A large group of bacteria cause disease in plants. they have specific characteristics and structure. There are different mechanism by which bacteria affect the plant and cause disease symptom. It is generally survive in soil and dead and decay organic matters and spread by water, agricultural implements, propagating materials, insects and humans. Hence, management practices are designed accordingly. Crop rotation, field sanitation, disinfestation of agricultural implements, use of disease free or resistant varieties and use of antibiotics are few of them.

1. Plant pathogenic bacteria
Dr Bhagyashree Khamari
Assistant Professor (Plant Pathology)
Department of Plant Pathology
Institute of Agricultural Sciences
Siksha O Anusandhan (Deemed to be University)
Bhubaneswar, Odisha.

2. Characteristics of bacteria
• Prokaryotes
• Single celled or unicellular
• Single cells usually group in masses or in chains
• Absence of well defined nucleus
• Microscopic
• Ubiquitous
• Parasitic, saprophytic and photosynthetic but most are
obligatory saprophyte (necrotrophs).

3. • Can be gram +ve or gram –ve.
• Can be cultured in artificial media.
• Motile or Non-motile
• Flagellate
• Bacteria grows in the intercellular spaces and do not
invade them.
• High degree of resistance to high temperature (75℃),
low temperature(-19℃) and severe drought.
• All the plant pathogenic bacteria are mesophilic (they
can grow at a temperature of 20-35ºC)

4. Reproduction
(asexual method)
 Binary fission
 Budding
 Conidia

5. Binary fission

6. • Bacteria enters through wound or natural
openings such as stomata, lenticels or
hydathodes.
• They can survive in soil (as soil inhabitant or
soil invaders), plant debris, organic matters.
• Spread by water (irrigation water or rain
water), agricultural implements, seed, insects,
human and animals.

7. • 80 species consisting many sub species (Pathovars
or pv) cause plant disease.
• Important plant pathogenic genera: Pseudomonas,
Xanthomonas, Erwinia, Pectobacterium, Pantoea,
Agrobacterium, Ralstonia, Burkholderia,
Acidovorax, Clavibacter, Streptomyces, Xylella.

8. • Bacteria produces toxins or enzymes or special
proteins that break down key structural
components of plant cells and their walls.
• Important symptoms: Galls and overgrowths,
wilts, leaf spots, specks, blights, soft rots, scabs
and cankers.

9. Gall
Soft rot
Canker Scab

10. Ooze exudation Ooze test
Wilt

11. Shape of Bacteria
Rod Shaped (Bacilli), Spherical (Cocci), Spiral
(Spirilli), Coma Shaped (Vibrios) Or Thread Like
(Filamentous).

12. Colour of Bacteria
 Single bacterium mostly appears as hyaline or yellowish
white under the compound microscope, when grown on a
medium
 The colonies of most of bacteria have a whitish or greyish
appearance but some of them develop yellow, red or other
colours.

13. Structure of Bacteria

14. Bacterial Cell wall
 A bacterium has a thin, relatively tough, rigid cell wall.
 It composed of peptidoglycan consisting of chain of
alternating N-acetyl muramic acid and N-acetyl
glucosamine units cross linked by tetrapeptide and
pentaglycine units
 Cell wall provide immuological distinction and variation
among strains of bacteria.
 It allows the inward passage of nutrients and the outward
passage of waste matter and digestive enzymes.

17. Difference between Gram+ve and Gram -ve
 Gram +ve
 Cell wall is thicker and
homogemous.
 Contains lower content of lipids (5-
10%)
 Peptidoglycan comprises up to 90%
of the cell wall and hence maximum
lipid.
 Techoic acid present.
 Cell wall has higher amino sugar
content (10-20%)
 Cell wall is simple in shape and is
single layered.
 Mesosomes more prominent.
 Retains violet dye
 Examples: Bacillus, Clavibacter,
Streptomyces
 Gram –ve
 Cell wall is thinner and usually thin
layered.
 Contains higher content of lipids (up
to 40%).
 Peptidoglycan comprises only 10%.
 Techoic acid absent.
 Low content of amino sugars
 Varying cell wall shape and is
tripartite (3-layered).
 Mesosomes less prominent.
 Retains red dye
 Examples: Erwinia, Pseudomonas,
Xanthomonas, Agrobacterium,
Xylell

18. Cell membrane:
 It is composed phospholipid (bilayer) and protein.
 Permeable to nutrients, ions and others.
Function:
 Regulate the passage of substance due to permeability.
 Synthesis of membrane lipids
 Synthesis of cell wall peptidoglycan
 Assembly and secreation of extra cytoplasmic proteins
 Co-ordination of DNA replication and segregation with
septum formation during cell division.

19. Mesosome
 Cytoplasmic membrane invagination in the form of
tubular or vesicle shaped is called as mesosomes.
 Mesosome in the centre (central mesosome) is used in
cell division.
 Peripheral mesosome is used in transport of
extracellulaar enzymes from cytoplasm to exterior
regions.

20. Capsule
 If many cells embedded in a common matrix then it is slime
layer.
 It is made up of viscous gummy material, mostly composed
of polysaccharides but may rarely contain amino sugars,
sugar acids, etc.
 When the layer is thick and firm, it is called capsule.
 Generally plant pathogenic bacteria lack capsule but some
of them like Pseudomonas and Xanthomonas produce
slime.
 Capsule or slime or micro capsule often called glycocalyx.
 Most capsule are polyssacharide but some are polypeptide.

22. Function
• Protection from temporary dryness
• Block attachment of bacteriophage
• Prevent phagocytosis.
• Provide virulence to the bacteria
• Promote attachment of bacteria
• Prevent cell aggregation in suspension by
electric charge.
• Important role in biofilm application

23. Flagella
 These are thread like structure, which are usually longer
than the cell
 Used for locomotion.
 They are very delicate and fragile, 10-12 nm in width.
 Thinner than eukaryotic flagella
 Made up of flagellin protein
 All spiral, few sperical and half of the rod shaped bacteria
are motile by flagella

24. Parts of a Flagellum
Filament: It is helical, outermost region of flagellum, composed of
flagellin (protein), synthesized in the cell, which moves to the hollow
core of the flagellum to the tip.
Hook: Filament is attached to hook which is wider than the flagellum.
This is 45 nm wide and made up of different types of protein.
The hook of gram positive bacterium is longer than that of gram
negative bacteria.
Basal body: It consists of small central rod which is inserted into a
system of rings.

26. classification of rod shaped plant pathogenic bacteria on the basis of flagellation
1. Atrichous : Without flagella.
2. Monotrichous: Single flagellum at one end.
3. Cephalotrichous/ Lophotrichous : Several flagella at one
end.
4. Amphitrichous: Atleast one flagellum at each end
5. Peritrichous: Flagella present on whole periphery/surface.

27. Atrichous Monotrichous Amphitrichous
Peritrichous
Lophotrichous
Cephalotrichous

28. Pili or Fimbriae
 These are hollow, non-helical, filamentous, thinner, shorter, numerous hair
like structures.
 Generally shorter than the flagella and are thicker (3-15 nm in diameter).
 They are made up of protein sub-units known as pilin.
 Common in gram –ve but also present in archae and gram +ve
 Both flagella and pili originate from cell membrane and extend outward
through the cell wall.
 Function: Adherence to the substrate, determine the virulence, provide
resistance from phagocytosis, involve in conjugation (sex pilli).

30. Genome:
 It includes both chrmosomal DNA and plasmid.
 Chromosomal DNA is a long coiled, double stranded, single
circular DNA.
 It appears as a spherical, ellipsoidal, dumb-bell or Y-shaped body
in the cytoplasm, but without any membrane.
 The nuclear material consists of large circular chromosome,
composed of DNA.
 It is also known as nucleoid or bacterial chromosome or chromatin
body.
 Some species also have additionally single or multiple copies of
smaller circular genetic material called plasmids

31. Plasmid
 These are small, circular, covalently closed, self replicating,
extrachromosomal DNA.
 They control specific characters like pathogenicity,
nodulation etc.
 Plasmids can move from bacterium to bacterium or
bacterium to plants. This special property is used in genetic
engineering for transformation of desired genes from one
plant to another by using it as vector.

32. Plasmid
Chromosomal DNA

33. Ribosomes:
 It is used in protein synthesis.
 Never bound to any organelles in cytoplasm.
Endospore
 It is a spore within the cells
 Resistant to unfavourable or stress condition.
 On arrival of adverse condition protoplast concentrates
into spherical form and a thick wall develops around it.
On return of favorable condition endospore comes out
of bacterial cell and protoplast germinates to give rise
to a new bacteria.

34. Prokaryotes
Gracilicutes Firmicutes Tenericutes
Classification of Bacteria
 Gram –ve
 Do not form
endospores
 Thin cell walls
consisting of outer
membrane
 E.g. Psudomonas
Xanthomonas,
Erwinia
 Gram+ve
 Some of them
produce
endospore.
 Thick (firm) cell
wall and unit
membrane but
without any outer
membrane.
 E.g. Streptomyces
 Lack of cell wall
and cells are
enclosed by a
unit membrane
only.
 E.g. Phytoplasma

35. Detailed Classification of Phytopathogenic Bacteria
Kingdom: Prokaryotae
Division I: Gracilicutes
Class: Proteobacteria (mostly single-celled, non-photosynthetic)
Order : Eubacteriales
Family1 : Enterobacteriaceae (They are peritrichous bacteria)
Genus: Erwinia
Family2: Rhizobiaceae
Genus: Agrobacterium, Rhizobium (Symbiotic, Nitrogen fixing bacteria)
Family3: Azotobacteriaceae
Genus: Azotobacter
Order: Pseudomonadales
Family: Pseudomonadaceae
Genus: Pseudomonas
Genus: Xanthomonas

36. Division 2: Firmicutes (Gram +ve)
Class 1: Firmibacteria (Simple gram positivebacteria)
Genus : Bacillus
Bacillus subtilis – biocontrol agent
Genus: Clavibacter (Corynebacterium)
Class 2: Thallobacteria (Gram positive, branching bacteria)
Order : Actinomycetales
Family 1: Actinomycetaceae
Genus: Actinomyces
Family 2: Streptomycetaceae
Genus : Streptomyces
Family 3: Mycobacteriaceae
Genus: Mycobacterium

37. Division 3: Tenericutes
Class: Mollicutes (wall less prokaryotes)
Family: Spiroplasmataceae
Spiroplasma citri causing citrus stubborn
Spiroplasma kunkelii causing corn stunt
Phytoplasma

38. 1. Use Resistant varieties
2. Use Bacteria-free seed or propagation materials.
3. Maintain proper sanitation
4. Disinfestation of pruning tools.
5. Crop rotation to reduce over-wintering.
6. Preventing surface wounds that permit the entrance of bacteria into the
inner tissues.
7. Prolonged exposure to dry air, heat, and sunlight will sometimes kill bacteria
in plant material.
8. Applications of copper-containing compounds or Bordeaux mixture.
9. Apply antibiotics such as streptomycin and/or oxytetracycline prior to
infection and reduce spread of the disease, but they will not cure plants that
are already diseased.
10. Insect control will help to eliminate vectors or reduce feeding wounds that
can provide points of entry.
11. The use of antagonistic for managing bacterial diseases of plants.
12. Implementation of Government Regulatory Measures to restrict the
introduction or movement of pathogens or infected plant material.
Management of Bacterial disease in Plants