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INFLUENCE OF DIF ON THE SUSCEPTIBILITY 0F FLORAL CROPS T0
BOT RYT IS CﬂVEREA

By

Patricia Marie Pritchard

A THESIS
Submitted to
Michigan State University
in partial fulﬁllment of the requirements
for the degree of

MASTER OF SCIENCE

Department of Botany and Plant Pathology

1995

Abstract

INFLUENCE OF DIF ON THE SUSCEPTIBILITY OF FLORAL CROPS TO
BOT RYT IS CHVEREA

By
Patricia Marie Pritchard

The susceptibility of maturing poinsettia bracts and foliage, and geranium, petunia
and impatiens foliage to Bonytis cinerea grown under varying day/night temperatures
(DIF) for three (experiment 1) or six (experiment 2) weeks was investigated. Following
DIF treatments of 16/16, 19/19, 22/22, 16/ 19, 19/22, 16/22, 19/ 16, 22/19, and 22/ 16C,
plants were inoculated with 2.7 x 105 B. cinerea conidia/ml water and incubated at 20C.
The proportion of infected tissue and tissue with sporulating B. cinerea within each
treatment were recorded for up to 15 days. DIF did not inﬂuence plant susceptibility to
B. cinerea on any crop. The proportions of infection and sporulation were greater on
bracts than foliage in poinsettia. Poinsettia maturity, measured by thermal time, was
statistically correlated with the proportion of bract and foliage infection, as well as bracts
and foliage with spomlating B. cinerea. The proportion of geranium foliage infected was
greater than in petunia or impatiens under comparable conditions. The use of DIF on the
crops studied does not warrant modiﬁcations to disease management programs for B.
cinerea control; however, rigorous disease management is needed for poinsettias and seed

geraniums.

Dedication

Dedicated to the glory of God

You called me by name from the darkest part of my life and asked me to follow
you and allow you to shape me. This journey has not always been easy, but you have
provided me with a strong faith, hope and perseverance to face the obstacles. Your love
has kept me ﬁll] of your spirit.

The pages of this manuscript are a testimony to your glory working in my life.

Acknowledgements

The success of any academic endeavor such as this can be attributed to the
contributions of many individuals. Appreciation is extended to the American Floral
Endowment for providing ﬁnancial support for this research, and to the members of my
committee, Dr. Mary Hausbeck, Dr. Melvyn Lacy, and Dr. Royal Heins for their
participation in this project.

To the colleagues who endured long hours of disease ratings with me, most
notably Jim Kalishek and Rob Sweeny, their support of this project is greatly appreciated.
Special thanks to Jim K. who was a continual source of humor when I needed it the most.
During our scouting trips he brought new meaning to the Statue of Liberty.

True ﬁiendships endure all things. I am grateful to Kay Cahall and Elaine
Feuerstein for showing me the meaning of true friendship, as well as their endless prayer
support.

My gratitude goes to my husband, Don, who provided unending resources to the
success of this project in the form of his academic and professional experience, ﬁnancial
support, and most importantly emotional support. His love, encouragement, and belief in

me are gifts I will cherish throughout my life.

TABLE OF CONTENTS

Page
Dedication ....................................................... iii
Aclmowledgements ................................................ iv
List of Tables ..................................................... vii
List of Figures ................................... ix
Literature Review
I. Introduction ................................. 1
1]. Importance of Floriculture to Agriculture in the United States ......... 2
Crop Economics .............................. 2
Production in the United States
Production in Michigan
Bedding Plants ............................... 3
Petunia
Impatiens
Seed Geranium
Potted Plants ................................ 4
Poinsettia
HI. Disease Cycle of Bonytis cinerea ....................... 6
Host plant susceptibility
Conidial formation
Penetration of host tissue
Infection
Sporulation
IV. Importance of Bonytis cinerea in Floriculture ................. 7
Wide host range
Epidemiology
Symptoms of disease
Control measures
V. Inﬂuence of Thermomorphogenesis on Plants ................. 10
Temperature manipulation to control height
Economics
Range of crops inﬂuenced by DIF
Plant response to DIF
VI. Bibliography ................................. 13

Section I

The Inﬂuence of DIF on the Susceptibility of 'Angelika White' poinsettias to

Battytis cinerea ................................... 17
1. Abstract ................................... 18
H. Introduction ................................. 19
111. Materials and Methods ............................ 22

Plant Culture

Inoculation Preparation

DIF Treatment

Disease Assessment
IV. Results .................................... 26
V. Discussion .................................. 28
VII. Bibliography ................................. 32

Section H

The Inﬂuence of DIF on 'thgo' geraniums, 'Red Dreams' petunias, and 'Super Elﬁn'

impatiens to Battytz‘s cinerea. ........................... 56
1. Abstract ................................... 57
II. Introduction ................................. 58
111. Materials and Methods ............................ 61
General Procedures

Plant Culture

Inoculation Preparation

DIF Treatment

Disease Assessment
IV. Results .................................... 65
V. Discussion .................................. 66
VII. Bibliography ................................. 68

Appendix

The Inﬂuence of DIF and Plant Maturity on the Susceptibility of Egphgcbig
WMgeﬁka White' to Bohytis cinerea .................. 81

List of Tables

2339
Section I
The Inﬂuence of DIF on the Susceptibility of 'Angelika White'
poinsettias to Bonytis cinerea.
Temperature setpoints and actual average day (DT) and night
temperatures (NT) for 1993 poinsettia experiments ............ 23

Inﬂuence of DIF, DT, and NT on the proportion of 'Angelika White'
poinsettia bracts and foliage infected with B. cinerea following a
3 or 6-weeks DIF treatment .............................. 35

Section II

The Inﬂuence of DIF on 'Ringo' geraniums, 'Red Dreams' petunias, and
'Super Elﬁn' impatiens toBotrytis cinerea.

Temperature setpoints and actual average day (DT) and night
temperatures (NT) for 1994 bedding plants experiments ......... . 62

Inﬂuence of DIF, DT, and NT on the proportion of infected and
sporulating leaves of 'thgo' geraniums inoculated with Battytis
cinerea following a 3 or 6-week DIF treatment ................ 72

Inﬂuence of DIF, DT, and NT on the proportion of infected and
sporulating leaves of 'Red Dreams' petunias inoculated with Botrytis
cinerea following a 3 or 6-week DIF treatment ................ 73

Inﬂuence of DIF, DT, and NT on the proportion of infected and
sporulating leaves of 'Super Elﬁn' impatiens inoculated with Botrytis
cinerea following a 3 or 6-week DIF treatment ................ 74

Appendix

The Inﬂuence of DIF and Plant Maturity on the Susceptibility of
W 'Angelika White' to Boaytis cinerea.

Temperature settings and actual day and night temperatures (DT and
NT, respectively)for all environmental treatments for the poinsettia
experiment, 1994. ...................................... 82

Inﬂuence of plant maturity on bract infection and Sporulation incidence
of Bottytis cinerea on Wm 'Angelika White'. . . . 86

Means and standard deviations ofbract infection and Sporulation

incidence of Botrytzs cinerea WW 'Angelika
White'. ............................................... 87

List of Figures

Section I

The Inﬂuence of DIF on the Susceptibility of 'Angelika White'
poinsettias to Botrytis cinerea.

Proportion of 'Angelika White' poinsettia bracts infected with B.
cinerea (I), and proportion of bracts with Sporulation (O) 8 days
after inoculation in experiment 1 (top graph) and experiment 2

(bottom graph) when NT=16C (—-) and DT=16C (-—). . ...... 37

AUDPC values for proportion of bracts (——) and foliage (- - - ) of
'Angelika White' poinsettias infected with B. cinerea 8 days after
inoculation at day temperatures of 16 (I), 19 (@L and 22C (A) in
experimentl.............................; ............ 39

AUDPC values for proportion of bracts (-—-) and foliage (- - - ) of
'Angelika White' poinsettias infected with B. cinerea 8 days after
inoculation at day temperatures of 16 (I), 19 (ﬂ), and 22C (A) in
experiment 2. .......................................... 4]

Proportion of 'Angelika White' poinsettia foliage infected with B.
cinerea (I ), and proportion of foliage with Sporulation (O) 8 days
after inoculation in experiment 1 (top graph) and experiment 2

(bottom graph) when NT=16C (—) and DT=16C (—-). ........ 43

Relationship between thermal time from 3 Nov. and 14 Dec., 1993

and AUDPC values for the proportion of 'Angelika White' poinsettia
bracts infected with B. cinerea when receiving - DIF (I), 0 DIF (O),
or + DIF (A) in experiment 1 (open symbols) and experiment 2

(ﬁlled symbols) ......................................... 45

Relationship between thermal time from 3 Nov. and 14 Dec., 1993 and
AUDPC values for the proportion of 'Angelika White' poinsettia bracts
with spomlating B. cinerea when receiving - DIF (-), O DIF (.),

or + DIF (A) in experiment 1 (open symbols) and experiment 2

(ﬁlled symbols) ......................................... 47

10

Bags

Relationship between thermal time from 3 Nov. and 14 Dec., 1993

and AUDPC values for the proportion of 'Angelika White' poinsettia
foliage infected with B. cinerea when receiving - DE (I), 0 DE (O),
or + DE (A) in experiment 1 (open symbols) and experiment 2

(ﬁlled symbols). ....................................... 49

Relationship between thermal time from 3 Nov. and 14 Dec., 1993

and AUDPC values for the proportion of 'Angelika White' poinsettia
foliage with sponrlating B. cinerea when receiving - DE (I), 0 DE
(O), or + DE (A) in experiment 1 (open symbols) and experiment 2
(ﬁlled symbols). ....................................... 51

Percentage of infection (——) and sporulation ( - - - ) of Botrytis

cinerea on bracts of 'Angelika White' poinsettias 8 days after

inoculation in experiment I (E1) and experiment 2 (I) for DE
treatment 16/ 16C ........................................ 53

Percentage of infection (-——) and sponrlation ( - - - ) of Botrytis

cinerea on foliage of 'Angelika White' poinsettias 8 days after
inoculation in experiment 1 (1‘21) and experiment 2 (I) for DE
treatment 16/ 16C ........................................ 5 5

Section [I

The Inﬂuence of DE on 'thgo' geraniums,'Red Dreams' petunias, and
'Super Elﬁn' impatiens to Bonytis cinerea.

AUDPC values for proportion of 'Ringo' geranium leaves infected with
Botrytis cinerea lS-days after inoculation at night temperatures of 16
(I), 19 (A), and 22 C(O) in experiment 2. . ................ 76

AUDPC values for proportion of 'Ringo' geranium leaves with
sporulating Bonytis cinerea lS-days after inoculation at day temperatures
of 16(I), 19 (A), and 22C (O) in experiment 2. . ............ 78

Proportion of 'Red Dreams' petunia foliage infection (—-) and
Sporulation (- - - ) with Battytis cinerea l4-days (experiment 1- I)
and lS-days (experiment 2- O ) after inoculation when NT= 16C. 80

Appendix

The Inﬂuence of DE and Plant Maturity on the Susceptibility
of Eaphorbia gulcherrima 'Angelika White' to Bonytis cinerea.

Relationship between thermal time and disease incidence of

Bottytis cinerea on Euphorbia Qulgherrima 'Angelika White'
bracts when receiving positive, negative, or zero DE treatments

and inoculated at preanthesis, anthesis, and 5-days postanthesis ..... 89

Literature Review

Introduction

Producers of ﬂoriculture crops are facing competition from off- shore producers,
increasingly restrictive worker protection regulations, decreased numbers of pesticides,
water-quality and availability issues, and increased consumer skepticism about pesticides.
Imperfections caused by disease or insect damage are not tolerated in ﬂoricultural crops.
Thus the occurrence of diseases such as Bonytis cinerea Pers. :Fr. in a crop can greatly
reduce a grower's proﬁt margin.

Growers must be excellent crop managers to remain competitive. Computerized control
of greenhouse environments has enabled growers to increase crop-management precision.
Plant height can be controlled using a strategy called DE, the mathematical DIFference
between day and night temperatures Erwin et al. (1992). A positive DE occurs when the
day temperature is greater than the night temperature. As DE becomes increasingly
positive, there is a corresponding linear increase in the length of plant intemodes. A
negative DE occurs when night temperatures are greater than day temperatures. As DE
becomes increasingly negative, there is a corresponding linear decrease in the length of
plant intemodes. While positive DE has been historically used by many commercial ﬂoral
producers in the United States and Europe, negative DE is currently being utilized as a
non-chemical method of controlling plant height. Using negative DE may decrease plant
growth regulator use.

Although DE's effects on a wide range of plant species is well documented, there is no

2

information regarding its effect on the susceptibility of plants to B. cinerea. A disease
management program for controlling B. cinerea on plants grown using negative DE has
not been established.

The purpose of this research was to determine if DE regimes inﬂuence the susceptibility
of ﬂoral crops to B. cinerea and whether current disease management practices need to

be modiﬁed when negative and/or positive DE is used to control plant height.

Importance of Floriculture to Agriculture in the United States
W19!

Floriculture is a signiﬁcant component of agriculture in the United States. In 1994,
receipts showed that U. S.-grown ﬂoricultural and horticultural crops were the fastest-
growing commodity of all major segments of agriculture (Dill, 1994). Greenhouse
production area totaled 814 million square feet of covered area and 29,561 square feet of
open grormd in 1993. The 1993 wholesale value of all crops produced by large operations
(those with $100,000+ in gross sales) totaled $2.83 billion. Of those businesses, two-
thirds grew bedding and garden plants. Fiﬁy-seven percent of large operations grew
potted ﬂowering plants (Agricultural Statistics Board, 1994).

The 1993 wholesale value of bedding and garden plants produced by Michigan growers
totaled approximately $95 million, representing 8% of the US bedding plant production.
Total potted ﬂowering plant production by Michigan growers represented $23 million,
with poinsettia (Euphorbia pulchem‘ma) production representing $10 million of the total

and 5% of the total US poinsettia production.

mm

The US. bedding plant industry has grown steadily since 1950. In 1993, bedding and
garden plant production represented 42% of the total wholesale value of production for
large growers (Agriculture Statistics Board, 1994). In 1993, California, Texas, and
Michigan were the three largest producers of bedding plants (Agricultural Statistics
Board, 1994). Impatiens Umpatiens wallerana), petunias (Petunia x hybrida), and
geraniums (Pelargonium x hortorum) are three commonly grown bedding plant crops.

Petunias were cultivated as early as 1880 and are one of the most important plant
species developed for the bedding plant industry (Carlson et al, 1992). Seed companies
began developing new petunia cultivars in the 1930s, and today there are several hrmdred
cultivars.

Impatiens, a common bedding plant native to Aﬁica, was ﬁrst brought to the United
States by the missionary Reverend Horace Waller (Coombes, 1991). Impatiens are known
for their succulent stems and leaves, ﬂowering profusely throughout the growing season.

Bedding plants such as (petunias and impatiens are typically produced in ﬂats containing
cell packs that may hold ﬁom 18 to 72 plants. Petrmias and impatiens are typically grown
under cooler temperatures (10-20C) to produce high quality plants with compact growth
(Carlson et al., 1992). During the last week of production, temperatures may be dropped
even further (9-10C) to acclimate plants for early season outdoor planting. When cooler

temperatures are maintained, media can remain wet for extendedperiods, increasing the

4

relative humidity ( RH) in the lower canopy and making the environment favorable for
B. cinerea.

There are approrn'mately 280 species of diploid geraniruns currently cultivated for
potted and landscape use in the US. The ﬁrst seed geranium, 'Nittany Lion Red', was
introduced in the late 19608 by Craig (Fonteno, 1992). Since that time, commercial
improvement of this crop has resulted in seeds with improved germination, and plants with
increased ﬂowering, and shatter-resistant ﬂowers.

Geraniums are grown between l3-25C. Night temperatures 5 13C slows growth and
delays ﬂowering. Craig and Walker (1961) found that seed geraniums did not ﬂower until
they received a minirmrm amount of solar radiation. However, Armitage et al (1981)
determined that once buds appeared, the number of days to ﬂowering was inﬂuenced by

temperature, rather than radiation levels.

W

The poinsettia is considered the most important ﬂowering potted plant in the United
States, with the greatest production in California, Ohio, Texas, and North Carolina
(Agricultural Statistics Board, 1994). The poinsettia is native to Mexico and was ﬁrst
introduced into the United States in 1825 by Joel Robert Poinsett.

Poinsettias are propagated vegetatively by cuttings from stock plants. Cuttings are

misted continuously and maintained between 24-27C/21C (day/night) for 10-14 days or
until roots have formed. Air movement is minimized to decrease transpiration. After 14-

21 days, the misting frequency is gradually reduced and light intensities are gradually

5

increased (Ecke et al. 1990; Hartley, 1992). Once rooted, optimal temperatures are
21-29C/16-21C (day/night). Night temperatures exceeding 22 C delay ﬂower initiation
and development (Ecke et al, 1990).

Poinsettias are photoperiodic and ﬂower in response to short days and long nights. As
day length increases, bracts become vegetative and lose their characteristic color. As day
length decreases, the critical day length necessary to initiate ﬂowers occurs and bract and
ﬂower development progresses if night temperatures are less than 23C. Bract coloration
and ﬂowering can be accelerated as temperatures within the above-mentioned range
increase. However, as temperatures decrease there is a corresponding decrease in bract
size that is attributed to a decrease in root activity, resulting in decreased nutrient uptake
(Ecke et al., 1990).

Bracts are modiﬁed foliage that develop brilliant hues of red, pink and white. The
ﬂowers (cyathia) are composed of a single female pistil having no petals or sepals and
surrounded by many male stamens. Nectaries are glandlike structures attached to the
cyathia that secrete a sticky, sugary substance when fully mature. As cyathia mature, the
color of the nectaries changes ﬁom green to deep yellow, coinciding with the production
of nectar. In natural settings honeybees, which perceive color in the ultraviolet to
yellow-green regions of the electromagnetic spectrum (310-650 nm), are attracted to the
mature yellow nectary. During the visitation, mature pollen adheres to the insects body.
Pollen is spread by insect visitation and fertilizes the mature ovary (Evans, 1984).

As poinsettias mature, the dense plant canopy reduces air circulation and the amormt of

light reaching the lower leaves results in senescent tissue susceptible to B. cinerea.

6

Sporulation of B. cinerea on infected tissue provides inocuhrm for nearby plants.

Disease Cycle of Battytis cinerea

Boayoﬁniaﬁickeliana (deBary) Whetz, the teliomorphic stage of B. cinerea, was ﬁrst
identiﬁed by Micheli in 1729 (Jarvis, 1980a). Bohytis cinerea conidia can germinate,
infect, colonize, and sporulate within a short time on senescing ﬂowers, foliage, ﬁnits,
wounded tissue, seedlings and monbrmd tissue. Seedlings contain large amounts of pectic
substances in their cell walls, which makes them very susceptible to degradation by
pectolytic enzymes produced by B. cinerea (Sutic and Sinclair, 1991). Likewise,
senescing tissue is susceptible to infection by B. cinerea. Nooden (1988), deﬁnes
senescence as the endogenously controlled deteriorative changes that results in the loss of
a cell's ability to maintain homeostasis. The deterioration of the plasma membrane during
senescence results in the loss of cell contents to the environment. Blakeman (1975)
concluded that anrino acids and carbohydrates increased germination and growth of germ
tubes of B. cinerea.

Mycelial growth is enhanced from 20—28C (Jarvis, 1977). Mycelia give rise to
branching conidiophores 2 mm or more in length and 16-30u in diameter (CMI, 1974) on
which conidia are formed. Conidia are 6-18 x 4-11 um in size, colorless or grey, smooth,
ellipsoidal or ovoid, with a slightly protuberant hilum (CMI, 1974). Conidium production
is favored by high RH (Hawker, 1950; Jarvis, 197 7). Microclimates in which RH levels
can exceed 93%, such as lower canopies, favor sporulation even though the RH above

the plant canopy may not (Miller and Waggoner, 1957).

7

Conidia are disseminated by splashing water (Jarvis, 1962a; Dillon-Weston and Taylor,
1948) air currents (Jarvis, 1980b), insects (Jarvis, 1980b), a rapid rise or fall in RH (Jarvis,
1962b), or grower activity (Hausbeck and Pennypacker, 1991). On susceptible plant
tissue, conidia can germinate and penetrate within six hours if temperatures are between
18-22C and free moisture is present (Jarvis, 1980; Hunter et al., 1972; Salinas et a1,
1989). Botrytis cinerea advances in host tissue by secreting pectic enzymes that degrade
cell walls (Jarvis, 1977). Loss of cell membrane integrity results in the initial symptoms of
small water-soaked areas. Salinas et a1. (1989) reported that in gerbera ﬂowers, epidermal
cells became necrotic ﬁrst and as blight symptoms increased, mesophyll cells became
necrotic. Blighted tissue appears soil and rotten because of the disintegration and
collapse of cells. As the host cells become moribtmd, hyphae penetrate them and exist as
saprophytes (Jarvis, 1977), obtaining nutrients from declining host cells. Conidiophore
formation and sporulation are promoted by light in the near ultraviolet wavelengths of the
electromagnetic spectrum (Jarvis, 1977). 11er (1972) found that on geranium leaves, as
temperatures increased up to 25C, conidial production increased up to approximately
1.6 x 10’ conidia/cm2 of infected tissue. This cyclic infection can repeat itself within eight
hours after initial infection (Jarvis, 1980b), resulting in an exponential increase in the

number of infective conidia.

Importance of Bouytis cinerea in ﬂoriculture
Battytis cinerea is the most common disease of greenhouse-grown crops, infecting

126 ornamental plant species within 49 plant families (Trolinger and Strider, 1985).

8
Economically signiﬁcant greenhouse-grown plants susceptible to B. cinerea include
poinsettia, geranium, aﬁican violet, Chrysanthemum, orchid, tulip, amaryllis, begonia,
caster lily, rose, azalea, pansy, petunia, and fuchsia.

Symptoms of B. cinerea include leaf and stem blight; stem, leaf; and blossom spotting;
stem cankers; plant wilting associated with stem cankers; damping off of seedlings; and
rot of storage tissues such as bulbs (Trolinger and Strider, 1985).

Flowers are highly susceptible to infection by B. cinerea and are believed to exude
substances that serve as a nutrient source for germinating conidia (Elad, 1988; Hunter et
a1, 1972; Nair and Allen, 1993). Tukey (1971) reported carbohydrate leaching in
poinsettia increased as plants matured, reaching a peak at full bloom. Hunter et a1
(1972) documented the effect of ﬂower exudates by preparing exudate solutions from
immature, mature, and senescent macadamia racemes. B. cinerea conidia were added to
the exudate solutions and incubated at 24C for 12 hours. A high percentage of conidia
germinated in the mature and senescent exudate solutions. Conversely, no conidia
germinated in the immature exudate solution.

Battytis cinerea is a signiﬁcant disease of poinsettia, causing leaf, bract, and ﬂower
blight when environmental conditions are conducive to infection. Symptoms ﬁrst appear
as water-soaked lesions, eventually coalescing and turning tan to brown. Manning, et
a1. (1972) tested the susceptibility of 14 poinsettia cultivars' bracts and ﬂowers to B.
cinerea and determined that three were resistant and the other 11 were highly susceptible.
Bracts and ﬂowers of white cultivars were more susceptible to B. cinerea infection than

the red and pink cultivars included in the study.

9
Botrytis blight aﬂ‘ects geranium, resulting in water-soaked leaf spots that enlarge and

coalesce into irregular, brown, water- soaked spots. Under favorable environmental
conditions, conidia that serve as sources of inocuhrm for surrounding plants are produced.
Infected blossoms appear faded and dehydrated and may also be covered with conidia.
When infected ﬂowers shatter, inoculum is spread to adjacent plants via infected petals,
which often results in infection of healthy foliage (Jarvis, 1977; Jarvis, 1980; Melchers,
1926). Hyre (1972) reported increases in the colonization and sporulation of geranium
foliage by B. cinerea when temperatures were 10-25C.

Botrytis infection can devastate a bedding plant crop rapidly if undetected. Production
practices for bedding plants can be conducive to B. cinerea epidemics because of poor
air circulation among tightly spaced plants and free water on the plant surface from
condensation dripping ﬁom plastic ﬁhn greenhouse materials or overhead irrigation. In
Michigan, 73% of the total covered greenhouse production area is comprised of plastic
ﬁlm greenhouses (Agricultural Statistics Board, 1994) that are typically not well
ventilated, resulting in high RH. Peterson et a1 (1988) found that the number of B.
cinerea conidia in British Columbian greenhouses was 14.5 times higher in ﬁberglass-
covered houses than in plastic-covered houses. The higher percentage of disease losses in
ﬁberglass houses was also attributed to increased succulence of plant material associated
with reductions in light intensities by ﬁberglass material

Laemmlen and Sink (1978) tested 16 different cultivars of petimia and formd that all of
them were susceptible to B. cinerea and supported proliﬁc conidial production. Female

pettmia ﬂowers emit a postpollination substance, thought to be ethylene, that induces rapid

10

senescence of ﬂower petals (N ooden, 1988). Rapidly senescing pollinated ﬂowers, B.
cinerea inoculum, and a favorable environment can lead to signiﬁcant disease pressure.

Control measures for B. cinerea include sanitation, environmental management, and
fungicide application. Sanitation measures include removing and destroying infected plant
tissue, removing senescing or moribund plant tissue, avoiding plant injury, and using ebb
and ﬂood or trickle irrigation to reduce the incidence of leaf wetness. Environmental
management strategies include maintaining a low RH by providing air circulation; venting,
heating or both; and increasing plant spacing. The number of effective ﬁrngicides for
control of B. cinerea on ornamental crops has declined over the last 20 years. Repeated
exposure to a limited number of chemicals has resulted in the natural selection of
populations of B. cinerea resistant to chemicals such as benzimidazoles and

dicarboximides commonly used for control (Moorman and Lease, 1992).

Inﬂuence of Thermomorphogenesis on Plants

In the production of all ﬂoricultural crops, plant height is a critical factor. Growers
commonly regulate plant height to meet buyers' demands or facilitate eﬂicient shipping of
a ﬁnal product. Plant height can be managed by synthetic chemical growth regulators,
such as daminozide (B-Nine), chlormequat (Cycocel), uniconazole (Sumagic),
paclobutrazol (Bonzi), and ancymidol (Arest) (Larson, 1992).

Went (1944 ) determined that day and night temperatures inﬂuenced stem growth in
Lycopersicum sp. Erwin et a1. (1989) determined that plant height was not inﬂuenced by

absolute day and night temperature, but rather the diﬂ‘erence between day and night

ll

temperatures. Erwin et al. (1989) established the use of DE (the mathematical diﬁerence
between day and night temperatures) as a nonchemical alternative for controlling plant
height. A positive DE occurs when day temperatures exceed night temperatures; a
negative DE occurs when night temperatures are greater than day temperatures; and a
zero DE occurs when the day and night temperature are the same. Temperature and stage
of development inﬂuence a plant's response to DE. Erwin et al. (1994) showed that
morphological development in many plant species was highly correlated with DE when
the temperature was 10 to 25C. DE is effective on fuchsia, lily, campanula,
chrysanthermrm, and poinsettia (Erwin et a1, 1992).

Changes in plant morphology in response to diurnal temperature variations include
stem elongation, ﬂower size, and leaf shape and orientation (Erwin et al, 1989). As DE
becomes increasingly positive, the length of plant intemodes increases, and leaves become
oriented in a more upright position in Easter lily. As DE becomes increasingly negative,
plant intemode length decreases, and leaf orientation curves downward.

Erwin et a1 (1994) examined the effects of diurnal temperatures on cell elongations and
division in Lilium longrﬂorum Thunb. Parenchyma and epidermal cell length and width
were measured on plants that had been forced under 37 different DE environments. The
results showed that DE eﬂ‘ectively inﬂuenced plant height from 10-25C. This height
increase was attributed to an increase in intemode length but not the number of
intemodes. Within the temperature range used in the study, stem parenchyma and
epidermal cell length and leaf epidermal cell length increased linearly as DE became

increasingly positive. However, DE had no inﬂuence on leaf epidermal cell width, stem

12
parenchyma cell width, or stem epidermal cell width.

Cell volume also increased linearly as DE increased. Interactions between DE and cell
number per intemode and DE and stomatal frequency were not statistically signiﬁcant.
Although Erwin et a1. (1989) showed that DE did inﬂuence cell elongation, they did not
identify the manner in which stem elongation occurred Bioactive gibberellin (GA) may
be responsible for the eﬂ‘ects of DE on stem elongation (Erwin et aL, 1989; Moo et a1,

1991; Zieslin and Tsujita, 1988).

Bibliography

Agricultural Statistics Board. 1994. Floriculture Crops: 1993 Summary. USDA, Natl.
Agric. Stat. Serv., Agric. Stat. Board, Washington, DC.

Armitage, AM., Carlson, W.H., and Flore, 1A 1981. The effect of temperature and
quantum ﬂux density on the morphology, physiology, and ﬂowering of hybrid geraniums.
J. Amer. Soc. Hort. Sci 106:643-647.

Blakeman, J. P. 197 5. Germination of Botrytis cinerea conidia in vitro in relation to
nutrient conditions on leaf surfaces. Trans. Br. Mycol. Soc. 65(2):239-247.

Carlson, W.H., Kaczperski, M.P., and Rowley, EM. 1992. Bedding Plants. Pages 511-
550 in: Introduction to Floriculture. Second Edition. R A. Larson ed. Academic Press,
San Diego, 636 pp.

Commonwealth Mycological Institute (CMI). Descriptions of Pathogenic Fungi and
Bacteria. 1974. No. 431.

Coombes, A 1991. Dictionary of Plant Names. Timber Press, Portland, OR

Craig, R and Walker, D. E. 1961. The ﬂowering of Pelargom‘um hortorum Bailey
seedlings as affected by cunnrlative solar energy. Proc. Amer. Soc. Hort. Sci 83:772-776.

Dill, Robyn A 1994. State of the industry: Packing a powerful prmch. Greenhouse
Grower. May: 16-36.

Dillon-Weston, W.A.R and Taylor, RE. 1948. The plant in health and disease.
Crosby Lockwood, London.

Ecke, P., Jr., Matkin, GA, and Hartley, DE. 1990. The Poinsettia Manual. Third
Edition. Paul Ecke Poinsettias. Encinitas, Ca.

Elad, Y. 1988. Scanning electron microscopy of parasitism of Botrytis cinerea on
ﬂowers and fruits of cucumber. Trans. Br. Mycol. Soc. 91(1): 185-190.

Erwin, J., Velguth, P., and Heins, R 1994. Day/night temperature environment
aﬂ‘ects cell elongation but not division in Lilium Iongrﬂorum Thunb. J. of Exp. Bot.
45(276):1019-1025.

Erwin, J.E., Heins, RD, Carlson, W. and Newport, S. 1992. Diurnal Temperature
Fluctuations and Mechanical Manipulation Aﬂ‘ect Plant Stem Elongation.
P.G.RS.A Quarterly. 20:1-17.

l3

l4

Erwin, J. E., Heins, RD. and Moe, R 1991. Temperature and photoperiod eﬁeas on
Fuchsia x hybrida morphology. J. Amer. Soc. Hort. Sci 116(6):955-960.

Erwin, J.E., Heins, RD, and Karlsson, MG. 1989. Thermomorphogenesis in
Lilium Iongrﬂorum. Amer. J. of Bot. 76(1):47-52.

Evans, Howard E. 1984. mm 1). 252-253. Addison Wesley Publishing,
Mass.

Fonteno, WC. 1992. Geraniums. Pages 452-475 in: Introduction to Floriculture.
Second Edition. R A Larson ed. Academic Press, San Diego, 636 pp.

Hartley, DE. 1992. Poinsettias. Pages 305-331 in: Introduction to Floriculture.
Second Edition. R A Larson ed. Academic Press, San Diego, 636 pp.

Hausbeck, M.K. and Pennypacker, SP. 1991. Inﬂuence of grower activity and
disease incidence on concentrations of airborne conidia of Botrytis cinerea among
geranium stock plants. Plant Dis. 75:798-803.

Hawker, L. 1950. Physiology of fungi. University Press, London.

Hunter, J .E., Rohrbach, K. G. , and Kunimoto, R K 1972. Epidemiology of
botrytis blight of macadanria racemes. Phytopathology 62:316-319.

Hyre, R A 1972. Eﬂ‘ect of temperature and light on colonization and sporulation
of the botrytis pathogen on geranium. Plant Dis. Rep. 56(2): 126-130.

Jarvis, W. R 1962a. Splash dispersal of spores of Botrytis cinerea. Nature.
193:599.

Jarvis, W. R 1962b. The dispersal of spores of Botrytis cinerea Fr. in a raspberry
plantation. Trans. Br. Mycol. Soc. 45(4):549-559.

Jarvis, W. R 1977 . Botryotina and Botrytis Species: taxonomy, physiology, and
pathogenicity. A guide to the literature. Canada Dept. of Agric.
Monograph No. 15. 195 pp.

Jarvis, W. R 1980a. Taxonomy. Pages 1-17 in: W. J.R Coley-
Srnith, K. Verhoeﬂ‘, and W.R Jarvis, eds. Academic Press, London, 318pp.

Jarvis, W. R 1980b. Epidemiology. Pages 219-250 in: W. J.R
Coley- Smith, K. Verhoeﬂ‘, and W.R Jarvis, eds. Academic Press, London, 318pp.

15

Laemmlen, RF. and Sink, KC. 1978. Evaluation of petunia cultivars for botrytis
resistance. Plant Dis. Rep. 62(4):361-365.

Larson, RL. Introduction to Floriculture. Second Edition. Academic Press, San Diego,
636 pp.

Manning, W.J., Feder, W.A, and Perkins, I. 1972. Eﬂ‘ects of Botrytis and ozone on
bracts and ﬂowers of poinsettia cultivars. Plant Dis. Rep. 56(9):814-816.

Melchers, LE. 1926. Botrytis blossom blight and leaf spot of geranium and its
relationship to the gray mold of head lettuce. J. Agric. Res. 32:883-894.

Miller, RM. and Waggoner, RE. 1957. Dispersal of spores ofBotrytis cinerea among
strawberries. Phytopathology 47:24-25.

Moe, R, Heins, RD., and Erwin, J. 1991. Stem elongation and ﬂowering of the long-
day plant Campanula isophylla Moretti in response to day and night temperature
alternations and light quality. Scientia Hortic. 48:141-151.

Moorman, G.W. and Lease, RJ. 1992. Benzirnidazole and dicarboximide resistant
Botrytis cinerea from Pennsylvania greenhouses. Plant Dis. 76:477-480.

Nair, N. G. and Allen, RN. 1993. Infection of grape ﬂowers and berries by Botrytis
cinerea as a function of time and temperature. Mycol Res. 97(8): 1012- 1014.

Nooden, LB. 1988. The Phenomena of Senescence and Aging. Pages 2-38 in:
Senescence and Aging in Plants. L.D. Nooden and AC. Leopold, eds. Academic Press,
Inc., San Diego.

Peterson, M.J., Sutherland, J.R, and Tuller, SE. 1988. Greenhouse environment and
epidemiology of grey mold of container grown douglas ﬁr seedlings. Can. J. For. Res.
18:974-980.

Salinas, J., Glandorl, DCM, Picavet, ED, and Verhoeﬂ; K. 1989. Eﬂ‘ects of
temperature, relative humidity and age of conidia on the incidence of spotting on gerbera
ﬂowers caused by Botrytis cinerea. Netherlands J. Plant Pathol 95:51-

64.

Sutic , DD. and Sinclair, J.B. 1991. Plant Cytopathology. Pages 1-79 in: Anatomy and
Physiology of Diseased Plants. CRC Press, Boca Raton.

Trolinger, J. C. and Strider, D.L. 1985. Botrytis Diseases. Pages 17-101in: Diseases of
Floral Crops Volume 1. D.L. Strider, ed. Praeger Scientiﬁc. New York.

l6

Tukey, I-LB. Jr. 1971. Leaching of substances from plants. Pages 67-80 in: Ecology of
Leaf Surface Micro-Organisms. Preece, TR and Dickinson, C.H., eds. Academic Press,
London.

Went, F. 1944. Plant growth under controlled conditions. II. Thermoperiodicity in
growth and ﬁniting of the tomato. Amer. J. Bot. 31: 135-150.

Zieslin, N. and Tsujita, MJ. 1988. Regulation of stem elongation of lilies by temperature
and the effect ofgibberellin. Scientia Hortic. 37: 165-169.

17

Section I

The Inﬂuence of DE on the Susceptibility
of 'Angelika White' Poinsettias

to Botrytis cinerea.

18

Abstract

The susceptibility of poinsettias with maturing bracts and foliage to Botrytis cinerea when
grown under varying day/night temperatures (DE) of 16/16, 19/ 19, 22/22, 16/19/ 19/22,
16/22, 19/ 16, 22/ 19, and 22/16C for three (Exp. 1) or six weeks (Exp. 2) prior to
inoculation was investigated. Plants were inoculated with 2.7 x 10‘ B. cinerea conidia/ml
water following the DE treatments and incubated at 20C. Area under the disease
progress curve (AUDPC) data indicated that the proportion of bracts and foliage infected
or sporulating with B. cinerea was not inﬂuenced by DE, but did increase as day
temperature (DT) or night temperature (NT) increased, and ranged from 30 to 100% and
2 to 96%, respectively, 8 days after inoculation. The proportion of foliage infected
increased as DT increased and ranged from 2 to 53% 8 days alter inoculation. Thermal
time was correlated with the proportion of bracts (r2 = 0.90) and foliage (r2 = 0.73)
infected, and the proportion of bracts (r’ = 0.86) and foliage (r‘2 = 0.74) with sporulating B.
cinerea. The proportion of leaves infected and with sporulating B. cinerea was 5 13%
for all treatments. The proportion of bracts with sporulating B. cinerea ranged from 18 to

79%.

19

Introduction

Floriculture is a signiﬁcant component of agriculture in the US. In 1993, cash receipts
for operators with $100M+ gross sales totaled $2.83 billion (Agricultural Statistics Board,
1994). In 1994, receipts indicated that ﬂoriculture was the fastest growing agricultural
commodity (Dill, 1994). The poinsettia (Euphorbia pulcherrima) is an important
ﬂowering potted plant in the US. with the wholesale value for all sales in 1993 equaling
$ 198 million, representing approximately 10% of the total ﬂoriculture receipts
(Agricultural Statistics Board, 1994). Michigan growers produce 5% of all poinsettias in
the U. S. (Agricultural Statistics Board, 1994).

In poinsettia production, plant height is a critical factor. Crop size and quality are
dictated by market demands. Horticultural aesthetics favor short, compact plants. For
this reason, growers must intensively regulate crop height to meet contractual
speciﬁcations or face the possible reﬁrsal of the crop by the buyer.

Plant height has connnonly been managed by a variety of synthetic chemical growth
regulators (Hartley, 1992). The efﬁcacy of these treatments varies with application rate,
stage of plant development, and crop. The improper use of growth regulators can result
in plant abnormalities that may compromise the salability of a crop. For example, the
growth regulator B-Nine (daminozide) used late in production can slow the development
of bracts and delay ﬂowering in poinsettia (Hartley, 1992).

Erwin et a1. (1992) established the use of a nonchemical means of controlling plant
height called DE. DE is the mathematical DIFference between day and night

temperatures. A positive DE occurs when the night temperature is less than the day

20

temperature. As DE becomes increasingly positive, there is a corresponding linear
increased in the length of plant intemodes. A negative DE occurs when the night
temperature is greater than the day temperature. As DE becomes increasingly negative,
there is a corresponding linear decrease in the length of plant intemodes. While positive
DE has been historically used by commercial ﬂoral producers in the United States and
Emope, negative DE is currently being utilized as a non-chernical method of controlling
plant height. Using negative DE may decrease plant growth regulator use.

Erwin et a1 (1994) reported that DE inﬂuences cell length and volume but not cell
division. As DE becomes increasing positive, there is a corresponding linear increase in
the length of stem epidermal and parenchyma cells in Easter lily between the temperatures
of 10-25C. Although the mode of action of DE is rmknown, several researchers
hypothesize that bioactive gibberellins are the factor reqronsible for the effects of DE
(Erwin et al, 1989, Moe et a1. 1991, and Zieslin and Tsujita, 1988). Research has been
conducted on the morphological changes associated with the use of DE (Erwin et al,
1992), but the effects on plant disease management resulting from various DE regimes
have not been investigated.

Botrytis cinerea Pers.: Fr. is a cormnon and serious disease of poinsettias and can occur
during all phases of production on all plant parts (Hartley, 1992). Botrytis management
is critical in poinsettia production because the ﬂoriculture industry is intolerant of plant
imperfections. A number of fungicides are available for control of B. cinerea on
poinsettias, however, eﬂ'rcacy has been compromised by repeated exposure to a limited

number of chemicals and has resulted in the resistance of B. cinerea to benzimidazoles

21

and dicarboximides (Moorman and Lease, 1992; Pommer and Lorenz, 1982).
Furthermore, ﬁmgicide applications are restricted on colored bracts because of unsightly
residues.

Additional strategies for disease management include environmental manipulation to
reduce the occurrence of free water on plant surfaces necessary for B. cinerea conidial
germination Cultural management, including plant spacing to assure adequate air
movement, subirrigation to keep plant foliage dry, and the removal of diseased plant
material reduces conditions favoring disease development (Strider and Jones, 1985).

The objective of this study was to determine whether DE regimes affect the
susceptibility of poinsettia bracts and foliage to B. cinerea and if current disease

management strategies need to be modiﬁed.

22

Materials and Methods

ﬂanLCulane

Ten-week-old 'Angelika White' poinsettias were obtained from a connnercial grower
(Post Gardens, Battle Creek, Michigan) on 3 November 1993. 'Angelika' poinsettias are
especially sensitive to B. cinerea compared to newer varieties (Brandts, 1992). Plants
were grown in 15.2-cm (pot volume = 2177 cm’) plastic pots containing a commercial
soilless potting mix (Mix #4, Sun Gro Horticulture, Inc., Bellevue, Washington)
composed of 40% perlite and 60% Sphagnum peat moss. Plants were spaced 13 cm apart
on 2.7 x 0.9 x 0.06 m aluminum benches in 4.8 x 4.2 or research glass greenhouses at
Michigan State University.

Plants were watered as needed using ebb and ﬂood irrigation with benches ﬂooded for
2 minutes. By using an AMI 1000 fertilizer injector (DGT Vohnatic, Vallensbaek Strand,
Denmark) 9 liters of fertilizer stock solution containing 50% KNO3 + Compound 111,
25% NIL N03, and 25% CaNO3 and 2 liters of acid stock solution containing 50%
phosphoric acid and 50% sulﬁrric acid were mixed with 81 liters of water was applied at
each irrigation. The pH of the irrigation water was maintained at 5.8.

Glasshouse temperatures were maintained at 16, 19, or 22C using a climate-control
computer and monitored by a datalogger (Campbell Scientiﬁc, Inc., Logan, Utah) with
thermocouples. Thermocouple readings were recorded every minute and averaged every
15 minutes. Actual average temperatures during the erqreriment did not vary from the

Settings by more than 1.4C (Table 1). Light levels were natural photoperiods.

23

Table 1. Temperature setpoints and actual average day (DT) and night temperatures (NT)

for 1993 poinsettia experiments.

 

 

 

 

IamperahueSetpomts AW
121‘. M 2T Ii]:
16 16 16.3 15.8
16 19 16.3 18.7
16 22 16.3 21.8
19 16 18.9 15.8
19 19 18.9 18.7
19 22 18.9 21.8
22 16 22.0 15.8
22 19 22.0 18.7

22 22 22.0 21.8

 

 

24

Marion

Botrytis cinerea was isolated from infected geranium tissue and grown on 20 ml of
potato-dextrose agar in 10—cm-diameter petri plates at 25C for approximately 20 days. A
conidial suspension was prepared by ﬂooding plates with sterilized, distilled water and
dislodging conidia using a glass rod. Conidial concentrations were quantiﬁed using a
hemacytometer and ranged from 2.2-3.2 x 10 5 conidia/ml. Tween 20 (0.04%) was added
to the suspension prior to spraying.

Plants were sprayed to runoﬂ‘ with the conidial suspension using a Prevail pressurized
atomizer (Precision Valve Corp., Yonkers, New York) on 25 November and 14
December, 1993 for erqreriments 1 and 2, respectively. Control plants were sprayed with
sterile distilled water. Each plant was placed in a 53 x 14 x 96 cm plastic bag with a 180-
ml cup of distilled water to assure constant high RH. Bags were sealed and placed on
aluminum benches 86 cm above the ﬂoor in a walk-in chamber maintained at 20C 1 1C
with a 12-hour photoperiod provided by high-pressure sodium lights.

W

Nine day/night temperature combinations were investigated: zero DE = 16/16, 19/19,
and 22/22; positive DE = 19/ 16, 22/19, and 22/16; and negative DE = 16/19, 19/22,
and 16/22. The experimental design was completely randomized with 5 inoculated and 5
1minoculated plants per treatment. Plants were moved among three glasshouses set at
16, 19, or 22C at 0700 and 1900 HR each day, and was completed in 15 minutes. All

plants received either a three- or six-week temperature treatment (experiments 1 and 2,

25

respectively). At the conclusion of the DE temperature treatment, bracts with at least
90% coloration were counted on each plant.
Wm

Disease and sporulation incidence was assessed 4, 6, and 8 or 3, 6, and 8 days after
inoculation in experiments 1 and 2, respectively by calculating the number of bracts and
foliage infected or sporulating on each plant and dividing this value by the total number of
bracts or foliage present on each plants in each treatment.

The area under the disease progress curve (AUDPC) representing the cunnrlative
proportion of bracts and foliage infected and sporulating over an 8-day period following

inoculation was calculated using the method of Shanner and Finney (1977)

i=1
AUDPC = 2: [(Y,.1 + Y.)/2] [tin - ti]
n

where n = total number of observations, Y, = cumulative disease expressed as a

proportion at the ith observation, and t,- = time (days) aﬂer inoculation at the ith
observation.

The eﬂ‘ects of DE, day temperature, night temperature and day/night interactions
were determined by performing an analysis of variance (AN OVA) of the AUDPC data

using the general linear means procedure of the Statistical Analysis System (SAS, 1988).

Q I'E' 13'le

Temperature is the primary factor that determines plant development and maturity.

26
Thermal time, or degree days, is the generally accepted method of quantifying
phenological development of plants. This method assumes a linear eﬂ‘ect of temperature
on development, and is calculated by summing the daily mean temperatures and

subtracting a base temperature (Ketring, et al., 1989).

 

" T.+T
tn=2(l n)-Tb
i-l it

Where tn = degree days in C, Ti = average daily temperature, Tn = the nth average daily

temperature, 11 = total number of average daily temperatures, and Tb = base temperature.
T, for poinsettia crops has been determined to be 5C (Heins, personal comrrnmication,
1995). A signiﬁcant linear eﬂ‘ect existed between disease incidence and day and night
temperature, therefore degree day values were regressed with AUDPC means using the

general linear means protocol of the Statistical Analysis System (SAS, 1988).

Results
AUDPC data indicated that the proportion of bracts infected and bracts with
sporulating B. cinerea was not inﬂuenced by DE in experiment 1 or 2 but increased as
day (DT) or night (NT) temperature increased (Table 2). As DT increased from 16 to
22C with NT held at 16C, and as NT increased ﬁom 16 to 22C with DT held at 16C, the
proportion of bracts infected increased from 50 to 87% (experiment 1), and was 100%
(experiment 2) 8 days after inoculation (Figurel). The proportion of bracts with

sporulating B. cinerea 8-days after inoculation increased from 5 to 32% in experiment 1 as

27

DT increased from 16 to 22C with NT of 16C, and from 16 to 72% in experiment 2 as NT
increased from 16 to 22C with DT of 16C (Figure l). A statistical interaction between
DT and NT occurred for AUDPC data representing the proportion of bracts infected in
experiments 1 (Figure 2) and 2 (Figure 3), and resulted ﬁ'om a decreased amount of
disease in the 22/22 treatment compared to the other treatments 8 days alter inoculation.

AUDPC data indicated that the proportion of foliage infected and proportion of
foliage with sporulating B. cinerea was not inﬂuenced by DE in either experiment.
AUDPC data representing the proportion of foliage infected was linearly associated with
DT in experiments 1 and 2, and with NT in experiment 2 (Table 2). AUDPC data
indicated that the proportion of foliage with sporulating B. cinerea was not inﬂuenced by
DT in either experiment or NT in experiment 1 (Table 2).

As DT increased from 16 to 22C with NT of 16C, and as NT increased from 16 to
220 with DT of 16C, the proportion of foliage infected 8 days after inoculation increased
from 9 to 33% and 9 to 36%, respectively, in experiment 1 (Figure 4) and from 5 to
17% and 5 to 13%, respectively, in experiment 2. As DT increased from 16 to 22C with
NT of 16C, and as NT increased from 16 to 22C with DT of 16C, the proportion of
foliage with sporulating B. cinerea ranged ﬁ'om 7 to 25% and 8 to 17%, respectively, in
experiment 1 (Figure 4), but did not exceed 8% in experiment 2.

Plants in experiment 2 matured an additional 3 weeks and had nearly double the
degree day accumulation than plants in experiment 1. Eight days after inoculation, the
proportion of bracts infected was 99% in experiment 2 compared to 50% in experiment 1

for treatment 16/16 (Figure 9). The proportion of bracts with sporulating B. cinerea for

28

treatment 16/ 16 was < 20% for both experiments for the same time period (Figure 9).
The proportion of foliage infected and the proportion of foliage with spomlating B.
cinerea 8 days after inoculation for treatment 16/16 was <10% for both experiments
(Figure 10).

As maturity increased as indicated by thermal time, AUDPC values representing the
proportion of bracts infected increased (r2=.90, P=0.001). AUDPC could be described by
the function: AUDPC= 17.2 + 0.80(x). AUDPC values indicated that as thermal time
increased the proportion of bracts with sporulating B. cinerea increased (r2=.86, P=0.001)
and AUDPC could be described by the function: AUDPC= -74.45 + 0.40(x). AUDPC
data representing the proportion of foliage infected and the proportion of foliage with
sporulating B. cinerea increased as thermal time increased (r’=.73 and .74, respectively ,
P=0.001). The proportion of foliage infected was best described by the function
AUDPC= -l9.0 + 0.10(x), and the proportion of foliage with sporulating B. cinerea as

AUDPC= -7155 + 0.04(x).

Discussion
DE did not inﬂuence the susceptibility of poinsettia bracts and foliage to B. cinerea
measured by the proportion of tissue infected and supporting sporulation. Although DE
causes changes in plant morphology including plant height, intemode length, and leaf
orientation attributable to elongation of stem parenchyma and stem and leaf epidermal
cells (Erwin et al. 1989, 1994), this study suggests that these changes do not inﬂuence the

susceptibility of poinsettia to B. cinerea. Although this study did not address the effects

29

of diurnal temperature variations on the infectivity of B. cinerea, Sammons et a1. (1982)
formd no differences in incidence of B. cinerea on poinsettia when plants were grown
under varying day-night temperatures.

AUDPC data indicated that the proportion of bracts and foliage infected and the
proportion of bracts and foliage with sporulating B. cinerea increased as DT or NT
increased with the exception of the proportion of foliage with sporulating B. cinerea in
experiment 2. Temperature is a signiﬁcant factor affecting the rate of plant development
(Johnson and Thomley, 1985) Seneca] et a1 (1989) observed that as NT increased ﬁ'om
9 to 17C, the number of days to anthesis in poinsettias decreased. Thermal time
measures the accumulation of heat in degrees above the temperature at which no plant
development occurs during a 24 hour period. Thermal time has been determined to be a
more accurate descriptor of plant development than chronological time (Rickman et al.,
1983). Thermal time calculations have been built into growth and development models of
many crops (Gallagher, 1979, Cox, 1979, Ritchie, 1991). In our experiments, an increase
in thermal time was highly correlated with an increased incidence of bract and foliage
infection and sporulation. Although bracts are modiﬁed foliage, they are similar in
morphology to ﬂowers (Nell and Barrett, 1986; Krizek et a1, 1985; Rudall, 1987; and
Weberling, 1989). Hunter et a1 (1972) determined that increased maturity of macadamia
racemes coincided with an increase in plant susceptibility to B. cinerea infection. As
plants senesce, there is a corresponding loss of integrity of the plasma membrane of the
cell, and cell contents such as amino acids and carbohydrates are lost to the environment

(Nooden, 1988). Blakeman (1975) determined that amino acids and carbohydrates

30

increased the germination and growth of germ tubes of B. cinerea.

In our experiments, infection and sporulation were much greater in bracts than foliage.
Increased bract infection in experiment 2 may be due to the use of poinsettias that were 3
weeks older than those in experiment 1. Plants in experiment 1 had not reached anthesis
and translocation of nutrients would predominant to developing bract tissue (Marshall and
Sagar, 1976). Plants in experiment 2, however, were at or near anthesis and it is likely
that the developing ﬂowers were the dominant sinks. It was observed that poinsettias
inoculated with B. cinerea at or 5 days beyond anthesis had increased levels of sporulation
on ﬂowers compared to plants inoculated prior to anthesis (personal observation).

There was an interaction between DT and NT in the infection of bracts in experiment 1
and 2. In experiment 1 the interaction and was attributed to the reduction in disease in the
22/22 treatment compared to other treatments. Although an interaction between DT and
NT was observed in foliar infection, the level was nearly 10 times less than that observed
on bracts.

The results of this experiment suggest that commercial growers using negative DE
treatments to control plant height do not need to modify current disease management
programs for the control of B. cinerea on poinsettias. These data suggest that the
infection process occurs more rapidly in more mature plants. In commercial production,
increased plant maturity conincides with plant ﬁnishing. The use of ﬁmgicides during this
time is cautioned due to residues or phytotoxicity, which can reduce the value of the crop.
Growers can reduce the occurrence of botrytis during this period by employing

preventative control measures such as manipulation of the environment which keeps

3 1
relative humidity levels below 85%; providing adequate plant spacing, which facilitates
adequate air movement beneath the lower plant canopy; removal of infected plant tissue,
which decreases the amount of inoculum available to infect surrounding plant tissue; and

subirrigation, which reduces amount of freewater on the plant surface.

Bibliography

Agricultural Statistics Board. 1994. Floriculture Crops: 1993 Summary. USDA, Natl.
Agric. Stat. Serv., Agric. Stat. Board, Washington, DC.

Berghage, RD. , Flore, J.A, Heins, RD., and Erwin, J.E.. 1990. The relationship
between day and night temperature inﬂuences photosynthesis but not light compensation
point or ﬂower longevity of caster lily, Lilium Longrﬂorum Thunb. Acta Hort. 272291-
95.

Blakeman, JP. 1975. Germination of Botrytis cinerea conidia in vitro in relation to
nutrient conditions on leaf surfaces. Trans. Br. Mycol Soc. 65(2):239-247.

Brandes, A 1992. 'Lilo' has best shelf life in Dutch test. In Euro Floratech Bulletin.
1(12):2.

Campbell and Madden, L. 1990. Temporal analysis of epidemics 1: Description and
comparison of disease progress cm'ves. Pages 16-202 in: Introduction to Plant Disease
Epidemiology. John Wiley and Sons, Inc.

Dill, Robyn A 1994. State of the industry. Packing a powerful prmch. Greenhouse
Grower. May: 16-36.

Erwin, J ., Velguth, P., and Heins, R 1994. Day/night temperature environment aﬂ‘ects
cell elongation but not division in Lilium Iongrﬂorum Thimb. J. of Exp. Bot.
45(276): 1019-1025.

Erwin, J. E., Heins, RD., Carlson, W. and Newport, S. 1992. Dirunal temperature
ﬂuctuations and mechanical manipulation aﬂ‘ect plant stem elongation. P. G.R S.A

Quarterly. 20: 1-17.

Erwin, J. E., Heins, RD., and Karlsson, MG. 1989. Thermomorphogenesis in Lilium
longrﬂorum. Amer. J. Bot. 76(1): 47-52.

Hartley, D. 1992. Poinsettias. Pages 305-331 in: Introduction to Floriculture. Second
Ed. R Larson Ed. Academic Press. San Diego

Hunter, J.E., Rohrbach, KG, and Kunimoto, RK 1972. Epidemiology of botrytis
blight of macadamia racemes. Phytopathology 62:316-319.

Johnson, LR and Thomley, J.H.M. 1985. Temperature dependence of plant and crop
processes. Ann. Bot. 55:1-24.

32

33

Jones, H. G. 1992. Photosynthesis and Respiration. Pages 163-214 in: Plants and
nricroclirnate. Second Ed. Cambridge University Press, Cambridge. 425pp.

Ketring, D.L. and Wheless, T. G. 1989. Thermal time requirements for phenological
development of peanut. Agron. J. 81:910-917.

Krizek, D.T., Wergin, WP, and Semeniur, P. 1985. Morphological and physiological
properties of poinsettia leaves and bracts in relation to sulfur dioxide sensitivity.
Environmental and Exp. Bot. 25(2): 165-173.

Marshall, C. and Sagar, GR 1976. Transport in the phloem. Pages 254-293 in: Plant
Structure, Function and Adaptation. M.A Hall ed. Macmillan Press, London.

Miller, W.B., Hammer, RA, and Kirk, T]. 1993. Reversed greenhouse temperatures
alter carbohydrate status in Lilium longrﬂorum Thunb. 'Nellie White'. J. Amer. Soc. Hort.
Sci. 118(6):736-740.

Moe, R, Heins, RD., and Erwin, J. 1991. Stem elongation and ﬂowering of the long-
day plant Campanula isophylla Moretti in response to day and night temperature
alternations and light quality. Scientia Hortic. 48:141-151.

Moorman, G.W. and Lease, RJ. 1992. Benzimidazole and dicarboximide resistant
Botrytis cinerea from Pennsylvania greenhouses. Plant Dis. 76:477-480.

Nell, TA. and Barrett, J .E. 1986. Growth and incidence ofbract necrosis in 'Gutbier V-
14 Glory' poinsettia. J. Amer. Soc. Hort. Sci 111(2):266-269.

Nooden, L.D. 1988. The phenomena of senescence and aging. Pages 2-38 in:
Senescence and Aging in Plants. L.D. Nooden and AC. Leopold, eds. Academic Press,
Inc., San Diego.

Pommer, Eli. and Lorenz, G. 1982. Resistance of Botrytis cinerea Pers. to
dicarboximide fungicides. A literature review. Crop Prot. l(2):221-230.

Rickrnan, RW., Klepper, BL, and Peterson, CM. 1983. Time distributions for
describing appearance of speciﬁc culms of winter wheat. Agron. J. 75:551-556.

Ritchie, IT. 1991. Modeling plant and soil systems. American Society of Agronomy:
Crop Science Society of America: Soil Science Society of America. Madison, WI.

Rudall, P. 1987. The Flower. Pages 50-62 in: Anatomy of Flowering Plants. Edward
Arnold Pub. Ltd., London. 80 pps.

34

SAS Institute, Inc. SAS/ STAT1M Users Guide, Release 6.03 Edition, Cary, NC: SAS
Institute. 1988. PP. 1028.

Sammons, B., Rissler, J.F., and Shanks, IR 1982. Development of gray mold of
poinsettia and powdery mildew ofbegonia and rose rmder split night temperatures. Plant
Dis. 66:776-777.

Seneca], M.B., Dansereau, and R Paquin. 1989. Fertilization and night temperature
eﬂ‘ects on growth and carbohydrate status of poinsettia. Can. J. Plant Sci 69:347-349.

Shanner, G. and Finney, RE. 1977. The eﬂ‘ect of nitrogen fertilization on the expression
of slow-mildewing resistance in knox wheat. Phytopathology. 67: 105 1- 1056.

Strider, D.L. and Jones, RK 1985. Poinsettias. Pages 351-403 in: Diseases of Floral
Crops Vol. 2. Praeger Publishers, New York

Weberling, F. 1989. Anatomical structure and coloring of the petals, ﬂower scent. Pages
58-61 in: Morphology of Flowers and Inﬂorescence. Cambridge University Press,
Cambridge. pps. 405.

Zieslin, N. and Tsujita, M.J. 1988. Regulation of stem elongation of lilies by temperature
and the effect of gibberellin. Scientia Hortic. 37:165-169.

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36

Figure 1. Proportion of 'Angelika White' poinsettia bracts infected with B. cinerea
(I), and proportion of bracts with sporulation (O) 8 days after inoculation in
experiment 1 (top graph) and experiment 2 (bottom graph) when NT=16C (-—-) and
DT=16C (--).

37

Figure l.

 

 

 

 

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38

Figure 2. AUDPC values for proportion of bracts (—) and foliage (- - - ) of 'Angelika
White' poinsettias infected with B. cinerea 8 days after inoculation at day temperatures of
16 (I), 19(@), and 22C (A) in experiment 1.

39

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40

Figure 3. AUDPC values for proportion of bracts (~--) and foliage (- - - ) of 'Angelika
White' poinsettias infected with B. cinerea 8 days aﬁer inoculation at day temperatures of
16 (I ), 19 0%), and 22C (A) in experiment 2.

41

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42

Figure 4. Proportion of 'Angelika White' poinsettia foliage infected with B. cinerea
(I), and proportion of foliage with sporulation (O) 8 days aﬂer inoculation in
experiment 1 (top graph) and experiment 2 (bottom graph) when NT=16C (-—)
and DT=16C (—).

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43

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44

Figure 5. Relationship between thermal time from 3 Nov. and 14 Dec., 1993 and AUDPC
values for the proportion of 'Angelika White' poinsettia bracts infected with B. cinerea
when receiving - DE (I), 0 DE (O), or + DE (A) in eiqreriment 1 (open symbols) and
experiment 2 (ﬁlled symbols).

45

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46

Figure 6. Relationship between thermal time from 3 Nov. and 14 Dec., 1993 and AUDPC
values for the proportion of 'Angelika White' poinsettia bracts with sponrlating B. cinerea
when receiving - DE (I), 0 DE (O), or + DE (A) in experiment 1 (open symbols) and
experiment 2 (ﬁlled symbols).

47

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48

Figure 7. Relationship between thermal time from 3 Nov. and 14 Dec., 1993 and AUDPC
values for the proportion of 'Angelika White' poinsettia foliage infected with B. cinerea
when receiving - DE (I), 0 DE (O), or + DE (A) in experiment 1 (open symbols) and
experiment 2 (ﬁlled symbols).

49

con

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50

Figure 8. Relationship between thermal time from 3 Nov. and 14 Dec., 1993 and AUDPC
values for the proportion of 'Angelika White' poinsettia foliage with sporulating B. cinerea
when receiving - DE (I), 0 DE (O), or + DE (A) in experiment 1 (open symbols) and
experiment 2 (ﬁlled symbols).

51

can

 

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52

Figure 9. Percentage of infection (—) and sporulation ( - - - ) of Botrytis cinerea on bracts
of 'Angelika White' poinsettias 8 days after inoculation in experiment 1 (IX!) and experiment
2 (I) for DE treatment 16/16C.

53

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54

Figure 10. Percentage of infection (—) and sporulation ( - - - ) of Botrytis cinerea on
foliage of 'Angelika White' poinsettias 8 days after inoculation in experiment 1 (IX!) and
experiment 2 (I) for DE treatment 16/ 16C.

55

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56

Section II

The Inﬂuence of DE on 'Ringo' geraniums,
'Red Dreams' petunias, and 'Super Elﬁn' impatiens

to Botrytis cinerea.

57

Abstract

The susceptibility of geraniums, petunias, and inrpatiens with maturing foliage to
Botrytis cinerea when grown under varying day/night temperatures (DE) of 16/16, 19/19,
22/22, 16/19/ 19/22, 16/22, 19/16, 22/19, and 22/16C for three (Exp. 1) or six weeks (Exp.
2) prior to inoculation was investigated. Plants were inoculated with a B. cinerea
suspension of 2.7 x 10’ conidia/ml following the DE treatments and incubated at 20C.
AUDPC data indicated that the proportion of leaves infected as well as the proportion of
leaves with sponrlating B. cinerea was not inﬂuenced by DE.

When day temperature (DT) was held at 16C and night temperature (NT) increased
ﬁom 16 to 22C, the proportion of infected geranium leaves ranged ﬁom 60-69% while
pettmias and impatiens ranged from 14-38% and <11%, respectively in experiment 1.

The results of this experiment suggest that commercial growers using negative DE
to control plant height do not need to modify current disease management programs for the
control of B. cinerea on geranium, petunia, or impatiens. However, more rigorous disease
management strategies are needed for production of seed geraniums than for petunias or

impatiens.

58

Introduction

Floriculture is a signiﬁcant component of agriculture in the US. In 1993, cash receipts
for operators with $100M+ gross sales totaled $2.83 billion (Agricultural Statistics Board,
1994). In 1994, receipts indicated that ﬂoriculture was the fastest growing agricultural
commodity (Dill, 1994). The U. S. bedding plant industry has grown steadily since 1950.
In 1993, bedding and garden plant production represented 42% of the total wholesale value
of ﬂoriculture production (Agricultural Statistics Board, 1994). Michigan growers
produced 8% of all bedding plants in the U. S. in 1993 (Agricultural Statistics Board, 1994).

In bedding plant production, plant height is a critical factor. Crop size and quality are
dictated by market demands. Horticultural aesthetics favor short, compact plants. For this
reason, growers nurst intensively regulate crop height to meet contractual speciﬁcations or
face the possible refusal of the crop by the buyer.

Plant height has commonly been managed by a variety of synthetic chemical growth
regulators (Fonteno, 1992; Carlson et a1, 1992). The eﬂicacy of these treatments varies
with application rate, stage of plant development, and crop. The improper use of growth
regulators can result in plant abnormalities due to phytotoxicity or delayed ﬂowering
which may compromise the salability of a crop (Carlson et al., 1992).

Erwin et a1. (1992) established the use of a nonchenrical means of controlling plant
height called DE. DE is the mathematical DIFference between day and night
tenrperatures. A positive DE occurs when the night temperature is less than the day
temperature. As DE becomes increasing positive, there is a corresponding linear increase

in the length of plant intemodes. A negative DE occurs when the night temperature is

59

greater than the day temperature. As DE becomes increasingly negative, there is a
corresponding linear decrease in the length of plant intemodes. While positive DE has
been hisstorically used by commercial ﬂoral producers in the United States and Europe,
negative DE is currently being utilized as a non-chenrical method of controlling plant
height. Using negative DE may decrease plant growth regulator use.

Erwin et a1 (1994) reported that DE inﬂuences cell length and volume but not cell
division. As DE becomes increasing positive, there is a corresponding linear increase in
the length of stem epidermal and parenchyma cells in caster lily between the temperatures
of 10-250. Although the mode of action of DE is unknown, several researchers
hypothesize that bioactive gibberellins are the factor responsible for the effects of DE
(Erwin et al., 1989, Moe et a1, 1991, and Zieslin and Tsujita, 1988). Research has been
conducted on the morphological changes associated with the use of DE (Erwin et al.,
1992), the effects on plant disease management resulting from various DE regimes has
not been investigated.

Botrytis cinerea Pers.: Fr. is one of the most important diseases in the production of
bedding plant crops (Jones and Strider, 1985). Bedding plant production favors the
occurrence of B. cinerea. Cultural conditions of bedding plant production such as high
fertilization rates, tight plant spacing, and frequent overhead watering are conducive to
blight caused by B. cinerea (Jones and Strider, 1985).

Most growers of bedding plants apply fertilizers with nitrogen levels ranging from 100
to 250 ppm at each irrigation (Carlson et al., 1992). Bedding plants are typically produced

in ﬂats that hold from 18 to 72 plants. Rapidly growing plants result in a dense canopy

60

that creates a microenvironment with increased relative humidity that is conducive to
disease development. Due to reduced light levels under this canopy, plant tissue senesces
and becomes a favorable host for B. cinerea. Bedding plants are ﬁ'equently irrigated
because the root system is contained in a small volume of soil and results in ﬁee moisture
on plant surfaces for extended periods of time. Conidia of B. cinerea can be disseminated
by splashing water and can germinate and infect adjacent tissue within six hours if
temperatures are 18-22C and free moisture is present (Jarvis, 1980).

A number of ﬁmgicides are available for control of B. cinerea on bedding plants;
however, eﬁcacy has been compromised by repeated exposure to a limited number of
chemicals and has resulted in the resistance of B. cinerea to benzimidazoles and
dicarboximides (Moorman and Lease, 1992; Pommer and Lorenz, 1982). Growers can
manage botrytis blight using cultural management practices such as maintaining the relative
humidity below 85%, removing dead or infected plant material to reduce inoculum levels,
and watering during periods that allow plant foliage to dry rapidly (Jones and Strider,
1985). The objective of this research was to determine if the use of varying DE regimes
to produce geranium, petunia, and impatiens inﬂuenced the susceptibility of these plant

tissues to B. cinerea and if current disease management strategies needed to be modiﬁed.

61

Materials and Methods
ﬂanLCultnLe

Seedlings of 'Ringo' geraniums, 'Red Dreams' petunias, and 'Super Elﬁn' impatiens
were obtained in 2 cm2 plugs from a commercial grower on 9 December 1993 and
transplanted into ﬂats with 18 cells, each containing one plant (8 cm2 , pot vohrme = 384
cm’) containing a commercial soilless mix (Michigan Grower Products, Galesburg,
Michigan) with an initial pH of 5.86. Six ﬂats of each species were placed on 2.7 x 0.9 x
0.06 m aluminum benches in 4.8 x 4.2 m glass research greenhouses at Michigan State
University.

By using an AMI 1000 fertilizer injector (DGT Vohnatic, Vallensbaek Strand,
Denmark), 9 liters of fertilizer stock solution containing 50% 16103 + Compound 11],
25% NIL N03, and 25% CaNO3, and 2 liters of acid stock solution containing 50%
phosphoric acid and 50% sulﬁuic acid were mixed with 81 liters of water and applied to
plants overhead as needed. The pH of the water was maintained at 5.5.

Glasshouse temperatures were maintained at 16, 19, or 22C using a clirnate-control
conrputcr and monitored by a datalogger (Campbell Scientiﬁc, Inc., Logan, Utah) with
thermocouples. Thermocouple readings were recorded every minute and averaged every
15 minutes. Actual average temperatures during the experiment did not vary from the
settings by more than a maximum of 1.5C (Table 1). Supplemental lighting was provided
by high-pressure sodium lamps between 0700 and 1900 H.

W

Botrytis cinerea was isolated from infected geranium tissue and grown on 20 ml of

62

Table 1. Tcnrperaturc setpoints and actual average day (DT) and night temperatures (NT)

for 1994 bedding plants experiments.

 

 

 

IcmparatruLScmnmts AW

III .1511 DI NT

16 16 17.4 16.7
l6 19 17.4 19.1
16 22 17.4 22.3
19 16 19.9 16.7
19 19 19.9 19.1
19 22 19.9 22.3
22 16 23.2 16.7
22 19 23.2 19.1

22 22 23.2 22.3

 

 

63

potato dextrose agar in lO-cm-diameter petri plates at 25C for approximately 20 days. A
conidial suspension was prepared by ﬂooding plates with sterilized distilled water and
dislodging conidia using a glass rod Conidial concentrations were quantiﬁed using a
hemacytometer and adjusted to an average 2.7 x 10 5 conidia/ml. Tween 20 (0.04%) was
added to the suspension just before spraying.

Plants were sprayed to nmoﬂ‘ with the conidial suspension using a Prevail pressurized
atomizer (Precision Valve Corp., Yonkers, New York) on 5, 6, and 7 or 21 and 22
January 1994 for experiments 1 and 2, respectively. Control plants were sprayed with
sterile distilled water. Each plant was placed in a 20 x 10 x 46 cm plastic bag with a 180
-ml cup of distilled water to assure constant high RH. Bags were sealed and placed on
aluminum benches 86 cm above the ﬂoor in a walk-in chamber maintained at 20C : 1C
with a 12-hour photoperiod provided by high pressure-sodium lights.

DWI]!

Nine day/night temperature combinations were investigated and included: zero
DE = 16/16, 19/19, and 22/22; positive DE = 19/16, 22/19, and 22/16; and negative
DE = 16/19, 19/22, and 16/22. The experimental design was completely randomized
and included 12 plants of each species per treatment. At the conclusion of the DE
treatment, 6 plants of each species served as treatment plants and 6 served as controls.

Plants were moved among three glasshouses set at 16, 19, or 22C at 0700 and 1900
HR each day and was completed within 15 minutes. All plants received either a three- or
six-week temperature treatment (experiments 1 and 2, respectively). At the conclusion of

the DE temperature treatment, leaves on geraniums were counted. Flowers or buds that

64

formed during the temperature treatment were removed.
12mm

Disease was assessed 3 times for impatiens and petunia and 4 times for geraniums at
two or three day intervals beginning 4 days aﬂcr inoculation. The occurrence of disease
and sporulation were determined in geraniums by counting the number of affected leaves
on each plant within a treatment and dividing this value by the total number of leaves on
each plant within a treatment. Counting infected leaves for petimia and impatiens was not
feasible because of the high number of leaves. Consequently, a visual assessment of
disease was made.

The area under the disease progress curve (AUDPC) representing the cunmlative
proportion of foliage infected and foliage with sporulating B. cinerea up to a 15-day
period following inoculation was calculated using the method of Shanner and Finney

(1977)

i=1
AUDPC = 2: [(Y... + Y.)/2] [tn - ti]
n

where n = total number of observations, Y,- = cumulative disease expressed as a

proportion at the ith observation, and t,- = time (days) alter inoculation at the ith
observation.

The effects of DE, day temperature, night temperature and day/night interactions were
determined by performing an analysis of variance (AN OVA) of the AUDPC data using the

general linear means procedure of the Statistical Analysis System (SAS, 1988).

65

Results
Geraniums

AUDPC data indicated that the proportion of leaves infected was not inﬂuenced by
DE in experiments 1 or 2 (Table 2) and was quadratically associated with DT (Figure 1)
and NT in experiment 2. In experiment 2 , as DT increased from 16 to 22C with NT of
16C, and as NT increased ﬁ'om 16 to 22C with DT of 16C, the proportion of leaves
infected decreased from 93 to 81% and ranged from 93 to 99%, respectively, 15 days after
inoculation. According to AUDPC data, DT and NT did not inﬂuence the proportion of
leaves infected in experiment 1 (Table 2). As DT increased from 16 to 22C with NT of
16C, and as NT increased from 16 to 22C with DT of 16 C, the proportion of leaves with
sporulating B. cinerea in experiment 1 ranged from 32 to 43% and 25 to 43%,
respectively, 15 days after inoculation.

AUDPC data indicated that the proportion of leaves with sporulating B. cinerea
(Figure 2) was quadratically associated with NT in experiment 2. In experiment 2, as DT
increased ﬁ'om 16 to 22C with NT of 16C, and as NT increased from 16 to 22C with DT
of 16C, the proportion of leaves with sporulating B. cinerea ranged ﬁom 62 to 73% and
73 to 94%, respectively, 15 days after inoculation.

DT and NT did not inﬂuence the proportion of leaves with sporulating B. cinerea in
experiment 1.
2mm

AUDPC data representing the proportion of leaves infected and proportion of leaves

66

with sporulating B. cinerea were not inﬂuenced by DE in experiments 1 or 2 (Table 3).
However, AUDPC data indicated that the proportion of infected and proportion of leaves
with sporulating B. cinerea were linearly and quadratically associated with DT in
experiment 1, and linearly associated with DT in experiment 2. The proportion of leaves
infected was also linearly associated with NT in experiment 2. As DT increased ﬁom 16
to 22C with NT of 16C, infection ranged ﬁom 26 to 53% fourteen days alter inoculation,
and less than 10%, ﬁfteen days after inoculation for experiments 1 and 2, respectively
(Figure 3). As DT increased ﬁ'om 16 to 22C with NT of 16C, sporulation increased from
17 to 43% fourteen days alter inoculation, and was less than 5% ﬁfteen days after
inoculation for experiments 1 and 2, respectively (Figure 3).
Impatiens

AUDPC indicated that the proportion of foliage infected and the proportion of foliage
with sponrlating B. cinerea was not inﬂuenced by DE in experiments 1 or 2 (Table 4).

Disease pressure was low (<14%) in both experiments 13 days after inoculation.

Discussion
DE did not inﬂuence the susceptibility of geranium, petunia, or impatiens foliage to B.
cinerea as measured by infection or sporulation. Although DE causes changes in plant
morphology including plant height, intemode length, and leaf orientation attributable to
elongation of stem parenchyma and stem and leaf epidermal cells (Erwin et a1 1989, 1994),
this study suggests that these changes do not inﬂuence the susceptibility of bedding plants

to B. cinerea. Although this study did not address the effects of varying day and night

67

temperatures on the infectivity of B. cinerea, Sammons et a]. (1982) found no differences
in the incidence on another ﬂoriculture crop when plants were grown rmder split day and
night temperatures.

There were no consistent trends in infection or sporulation among the bedding plants
examined in this study. However, in petunia DT inﬂuenced the infection and sporulation
of B. cinerea in both experiments. The proportion of infected petunia leaves and
proportion of petunia leaves with sporulating B. cinerea was greater in experiment 1 than
in experiment 2. The proportion of geranium leaves infected was much greater than that
of either petunia or impatiens foliage under comparable environmental conditions and time.
These data suggest that more rigorous disease management strategies are needed for
growers producing seed geraniums compared with petimias or impatiens. Suggested
strategies to reduce the amount of crop damage due to B. cinerea include environmental
manipulation, proper plant spacing, scouting, segregation of high risk crops from other
crops, and the efﬁcient use of fungicides. The incorporation of these strategies may
provide more effective control of B. cinerea than fungicide application when high levels of
disease are apparent.

The introduction of contaminated or infected plant material into the greenhouse is a
primary source of inocuhrm introduction (Jarvis, 1992). Growers obtaining preﬁnished
plant material should be aware that B. cinerea may be resident on plant sm'faces in a
dormant phase (Hausbeck and Pennypacker, 1991a). When environmental conditions
become favorable for germination, infections can rapidly establish. Plants are especially

susceptible when foliage becomes dense and the canopy closes. Because air movement is

68

impeded, relative humidity below the canopy is often higher than that above the plant
canopy and provides favorable conditions for disease development (Hausbeck and
Pennypacker, 1991b). A fungicide application prior to canopy closure may prevent
infection. Moorman and Lease (1993) have demonstrated that ﬁrngicidc mixtures can
provide extended control and are more effective than when used seperately.

Rapid increases in disease incidence, such as those seen in geraniums in this research,
can translate to the rapid onset of an epidemic within a crop. Scouting can alert growers
to areas within a crop where infection may already be established, or conditions that may
be occurring that are conducive to disease outbreak, such as ﬁee water present on the
plant surfaces due to condensation from the greenhouse roof Determination of the
incidence of disease within a geranium crop, would also make growers aware of the levels
of inoculum that may be present within greenhouse ranges.

Growers who monitor the environment in their greenhouse ranges can avoid placing
high risk crops, such as geraniums, in ranges where environmental conditions may be
favorable for disease incidence, such as polyhouses that have condensation accurrnrlation
problems and a poor ventilation system Irrigation methods may also need to be modiﬁed
for crops that are highly susceptible. Overhead irrigation of seed geraniums should be
avoided to reduce the amount of freewater introduced onto leaf surfaces. Irrigation
methods such as drip tube or ebb and ﬂood are recommended to reduce the incidence of
water on foliage surfaces and splashing.

Attempting to restrict the area in which high risk crops, such as geraniums, are located

in the greenhouse can reduce the liklihood that the pathogen will come into contact with

69

other plants being grown in the greenhouse. Geraniums should be segregated from other
bedding plants in the greenhouse by keeping them in a designated area within the
greenhouse or in a separate greenhouse. High risk crops should be scouted more
frequently, resulting in earlier detection and removal of infected plant material The
containment of high risk plants may also reduce the amount of ﬁmgicide application
needed on other crops in the greenhouse.

The integration of sanitation, scouting, environmental manipulation, and the eﬂicient
use of fungicides to control disease pests among bedding plants crops can be an effective

safeguard against crop losses due to B. cinerea.

Bibliography

Agricultural Statistics Board. 1994. Floriculture Crops: 1993 Summary. USDA, Natl.
Agric. Stat. Serv., Agric. Stat. Board, Washington, DC.

Bethke, CL. 1986. Growth and developmental responses of hybrid geraniums to light
and temperature. Ph. D. dissertation, Michigan State University.

Carlson, W.H., Kaczperski, MP and Rowley, EM. 1992. Bedding Plants. Pages 511-
550 in: Introduction to Floriculture. Second Ed. RA Larson, Ed. Academic Press, San
Diego.

Dill, Robyn A 1994. State of the industry: Packing a powerﬁrl punch. Greenhouse
Grower. May: 16-36.

Erwin, J ., Velguth, P., and Heins, R 1994. Day/night temperature environment aﬂ‘ect5
cell elongation but not division in Lilium longrﬂorum Thimb. J. of Exp. Bot.
45(276):lOl9-1025.

Erwin, J. E., Heins, RD, Carlson, W. and Newport, S. 1992. Diumal temperature
ﬂuctuations and mechanical manipulation affect plant stem elongation. P. G.R S.A
Quarterly. 20:1-17.

Erwin, J. E., Heins, RD, and Karlsson, MG. 1989. Thermomorphogenesis in Lilium
longiﬂorurn Amer. J. Bot. 76(1): 47-52.

Fonteno, W. C. 1992. Geraniums. Pages 451-475 in: Introduction to Floriculture.
Second Ed. R Larson Ed. Academic Press San Diego.

Hausbeck, M.K and Pennypacker, S.P. 1991a. Inﬂuence of grower activity on
concentrations of airborne conidia of B. cinerea among geranium cuttings. Plant Dis.
75:1236-1243.

Hausbeck, M.K and Pennypacker, S.P. 1991b. Inﬂuence of grower activity and disease
incidence on concentrations of airborne conidia of B. cinerea among geranium stock
plants. Plant Dis. 75:798-803.

Jarvis, W.R 1992. Eliminating Inoculurn Pages 89-132 in: Managing Diseases in
Greenhouse Crops. APS Press, St. Paul

Jarvis, W.R 1980. Epidemiology. Pages 219-250 in: The Biology of Botrytis. J.R

70

71

Coley- Smith, K Verhoeﬂ‘, and W.R Jarvis, eds. Academic Press, London, 318 pp.

Jones, RK and Strider, D.L. 1985. Bedding Plants. Pages 409-422 in: Diseases of
Floral Crops Volume 1. D.L. Strider Ed. Praeger Publishers, New York.

Moe, R, Heins, RD, and Erwin, J. 1991. Stem elongation and ﬂowering of the long-day
plant Campanula isophylla Moretti in response to day and night temperature alternations
and light quality. Scientia Hortic. 48:141-151.

Moorman, G.W. and Lease, RJ. 1992. Benzinridazole and dicarboximide resistant
Botrytis cinerea from Pennsylvania greenhouses. Plant Dis. 76:477—480.

Pommer, Eli. and Lorenz, G. 1982. Resistance of Botrytis cinerea Pers. to
dicarboximide fungicides. A literature review. Crop Prot. 1(2):221-230.

SAS Institute, Inc. SAS/STAT1M Users Guide, Release 6.03 Edition, Cary, NC: SAS
Institute. 1988. PP. 1028.

Sammons, B. Rissler, J.E., and Shanks, IR 1982. Development of gray mold of
poinsettia and powdery mildew ofbegonia and rose under split night temperatures. Plant
Dis. 66:776-777.

Shanner, G. and Finney, RE. 1977. The eﬂ‘ect of nitrogen fertilization on the expression
of slow-mildewing resistance in knox wheat. Phytopathology. 67:1051-1056.

Zieslin, N. and Tsujita, M.J. 1988. Regulation of stem elongation of lilies by temperature
and the effect of gibberellin. Scientia Hortic. 37:165-169.

72

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Figure l. AUDPC values for proportion of 'Ringo' geranium leaves infected with Botrytis

cinerea lS-days aﬁer inoculation at night temperatures of 16 (I), 19 (A), and 22 C(.) in
experiment 2. ‘

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Figure 2. AUDPC values for proportion of 'Ringo' geranium leaves with sporulating
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Figure 3. Proportion of 'Red Dreams' petunia foliage infection (— ) and sporulation (- - - )
with Botrytis cinerea 14-days (experiment 1- - ) and 15-days (experiment 2- C ) aﬁer
inoculation when NT= 16C.

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Appendix

81

Appendix

The Inﬂuence of DIF and Plant Maturity on the Susceptibility

of Wm 'Angelika White' to Botrytis cinerea.

Materials and Methods
ElanLCulm

Eight-week-old 'Angelika White' poinsettias were obtained from a commercial
grower (Snobelt Greenhouse, Kalamazoo, Michigan) on 12 October 1994. Plants were
grown in 15.2-cm (pot volume = 2177 cm’) plastic pots containing a commercial potting
mix (Michigan Grower Products, Galesburg, Michigan). Initial pH of the growing medium
was 6.10. Plants were spaced 13 cm apart on 2.7 x 0.9 x 0.06 m aluminum benches in 4.8
x 4.2 m research glass greenhouses at Michigan State University.

Plants were watered as needed using ebb and ﬂood irrigation with benches ﬂooded
for 2 minutes. Using a Volmatic AMI 1000 injector, 9 liters of fertilizer stock solution
containing 50% 10103 + Compon 111, 25% NIL N03, and 25% CaNO3 and 2 liters of
acid stock solution containing 50% phosphoric acid and 50% sulfuric acid were mixed with
81 liters of water was applied at each irrigation. The pH of the irrigation water was
maintained at 5.8. The pH of the water was maintained at 5.8.

Glasshouse temperatures were maintained at 17 and 22C using a climate-control
computer and monitored by a datalogger (Campbell Scientiﬁc, Inc., Logan, Utah) with

thermocouples. Thermocouple readings were recorded every minute and averaged every

82
15 minutes. Actual temperatures during the experiment did not vary from the settings by

more than a maximum of 1.3C (Table 1). Light levels were natural photoperiods.

Table 1. Temperature settings and actual average day and night temperatures (DT and

NT, respectively) with standard deviations for all environmental treatments for poinsettia

 

 

 

 

 

 

 

experiment, 1994.
DT Setting (C)

NT

Setting (C) 22 17
Actual temperature (DT/NT)

22 22.2 : 0.6/22.2 : 0.6 17.4 i 1.3/22.2 : 0.6

17 22.2 i 0.6/17.31 1.2 17.4 : l.3/l7.3 i 1.2
Inornlumhenaratinn

Botrytis cinerea was isolated from infected geranium tissue and grown on 20 ml of
potato dextrose agar in lO-cm-diameter petri plates at 25C for approximately 13 days. A
conidial suspension was prepared by ﬂooding plates with sterilized, distilled water and

dislodging conidia using a glass rod. Conidia concentrations were quantiﬁed using a

83

hemocytometer and adjusted to an average 2.5 x 10 5 conidia/ml Tween 20 (0.04%) was
added to the suspension just before spraying.

When a majority of the plants assigned to a temperature treatment attained the
desired stage of maturity, all plants in the treatment were inoculated. Plants were
inoculated on 7, 20, 22, 23, 28, 29 November and 1, 4, 7 December 1994 by spraying
them with the conidial suspension until runoff using a Prevail pressurized atomizer
(Precision Valve Corp., Yonkers, New York). Control plants were sprayed with sterile
distilled water. Each plant was placed in a 53 x 14 x 96 cm plastic bag with a ISO-ml cup
of distilled water to assure constant high RH. Bags were sealed and placed on aluminum
benches 86 cm above the ﬂoor in a walk-in chamber maintained at 20C 3: 1C with a 12-
hour photoperiod provided by high-pressure sodium lights.
W

Four day/night temperature combinations (zero DIF = 22/22, 17/17; positive

DIF = 22/17; and negative DIF = 17/22) and 3 maturity levels (preanthesis, anthesis, and

postanthesis) were investigated. The experimental design was completely randomized with
5 inoculated and 5 uninoculated plants per treatment.

Plants were moved between two controlled-environment glasshouses set at 17 or
22C at 0700 and 1900 HR each day until they reached anthesis or postanthesis. Plant
movement was completed in 10 minutes. Anthesis was deﬁned as pollen shed, pistil
emergence and separation, and yellowing of the nectary. Postanthesis was deﬁned as the
ﬁﬂh day following anthesis. When plants reached the desired maturity, bracts expressing

at least 90% coloration were counted on each plant.

84
W

Within each treatment, disease was assessed 4 times at two or three day intervals
beginning 2 days aﬁer inoculation by calculating the percentage of bracts infected and
supporting sporulation. Severity of disease was assessed using the rating scale used in the
1993 poinsettia DIF experiment.

Rating values were used to calculate a disease progress curve for each DIF
treatment. The area under the disease progress curve (AUDPC) was used to represent the
quantitative descriptor of a disease epidemic over time (Shanner and Finney, 1977). To
express the cumulative incidence of bract infection and sporulation, AUDPC values were

calculated using the formula

n- 1
AUDPC = 2 [(Yi+1 + Yi)/2] [ti+1 " ti]
1
where n is the total number of times observations were made, Y,- is the cumulative disease
incidence expressed as a proportion of the ith observation, and t,- is the time (in days after
inoculation) at the ith observation. The AUDPC data were analyzed using a protocol of the
Statistical Analysis System (SAS, 1988).
Results
Bract infection among all contrasts examined were non signiﬁcant with the exception
of the comparison between anthesis with preanthesis (P=.0422). Bract sporulation was
statistically signiﬁcant in comparisons between +/- DIF anthesis vs. post anthesis, + DIF vs.
- DIF at anthesis, +DIF vs. -DIF at post anthesis, anthesis vs. postanthesis trmts, and 0 DIF

22 vs. 17 preanthesis.

85
Bibliography

SAS Institute, Inc. SAS/STAT1M Users Guide. Release 6.03 Edition, Cary, NC: SAS
Institute. 1988. PP. 1028.

Shanner, G. and Finney, RE. 1977. The eﬂ‘ect of nitrogen fertilization on the expression
of slow-mildewing resistance in knox wheat. Phytopathology. 67: 1051-1056.

86

Table 2. Inﬂuence of plant maturity on bract infection and sporulation incidence of Botrytis
cinerea on W 'Angelika White'.

 

 

Bract Infection Bract Sporulation
Contrast Incidence Incidence
Pr > F
anthesis vs post anthesis 0.4237 0.0001
+ DIF vs - DIF 0.3847 0.6464
+ DIF vs - DIF at anthesis 0.2858 0.0555
+ DIF vs - DIF at post anthesis 0.8726 0.0119
0 DIF preanthesis vs anthesis 0.5815 0.5448
anthesis vs preanthesis 0.0422 0.0955
anthesis vs postanthesis 0.0824 0.0002
0 DIF 22 vs 17 preanthesis 0.5326 0.0096
22 vs 17 anthesis 0.9877 0.2565

 

 

87

Table 3. Means and standard deviations of bract infection and sporulation incidence of
Botrytis cinerea on W 'Angelika White'.

 

 

 

----- Inﬂuence on Infection ----- ---Inﬂuence on Sporulation ---
Treatment Mean Standard Deviation Mean Standard Deviation
1 502.78 71.11 111.90 49.78
2 539.22 25.82 169.50 16.93
3 729.60 15.77 332.02 20.34
4 593.76 5.54 176.04 31.09
5 580.16 11.22 99.68 42.65
6 523.12 136.55 177.44 63.84
7 566.26 17.73 147.20 14.41
8 425.28 56.64 52.06 28.47
9 558.84 11.39 115.56 27.40
10 579.82 10.45 102.12 44.85
11 525.40 39.59 141.20 20.22
12 525.90 36.28 169.08 58.77
Treatments:

1 = preanthesis, zero DIF, 22C DT/22C NT

2 = anthesis, +5 DIF, 22C DT/17C NT, from 22/22 house

3 = anthesis, -5 DIF, 17C DT/22C NT, from 22/22 house

4 = 5-days postanthesis, +5 DIF, 22C DT/17C NT, from 22/22 house
5 = 5-days postanthesis, -5 DIF, 17C DT/22C NT, ﬁom 22/22 house
6 = preanthesis, 0 DIF, 17C DT/17C NT

7 = anthesis, +5 DIF, 22C DT/17C NT, from 17/ 17 house

8 = anthesis, -5 DIF, 17C DT/22C NT, ﬁom ”/17 house

9 = 5-days postanthesis, +5 DIF, 22C DT/17C NT, ﬁ'om 17/ 17 house
10 = S-days postanthesis, -5 DIF, 17C DT/22C NT, ﬁ'om 17/ 17 house
11 = anthesis, 0 DIF, 22C DT/22C NT

12 = anthesis, 0 DIF, 17C DT/17C NT

88

Figure 1. Relationship between thermal time and disease incidence of Botrytis cinerea on
Eughorbia mlgherrimg 'Angelika White' bracts when receiving positive, negative, and zero
DIF treatments and inoculated at preanthesis, anthesis, and 5-days postanthesis.

Treatments include:

1 = preanthesis, zero DIF, 22C DT/22C NT

2 = anthesis, +5 DIF, 22C DT/17C NT, from 22/22 house

3 = anthesis, -5 DIF, 17C DT/22C NT, from 22/22 house

4 = S-days postanthesis, +5 DIF, 22C DT/17C NT, ﬁ'om 22/22 house
5 = 5-days postanthesis, -5 DIF, 17C DT/22C NT, ﬁom 22/22 house
6 = preanthesis, 0 DIF, 17C DT/17C NT

7 = anthesis, +5 DIF, 22C DT/17C NT, from 17/17 house

8 = anthesis, -5 DIF, 17C DT/22C NT, from 17/17 house

9 = 5-days postanthesis, +5 DIF, 22C DT/17C NT, from 17/17 house
10 = 5-days postanthesis, -5 DIF, 17C DT/22C NT, from 17/17 house
11 = anthesis, 0 DIF, 22C DT/22C NT

12 = anthesis, 0 DIF, 17C DT/17C NT

89

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