A Flower Blight of Euphorbia milii Caused by Amphobotrytis ricin

Comments

Transcription

A Flower Blight of Euphorbia milii Caused by Amphobotrytis ricin
Table 5. Experiment IV. Effect of hot water treatments on root-knot nematodes and plant growth, 15 May 2000. Treated tubers were planted into
nematode-free soil 19 October 1999.
Nematodes
Plant
per
fresh weight
be carefully monitored to ensure a constant temperature of
sterilized soil
tuber
(g)
50°C to avoid plant damage and ensure complete control of
nematodes. Caladium tubers infested with root-knot nema
todes, when used to propagate another generation of plants,
0.00 a
0.00 a
50.22 a
0.00 a
0.00 a
35.97 a
0.00 a
0.00 a
42.67 a
38.00 b
4.50 b
7.77 b
Mean
development. The temperature of the hot water bath should
Nematodes
per 100 cm3
52°C 20 min
Control
treatments at temperatures greater than 50°C, using shorter
time intervals were not compatible with caladium growth and
50°C 30 min
54°C 10 min
and did not impede plant development or growth. Hot-water
1.12
9.50
34.15
Data are means of six replications.
Means in columns followed by the same letter do not differ at P < 0.01.
offset costly soil treatments, and treated tubers produce great
er quantities of foliage and larger tubers. When harvested
from root-knot infested fields, caladium tubers should be
treated before replanting to avoid nematode transmission
and plant damage.
Literature Cited
Discussion
Esser, R. P. 1973. Nematodes associated with caladium in Florida. Plant Dis.
Reptr. 57:558-560.
The results of the last experiment indicate that root-knot
nematodes survive on untreated tubers and interfere with
plant performance when propagated into nematode-free
soils. Root-knot nematodes were not found in soils that were
previously steam-pasteurized and planted with treated tubers,
and nematodes were not found on the treated tubers after sev
eral months of growth. Tubers that received a treatment also
produced more fresh plant mass in the nematode-free soil.
Rhoades (1964) reported a slight delay in caladium emer
gence when tubers were subjected to a treatment, but also ob
served improved plant growth and increased tuber size in
treated plants at the end of the growing season. The caladium
tubers that received a 50°C treatment in experiment I were
not statistically different from the control, but did emerge an
average of three days faster than the control. However, emer
gence and leaf development was significantly delayed in caladiums that received a treatment greater than 50°C.
Immersion of tubers in a temperature-controlled water
bath at 50°C for 30 min successfully eradicated nematodes
Freed, R., S. P. Eisensmith, S. Goetz, D. Reicosky, V. W. Smail and P. Wolberg.
1991. User's guide to MSTAT-C. Michigan State University, East Lansing, MI.
Hussey, R. S. and K. R. Barker. 1973. A comparison of methods of collecting
inocula of Meloidogyne spp., including a new technique. Plant Dis. Reptr.
57:1025-1028.
Jenkins, W. R. 1964. A rapid centrifugal-flotation technique for separating
nematodes from soil. PL Dis. Reptr. 48:692.
McSorley, R., R. T. McMillan, Jr. andj. L. Parrado. 1984. Meloidogyne incognita
on society garlic and its control. Plant Disease 68:166-167.
McSorley, R. andJ.J. Frederick. 1994. Response of some common annual bed
ding plants to three species of Meloidogyne. Suppl. J. Nematol. 26:773-777.
McSorley, R.,J. J. Frederick and R.J. McGovern. 1999. Extraction of Meloid
ogyne incognita from caladium corms. Nematropica 29:245-248.
Rhoades, H. L. 1961. Preliminary studies on eradication of root-knot in cala
dium tubers. Proc. Fla. State Hort. Soc. 74:393-397.
Rhoades, H. L. 1964. Effect of hot water treatment of seed tubers and soil fu
migation for control of root-knot on yield of caladiums. Plant Dis. Reptr.
48:568-571.
Rodriguez-Kabana, R., and M. H. Pope. 1981. A simple incubation method
for the extraction of nematodes from soil. Nematropica 11:175-185.
Tayolr, A. L. and J. N. Sasser. 1978. Biology, identification, and control of
root-knot nematodes (Meloidogynespecies). North Carolina State Univer
sity Graphics, Raleigh, NC.
Proc. Fla. State Hort. Soc. 113:161-165. 2000.
A FLOWER BLIGHT OF EUPHORBIA M/L//CAUSED BY AMPHOBOTRYTIS RICINI
R. T. McMillan, Jr., L. I. Acosta and W. R. Graves
University of Florida
Tropical Research and Education Center
Homestead, FL 33031
Additional index words. Flower blight, Super grandiflorum,
Euphorbia milii, Amphobotrytis ricini, Sclerotinia ricini.
Abstract. The purpose of this study was to confirm whether or
not Amphobotrytis ricini was a pathological agent on Euphor
bia milii by following the guidelines of Koch's postulates. It
was hypothesized that A. ricini does infect E. milii, as it has
been found on other plants of the Euphorbia genus. Lesions
with few to many brownish specks on expanding petals en-
Florida Agricultural Experiment Station Journal Series No. N-01971.
Proc. Fla. State Hort. Soc. 113: 2000.
large until the whole flower turns brown and drops. Cultured
Amphobotrytis ricini on potato dextrose agar is characterized
by elongated Sclerotia usually 3-9 mm. long and occasionally
up to 2.5 cm. The conidiophores were much branched, dichotomously with spherical, 6-12 (mostly 7-1 Oji) diameter conidia
and consistently isolated from diseased tissue plated on cornmeal agar. In initial tests, fully opened flowers were inoculated
by dipping a cotton swab into a conidia rich A. ricini culture
that was cultured on potato dextrose agar. Inoculated and noninoculated flowering plants were placed in plastic bags and
held at room temperature in the laboratory for 48 hrs. The in
oculated and non-inoculated plants in the plastic bags were
moved to a greenhouse and held at a day temperature of 27 C
and a night temperature of 20 C. Each treatment consisted of
five inoculated and five non-inoculated plants. After 48 hrs the
plants were removed from the plastic bags and observed for
flower blight symptoms. The lesions were visible within 8 days
after inoculations and were over 25 mm in diameter in 10 days.
161
Progression of flower blight was very fast at the ambient tem
peratures of the greenhouse. Controls remained symptomless.
Amphobotrytis r/c/7?/was reisolated from infected flowers.
The fungus Amphobotrytis ricini was first found in a small
nursery in south Florida on January 19,1999. The nursery had
a small number of a new cultivar of Euphorbia milii that had
been imported from Asia. The nursery person mentioned
that she was having a flower blight problem. The isolated or
ganism from the flowers appeared to be Botrytis ricini as de
scribed by Ellis (Ellis, 1971). The isolated fungus was sent to
the Florida Department of Agriculture, Division of Plant In
dustry and subsequently identified as Amphobotrytis ricini by
Dr. T. Schubert. In south Florida A. ricini occurs on suscepti
ble Euphorbia during the wet warm summer months. Recently,
Amphobotrytis ricini was found on the flowers of commercial
nursery potted E. milli cultivar Super grandiflorum.
The disease flower blight on Super grandiflorum oc
curred as a severe blight in several nurseries, affecting 10 to
25% of the potted nursery stock during periods of heavy irri
Figure 1. Naturally infected Euphorbia milii nursery grown flowers from
which the original Amphobotrytis ricini culture was isolated.
gation from January through May of 1999. The fungus Sclero-
tinia ricini Godgrey with A. ricini as its anamorph was first
reported in 1919 (Ellis, 1971). Since then it has been ob
er blight was very fast at the ambient temperatures of the
served in Brazil, Bulgaria, Ghana, Jamaica, Malawi, Nigeria,
greenhouse. Controls remained symptomless (Fig. 6). Ampho
Rhodesia and Sierra Leone.
botrytis ricini was reisolated from infected flowers consistently.
In the U.S. the fungus occurs mostly on Ricinus but it also
Cultures of A. ricini on PDA were characterized by elon
occurs on species of Acalypha, Euphorbia, and Phyllanthus as
gated sclerotia, 3-9 mm long, occasionally up to 2.5 cm (Fig.
well as Ricinus in those countries listed above. (Ellis, 1971).
10). The conidiophores were much branched, dichotomously
Grades and standard reduction resulted from severe flow
er blight. This epiphytotic occurred during an abnormal pe
riod of excessive rainfall and high temperatures.
The purpose of this research was to confirm whether or
not A. ricini was a pathological agent on E. milii by following
the guidelines of Koch's postulates.
Materials and Methods
A culture of A. ricini originally isolated from naturally in
fected E. milii (Fig. 1) on Difico corn meal agar (CMA) and
transferred periodically on Difico potato-dextrose agar
(PDA) and maintained at 25°C. This isolate was employed
throughout this study.
All inoculations were accomplished by inoculating 30 mm
rooted cuttings of E. milii with fully opened flowers potted in
30 mm pots. The fully opened flowers of the test plants were
inoculated (Fig. 2) by dipping a cotton swab into a conidia
rich A. ricini culture that was cultured on PDA. Inoculated
and non-inoculated control flowering plants were placed in
plastic bags to maintain a high humidity and held at ambient
room temperature for 48 hrs (Fig. 3). The inoculated and
non-inoculated control plants in the plastic bags were moved
m&.
to a greenhouse and held at a day temperature of 80F and a
night temperature of 68F (Fig. 4). Each treatment consisted
of five inoculated and five non-inoculated control plants. Af
ter 48 hrs the plants were removed from the plastic bags and
observed for flower blight symptoms (Fig. 5).
Results and Discussion
All of the inoculated Super grandiflorum (E. milii) plants
developed symptoms and signs of A. ricini (Table 1). The flow
er lesions were visible within 8 days after inoculations and were
over 25 mm in diameter in 10 days (Fig. 7) Progression of flow162
Figure 2. All inoculations were accomplished by inoculating 30 mm root
ed cuttings of Euphorbia milii with fully opened flowers potted in 30 mm pots.
The fully opened flowers of the test plants were inoculated by dipping a cot
ton swab into a conidia rich Amphobotrytis ricini culture that was cultured on
potato dextrose agar.
Proc. Fla. State Hort. Soc. 113: 2000.
Figure 3. Inoculated and non-inoculated control flowering plants were
placed in plastic bags to maintain a high humidity and held at ambient room
temperature for 48 hrs.
Figure 5. After 48 hrs the plants were removed from the plastic bags and
observed for flower blight symptoms.
Figure 4. The inoculated and non-inoculated control plants in plastic
bags were moved to a green house and held at a day temperature of 26°C and
a night temperature of 20°C for 48 hrs. Note the high humidity maintained
in the plastic bag acting as a dew chamber.
Proc. Fla. State Hort. Soc. 113: 2000.
Figure 6. All of the Euphorbia milii non-inoculated controls remained
symptomless.
163
Table 1. Pathogenisity of Amphobotrytis ricini on Euphorbia milii.
Treatment
Number of
Number of
Plants
Infected Plants
Non-Inoculated (Control)
Inoculated
with spherical, 6-12 (mostly 7-10)|H diameter conidia (Ellis,
1971) (Figs. 8 and 9) and consistently isolated from diseased
tissue plated on CMA.
This study documents symptoms associated with infection
by A. ricini in potted plants grown in a commercial shadehouse in south Florida.
In the absence of diagnostic symptoms, potted plants in
fected with A. ricini may escape detection at the wholesale shadehouses. The stress plants may undergo at the retail centers
can prompt further symptom development. The retail outlets
are run mainly by sales personnel who more than likely would
not recognize obvious symptoms associated with plants infect
ed by A. ricini. Thus, A. ricini may spread by the wind or splash
ing rain to other susceptible potted Euphorbia plants.
Figure 8. Amphobolrytis ricini culture showing conidiophores with spheri
cal, 6-12 (mostly 7-10(1) diameter conidia.
Figure 7. The flower lesions were visible within 8 days after inoculation
and were over 25 mm in diameter in 10 days.
164
Figure 9. The conidiophores of Amphobotrytis ricini are much branched,
dichotomously.
Proc. Fla. State Hort. Soc. 113: 2000.
In summary, the results of this study provide information
to nursery producers, extension agents and nursery inspectors
on the symptoms associated with A. ricini infection of E. milii
The awareness of A. ricini in E. milii in bedding plant nursery
will assist in reducing the spread of this fungus through retail
garden stores to the public growers.
Literature Cited
Ellis, M. B. 1971. Dematiaceous Hyphomycetes. Commonwealth Mycological
Institute, Kew, Surrey, England. M. F. Clark and A. N. Adams. 1971.
Figure 10. The Amphobotrytis state of Sclerotinia ricini showing elongated
sclerotia, 3-9 mm long, occasionally up to 2.5 cm.
Proc. Fla. State Hort. Soc. 113:165-169. 2000.
A PEER REVIEWED PAPER
RESPONSE OF SPATHIPHYLLUM CULTIVARS TO CHILLING TEMPERATURES
L. Qu, J. Chen* R. J. Henny, C. A. Robinson,
R. D. Caldwell and Y. Huang
University of Florida, IFAS
Mid-Florida Research and Education Center
2725 Binion Road
Apopka, FL 32703
Additional index words. Chilling injury, foliage plants, peace lily.
Abstract. The response of 15 Spathiphyllum cultivars after 2, 5
or 10 days of exposure to chilling temperatures of 3.3, 7.2,10
or 11.1 C was evaluated using rooted three-month old tissue
culture derived plants. Chilling injury at 3.3 and 7.2 C varied
among cultivars from slight leaf necrosis to plant death;
younger leaves were more resistant to chilling than older ones
with the exception of one cultivar. At 10 or 11.1 C, no visible
tissue breakdown occurred. However, small growth indices
and low quality ratings were indicative of otherwise invisible
injury at these temperatures. Such invisible injury could be
wrongly diagnosed as insufficient fertilization or other improp
er cultural practices. These findings suggest that genetic dif
ferences in chilling resistance exist among Spathiphyllum
cultivars and can be used as a basis for cultivar selection.
The genus Spathiphyllum includes 36 species of evergreen
rhizomatous perennials, commonly called peace lily, origi
nates from tropical forest habitats (Huxley, 1994). Because of
its elegant white or creamy spathes and deep green foliage,
Florida Agricultural Experiment Station Journal Series No. R-07717.
*Corresponding author.
Proc. Fla. State Hort. Soc. 113: 2000.
Spathiphyllum has become one of the most popular foliage
plants in the ornamental industry. Ranked as a top-seller in
the market, there are currently more than 50 species and/or
cultivars produced in Florida.
Due to its tropical rain forest origin, Spathiphyllum is natu
rally sensitive to chilling temperatures (2-10°C, as defined by
Lycons, 1973). Marousky (1980) found that a one-day expo
sure of Spathiphyllum 'Clevelandii' to 10°C resulted in notice
able leaf injury characterized by necrotic patches along leaf
margins. Chilling injury can cause severe losses in production
if heating systems are not available during winter and early
spring in Florida. Chilling injury may also occur during Spath
iphyllum shipment, retail display and interior decoration.
Since Spathiphyllum is grown for its aesthetic appearance, any
damage on leaves or flowers could greatly reduce its orna
mental value in the market place.
In an attempt to improve the resistance of foliage plants
to chilling, we have been exploiting the genetic potentials of
existing cultivars to chilling through a systematic evaluation.
Previously, we were able to identify Aglaonema cultivars that
can withstand 1.7°C, whereas sensitive ones were injured at
12°C (Henley et al., 1998; Chen et al., 1998). Resistant culti
vars are important not only to growers in production, but also
have been incorporated into our research program for cultivar improvement.
So far, no report has addressed cultivar differences of
Spathiphyllum in resistance to chilling temperatures and no re
sistant cultivars have been identified. The objectives of this
study were to evaluate cultivar responses to chilling and iden
tify resistant ones for the industry and for our subsequent
breeding program.
165

Similar documents