Bacterial Plant Pathogens

• What are bacteria?What are bacteria?• Bacterial identificationBacterial identification• Generalized disease cycleGeneralized disease cycle• Disease symptomsDisease symptoms• Disease controlDisease control

Bacterial Plant Pathogens

Size (0.3-1.5 x 0.7-5 um )

Generally single celled

Reproduce by simple fission

Prokaryotes

No membrane bound nucleus or organelles

Lack chlorophyll

Most have cell wall

Some are motile – flagellum (a)

Single circular chromosome

Structure

cell shape

colony appearance

motility (flagella)

Identification

Identification

Biochemicalcell wall composition

Identification

Respiration aerobic, anaerobic, facultative

anaerobic

Nutritional requirement (C, N, {Biolog})

Fatty acids {FAME}

SerologyNucleic acids

Identification

Pathogenicity

Plant Pathogenic Bacteria Plant Pathogenic Bacteria (for PLPA3004)(for PLPA3004)

• 8 genera of bacteria, 1 of uncertain 8 genera of bacteria, 1 of uncertain IDID

• 2 genera of Mollicutes (lack cell 2 genera of Mollicutes (lack cell wallswalls

• Approximately 50-60 spp. (200 Approximately 50-60 spp. (200 pathovars {pv.})pathovars {pv.})

• Pathovar – pathogenic on a specific Pathovar – pathogenic on a specific host (crop)host (crop)

Plant Pathogenic Bacteria Plant Pathogenic Bacteria (for PLPA3004)(for PLPA3004)

• Most are facultative parasites, Most are facultative parasites, – Except fastidious bacteria and Except fastidious bacteria and

mollicutesmollicutes

• Most are gram-, rod-shaped Most are gram-, rod-shaped bacteriabacteria

Fastidious vascular Fastidious vascular bacteriabacteria

• Vectored by leafhoppers, except Vectored by leafhoppers, except ClavibacterClavibacter

• Unknown-phloem limited bacterium Unknown-phloem limited bacterium not culturablenot culturable

• Symptoms – stunting, leaf scalding, Symptoms – stunting, leaf scalding, declinedecline

• Xylella – Pierce’s disease of grapeXylella – Pierce’s disease of grape

MollicutesMollicutes

• Lack cell wallLack cell wall• Phloem limitedPhloem limited• Transmitted by leafhoppersTransmitted by leafhoppers• Phytoplasmas – amorphousPhytoplasmas – amorphous• Spiroplasmas - helicalSpiroplasmas - helical• Symptoms – yellows diseases, witches’ Symptoms – yellows diseases, witches’

brooming, stuntingbrooming, stunting• Sensitive to TetracyclineSensitive to Tetracycline

Disease cycle

Overseasoning

2 cycle

Dissemination

PenetrationDiseasedevelopment

Reproductiono

Disease cycle

A. OVERSEASONING

1. Infected or infested seed

2. Infected plant parts or plants

3. Plant residues

4. Alternative hosts

5. Soil

6. Insects

A. OVERSEASONING

1. Infected or infested seed

2. Infected plant parts or plants

3. Plant residues

4. Alternative hosts

5. Soil

6. Insects

Protected environment

Disease cycle

B. DISSEMINATIONB. DISSEMINATIONshort distance

1.Water

2. Soil

3. Tools and equipment

4. Insects

Disease cycle

long distance

5. Insects

6. Storage, shipping containers

7. Movement of infected plant parts (seeds, tubers, bulbs, fruit, transplants, nursery stock)

long distance

5. Insects

6. Storage, shipping containers

7. Movement of infected plant parts (seeds, tubers, bulbs, fruit, transplants, nursery stock)

B. DISSEMINATIONB. DISSEMINATION

Disease cycle

C. PENETRATION (INDIRECT ONLY)

1. Natural openings (stomates, hydathodes, nectaries)

2. Wounds (tools, equipment, insects, hail)

C. PENETRATION (INDIRECT ONLY)

1. Natural openings (stomates, hydathodes, nectaries)

2. Wounds (tools, equipment, insects, hail)

Disease cycle

D. DEVELOPMENT

1. Intercellular

2. Wilts (xylem and surrounding cells)

3. IntracellularPhloem-limited

D. DEVELOPMENT

1. Intercellular

2. Wilts (xylem and surrounding cells)

3. IntracellularPhloem-limited

Disease cycle

E. REPRODUCTION

F. SECONDARY CYCLE

E. REPRODUCTION

F. SECONDARY CYCLE

Disease control

A. Often difficultrapid reproductionoverwinter in protected sitesrapid penetrationreadily disseminatedfew effective chemical controls

A. Often difficultrapid reproductionoverwinter in protected sitesrapid penetrationreadily disseminatedfew effective chemical controls

Disease Control

B. Common controls1. Pathogen free plants

certified seeddisease-free transplants

2. Sanitationdestroy infected materialsincorporate plant debrisclean tools, shipping containers,storage facilities

B. Common controls1. Pathogen free plants

certified seeddisease-free transplants

2. Sanitationdestroy infected materialsincorporate plant debrisclean tools, shipping containers,storage facilities

Disease Control

3. Minimize wounding

4. Control insect vectors

5. Eliminate alternate hosts

6. Disease resistance

3. Minimize wounding

4. Control insect vectors

5. Eliminate alternate hosts

6. Disease resistance

Disease Control

7. ChemicalsStreptomycinKocide (copper containing compounds)

7. ChemicalsStreptomycinKocide (copper containing compounds)

Symptoms

A. Soft rotssoft rot of vegetables (Erwinia carotovora pv. carotovora)

B. Leafspotsbacterial blights of bean (Xanthomonas campestris pv. phaseoli, Pseudomonas syringae pv. phaseolicola)

C. Blightsfireblight of apples, pears(Erwinia amylovora

A. Soft rotssoft rot of vegetables

B. Leafspotsbacterial blights of bean

C. Blightsfireblight of apples, pears

Symptoms

D. Vascular wiltssouthern bacterial wilt of tomatoPseudomonas solanacearum

E. Gallscrown gallAgrobacterium tumefaciens

F. Cankersfireblight of apples, pears(Erwinia amylovora)

D. Vascular wiltssouthern bacterial wilt of tomato

E. Gallscrown gall

F. Cankersfireblight of apples, pears

Symptoms

G. Scabspotato scab(Streptomyces scabies)

H. Mollicute diseasesyellowing, witches brooming, stunting, declineAster yellow MLO

I. Fastidious vascular bacteriaXylem-limited stunting,leaf scalding or scorching, declinePhloem-limited stunting, witches' brooming, greening of flower parts

G. Scabspotato scab

H. Mollicute diseasesyellowing, witches brooming, stunting, decline

I. Fastidious vascular bacteriaXylem-limited stunting,leaf scalding or scorching, declinePhloem-limited stunting, witches' brooming, greening of flower parts