C
s—e 10°C
«g
2 1504 ‘
v I‘ 3
5 .I
0:
< 100.. 10/9/87 HARVEST
.J
<
m «1
3 u
LI. 50 " L‘ 5
o .. .
O 4 8 12

WEEKS IN STORAGE

Figure 4.16. Effect of storage temperature and

duration on floral production of Qigggtrg spectabilig
crowns harvested October 9, 1987. Means based on

crowns with at least one broken eye.

LIST 0? REFERENCES

Arney, S.E. 1955. Studies of growth and development in
the genus gregarig. Ann. Bot. (n.s.)19:265-276.

Austin, M.E. and x. Bondari. 1987. Chilling hour
requirement for flower bud expansion of two rabbiteye
and one highbush blueberry shoots. HortScience 22:1247-
1248.

Bailey, J.S. and A.M. Rossi. 1964. Response of Catskill
strawberry plants to digging date and storage period.
Proc. Amer. Soc. Hort. Sci. 84:310-318.

Beattie, D.J. and E.J. Holcomb. 1983. Effects of
chilling and photoperiod on forcing astilbe.
HortScience 183449-550.

Bryne, T.G. and A.M. Halevy. i986. Forcing herbaceous
peonies. J. Amer. Soc. Eort. Sci. 111:379-383.

Cameron, A.C. and M. Maqbool. 1986. Postharvest storage
of bare-root hardy perennials: The relation of water
loss to storage survival. Acta Hort. 181:323-329.

Chouard, P. 1960. Vernalization and its relation to
dormancy. Annu. Rev. Plant Physiol. 11:191-238.

De Eertogh, A.A. 1974. Principles for forcing tulips,
hyacinths, daffodils, Easter lilies and Dutch irises.
Scientia Eort.2:313-355.

De Hertogh, A.A., L.H. Aung, and M. Benschop. 1983. The
tulip: botany, usage, growth, and development. Hort.
Rev. 5:45-125.

10. Dennis, F.O., Jr. 1987. Two methods of studying rest:

temperature alternation and genetic analysis.
HortScience 22:820-824.

11. Erwin, J., R. Eeins, M. Earlsson, w. Carlson, and J.

Biernbaum. 1987. Producing Easter lilies. Cooperative
Extension Service Bulletin 3-1406, Michigan State
University.

124

12.

13.

14.

15.

16.

17.

18.

19.

20.

21.

22.

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24.

125

Flemion, F. and E. Waterbury. 1945. Further studies with
dwarf seedlings of non-after-ripened peach seeds. Cont.
Boyce Thompson Inst. 13:415-422.

Fuchigami, L.H. and C-C. Nee. 1987. Degree growth stage
model and rest-breaking mechanisms in temperate woody
perennials. HortScience 22:836-845.

Guttridge, C.G. 1958. The effects of winter chilling on
the subsequent growth and development of the cultivated
strawberry plant. J. nort. Sci. 33:119-127.

Hartsema, A.M. 1961. Influence of temperatures on flower
formation and flowering of bulbous and tuberous plants.
Encyl. of Plant Physiol. 16:123-167.

Ramerbeek, G.A. and W.J. Munk. 1976. A review of
ethylene effect in bulbous plants. Scientia Mort.
43101-115.

Kronenberg, J.G., L.M. lassenaar, and C.P.J. Van de
Lindeloof. 1976. Effect of temperature on dormancy in
strawberry. Scientia Hort. 4:361-366.

Langhans, R.M. and T.C. leiler. 1968. Vernalization in
Easter lilies? HortScience 3:280-282.

Langhans, R.W. and T.C. Wieler. 1971. The effects of
warm storage on the growth and flowering of Liligm
lgpgiglgrgg (Thunb.) \Ace'. Acta. Hort. 23:66-70.

Lazarz, S.A., M.R. Zillis, and E.C. Sink. 1982. L3 vitro

propagation of Dicentra gpggtgbilig. HortScience 17188-
189.

Lopes, L.C. 1974. Growth and flowering of giggggrg
gpggtgbilig. PhD Diss., Purdue University, Lafayette,
IN. (Dias. Abstr. 75-17237).

Lopes, L.C. and T.C. Weiler. 1977. Light and temperature

on the growth and flowering of pigggtgg spectgbilis
(L.) Lem. J. Amer. Soc. Eort. Sci. 102:388-390.

Maqbool, M. 1986. Postharvest handling and storage of
bare-root herbaceous perennials, MS Thesis. Michgan
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Milliken, G.A. and M. D. Remmenga. 1989. Statistical
analyses and the personal computer. HortScience 24:45- ‘
52.

25.

26.

27.

29.

30.

31.

32.

33.

34.

35.

36.

126

MSU Agricultural Weather Service. 1986, 1987. Weather
data listing for Trevor Nichols Experimental Farm,
Fennville, MI. Dept. of Entomology, Michigan State
University, East Lansing, MI.

Moe, R. and A. Uickstrom. 1973. The effect of storage
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Moe, R. and A. Iickstrom. 1979. Effect of precooling at
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J. Plant Physiol. :359-369.

CHAPTER 5

EPPECT OP TEMPERATURE
ON EYE DEVELOPMENT or 2191313; SPECTAEILIS

Chilling is required for rapid budbreak and subsequent
stem elongation of fall-harvested Diggntrg gpggtabilig when
grown under greenhouse conditions. Chilled eyes also flower
more quickly and more profusely than non-chilled eyes
(Chapters 1,2,4). This implies that chilling promotes
floral bud development as well as elongation of the
flowering axis but anatomical data for Dicegtra is lacking.
The phenology of floral development during the growth cycle
is unknown.

Langhans and Ueiler (13) describe four consecutive
stages in floral development. During flower initiation,
there is a visible transformation of the meristem from
vegetative to floral. Differentiation, the formation of the
floral parts, follows initiation. During the maturation
stage, the floral parts grow and sporogenesis occurs. The
final step in flower development is anthesis, the opening of
the flower bud.

In plants requiring vernalization, cold treatment
induces the initiation of flower primordia (5). Initiation
itself takes place after transfer to growing conditions.
Many biennials and perennials require vernalization to

127

128
flower including lily (13), but many do not. ‘Anatomical
examination of tulip, narcissus, and hyacinth has shown that
the meristem is never developmentally at rest (9).

Floral organogenesis in bulbs begins soon after
flowering ends in spring and continues through subsequent
warm and cold periods experienced in the field or in
commercial handling. Flower formation itself is completed
in several months under normal conditions (16).

Bryne and Ealevy (3) have demonstrated similar floral
phenology in herbaceous peony. Other plants such as bulbous
iris (16), strawberry (1,12), and many woody perennials
initiate floral primordia with the onset of cool fall
temperatures and complete flower formation during chilling.

The purpose of this study was to examine floral
development in Dicentra gpggtahilig at the anatomical level

in relation to constant temperature.

ELZEEILLE LED EEIEQDQ

One year-old crowns of Dicentra gpgggabilig (L.) Lem.
were harvested from southwestern Michigan fields (DeGroot
Nurseries, Coloma, MI, on October 9, 1987. At harvest,
ten field soil temperatures at 10 cm depth were measured. Records
of soil temperatures were also obtained from the Trevor
Nichols Experimental Farm, Fennville, MI (15). Crowns were
harvested one week after minimum soil temperatures dropped
below 10C. Loose soil was removed by shaking and any green

material was trimmed, leaving the eyes intact. The crowns

129
were packed in a moistened 1:1 peat:perlite mixture in
polyethylene-lined crates to avoid desiccation stress (4)
and simulate in sign chilling, and held for 0, 4, 8, or 12
weeks at 5, 7.5, or 10C. Five crowns were sampled per
treatment.

Fresh sections were cut freehand from several excised
eyes from each crown and from roots of 5 mm diameter or
more. Tissues were stained with aqueous solutions of
safranin, fast green, aniline blue, and potassium iodide
(10,11). Plant organs were examined using an Olympus zoom
stereo microscope which allowed examination of structures
too large for a dual objective microscope and too small for
a standard stereoscope. Magnification ranged from 7.5x to
64!. The automatic photomicrographic system and variable
illumination by three light sources provided a photographic

record of perishable fresh sections.

BEQELTE

piggntgg roots over 5 mm in diameter exhibited well-
defined secondary growth (Figure 5.2a). Primary vascular
elements were still present in these 6 month old tuberous
roots although secondary xylem and phloem were well
developed. Roots began to slough the papery brown cortex
after 4 weeks at all temperatures, leaving behind smooth,
white periderm. No other changes were observed in basic
root morphology as crowns were chilled, except in staining.

As storage was prolonged, root sections did not seem to

130
stain as darkly with potassium iodide. Starch content in
the roots may have decreased over time as has been observed
in strawberry (2).

Cross sections near the base of the eye contained
widely spaced vascular bundles with little evidence of
secondary growth (Figure 5.2b). Many small adventitious
roots were noted in this area of junction between stem and
rootstock. The eye itself (Figure 5.2c) was identified as
an overwintering structure of scales that tightly enclosed
primary and secondary buds (Figure 5.3). Vegetative
meristems were dome-shaped and surrounded by 3 to 5 pairs of
young leaves (Figure 5.2d). .

A marked change in meristem shape from domed to pointed
was associated with flower bud initiation (Figure 5.4a).
With time, more leaves were formed around the dome and the
meristem elongated into a spike bearing floral primordia
(Figure 5.4b). At temperatures of 7.5 and 10C, many floral
primordia developed in the highly etiolated eyes while the
number of leaf primordia decreased. Elongation of the eye
without opening of bud scales occurred as cortical and
vascular cells in the central and basal regions lengthened.
Some necrosis and disease in the etiolated tips was noted,
reminiscent of tulip bud necrosis (6,7).

At 5C, eyes retained their integrity, presenting a firm
and healthy appearance. Floral development was accompanied

by leaf development and was less rapid than at 7.5 or 10C

131
(Table 5.1). Flower buds were first noted at 10C after 4

weeks of exposure, but only after 8 weeks at 5C.

DIEQEEQIQE

Although early-harvested, unchilled 2; spectabilis
appeared to be endodormant, the eyes were undergoing major
developmental changes. These changes involved cell
elongation, meristem differentiation, and increasing
vascular complexity, as well as previously demonstrated
physiological modifications (Chapters 1,2,4).

Crowns clearly did not require vernalization to induce
flowering. Initiation of floral meristems occurred at 5C
but development was more rapid at 7.5 and 10C, temperatures
which do not satisfy the chilling requirement for stem
elongation (Chapter 4). In fact, Lopes (14) found that
chilling at 5C inhibited flower initiation in plants kept
vegetative by constant pinching.

Despite rapid floral organogenesis, warmer temperatures
did not promote successful flowering of Dicentra gpgctabilis
since flower axes were not able to elongate (Chapter 4,
Figure 4.12). The result of these opposing factors was the
occasional dwarfed plant with one expanded flower and
essentially no leaves or stems, or'a vigorous plant with

a few aborted buds but no flowers.

132

TABLE 5.1. Effect of storage temperature and duration on
percent of Dicentra crowns with floral buds as observed in
fresh sections at 7.5 to 64x magnification. 5 crowns per
treatment. No floral buds were observed at 0 weeks.

 

 

STORAGE WEEKS IN STORAGE
TEMPERATURE 4 8 12
5C 0 4O --
7.5 O 80 100

10 20 100 100

 

133

 

24-
221 1 987
201
18J
15‘
14~
12-I
104 x
3'1
64
4-1
21 l (XXDMA

- FENNWUiI

r . . 4r :ji . A: 4 r

9/11 9/25 10/9 10/23 11/6

SOIL TEMPERATURE (0c)

 

r

T

 

11/20

Figure 5.1. Minimum daily soil temperatures at 10 cm
depth at Trevor Nichols Experimental Farm, Fennville,
MI, and average soil temperature at 10 cm depth at

10:00 am in Dicentra gnggtabilig field in 1987 in
Coloma, MI. Coloma SE=0.1.

 

134

Figure 5.2. Vegetative anatomy of fall-harvested
Dicentra gpegtabilis.

A. Root, cs.
8. Ease of eye, cs.
C. Vegetative eye, ls.

D. Vegetative meristem, ls.

135

 

1. ._ . .
. z ...,_._...........,.....z.-...

 

   
 

(E

f
I. 3
5 .l
. :' - .'
e . 9‘ ,

o"
‘v

‘.

_' l
I
I

 

II

 

e
.

\II

‘III

A

‘

I

.../.-
I
3
i

136

 

 

 

I

 

 

 

bud scales

leaf primordia

meristem
1°bud

2°bud

vascular cambium

Figure 5.3. The eye of Dicentra spectabilis.

137

Figure 5.4. Anatomy of floral eyes of Dicentra
w.

A. Floral eye, ls.
8. Floral meristem, ls.

C. Zone of elongation in floral eye, ls.

 

10.

11.

12.

LIST OF REFERENCES

Arney, S.E. 1955. Studies of growth and development in
the genus 1:335:13. Ann. Bot. (n.s.)19:265-276.

Bringhurst, R.S., V. Voth, and D. VanHook. 1960.
Relationship of root starch content and chilling to
performance of California strawberries. Proc. Amer.
SOC. Hort. SCi. 75:373-381.

Bryne, T.G. and A.H. Halevy. 1986. Forcing herbaceous
peonies. J. Amer. Soc. Hort. Sci. 111:379-383.

Cameron, A.C. and M. Maqbool. 1986. Postharvest storage
of bare-root hardy perennials: The relation of water
loss to storage survival. Acta Hort. 181:323-329.

Chouard, P. 1960. Vernalisation and its relation to
dormancy. Annu. Rev. Plant Physiol. 11:191-238.

DeMunk, W.J. 1971. Sud necrosis, a storage disease of
tulips. IV. Analysis of disease-promoting storage
conditions. Neth. J. Plant Path. 77:177-186.

DeMunk, W.J. 1973. Eud necrosis, a storage disease of
tulips. IV. The influence of ethylene concentration and
storage temperature on bud development. Neth. J. Plant

Esau, x. 1977. Anatomy of seed plants, 2nd ed. John
Wiley 8 Sons, New York.

Hartsema, A.M. 1961. Influence of temperatures on
flower formation and flowering of bulbous and tuberous
plants. Encyl. of Plant Physiol. 16:123-167.

Johansen, D.A. 1940. Plant microtechnique. McGraw-Hill,
New York.

klein, D.T. and R.M. Klein. 1970. Research methods in
plant science. Natural History Press, Garden City, New
York.

Kronenberg, E.C., L.M. Wassenaar, and C.P.J. Van de
Lindeloof. 1976. Effect of temperature on dormancy in
strawberry. Scientia Hort. 4:361-366.

139

13.

14.

15.

16.

140

Langhans, R.W. and T.C. Weiler. 1968. Vernalisation in
Easter lilies? HortScience 3:280-282.

Lopes, L.C. 1974. Growth and flowering of Dicentra
gpggtabilig. PhD Diss., Purdue University, Lafayette,
IN. (Diss. Abstr. 75-17237).

MSU Agricultural Weather Service. 1987. Weather data
listing for Trevor Nichols Experimental Farm,
Fennville, MI. Dept. of Entomology, Michigan State
University, East Lansing.

Rees, A.R. 1966. The physiology of ornamental bulbous
plants. Bot. Rev. 32:1-23.

SUMMARY

Each of four separate growth responses in Dicentra
gpggtabilig--eye etiolation, budbreak, stem elongation, and
flowering--had a different time/temperature requirement as
summarized in Chapter 4. Stem elongation, for example, was
promoted by 4 weeks of storage at temperatures of 5C or
less. Below the "chilling threshold", the rate of
subsequent elongation was dependent upon temperature and
length of exposure. Above some critical temperature between
5 and 7.5C, there was no promotion of stem elongation but,
rather, promotion of eye etiolation.

This work did not test hypotheses of mechanism, but a
few can be suggested as bases for future physiological
studies of Dicentra and bud dormancy. The quantitative
response to chilling at 55C could be due to temperature-
dependent sythesis/metabolism of a growth promoter/inhibitor
such as gibberellin or other plant growth regulators. The
important reaction could also be one involving conversion of
respiratory substrates or their distribution through the
phloem in the developing stem. The lag time of 4 weeks may
be necessary to build up sufficient quantities of the
substance or its precursor before transfer to growing

conditions.

141

142

More unusual is the sharp change in response at the
chilling threshold, reminiscient of sudden injury in
chilling sensitive tissues. This on/off response to
temperature by Dicentra could depend on a change in membrane
structure or protein conformation, which could then promote
or prohibit the quantitative response of stem elongation.
Perhaps this same mechanism could also control the promotion
of eye etiolation, acting as an input/output logic gate,
returning one answer for temperatures below the threshold
and another for temperatures above it.

Obviously, a great deal of research needs to done in
order to test these hypotheses. The current work serves to
characterize the chilling requirements and demonstrate that
Dicentra spectabilig could prove an excellent subject for
further basic research on dormancy and growth of perennial

plants.

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