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CoA L. BACTERIAL BLIGHT OF FOLIAGE PLANTS
CAUSED BY PSEUDOMONAS CICHORII
A. R. Chase
IFAS, University of Florida
Agricultural Research Center Apopka
ARC-A Research Report RH-84-2
Many bacterial pathogens in the genera Erwinia, Agrobacterium,
Xanthomonas and Pseudomonas cause losses in the foliage plant industry.
During the past year, many new bacterial diseases have been described.
The purpose of this report is to review the diseases caused by one
bacterial pathogen: Pseudomonas cichorii.
Pseudomonas cichorii was first described as a pathogen of Cichorium
endivia (endive or escarole) from which the scientific name of the path-
ogen is derived. Other vegetables found to be hosts of this pathogen
include Brassica oleracea (cabbage) (8), Apium graveolens (celery) (7)
and Lactuca sativa (lettuce) (3), with many of the original reports made
from Florida or California. In addition to reports on these vegetables,
many ornamental plants were identified as hosts of P. cichorii. One of
the first serious outbreaks of P. cichorii in ornamentals occurred in
Florida on Chrysanthemum morifoTium (florist's chrysanthemum) in the
early 1960's (5). Since that time other flowering and many foliage
plants have been added to the list of P. cichorii susceptible plants
Bacterial leaf spot of Araceae, described in 1966 (9), is character-
ized by round to irregularly shaped spots of varying sizes which are
scattered across the leaf surface. Many lesions begin at the edge of the
leaf where the bacterium enters wounds or hydathodes. Lesions are generally
very dark, enlarge rapidly and are water-soaked. Inactive lesions may be
tan to medium brown and papery, while most active lesions are black and
wet. Infection is favored by high moisture (relative humidities and free
water on the leaf surface). Cuttings in mist areas are most easily in-
fected. On some hosts, such as Schefflera arboricola, leaflet abscission
occurs. Lesions may enlarge until the entire leaflet or leaf is affected,
sometimes only 3 4 days after infection (1). Sometimes the lesions are
surrounded by a chlorotic margin or halo. Temperatures near 75 80 F
appear to favor disease development on foliage plants. Wounding which occurs
when plants are handled roughly further increases the severity of bacterial
Studies on geranium showed that while bactericides decreased severity
of disease, they did not eliminate its occurrence. Kocide 404S (contains
sulfur) provided the best control of P. cichorii with Kocide 101 77W and
combinations of copper and mancozeb also moderately effective (2). The
best control method involves avoidance of the disease which can be accom-
plished using the following methods: 1) use pathogen-free plants; 2) grow
on raised benches in enclosed structures; and 3) avoid overhead watering.
The table has been provided as a summary of the known hosts of P. cichorii.
Since the isolates of the bacterium do not show any host specificity, an
outbreak on chrysanthemum could easily spread to schefflera, Transvaal
daisy or any other host in the same growing area.
1. Chase, A. R., and D. D. Brunk. 1984. Bacterial
Schefflera arboricola and some related plants,
cichorii. Plant Disease 68:73-74.
leaf blight of
incited by Pseudomonas
2. Engelhard, A. W., H. C. Mellinger, R. C. Ploetz, and J. W. Miller.
1983. A leaf spot of florist's geranium incited by Pseudomonas cichorii.
Plant Disease 67:541-544.
3. Grogan, R. G., I. J.
and R. Bardin. 1977.
California caused by
Misaghi, K. A. Kimble, A. S. Greathead, D. Ririe,
Varnish spot, a destructive disease'of lettuce in
Pseudomonas cichorii. Phytopathology 67:957-960.
4. Jones, J. B., A. W. Engelhard, and B. C. Raju. 1983. Outbreak of a
stem necrosis on Chrysanthemum incited by Pseudomonas cichorii in
Florida. Plant Disease 67:431-433.
5. McFadden, L. A. 1961. A bacterial leaf spot of florist's chrysanthemum,
Chrysanthemum morifolium. Plant Disease Reporter 45:16-19.
6. Miller, J. W., and J. F. Knauss. 1973. Bacterial blight of Gerbera
jamesonii incited by Pseuddmonas cichorii. Plant Disease Reporter 57:
7. Thayer, P. L., and C. Wehlburg. 1965. Pseudomonas cichorii, the cause of
bacterial blight of celery in the Everglades. Phytopathology 55:555-557.
C. 1963. A bacterial spot of cabbage caused by Pseudomonas
Proc. Fla. State Hort. Soc. 76:119-122.
9. Wehlburg, C., C. P. Seymour, and R. E. Stall. 1966. Leaf spot of Araceae
caused by Pseudomonas cichorii (Swingle) Stapp. Proc. Fla. State Hort.
Table 1. Hosts of Pseudomonas cichorii.