- Bacterial spot of tomato is caused by several species of gram-negative bacteria in the genus Xanthomonas. In culture, these bacteria produce yellow, mucoid colonies. A mass of bacteria can be observed oozing from a lesion under the microscope. - The disease affects tomatoes and peppers. Symptoms include small, dark lesions on leaves that enlarge and become angular in shape. Lesions also form on fruits. The bacteria overwinter in crop debris and seeds and is spread by splashing water or contaminated transplants. - Management includes crop rotation, producing disease-free transplants, seed treatment, eliminating volunteers, and applying copper bactericides or plant inducers like Actigard. Bacteriophages

1. Bacterial spot of tomato
Causal organism :
Xanthomonas campestris pv. Vesicatoria
History :
• Bacterial spot was first observed on tomato in
South Africa as early as 1914.
• For almost half a century, a single bacterial
species, classified as Xanthomonas vesicatoria
and later as X. campestris pv. vesicatoria, was
considered the cause of bacterial spot of both
pepper and tomato

2. Pathogen Biology
• X. vesicatoria is an aerobic, mobile, Gram-
negative rod, occurring singly or in pairs, 0.6
x1.0-1.5 µm, with a single polar flagellum.
• On yeast dextrose chalk agar and nutrient
dextrose agar, colonies are large, smooth-
domed, mucoid-fluidal and yellow with
entire edges.

3. • Bacterial spot is caused by
several species of gram-
negative bacteria in the genus
Xanthomonas.
• In culture, these bacteria
produce yellow, mucoid
colonies .
• A "mass" of bacteria can be
observed oozing from a lesion
by making a cross-sectional cut
through a leaf lesion, placing
the tissue in a droplet of water,
placing a cover-slip over the
sample, and examining it with a
microscope.

4. HOSTS
• The principal hosts are tomatoes and Capsicum.
• Various other Solanaceae, mainly weeds, have
been recorded as incidental hosts: Datura
spp.,Nicotiana rustica, Physalis spp., Solanum spp.
(e.g. on fruits of potato).
• The forms of 'X.vesicatoria' reported many years
ago (Hayward & Waterston, 1964) to attack
Brassicaceae as well as Solanaceae are now
referred to X. campestris pv. raphani

5. Symtomps
• On leaves
• The bacterial spot pathogen may
produce lesions on all aboveground
parts of the plant - leaves, stems,
flowers and fruit.
• Initial leaf symptoms are small,
circular-to-irregular, dark lesions,
which may be surrounded by a
yellow halo.
• The lesions tend to concentrate on
the leaf edges and tip and may
increase in size to a diameter of 3-5
mm.

6. Symptoms
• The most obvious symptoms occur
on leaves, the disease is often
referred to as "bacterial leaf spot."
• Symptoms begin as small, yellow-
green lesions on young leaves
which usually appear deformed
and twisted, or as dark, water
soaked, greasy-appearing lesions
on older foliage .
• Lesions develop rapidly and
become brownish-red.
• Lesion shape is defined by leaf
veinlets, so the shape is angular
rather than the round shape that is
more typical of fungal leaf spots or
injury caused by some pesticides or
other chemical sprays.

7. Symptoms
• Lesions often are more
numerous at the tip and
margin of the leaf where
moisture such as dew is
retained.
• When spots are numerous,
foliage turns yellow and
eventually dies, leading to
defoliation of the lower
portion of the plant.

8. Symptoms
• On Fruits
• Fruit lesions are initiated
only on green fruit, most
likely because infection
occurs through fruit
hairs, which are present
only on immature fruit.
• On fruit, the first
symptoms are small,
dark brown-to-black,
raised spots.

9. Perpetuation
• The bacterial spot bacterium persists from
one season to the next in crop debris, on
volunteer tomatoes, and on weed hosts.
• The bacterium is seedborne and can occur
within the seed and on the seed surface.
• The pathogen is spread with the seed or on
transplants.

10. • Secondary spread within a field occurs by
splashing water from sprinkler irrigation or
rain.
• Infection is favored by high relative humidity
and free moisture on the plant.
• Symptoms develop rapidly at temperatures of
20°C and above.
• Night temperatures of 16°C or below suppress
disease development regardless of day
temperatures.
• Some pathogen strains are virulent on either
tomato or pepper and some may be virulent on
both.

11. EPIDEMIOLOGY
• Organism survives on tomato volunteers and
diseased plant debris.
• Contaminated seed serves as inoculum source.
• Disease development favoured by high
temperatures and high precipitation.
• Bacterium disseminated by wind-driven rain
droplets, clipping of transplants and aerosols.
• Bacterium penetrates through stomata and
wounds.

12. DISEASE CYCLE

13. DISEASE MANAGEMENT
• CULTURAL CONTROLS:
• Crop rotation to avoid carry-over on
volunteers and crop residue.
• Production of disease-free transplants.
• Seed treatment should be used.
• Eliminate any volunteers.

14. Biological control
• Biological control options for bacterial spot are
limited.
• However, a biological control method that uses
bacterial viruses (bacteriophages) that
specifically kill the bacterial pathogens is now
available.
• Treatments with these bacteriophages,
marketed as “AgriPhage,” have been successful
in reducing disease, especially in greenhouse
transplant production.

15. CHEMICAL CONTROL
• Copper bactericides used in combination
with mancozeb provides control of many
copper-tolerant strains.
• The plant inducer, Actigard ®(a systemic
compound containing the active ingredient
acibenzolar-S-methy), provides significant
disease control.
• Bacteriophages with specificity to the target
bacterial strains provide significant control.

16. Thank you