The publications in this collection do
not reflect current scientific knowledge
or recommendations. These texts
represent the historic publishing
record of the Institute for Food and
Agricultural Sciences and should be
used only to trace the historic work of
the Institute and its staff. Current IFAS
research may be found on the
Electronic Data Information Source
site maintained by the Florida
Cooperative Extension Service.
Copyright 2005, Board of Trustees, University
RHIZOPUS BLIGHT OF-ORNAMENTAL CROPS IN FLORIDA
A. R. Chase and A. W. Engelhard1
University of Florida, IFAS
Agricultural Research and Education CenteyUi~JE L'BR RY
AREC-A Research Report RH-84-15
During the past several years in Florida,.poinsettia (EPnioAria-03
pulcherrima Willd.), crown-of-thorns (Euphorbia milii ;h. des Moulins),
gerbera daisy (Gerbera jamesonii Bolus) and crossandra pAr an v. of Florida
infundibuliformis (L.) Nees) plants were affected by a rel at4ve4y-uncommon -.---
disease, Rhizopus blight. This disease is caused by the fungus Rhizopus
stolonifera [(Ehrenb. ex Fr.) Lind.]. The name R. stolonifera is
synonomous with R. nigricans, and is the preferred name (2).
Occurrence of Rhizopus blight in Florida
Thousands of poinsettia cuttings under mist propagation were killed
in July, 1982, by Rhizopus blight. Observations indicated the cultivars
V-14 Glory and V-14 White were especially susceptible while Annette Hegg
cultivars were less susceptible. In one nursery, potted poinsettia plant- -
in a glasshouse were affected in the fall of 1982, potted gerbera daisy
plants in the fall of 1983, and potted crown-of-thorns and crossandra
plants were affected in a glasshouse during the 1983-84 winter.
In all cases of Rhizopus blight, flowers, leaves and stems were
infected by the pathogen. On flowers, a mass of white mycelium grew as a
dense spider web over the tissue. The black fruiting bodies (sporangia)
of the fungus formed very quickly and appeared as specks of pepper or sand
caught in a mass of cotton. Mycelia spread from infected flowers down stems
and into plant crowns, causing a soft, mushy brown rot which eventually
killed the plants. Tissue isolations made from infected plants and micro-
scopic examinations revealed the presence of the pathogen, R. stolonifera.
Poinsettia plants were included in one inoculation test and poinsettia,
crossandra, crown-of-thorns and gerbera plants in another. Plants were
inoculated with spores of R. stolonifera and in each case typical disease
symptoms developed with infection starting in the flowers. The pathogen was
re-isolated from the diseased plants.
Rhizopus on Ornamentals
Rhizopus stolonifera has been reported as a pathogen on flowers and
foliage of ornamental plants. Rhizopus stolonifera caused a soft rot of the
fleshy Euphorbia trigona (African milk tree or Abyssinian Euphorbia) in
California in 1978 (3). The authors also found three other fleshy species
of Euphorbia, E. lactea, E. mammilaris, and E. leuconeura susceptible but
the woody E. nvula and E. tirucalii were resistant. It is of interest that
two of the susceptible plants reported herein, poinsettia and crown-of-thorns,
are fleshy members of the family Euphorbiaceae also.
1Associate Professor, Plant Pathology, Agricultural Research and Education
Center, 2807 Binion Road, Apopka, FL 32703; Professor of Plant Pathology,
Gulf Coast Research and Education Center, Bradenton, FL 33508, respectively.
Rhizopus stolonifera, common bread mold, is a well known post harvest
and storage pathogen of fruits, vegetables and flower bulbs (4,5,6) and a
reported pathogen of poinsettia (1) and other species of Euphorbia (3).
Rhizopus is a fast growing pathogen when the temperature is in the
21-32C (70-900F) range. The white mycelia grow prolifically and rapidly
over infected tissue. Long sporangiophores develop in abundance over the
mycelium giving the appearance of whiskers on the mycelial growth. A mass
of spores develops in a blackhead at the top of each sporangiophore. The
spores are windborne or splashed about by water. Wounds on vegetables and
bulb crops have been shown to increase susceptibility to this disease (5).
Control of this disease may be aided by maintaining optimal temperature,
nutrition and humidity for growth of the plants. Engelhard (1) suggested
this pathogen may be an opportunistic organism that attacks physiologically
old plants or ones growing under unfavorable conditions. Poinsettia plants
in one experiment were inoculated with another pathogen, bagged and held at
16, 21, 27, and 320C (60, 70, 80 and 900F), respectively. The plants held
at 320C (900F) were chlorotic, grew poorly, and were the only plants which
showed symptoms of Rhizopus blight, apparently due to a natural infection.
Control of disease on Euphorbias in California (2) was suggested by manipu-
lating temperature since the pathogen did not infect plants grown above 320C
Although several fungicides are effective in controlling Rhizopus rot
on harvested stone fruits, none are currently labelled for use on ornamental
crops and no recommendations can be made. The fungicide dicloran (BotraiW
or AllisanI) is sold for use in the stone fruit industry to control post
harvest decay caused by Rhizopus spp. Mixtures of dicloran and benomyl
(Benlated) were very effective in disease control of Rhizopus rot on sweet
cherries in California (6) and could prove effective on ornamentals as well.
1. Engelhard, A. W. 1982. Poinsettia diseases and their control. Bradenton
AREC Research Report, B R A 1982-21, 13 pp.
2. Johnston, A., and C. Booth. 1983. Ed. Plant Pathologist's Pocketbook.
Second Edition. Commonwealth Mycol. Inst., 439 pp.
3. Mulrean, E. N., and A. M. McCain. 1979. A soft rot of Euphorbia trigona
caused by Rhizopus stolonifera. Phytopathology 69:1049. Abstr.
4. U.S.D.A. 1960. Index of plant diseases in the United States. Agric.
Handbook No. 165, 531 pp.
5. U.S.D.A. 1953. Plant diseases the yearbook of agriculture, 940 pp.
U.S. Government Printing Office.
6. Wilson, E. E., and J. M. Ogawa. 1979. Fungal, bacterial, and certain
non parasitic diseases of fruit and nut crops in California. Regents
of the University of California, Berkeley, 190 pp.