Download Plant pathogenic bacteria

Plant pathogenic bacteria
General characteristics
Anton von Leuvenhook: first observation of bacteria
1683
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Koch’s postulates (1876)
• Pathogen is the microorganism, which
- can be isolated from the diseased organism,
- can be grown in a pure culture
- can infect the original host (with the original
symptoms)
- can be re-isolate from the new, infected host
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Bacteria
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The smallest living organisms,
Usually one cell, only few micrometer large,
Shape: coccus, bacillus and spirillum
Occurre everywhere, constant and important
constituents of biosphere
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Big discoveries in bacteriology
• Leuwenhook 1683 First observation of bacteria
• Koch 1876: anthrax bacillus: Bacillus anthracis
• Burrill 1879: Erwinia amylovora – bacteria can cause
disese of plants (fire blight)
• Erwin Smith: First description of many bacteria
• Pammel 1895: Xanthomonas campestris – from
cabbage
• Smith 1896: Pseudomonas solanacearum – from
potato
• Smith 1907: Agrobacterium tumefaciens – from fruit
trees
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Plant pathogenic bacteria
1950 Zoltán Klement the pioneer of plant bacteriology
in Hungary
Among 1600 bacterium genera only about 300 cause
diseases on plants
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Main properties of plant pathogenic bacteria
• Heterotrophic organisms
• Facultative parasites (usually can be cultured in pure
cultures on artificial media)
• Usually contains only single cells
• Complex layer of cell wall
• Shape: bacillus, coccus, spirillum
• Majority Gram negative stained
• Aerobe, seldom facultative anaerobe living style
• No real nucleus, only chromatin, containing DNA
• DNA containing small, round plasmids in the cytoplasm
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Living forms of bacteria
• Autotrophs (from the energy supply
independent species, using the carbon dioxide
as carbon source), chemotrophs,
photoautotrops
• Heterotrophs (using organic carbon source)
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Main components of the bacterial cell
• Cell membrane (lipid)
• Cell wall (double structures of phospholipids
and carbohydrates)
• No independent membrane bound organelles
(cell nucleus, plastids, endoplasmic reticulum)
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Construction of bacterial cell
• Complex cell wall, about 10-20 nm thick,
mucoproteid skeleton, external membranes
• (Gram + and -) groups
• Plant pathogenic bacteria are usually Gram -, (G+
mucoproteid skeleton is loose, or G- is compact)
- Inner cytoplasm membrane,
- Periplasmic space (peptidoglucane),
- Outer membrane (lipids, proteins, LPSlipopolysaccharids)
- Cytoplasm: ribosomes, proteins, nucleic acids,
plasmids
- EPS envelope (extra-cellular polysaccharide)
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Bacterial taxons
• Gram positive (no outer membrane)
e.g. Actinobacteria
• Gram negative (with outer membrane)
e.g. Proteobacteria
• Unknown, non classified bacteria
e.g. Cyanobacteria
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Extracellular structures
• Bacterial cell wall (peptidoglucan)
- Gram + type, thick, contains peptidoglucane and
lipoteicnoinic acid
- Gram – type thin, contains only lipopolysaccharides
• Outher capsula (envelope) contains alginate and EPS
(extra cellular polysaccharides)
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Genetic material
• No real, independent nucleus (prokaryotic
organisms)
• Irregular, round shaped DNAs in the nucleotide zone,
only one giant chromosome
• The genome contains about 300 genes with about
4Mbp
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Cytoplasmic genetic elements
• Chromatin (chromosome)
• Plasmids: independent round shaped DNA
molecules, coding few proeteins, responsibles for
few properties (eg. antibiotic resistance)
• Ribosomes and RNAs, producing proteins
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Transposons
• Special bacterial genetic elements, which can be
translocated randomly from one part of the genome
to other place
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Movement organelles of bacterial cells
• Flagellum (plural - flagella) 10-20 nm thick, 20-70 mm
long, originated from thy cytoplasm
• Types of flagella:
- atrich (without flagellum);
- monotrich (one): Xanthomonas;
- lophotrich (lot in one side): Pseudomonas;
- amphitrich (on two poles);
- peritrich (around the whole surface) : Erwinia
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Bacterial colonies
• Development of colonies is characteristic for the
bacteria
• Emerging, round shape, slightly wave like…forms
• Some are producing color substances (stains)
(Corynebacterium michiganense yellow, C. insidiosum
blue)
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Reproduction types
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Rest (leg) phase, (time of DNS replication)
Log phase (time of reproduction), 3-4 hrs
Stationer phase, 24-78 hrs
Asexual (division by bipartition) and sexual
(conjugatio) by the pilus, with DNA
• Decline phase
• Plant pathogenic bacteria reproduce slower than
animal ones
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Environmental factors influencing the multiplication
• Temperature: 2-5 oC minimum, 25-30 oC optimum,
over 50 oC will die
• Nutrients: water, carbohydrates, alkali pH.
Autotrophic and heterotrophic type of living. Aerobe
and anaerobe types
• Light: Not as sensitives as the animal pathogens. UV
light is harmful for DNA
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Characterisation protocol of an unknown bacterium 1.
• Isolation from diseased tissue on nutrient agar
• Separation of colonies
• Pathogenicity experiments on tobacco plants (HR)
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Characterisation protocol of an unknown bacterium 2.
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Testing of bacteria producing HR on tobacco plants
Physiological and biochemical tests
Pathogenicity tests
Ice nucleation tests
Production of antibiotics
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Characterisation protocol of an unknown bacterium 3.
Pathogenicity test
• On young fruits
• On young sprouts
• On intact plants
• On cuttings
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Identification methods
• Gram staining: (1884) pararosaniline (Gentiana
violet+ KOH). Generally G-, but Clavibacterium G+
• Morphological properties: shape, form, flagella
• In vitro studies: form, colour of colonies
• Biochemical reactions: nitrate reduction,
carbohydrate utilization, gelatine hydrolysis, gas
production etc.
• Pathogenicity according to Koch’s postulates
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Gram (+) staining of bacterial cells
Foto: T.Vigh
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Diagnostic methods
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Symptoms (macroscopic or microscopic)
Isolation on artificial media, growing in pure cultures
Colonies, type of colonies
Microscopic studies (form, shape, flagella)
Chemical diagnosis: production of different
metabolites
• Phage analysis
• Molecular diagnosis: proteins and nucleic acids
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Serological diagnosis of bacteria
• Serological methods:
- antigen – antibody relation,
- serological reactions: agglutination (cell level),
precipitation (in colloid form), immuno-electron
microscopy, immuno blotts etc.
Enyme Linked Serological Assay - ELISA
• Antigens: lipoproteins, flagellin
• Agglutination titre for estimation of taxonomic
relation. Polyclonal and monoclonal antisera
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Immunodiffusion test with serologically related strains
Antiserum
Antigen samples
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Molecular diagnosis of bacteria
• Extraction of proteins or total nucleic acids
• Separation of proteins or nucleic acids by
electrophoresis
• Sequence analysis of nucleic acids by restriction
endonucleases (produced by fungi)
• PCR – polymerase chain reaction for amplification of
nucleic acids
• Hybridization (Western, Southern, Northern blot)
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Phage analysis
• 1915 Twort and D’Herelle – discovery of
bacteriophages by specific lyses of bacterial colonies
• Bacteriophages are viruses infecting bacteria
(Delbrück and Luria): No independent metabolism,
nucleoproteins, specific for bacterial genera
• Adsorption, vegetative phase, lyses
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Characteristics of phage infection
• Adsorption, penetration of phage nucleic acid into the cell.
Only one phage infects!
• Vegetative phase: New protein synthesis, respiration does
not change, division (reproduction) stops
• Biosynthesis of new virions, disruption of cell walls
(production about 10-300 new phages in a single bacterial
cell)
• Plaque formation (8-12 hrs). Plaque counting. Specific!
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Transmission of bacteria
• Mechanical way (through by wounds), through by the
stomata and lenticels, etc.
• By seed transmission, from the surface and from the
endospermium
• Pollen transmission: Erwinia amylovora
• Vegetative mode: tubers, bulbs, grafting etc.
• Vectors: insects, nematodes, humans etc.
• Water (the most common)
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Pathogenicity of plant pathogenic bacteria
• Evolution of bacteria: saprophytic, symbiontic,
parasitic (P. fluorescens - P. tabaci, AgrobacteriumRhizobacterium relationship)
• Pathogenicity: toxin production, pectinases,
hormones causing hypertrophy or other growth
abnormalities
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Infection conditions of phytopathogenic bacteria
• Infection conditions: pathogen, susceptible plants,
favourable environmental conditions
• Infection by wounds and natural openings!
• Starts fom the soil, through plant debrids, seeds,
wounds of phloem and xyleme vessels
• Vectors: insects, bees, etc.
• Physiological and developmental stage of plants
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Living types of bacteria
Autotrophs (autonomous energy supply,
species, using carbon dioxide of the air as
carbon source), chemotrophs,
photoautotrophs, etc.
Heterotrophs (using organic carbon sources)
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Bacterium domens
• Archaea – thermophil fossil organisms from
about 2,5 – 3 milliard years ago, altered type
of evolution. Characterization on the basis of
16S ribosomal RNA
• Bacteria - recent taxon, developed approx. 4
milliard years ago
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Phases of bacterial infection
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Penetration into the intercellular space
Avoid of defence reactions
Alteration of host metabolism
Genetic transfer by plasmids (Agrobacterium)
Colonization of nutrient reach tissues
Secondary colonization (soft rots)
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Defence reactions against bacterial infection
• General, non-specific defence reaction
• Specific defence reaction (Hypersensitive reaction,
HR) Resistant plant, incompatible - host parasite
relation
• Lack of defence reaction (susceptible plant)
compatible host – parasite relation)
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Disease induction (in susceptible host)
• Susceptible plant (compatibility)
• Avoid the recognition by EPS
• Inhibition of HR (products of Avr genes do not react
with the R genes)
• Water and nutrient supply in the intercellular space
• Alteration of pH (efflux of K ions and influx of H ions)
• Moderate production of oxygen free radicals
• Efflux of glucose into the intercellular spaces
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Necrobiosis in the susceptible host
• Rapid bacterial multiplication in the intercellular
space (water soaking spots)
• Glucose exhaustion, new bacteria will produced
without EPS
• Recognition of bacteria by the host
• Bacterial reproduction stops,
• Bacteria will be killed by the necrosis
• Typical bacterial symptoms will develop (necroses,
wilting, yellowing etc.)
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Specific defece reaction (HR)
• Induction phase: attachment of bacteria on the cell
surface
• Activation of hrp (genes of hypersensitivity and
pathogenicity) in the bacterial cell
• Latency phase: introduction of Avr or Vir gene
products into the host cell
• Activation of R (resistant) genes of the plant
• Increase and accumulation of reactive oxygen radicals
• Activation of antioxidants and antioxidant enzymes
• Necrotic phase: Active destruction of pathogen
• Programmed cell death (HR)
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Genes of hypersensitivity and pathogenicity (hrp)
• Characterization by transposon mutagenesis
• Because the spoiled genes of the mutants do not
induce HR, their reproduction rate decrease
• Organized in gene clusters 25-30 kb. (in the „island of
pathogenicity”)
• Localized in the chromosomes or in plasmids
(Ralstonia)
• Incorporation into pathogens will induce HR
• Proteins of the III. rd type of secretion mechanism
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Hypersensitivity
• Hypersensitivity is the hyperergic expression of
incompatibility
• During the HR by the rapid death of the host cell the
bacteria will also be killed
• In the majority of cases the HR leads to resistance
(but itself it is not the resistance, only the
consequence of the resistance)
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Main types symptoms caused by bacterial infection
• Leaf spots, local necroses (Pseudomonas,
Xanhomonas)
• Cankers , wounds (Pseudomonas syringae, Erwinia
amlylovora)
• Wiltings (irreversible and reversible) (Ralstonia
solanacearum)
• Tuber soft rot (Erwinia carotovora)
• Tumors (Agrobacterium tumefaciens)
• Scab (Streptomyces scabies)
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Necroses, leaf spots
• Local spots, water soaked spots, later necroses
• Necrotic spots on the leaves, stems, flowers and
fruits
• Bacterial slime
• Chlorosis (effect of toxins), wilting
• Largr necroses, cankers
• Usually caused by Pseudomonads and
Xanthomonads
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Water soaking and necrosis (Pseudomonas syringae pv. phaseolicola)
Photo: S. Kadlicskó
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Necroses - Cankers
• Cankers of woody plants: Pseudomonas morsprunorum
• Apoplexy: Necrogenic bacteria, ice nucleation,
exhaustion of glucose in the vascular system, frost
injury, necrosis in cambium. Caused by:
Pseudomonas syringae pv. syringae
• Fire blight of apple trees: Bacterial mass blocks the
nutrient transport, causing wilting and necrosis on
twigs and trunks. Caused by: Erwinia amylovora.
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Necrosis of fire blight (Erwinia amylovora)
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Wilting
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Blocking of vascular system (ring necrosis)
Wilting (sometimes temporary)
Ralstonia solanacearum wilt
Curtobacterium flaccumfaciens, P. syringae pv.
phaseolicola, Xanthomonas campestris pv. phaseoli
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Wilt caused by vascular block
Ralstonia
solanaceraum
blocks the
vascular system
and causes
temporary wilting
of potato plants
and ring necrosis
on tubers
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Soft rots caused by bacteria
• Tubers of potato, bulbs of onion, cabbage head
• Pectolitic enzymes (pectinases, pectin
metylesterases) lisate the tuber tissues
• Pathogenicity depends on the enzyme activities
• Erwinia carotovora group
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Soft rot of carrots caused by Erwinia carotovora
Fotos: T. Vigh
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Potato soft rot (Erwinia carotovora)
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Bacterial tumors
• Cell and tissue proliferation in Dicots by the transfer
of bacterial plasmid DNA
• Crown gall caused by Agrobacterium tumefaciens, A.
vitis
• Pseudomonas savastanoi on oil trees
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Tumors on olive trees (Pseudomonas savastanoi)
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Crown gall caused by Agrobacterium vitis
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Actinomyces are bacteria, not fungi!
• 1875 first report on potato scab
• 1891 Streptomyces scabies
• Formerly independent taxon, recently belongs to
bacteria (Actinomycetales, Streptomyces)
• No real nucleus, cell wall does not contain chitin
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Plant pathogenic bacteria
Economically important
bacterial diseases
Taxonomy of most important bacteria
Class
Family
Genus
Alpha Proteobacteria Rhizobiaceae
Agrobacterium
Beta Proteobacteria
Ralstoniaceae
Ralstonia
Gamma Proteobacteria Pseudomonadaceae
Pseudomonas
Xanthomonadaceae
Xanthomonas
Enterobacteriaceae Erwinia
Actinobacteria
Microbacteriaceae
Corineabacteriaceae
Streptomycetaceae
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Clavibacter
Curtobacterium
Rhodococcus
Streptomyces
Taxonomy of Pseudomonas genus
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Bacteria (Gram -)
Phylum: Proteobacteria
Class: Gamma Proteobacteria
Order: Pseudomonadales
Family: Pseudomonadaceae
Genus: Pseudomonas
• Inside the Pseudomonas genus there are animal-,
human- and plant pathogenic species
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Plant pathogenic Pseudomonas species
• Pseudomonas species:
• Pseudomonas syringae: species with wide range of
hosts, over 50 different pathovars
• Pseudomonas savastanoi – infects oil trees
• Pseudomonas viridiflava – infects sweet pepper
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Pseudomonas syringae
• Rod shaped, Gram-negative bacterias with polar
flagella
• Infect a range of plant species
• Presence of INA (ice nucleation active) proteins
• Infection: wet, cool temperature (optimal 12-25 Co),
could be seed-borne, can live as saprophyte
• Pathovars:
- P. s. pv. atrofaciens – infects Triticum aestivum
- P. s. pv. pisi – infects Pisum sativum
- P. s. pv. syringae – infect Syringa, Prunus, Phaseolus
species
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Bacterial necroses on tobacco leaf
Serious disease of
tobacco plants
caused by Pseudomonas
syringae
pv. tabaci
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Pseudomonas syringae pv. syringae
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Apoplexy of apricot trees
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Rapid wilting and necrosis of apricot branches
Necrosis in vascular system
Causal agent: Pseudomonas syringae pv. syringae
Bacteria multiply in vascular tissues, utilizing its sugar
content
• Ice nucleating strains cause frost damage and stem
necrosis
• Control: removal of infected parts (truncation)
• Pruning not in winter, but in spring
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Truncated apricot tree after bacterial infection
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Died apricot tree : Apoplexy
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Pseudomonas syringae pv. phaseoli
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Pseudomonas viridiflava
• Fluorescent soil borne
pathogen infects
tomato (stem
necrosis, dark
blotches on pruning
sites of the stem),
soft rot on sweet
pepper, the runner
beans etc.
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Pseudomonas viridiflava infection on sweet pepper
Photo:Z. Klement
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Pseudomonas savastanoi
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Taxonomy of Xanthomonas genus
• Gram negative bacteria, with rod shaped flagella
bacteria grow almost exclusively in plants
• Phylum: Proteobacteria
• Class: Gamma Proteobacteria
• Order: Xanthomonadales
• Family: Xanthomonadaceae
• Genus: Xanthomonas
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Xanthomonas campestris
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Cause a large variety of plant diseases
Pathovars classification based on the host plant
Important pathovars:
- pv. campestris.
- pv. caroteae
- pv. juglandis
- pv. malvacearum
- pv. pelargonii
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Xanthomonas campestris pv. vesicatoria
• Aerobic. Gram negative, mobile (single polar
flagellum)
• Principal hosts: tomatoes, sweet pepper and other
Solanaceous plants
• Occurs widely in pepper and tomato growing areas,
infects under warmer, humid conditions (above 30 oC)
• Survives in seeds, infested debris, stalks
• In glasshouses seed borne infection
(survive on tomato and pepper seeds for 10 years)
• Disseminated by rain splash, irrigation, handling,
aerosols
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Symptoms on pepper caused by X. vesicatoria pv. vesicatoria
• Corky spots and
scabs, water soaking
margins , black
necrotic lesions on
the leaves with
yellow haloes
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Xanthomonas campestris ssp. vesicatoria
Control:
healthy seed,
care in
handling,
phytosanitary
measures,
resistant
variety
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Xanthomonas campestris pv. juglandis
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Ralstonia solanacearum
• Quarantine, aerobic, Gram-negative, soil-borne
bacteria with polar flagella
• One of the most important bacterial pathogen,
infects over 250 species of 50 families
• Phylum: Proteobacteria
• Class: Beta Proteobacteria
• Order: Burkholderiales
• Family: Ralstoniaceae
• Genus: Ralstonia
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Ralstonia solanacearum
• Host range: potato, tomato, pepper, tobacco,
eggplant, banana, etc.
• Symptoms: reversible, later irreversible wilting of the
leaves. Bacterial exudates accumulate in the vascular
system. Ring necrosis in potato tubers
• Overwinters in diseased plants, plant debris, in seed
and tubers. Occurs in surface waters, including rivers.
Can be spread by irrigation , mechanical tools and by
seeds
• Infects by wounds. Wilting occurs at high
concentration of bacteria in the xylem (EPS)
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Erwinia amylovora
• Contagious, quarantine, Gram-negative bacteria, causal
agent of „fireblight disease” of apple trees, affecting
apples, pears, quinces and other members of family
Rosaceae (Cotoneaster, Pyracanthus etc.), Class: Gamma
Protobacteria
• Order: Enterobacteriales
• Family: Enterobacteriaceae
• Infects in warm, wet conditions in spring in blossom time.
Affected areas are dying quickly and tender new shoots
and leaves. Bacterial exudates
• Dissemination by rain, honeybees, birds and insects
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„Shepherds crook” symptom of fire blight
Photo: Cs. Pintér
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Symtoms of late infection caused by Erwinia amylovora
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Secondary infection of fire blight on pear
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Control of fire blight disease
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Resistant (?) variety
Rather difficult. Routine inspection in the orchard
Removal and burning of infected branches
Antibiotics are not allowed!
Chemical control by copper containing fungicides
with special care of honeybees
• Quarantine measures
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Erwinia infection on apple shoots
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Apple shoot necrosis
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Canker of apple trees caused by Erwinia amylovora
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Erwinia carotovora
• Rod shaped Gram negative, peritrichously flagellated
facultative anaerobe bacterium
• Class: Beta Proteobacteria,
• Order: Enterobacteriales,
• Class: Enterobacteriaceae
• Causes diseases of many plants
• Infects a wide host range, causing soft rot on carrots,
potato, tomato, cucurbits, onion, etc.
• Important as post-harvest pathogen
• Produce proteolitic enzymes (pectinases, cellulases)
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Erwinia carotovora on cabbagge
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Erwinia carotovora infection
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Erwinia carotovora on carrot
Photos: T. Vigh
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Soft rot of paotato caused by Erwinia carotovora
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Potato soft rot
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Test for pectolitic enzymes on potato slices
Photo: M. Kállay
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Agrobacterium tumefaciens
• Rod shaped, Gram negative soil bacterium with
flagella
• Causal agent of crown gall disease
• Ti plasmid is responsible for tumor formation
• Class: Alpha Proteobacteria
• Order: Rhizobiales
• Family: Rhizobiaceae
• Genus: Agrobacterium
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Infection by Agrobacterium tumefaciens
• Bacteria chemotactically move to the root cells
• Vir A and transmembrane proteins recognize the cell
exudates
• Bacteria synthesize cellular fibrils, anchoring bacteria
to the host cell
• Cut out of transfer DNA (T-DNA) from the circular (Titumor inducing) plasmid
• One copy of T-DNA (activated by vir genes)
transferred into the plant cells by T pilus
• Incorporation of T-DNA into the plant chromosome
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Genes in the Ti plasmid transfer (T) DNA
•
•
•
•
Vir genes cut out T-DNA region from Ti plasmid
Gene of indole acetic acid (IAA) production
Gene of cytokinin production
Gene for encoding opines (octopine and nopaline
• Only one copy of T-DNA is exported to the host cell!
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Agrobacterium as gene vector
• Cloning and amplification of a desired gene (DNA)
sequences (e.g. in Escherichia coli)
• Incorporation of the cloned DNA into Agrobacterium
tumefaciens Ti plasmid (transformed bacteria)
• Agroinfection of isolated plant cells or protoplast by
transformed A. tumefaciens
• Transformation of host cells by modified Ti plasmid
containing the desired gene
• In vivo culture of transformed cells to plants in tissue
cultures
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Tumor formation on fruit tree
Infection of
Agrobacterium
means a natural
genetic
transformation,
a genetically
modified plant!
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Crown gall caused by Agrobacterium
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Tumor formation of Agrobacterium vitis
• A.
vitis DNA has small
differences in its DNA from
A. tumefaciens
•A. vitis causes systemic
infection on grapes!
•Properties: similar to
Agrobacterium tumefaciens
•Control: Eradication,
sanitary measures
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Agrobacterium rhizogenes
•
•
•
•
Symptoms: root proliferation
Host plants: fruit trees
Agent: Agrobacterium rhizogenes
Contains Ri plasmid responsible for the infection and
symptoms
• Control: see A. tumefaciens
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Control of bacterial diseases
• Use of resistant (or tolerant) varieties
• Quarantine measures: Erwinia amylovora, Ralstonia
solanacearum
• Agro technical methods: prevention, hygiene,
prevention of transmission, soil disinfection
• Chemical methods: antibacterial chemicals (no
antibiotics are allowed !)
• Biological methods: antagonistic bacteria, e.g.
Agrobacterium K84 strain produces bacteriocin
against Ti plasmid containing Agrobacterium strains
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Agrotechnical and chemical control
• Keep the quarantine rules
• Agro technical methods:
• Proper nutrient supply, isolated propagation,
preventive measures to avoid of infection, soil
disinfection, forecasting
• Hygienic rules
• Chemical control: bactericides, no antibiotics
allowed!
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Use of resistant varieties to bacterial infection
Resistant and
susceptible cabbage
lines in the
experimental field
Photo: Z. Klement
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Taxonomic position of Actinomycetes
• Group of soil-and water-borne, Gram positive
organisms, probably the oldest living organism on
Earth
• Domain: Bacteria
• Phylum: Actinobacteria
• Class: Actinobacteridaceae
• Order: Actinomycetales
• Specific group of bacteria, morphologically
resembling to the fungi, because of elongated cells or
filaments or hyphae.
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Streptomyces scabies
• Unusual filamentous pathogen, similar to fungi
• Causative agent of common scab of potato and other
root crops
• Present in soils of potato growing areas
• Symptoms: russet and pitted lesions, later necrotic
areas on the surface, corky tissues
• Gray, spiral vegetative hyphae are fragmented into
spores
• Spores survive in the soil, spread through water
infect by wounds
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Phytoplasma
• A distinct group of plant pathogenic organisms,
belonging to the bacteria
• There are living in the intercellular space and in the
phloem tissues of the plants
• Its genome contains both DNA and RNA
• Have no differentiated cell wall, only cell membrane
• Therefore, their shape is generally round, but variable
(pleomorph), about 100 nm in diameter
• Spread by leafhoppers in a persistent manner
• Diseases can be cured by antibiotics
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Most important properties of phytoplasma
• 1967 Yoi Doi et al. separation from viruses according
to the type of genome (RNA and DNA)
• Propagation in artificial media is not successful
• Two living cycles: in planta and in the vector
• Symptoms: dwarfing, yellowing, deformation of
flowers, witches broom, hormonal abnormalities
• Taxonomy: formerly according to the symptoms,
recently: Candidatus, on the basis of 16r (ribosomal)
DNA
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Special characteristics of phytoplasma
• Now total DNA sequences of two species (AYWB and OY)
are known (530-1350 kb), with about 671-754 genes
• Have plasmids (similarly to bacteria)
• There are missing some genes characteristic to bacteria
(for de novo amino acid, fatty acid, nucleotide- and ATP
synthesis)
• There are depended on the metabolism of their host
(plant or leafhopper)
• Membrane transport is affected (no tubulin has found
necessary for cell division)
• The most primitive forms of auto replication
• Because of repetitive DNA sequences, horizontal gene
transfer is possible (recombination among the
chromosomes and the plasmids)
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Aster yellows phytoplasma
• Chronic, phloem limited bacterial-like organisms
affects approx. 300 species in 38 families (onion,
letuce, celery, carrot etc.)
• Symptoms: virescence, chlorosis, stunting, sterility of
flowers
• Vectored by leafhopper Macrosteles quadrilineatus
• Control: infected plants should be removed and
eliminated. Control of insect vectors and weeds. No
cure possibilities
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Aster yellows phytoplasma on cabbage
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Stolbur phytoplasma
• The most common phytoplasma agent in Hungary
• Spreads by leafhoppers
• Infects tomato (flower deformation)
- green pepper (wilting)
- potato (air bulbs)
- tobacco (flower abnormalities)
- grapes (yellowing, redding, gummy shoots)
- and a lot of other plants
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Flower abnormalities caused by stolbur phytoplasma
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Yellowing and formation of new branches of tomato
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Stolbur phytoplasma on tobacco
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Wilt of pepper plants caused by Stolbur phytoplasma
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Aerial bulbs on Stolbur phytoplasma infected potato
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Convolvulus sp. infected by stolbur phytoplasma
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Stolbur infection on almond and Polygonathum
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Stolbur infection on white grape
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Matured and non matured grape shoots
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European stone fruit phytoplasma
•
•
•
•
Infects fruit trees (apricot, peach, plum, etc.)
Transmitted by leafhoppers in persistent manner
Control of vector species
Characterization according to 16S rDNA
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Symptoms caused by European stone fruit phytoplasma
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Symptoms caused by European stone fruit phytoplasma
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Clover green pethal phytoplasma
•
•
•
•
Phyllody and greening of flowers
Disseminated by leafhoppers
No economic importance
Differentiation on the basis of 16S rDNA
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Clower green petal phytoplasma
Healthy
Diseased
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Növénypatogén baktériumok
Dr. Richard Gáborjányi
Georgikon Kar
Növényvédelmi Intézet
AZ ELŐADÁS LETÖLTHETŐ:
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