Bacterial Speck Causing Larger Lesions
The Tomato Magazine
The bacterial speck pathogen this past spring was associated with much
larger lesions on tomatoes in Florida than has been observed in the past,
according to Jeffrey B. Jones with the University of Florida/IFAS Plant
Pathology Department in Gainesville.
Speaking during the annual Florida Tomato Institute last September in
Naples, Fla., Jones noted the change, indicating that all strains to
date have been identified to be race O (Race 0 is the typical race that
was originally present. The fruit size is not a result of the race change).
In Florida, bacterial spot is considered the most destructive bacterial
disease when high temperatures are accompanied with excessive moisture,
Jones told the group. Bacterial leaf spots associated with tomato have
primarily been bacterial spot incited by Xanthomonas campestris pv. vesicatoria
and bacterial speck incited by Pseudomonas syringae pv. tomato.
Bacterial spot is considered a warm weather pathogen and thus in the
spring is not as aggressive as in the fall, the researcher pointed out.
Hence, bacterial leaf spot in Florida is not a significant concern to
spring crops of tomato because of typically drier weather then.
Likes Cool Weather Conditions
Bacterial speck, however, is favored by relatively cool weather conditions
such as occurred in Florida tomato fields in the spring of 2005, Jones
said. Therefore, it was considered “the more likely candidate” to
be associated with a spring epidemic.
“Bacterial speck has been a problem in Florida tomato production during
periods of significant rainfall during spring production,” Jones
said, adding that one such period was 1983, when bacterial speck proved
a major problem in a spring tomato crop in several fields in Manatee
County. That particular year was cool and extremely wet.
In the past, bacterial speck has been a chronic problem in the Homestead
area during winter tomato production, he said. Researchers, however,
attribute much of the problem to the use of overhead irrigation.
Looking at the 2005 spring crop, Jones said Florida weather conditions
were “unusually wet,” and, hence, were conducive for bacterial
“A number of fields were affected by what was thought to be bacterial
leaf spot,” he said. “The fruit was also affected and was
unusual in appearance. The lesions were large, sunken and distinctly
black. They resembled bacterial speck more than bacterial spot, although
the lesions were atypical in their rather large size (Figure 1a) unlike
the ‘speck’ size lesions normally observed on the fruit.
“Large fruit lesions caused by the bacterial speck pathogen, although
rare, have been observed previously in Florida by
Dr. K.L. Pernezny (personal communication),” Jones explained. “Although
bacterial speck does occur frequently on fruit, only very young developing
fruit are susceptible. Furthermore, it requires optimal conditions and
inoculum for infection, as demonstrated by Getz et. al. (1983) for bacterial
speck and by Scott et. al. (1989) for bacterial spot. In both studies,
it was demonstrated that fruit infection only occurs during a short time-frame
To conclusively show that the problem was associated with bacterial speck,
Jones said isolates were taken from lesions in samples from three fields.
All Lesions Were Infected
In all the lesion samples, a bacterium was present which was characteristic
of the bacterial speck pathogen (Pseudomonas springae pv. tomato), and
in a number of isolations we recovered two types of organisms, the bacterial
speck pathogen and another one that was characteristic of the bacterial
spot pathogen (Xathomonas campestris pv. vesicatoria),” he said. “The
strains that were suspected of being the bacterial speck pathogen were
P. syringae pv. tomato strains….”
During additional research, Jones and colleagues inoculated some very
young fruit in the greenhouse to determine if large fruit lesions could
be reproduced. This effort “conclusively demonstrated that P. syringae
pv. tomato can cause large speck lesions,” he reported.
“Control of bacterial spot and bacterial speck requires an intensive program,” the
researcher cautioned. He recommended the following:
• Clean Transplants: Make sure they are free of bacterial diseases going
into the field.
• Good Isolation: All fields need to be isolated from production fields
from the previous season given that bacterial cells can be transported
long distances to infect healthy crops.
• Reduced inoculum: It is important to eliminate volunteers or adjacent
fields as sources of inoculum.
• Bactericides: These are an important component of an integrated approach
for controlling bacterial diseases of tomato. Copper has been used for
many years and has been shown many times to be significantly more effective
if applied in a tank mix with an EBCD compound.
• Activators: A second group of compounds that have proven effective
are plant activators. Actigard has been shown in many studies to reduce
bacterial spot and bacterial speck disease severity (Louws et. al., 2001).
• Bacteriophages: A very promising approach for controlling bacterial
spot has been to use bacteriophages (Flaherty et. al., 1999; Balogh et.
al., 2001; Obradovic et. al., 2004).
“We have demonstrated in the field that bacteriophage applications result
in significantly higher fruit yields compared to the control or other
standard treatments,” Jones said. “A similar strategy should
be effective for controlling bacterial speck.”
Editor’s note: The research reported here was
conducted by J.B. Jones, Ellen R. Dickstein and R.E. Stall, all with
Pathology Department, Gainesville, Fla. Jones can be contacted by e-mail
at: jbjones@ ufl.edu.
© 2006 Columbia Publishing
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