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People that contributed to Phytobacteriology
- -Woronin 1866: bacteria in Lupin nodules
- -Significant Contributions:Burrill 1878 in IL (Fire blight of pear and apple)apple): transmitted the disease from diseased to healthy
- -Wakker 1883Arthur 1885 at Cornell (first PhD in Science from Cornell)bacteria in hyacinth yellows
- -Arthur 1885 at Cornell: Koch’s postulates for fire blight
- -E. F. Smith 1893-1900Significant Contributions:Bacteria in Relation to Plant Diseases Bacterial Diseases of Plants (3 vols) Studied crown gall disease: ‘cancer’ of the plants
- -1977: Mary Dell Chilton’sgroup: crown gall bacterium physically transfers part of its plasmid
- -C. Elliott 1930Manual of Bacterial Plant Pathogens
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Characteristics of bacteria
- -Prokaryotic
- -Microscopic 0.6-3.5 μm x 0.5-10 μm
- -Unicellular = single-cells
- -Cell walls in most
- -no sub-cellular organelles; genetic material (DNA) is not bound by a membrane (no nucleus)
- -Ubiquitous (everywhere!)
- Can be motile
- absorbs nutrients via extracellular enzymes
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Characteristics of bacteria cell walls
- Cell walls present (in most!)
- •peptidoglycan, teichoic acid, protein, polysaccharide, lipoprotein, and lipopolysaccharide•Slime layer or capsule
- -Gram-stain reaction
- gram-negative = g- (pink) gram-positive = g+ (Purple)
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Examples of g+ and g– genera of plant pathogenic bacteria
- g+: Clavibacter, Curtobacterium
- g-: Agrobacterium, Erwinia, Pseudomonas, Xanthomonas, Xylella
- -A majority of the plant pathogenic bacteria are gram negative!
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Name the different shapes of bacteria
- Cocci or spherical
- Bacilliform, rod-shaped,or coryneform
- Spiral or helical
- Filamentous
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How do bacteria reproduce?
- reproduce by binary fission (asexual only)
- growth is logarithmic
- known as doubling time
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Genetic characteristics of bacteria
- 1 circular chromosome/cell
- Plasmid:
- Circular, extra chromosomal
- element; autonomous
- in replication; (one to many copies)
- replicates along with the chromosome
- Some confer antibiotic resistance to the
- bacterium
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Types of bacterial DNA exchange
- Transformation (physical uptake of a piece
- of DNA or ‘whole’ plasmid DNA)
- Conjugation (mating between two
- bacterial cells)
- Transduction (phage-mediated
- DNA transfer)
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Additional Characteristics of
Phytopathogenic Bacteria
- Mode of parasitism:
- mostly facultative saprophytes
- Survival:
- epiphytically (grows harmlessly on another plant) ooze, seed, vectors
- Dissemination:
- water debris, humans, vectors
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What causes Crown gall
Agrobacterium tumefaciens
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What does the Ti plasmid do?
- Ti plasmid Determines the virulence and host range
- 200 kbp in size
- T-DNA is transferred to plant cell;
- Transcribed by plant cell machinery: produces auxin, cytokines, opines: results in abnormal cell division, cell enlargement, uncontrolled growth (Opines are good nutritional source for the pathogen)
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Pathogenic Specialization of phytobacterium
- Host species = pathovar; pv.
- e.g. Pseudomonas syringae
- pv. phaseolicola - bean
- pv. pisi - pea
- pv. tomato - tomato
- 42 pathovars at last count!
- Cultivar = race
- e.g. Pseudomonas syringae
- pv. phaseolicola race 1
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How to Identify Bacteria
- Visible characteristics:
- Size & shape rod-shaped, except actinomycetes
- Colony characteristics shape, growth rate & color
- e.g. Xanthomonas, “coryneforms”
- Gram-stain reaction
- Bacterial Pigmentation ex. Clavibacter sp. have yellow halo with orange center
- Physiological characteristics
- Nutritional tests food sources
- tolerance/toxicity
- Oxygen requirements
- most are obligate aerobes except some Pectobacterium
- Gram Stain
- Molecular techniques (DNA fingerprinting/RFLP/PCR)
- Selective media
- Biochemical analyses: fatty acid profiles
- Pathogenicity tests (on various species and
- varieties of host plants)
- Fatty acid profiles
- Pathogenicity tests
- Selective media
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What is the most common way to ID bacteria?
Selective media
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What causes Watermelon fruit blotch?
- Acidovorax avenae subsp.
- citrulli
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List Symptoms Caused by Bacteria
- leaf spots
- blights
- soft rots of fruits, roots, and storge organs wilts
- overgrowths
- scabs
- cankers
- A given type of symptom may be caused by more than one type of bacterial pathogen
- A given baterial pathogen can cause different types of symtpoms
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