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EPP 512 - Soilborne Plant Pathogens
Terms in this set (210)
What should you do when sampling for plant pathogens?
Is a pathogen present?
What part of the plant should be sampled?
ei. Bipolaris sorokinana sample at the sub-crown internode
Aphanomyces cochliodes sample at the hypocotyl of diseased sugarbeet
Fusarium and verticillium sample aerial parts of plant (stems/leaves)
How should you sample the soil for plant pathogens?
Presence, inoculum density, and spatial distribution
Timing is very important
How many soil samples should you take and where?
You should have a sampling strategy -
the simplest method would be diagonally (10-20 samples)
most effective would be diamond or W-shape (20-30 samples)
Should you surface-disinfest the tissue?
Depends on the sample type (seed, leaf, stem, root)
Consider time period for disinfestation (secs,mins,hours)
Consider the type of disinfectant (ethanol, Clorox, peroxide, hot water, acid, etc.)
What are the steps of soil dilution?
1. dry the soil
2. sieve the soil through 2mm mesh
3. add 10g of soil to 200ml of 0.2% water agar in a screw cap bottle
4. mix for 20 minutes
5. withdraw 1ml and add to 9ml of 0.2% water agar, then shake for 4 min
6. Withdraw 1ml from previous dilution, add to 49ml of .2% water agar, shake for 2min
7. Transfer 1ml of the final dilution to each of the 5 sterile petri dishes containing 17ml of cooled (45c) culture medium
8. Disperse soil particles evenly by circular agitation of the dishes
9. Incubate dishes under conditions for fungus of interest
What can you do to isolate pathogens?
Using selective or differential medium
What is selective medium?
Culture media that contains substances that specifically inhibit or prevent growth of some microorganisms or promote the growth of some organism over others; most have antimicrobial chemicals added
What is differential medium?
Culture media that is used to distinguish between the organisms that grow on it
Even a weak pathogen can cause disease in plants with genetic resistance or field tolerance if excessive amounts of inoculum are used
What is field tolerance
Yield is not affected by disease
General rule for amount of inoculum: Use sufficient inoculum to result in 50% disease in controls
Steps of Koch's Postulates
Organism consistently assocuated with diseased tissue
Organism must be isolated and grown in pure culture
Organism must be inoculated into healthy plant and produce the same disease as originally observed
Organism must be re-inoculated into a healthy plant to produce the same disease
What was modified of kochs postulates for bacteria?
Microscopic examination of diseased tissue
Remission of symptoms with antibiotic therapy
What is the classifcation of Pythium and Phytophthora
Not true fungi -
Characteristics of Pythium and Phytophthora
Elongated mycelium, no crosswalls (except at base of reproductive structures)
Cell walls composed mainly of B-1,3-gulcans with small amounts of cellulose
What are the resting spores of Pythium and Phytophthora?
What are the asexual spores of Pythium and Phytophthora?
Zoospores or zoosporangia
Pythium - Are all species pathogens?
Pythium- All plant pathogenic speices are soilborne
What is Pythium insidiosum?
An animal pathogen caused by P. insidiosum
Phytophthora - Are all species pathogens?
Phytophthora - Not all species are soilborne
Phytophthora - Species that are not soilborne can cause disease on?
Aerial parts of the plants
What life stage does Pythium affect?
Seeds, seedlings, older plants.
Most damaging on seeds and seedling roots.
Pre - and post- emergence damping-off
Older plants: reduces vigor but rarely killed by Pythium infection
What are the four new sub-divisions of Pythium?
What are some common plant pathogenic species of pythium?
What is the ASEXUAL disease cycle of Pythium?
mycelium = mass of hyphae
Vesicles with contents from filamentous sporangia; zoospores have almost completely formed (Pythium species)
What are survival structures of Pythium
What is the SEXUAL disease cycle of Pythium?
Oogonium - female
Antheridium, male nuclei
How does Pythium develop?
Invades by direct penetration or entering natural cracks
Once inside, pathogen invades tissues by mechanical pressure and enzymes that degrade the middle lamella
Older plants are more resistant and pythium may be restricted to the root tips and young cells
Pythium ultimum - common damping off pathogen in beans
Geranium with Pythiumblight
Black rotted stem tissue at the soil line or within the "splash zone" may expand to girdle a seedling
What are some environmental effects that makes Pythium more severe?
When soil moisture is too high
When soil temperature is either too low or too high for the developing plant
With excess nitrogen
How can you control Pythium
Genetic - not available
Seed or bulb treatment: thiram, chloranil, captan, dichlone, ferbam, diazoben
Applied to soil (in come cases seed): mefenoxam, metalaxyl, propamocarb, benzimidazoles, acylalanine, some copper products, fosetyl-Al, pyraclostrobin, cyazofamid, strobilurin
Surfactants (hydroponics systems)
Biological-Primastop (Gliocladium catenulatum; ornamental, vegetable, and tree crops)-RootShield, Plant Shield, T-22 Planter Box (Trichoderma harzianum Rifai strain KRL-AG2; trees, shrubs, transplants, ornamentals, cabbage, tomato, cucumber)-SoilGard (Trichoderma virens; ornamental and food crops grown in greenhouses, nurseries, homes and interiorscapes)-YieldShield (Bacillus pumilus GB34; soybean)
Cultural - soil sterilization, maintain good soil drainage, avoid excess nitrogen
Phytophthora attacks what kind of plants?
Many different plants, from annual seedlings to mature trees
Are Phytopthora species host specific?
Sometimes but not alwasy
What are some common species of Phytophthora
What does Phytopthora overwinter as?
oospores (zygote), chlamydospores (asexual resting structure), or mycelium in infected roots
Disease cycle of Phytopthora
Oospores and chlamydospores germinate to form a germ tube, which forms a mycelium or a sporangium with zoospores
Mycelium may also produce a sporangium with zoospores
Zoospores infect roots
What makes Phytopthora more severe?
Soil moisture needs to be high and when temperatures are between 15-23 c
What are control methods of Phytopthora?
Genetic - plant resistant cultivars when available
Chemical - fungicides: mefenoxam, metalaxyl, fosetyl Al, ethazol, propamocarb, strobilurins
Cultural - resistant cultivars, soil sterilization, good soil drainage, tree bark mixes and composted mixes for ornamentals
Biological - nothing that is effective
Sclerotinia affects what growth stages?
Seedlings, mature plants, and harvested products
Common species of Sclerotinia are
Sclerotinia disease cycle
Sclerotia germinate in spring to form slender stalks with an apothecium (sexual reproductive structure)
Apothecia contain asci with ascospores(product of meiosis)
Ascospores or mycelium from germinating sclerotia may infect plant tissue
Sclerotinia overwinter as
Disease development of Sclerotinia looks like
Cottony white mycelial growth on infected plant
Large sclerotia (2 to 10 mm) appear
Brown lesions form at the base of stems
Foliage above stem lesions wilt and die
Wet rot of fleshy fruits
What is the Phylum in which it is classified - Sclerotinia?
Name some host of Sclerotinia
Succulents, veggies, flowers, and some shrubs, peanuts, lettuce, forage legumes, turf
What are control methods of Sclerotinia?
Chemical - metham sodium (sprayed on soil); dichloran, thiophanate-methyl, iprodione, and vinclozolin (sprayed on plants)
Cultural - good soil drainage, adequate spacing, remove infected plants, rotate with a nonhost crop such as corn or small grains
Biological - mycoparasites of sclerotia
Worldwide but in termperate regions
What is a common name of Gaeumannomyces?
What growth stage does Gaeumannomyces attack?
but can kill young seedlings and cause severe yield loss in mature plants
What are some common species of Gaeumannomyces?
G. graminis var. tritici
G. graminis var. avenae
G. graminis vae. graminis
What are specific plant host for Gaeumannomyces var tritici?
Attacks most cereals and grasses BUT not oats
What are specific plant host for Gaeumannomyces var avenae?
Attacks all cereals including oats
What are specific plant host for Gaeumannomyces var graminis?
Causes crown sheath rot of rice; most isolates are only slightly pathogenic on other cereals and grasses
What is the overwintering stage of Gaeumannomyces
Mycelium in infected roots and crowns
What is the disease cycle of Gaeumannomyces
Overwinters as mycelium in infected roots and crowns
Most infections caused by mycelium contacting roots
Cortex and vascular tissue of root invaded by fungus
Young plants may be killed, fungus restricted to roots of older plants
Perithecia (sexual structures) containing ascospores found on leaf sheaths of infected plants
Disease development of Gaeumannomyces
Infected seedlings are yellow and stunted
Infected plants produce few tillers and ripen prematurely, but heads are white and do not contain grain
Roots are black and break off near the crown
Fungus extends from roots up to lower leaves
Thick brown strands of runner hyphae is visible
What are some controls of Gaeumannomyces?
Genetic - No cultivars available
Chemical - Seed treatments are marginally effective (often too expensive)
Cultural - Crop rotation to non-host (except soybean), soil ph < 6, use ammonium-N, no plant resistance but some tolerance
Biological - Pseudomonas, Bacillus, and Trichoderma spp.
Where does Armillaria occur?
Worldwide in temperate and tropical regions
Armillaria is the most common fungi found in forest soils
What does Armillaria affect?
Fruit trees, vines, shrubs, shade, and forest trees, potatoes, and strawberries
Most common species of Armillaria
What are the host of Armillaria mellea
Aggressive on hardwords and conifers
What are the host of Armillaria ostoyae
What are the host of Armillaria gallica
What are the host of Armillaria tabescens
Oak and orchard trees common in the southeast
What is the overwintering stage of Armillaria
mycelia or rhizomorphs
How does the disease of Armillaria develop?
Infected trees are smaller and have reduced growth and yellowish leaves
Twig and branch dieback
White fan-shaped mycelial mats appear on bark and roots of infected trees
Reddish brown to black rhizomorphs appear on roots under bark
How do you control Armillaria?
Cultural - In managed forests, remove infected stumps, avoid planting hosts in reclaimed forest land for several years, match species with site selection to avoid environmental stress, dig trench around infected trees in orchards
Chemical - fumigation of specific sites with chloropicrin or carbon disulfide after removal of infected tree
Biological - work with Trichoderma spp. Product = Tenet
Control of Armillaria is usually not attempted in a natural forest
Phymatotrichopsis primary economic host is
What is the distribution of Phymatotrichopsis?
Very restricted to southwest US and Mexico, Venezuela, Libya
What is the one species of Phymatotrichum root rot?
What is the disease cycle of Phymatotrichopsis?
Mycelial and rhizomorph or strand
What is the overwintering stage of Phymatotrichopsis
rhizomorph or sclerotia
What is the disease cycle of Phymatotrichopsis
Sclerotia germinate rhizomorphs form and grow through soil until they contact a root
Rhizomorphs wrap around root and grow upward toward the soil surface where the roots are killed
New sclerotia form in chains on the roots, or in masses
Disease development of Phymatotrichopsis
Infection results from enzymatic and mechanical action of the pathogen
Mycelium enters the root and spreads through the periderm, phloem, and cambium
Fungus eventually enters the xylem and produces vascular occlusions
What are some of effects of the environment that makes the disease more severe?
High sodium content in clay soils
Fungus is most destructive when temperature are high and moisture is adequate and soil ph is about 7
fungus cannot survive freezing temps
What are some control methods of Phymatotrichopsis
Crop rotation (3-4 yr) with cereals
Plant early maturing cotton cultivars
Weed control (harbor pathogen)
Deep plowing (causes erosion problems)
Plant (monocot) barriers around an infection site
Apply nitrogen as ammonia (fumigation effect)
Where does Fusarium (root and stem rot) occur?
Name common species of Fusarium (root and stem rot)
Fusarium sp. are speicies complex
Name other species of Fusarium that cause fruit, stalk, stem and root rots
Fusarium solani produce what asexual spores (root and stem rot)
Mirco-and macro- conidia
What is the Phylum in which Fusarium is classified
What does Fusarium overwinter as? (root and stem rot)
Mycelium or spores infected or dead tissues or seed
How is Fusarium spread? (root and stem rot)
Air, equipment, or water
What is Forma specialis?
Is a taxonomic grouping allowed by the International Code of Botanical Nomenclature that is applied to a parasite (most frequently a fungus), which is adapted to a specific host, i.e. Fusarium oxysporum f. sp. lycopersici.
Disease development of Fusarium (root and stem rot)
Infected roots are red to brown in color
Cracks form along main root, secondary roots are killed
Infected plants will be stunted or die with or without wilt symptoms
Pink or reddish lesions on stem at or below soil line
Rots of tubers, corms, and bulbs are dry and firm
What are some host of F. solani
What are some host of F. acuminatum
What are some host of F. culmorum
Basil, garlic, wheat
What are some host of F. oxysporum
What are some host of F. graminearum
What effects of the enviroment make Fusarium more severe? (root and stem rot)
When plants are stressed
Drought or excess water
What are controls of Fusarium? (root and stem rot)
Cultural - Reduce losses in the field by
Loosen compacted soil with subsoiler chisels (reduces soil moisture)
Crop rotation with nonhost
Maintain good soil drainage
Plant disease-free seed
Fertilize with nitrate-N
Plant resistant cultivars when available
Soil sterilization in greenhouse crops
Fungicide sprays can reduce field losses - look for products labeled for specific crops
HiStick N/T Intercept
Rootshield, Plant Shield, T-22 Planter box, and YieldShield
What makes Fusarium (vascular wilts) more severe?
warm climates and warm soil temperatures
air temperature >28ºC, adequate soil moisture, low N and P, high K, low soil pH, short day length, low light intensity
WheWhere does Fusarium (vascular wilts) occur?re does Fusarium (vascular wilts) occur?
Fusarium oxysporum f. sp. lycopersici overwinters as
mycelium, micro- or macroconidia, or chlamydospores
Virulence of Fusarium oxysporum f. sp. lycopersici is enhanced with ammonium-N and decreased with nitrate-N
Disease development of Fusarium (vascular wilts) ?
Stunting of seedlings, which wilt and die
Older plants leaves turn yellow often only on one side of the plant
Plants wilt on the hottest parts of the day then will recover
Wilting becomes more extensive and plants collapse and die
Where does What makes Fusarium (vascular wilts) enter the plant?
Enters through the root tips directly or through wounds
Fungus then grows in cortex between cells then enters xylem vessels through pits
Fungus remains in xylem vessels and travels upward by release of microconidia
Vessels are clogged, plant dies
How to control Fusarium (vascular wilts)?
Genetic - Plant resistant cultivars
Soil pH of 6.5 to 7.0
Fertilize with nitrate-N
Avoid spreading pathogen
Crop rotation of 4-5 years
Soil fumigation for commercial crops
Ongoing work with Pseudomonas, Trichoderma, and nonpathogenic F. oxysporum as biocontrol agents
Where does Verticillium occur?
What does Verticillium affect?
Affects >200 plant species (annual vegetables and flowers, fruit trees, field crops, shade and forest trees)
What are some species of Verticillium?
What does Verticillium overwinter as?
V. dahliae overwinters as microsclerotia; both species overwinter as mycelium in the propagative organs of perennial hosts, or in plant debris
How does Verticillium enter the plant?
Wounds or enters dirrectly
How is Verticillium spread?
Contaminated seed, cuttings, wind, flooding, and soil
What is the differences in symptoms of Verticillium and Fusarium?
differencesare Verticillium causes disease at lower temperatures, symptoms develop more slowly and appear on lower or outer part of plant
What are some host of V. dahliae?
Tomato, cucumber, lettuce,
What are some host of V. albo-atrum?
Tomato, okra, alfalfa, barley
How do you control Verticillium?
Plant resistant cultivars
Grafting onto resistant rootstock
5-year crop rotation
Chemical-Fumigation for commercial crops
Where does Thielaviopsis occur?
What is a major symptom of Thielaviopsis?
discrete, black, necrotic lesions or coalescing lesions on root
Thielaviopsis is a cool weather disease
What is the lifecycle of Thielaviopsis?
Hyaline (colorless) non-reproductive hyphae (no spores produced)
Pigmented hyphae produce asexual spores(C. elegans endoconidia - colorless, cylindrical)
Dark chlamydospores produced in chains (T. basicola) - overwintering structure
What are the overwintering structures of Thielaviopsis?
What conditions does the disease caused by Thielaviopsis favor?
cool, wet, alkaline soils
What are control methods for Thielaviopsis?
Cultural- Rotations with monocots
Maintain soil pH near 6.0
Sterol inhibitor fungicides (triazoles)
Genetic -Resistant cultivars are available in some crops
Where does Rhizoctonia diseases occur?
Name some species of Rhizoctonia
Binucleate Rhizoctonia spp
Perfect (sexual) stage of Rhizoctonia
What are characteristics of Rhizoctonia?
Mycelium is colorless at first, but becomes yellow to light brown with age
Right angle branching hypha with a constriction at point of attachment of branch to main hypha
Brown to black loosely formed sclerotia
What is anastomosis?
fusion of touching hyphae; represents vegetative compatibility groups; results in heterokaryon cells
What does Rhizoctonia overwinter as?
mycelium or loosely-formed brown to black sclerotia in soil and infected plant material
When is Rhizoctonia more severe?
When soil is moderately wet and air temp is 15-18 c
Disease development of Rhizoctonia
Damping-off of seedlings
Stem canker or soreshin at soil line
Root lesions girdle the root which is eventually rotted through leaving a spear tip appearance
Reddish brown sunken lesions on lower leaves
On turf grass, only the leaves are killed (brown patch appearance)
On potato, hard black sclerotia form on the tuber surface
Thanatephorus cucumeris (sexual stage) causes necrotic lesions on leaves of tobacco (target spot)
What are some controls of Rhizoctonia?
plant on well-drained soil, adequate spacing between plants, tillage
Soil drenches with PCNB, drenches on soil or seedlings with chlorothalonil, thiophanate methyl, or iprodione
Biological - work with Pseudomonas, Trichoderma, Gliocladium, Laetisaria, and Bacillus
Where does Sclerotium diseases occur?
Worldwide in warm climates
What are some identifying symptoms of Sclerotium?
seedling damping-off; stem cankers; rot of crowns, roots, tubers, bulbs, and fruits
What does Sclerotium affect?
egetables (carrot, celery, crucifers, eggplant, lettuce, okra onion, peppers, tomato), flowers, cereals, field crops (cereals, peanuts, cotton, tobacco), forage plants, and weeds
Name some species of Sclerotium
What is the Phylum in which Sclerotium is classified
What does Sclerotium overwinter as?
What is the disease cycle of Sclerotia?
Fungus kills and disintegrates tissue directly by producing oxalic acid; fungus also produces pectinolytic and cellulolytic enzymes
Fungus attacks at soil line
What conditions make Sclerotium more severe?
Soil moisture is high and air temperature = 30 to 35ºC
How does Sclerotium develop?
Infected seedlings killed quickly
Fungus grows into the cortex and girdles the stem at the soil line (dark brown lesion on stem)
Lower leaves turn yellow and wilt
Fungus progresses up the stem and down to the roots
Fungus grows as a white mycelium on the soil surface to infect the next plant
Small, round sclerotia that are at first white, then become dark brown to black, are produced on infected tissue
What are host of Sclerotium rolfsii?
Soybean, melon, lettuce, onion, tomato, alfalfa, barley, sorghum,
What are host of Sclerotium cepivorum?
How do you control Sclerotium?
Cultural - crop rotation with a nonhost (corn, wheat), deep plowing to bury sclerotia, using ammonium-N fertilizers, and soil solarization
Soil drenches with PCNB, captafol, and dichloran
Biological - work with Pseudomonas, Trichoderma, and Streptomyces
Where does Macrophomina occur?
Macrophomina has a large host range
What growth stages does it affect?
Young and mature plants
What is the Phylum in which Macrophomina is classified
How many species are there of Macrophomina?
What does Macrophomina overwinter as?
What is a Pycnidia? (Macrophomina)
structure that is immersed in host tissue and erupts; contains conidiophores that produce thousands of single-celled conidia
What is the resting structure of Macrophomina?
Macrophomina can persist in soil for up to
What causes infection for Macrophomina?
Germ tube penetration
How does Macrophomina develop?
Macrophomina restricts water movement in the plant by mechanical plugging of the water-conducting vessels with mycelium and microsclerotia
Fungus secretes toxins and enzymes that kill host tissues
Fungus does not survive well in wet soils (microsclerotia may last 7-8 weeks, mycelium lasts a few days)
What conditions make Macrophomina more severe?
Temperatures of 82 to 95°F (28 to 35°C) - hot, dry conditions promote disease
What are some host of Macrophomina phaseolina
Sorghum, soybean, bean, melon,
How do you control Macrophomina?
Plant high-quality, certified, disease-free seed
Plant seeds at the recommended rate. Over-crowding makes seedlings more susceptible to infection.
Fertilize, based on a soil test
Rotate to non-host crops (cereals) for 1-3 years, depending on crop
If possible, irrigate during extended periods of hot, dry weather
Plow down/ remove infected crop residue (if erosion is not a problem). This leaves sclerotia in soil where they are more subject to attack by other soil microorganisms
No effective fungicides available
What is the Phylum in which Magnaporthe is classified
What are the main host of Magnaporthe?
Hosts are mainly members of Poaceae (barley, millet, rice, wheat, turfgrasses, grass weeds)
What is the distribution of Magnaporthe?
Worldwide wherever host are grown
What does Magnaporthe affect?
Foilage and roots
causes seed and seedling rots, wilt, and leaf spot
Name some species of Magnaporthe
Magnaporthe grisea (rice blast disease and other cereals)
M. oryzae (blast disease of rice and other cereals)
M. poae (summer patch of turfgrass)
M. rhizophila (cereals, grasses)
M. salvinii (stem rot of rice)
What are some characteristics of Magnaporthe grisea?
Spindle-shaped, necrotic lesions on rice leaves
Anamorph = Pyricularia grisea
How does Magnaporthe overwinter?
Hyphae in dead plant tissue, previously colonized by the fungus
What is the disease cycle of Magnaporthe?
Hyphae in dead plant tissue, previously colonized by the fungus (overwintering stage) comes in contact with healthy roots
Invades vascular tissue
Sexual stage can be formed (perithecia with ascospores)
Asexual spores formed, serve to spread the pathogen to aerial regions
How does Magnaporthe develop?
Fungus enters the plant either through the cuticle or via stomata
Latent periods require 4 - 6 days at optimal temperatures (24-28°C)
At RH >93%, conidia are produced within 6 days after germination
Blast is a polycyclic disease, with 7 - 8 cycles per year in temperate environments, compared with 10 - 15 cycles per season and 2 - 3 seasons per year in tropical environments
How do you control Magnaporthe?
Plant resistant cultivars
Avoid excess fertilizer
Optimize water management
Chemical - seed treatments
Carpropamid, probenazole, tricyclazole, pyroquilon
Foliar chemical treatments
Phosphorothiolates, strobilurins, melaninbiosynthesis-inhibitors, kasugamicin, blasticidin
Ralstonia solanacearum is a
Gram-negative rod, aerobic bacterium
Pathogenic colonies of Ralstonia solanacearum
opaque, no flagella
Diseases caused by Ralstonia solanacearum
Wilt of several hundred plant species (tobacco, tomato, potato, pepper, eggplant, peanut, soybean, banana)
What is the distribution of Ralstonia solanacearum?
Worldwide in warm climates
Is it unusual for 100% of a solanaceous field crop to be killed quickly by Ralstonia solanacerum?
Common disease names of Ralstonia solanacearum?
Southern bacterial wilt (or bacterial wilt) of vegetables
Granville wilt of tobacco
Moko disease of banana
Brown rot of potatoes
Races of R. solanacearum
Race 1 - common in the USA on solanaceous crops and weeds, peanuts, soybeans, diploid bananas
Race 2 - triploid bananas, Heliconiaspp.
Race 3 - potato, tomato, weakly pathogenic on tobacco (not in USA)
Race 4 - ginger, found in Asia
Symptoms of Ralstonia solanacearum
Yellowing, stunting, dwarfing, development of adventitious roots, wilting
Infected young plants die quickly
In older plants, wilting of the youngest leaves or only on one side may occur first, followed by irreversible wilting
Discolored vascular tissue and bacterial ooze
What is the disease cycle of Ralstonia solanacearum?
can survive in soil without host tissue, and can survive in diseased plant tissue, seeds, tubers, and weed hosts
Wound parasite; injury (usually roots) is essential for infection
After entering a wound, the bacteria reach the large xylem vessels and produce pectolytic enzymes and cellulases
Cavities filled with bacteria are created inside the plant
What are controls of Ralstonia
Crop rotation or fallow
Steam treatment of soil
Plant disease-free planting materials
Control root-chewing insects and nematodes
Plant crops early
Resistant cultivars (for some plants)
Biological-Research with antagonistic bacteria and nonpathogenic R. solanacearum
Chemical-Fumigation of soil with chloropicrin
Events of September 11, 2001 and the subsequent anthrax murders precipitated legislation to regulate the importation, movement, and possession of agents and toxins that could be used in biological warfare
Bioterrorism Act of 2002
List of Select Agents
R. solanacearum, race 3, biovar 2
Causes a serious brown rot of potatoes and wilt disease of other hosts (tomatoes, peppers, bean, geranium, etc.) in temperate and subtropical climates
Distributed worldwide, except U.S. and Canada; found in the U.S. and Canada on geranium imported from Guatemala in 1999 and Kenya in 2003.
Most bacteria that cause plant disease cannot survive outside of the plant
Nutrition and moisture are critical for bacteria
Bacteria occur in ____ in the soil
Bacteria can move ___ cm/day in soil water
What is a Rhizosphere?
The portion of the soil that directly influenced by substances excluded from roots in soil solution
What is a strain
Descendents derived from a single colony in pure culture
What is a clone?
Descendants derived from a single parent cell
What is a culture?
Population of bacteria in a test tube or on an agar plate
Where does agrobacterium occur?
What family does Agrobacteria belong to?
What is agrobacterium tumefaciens?
Aerobic, rod-shaped bacteria, gram negative cell wall structure. 1-6 flagella used to swim
Name some species of Agrobacterium
Each of the four species contian pathogenic and non-pathogenic strains
Formally, where was all the non-pathogenic strains place?
What is a plasmid?
Small, extra-chromosomal, hereditary, circular DNA
Replicates or multiplies independently of the bacterial chromosome
What is the disease cycle of Agrobacterium tumefaciens?
A. tumefacienscan survive in soil without host tissue
Wound parasite, plant injury is essential for infection
Disease developement of A. tumefaciens
After entering a wound, the bacteria attach to the plant cell
Plant produces phenolics in response to wounding (these compounds are toxic to many plant pathogens)
But, in response to plant phenolics, A. tumefaciens begins processing T-DNA(Transfer-DNA), which is carried on the Ti plasmid
T-DNAis transferred to the plant cell and becomes integrated into the plant cell's genetic material
This permanent genetic change is called transformation
What is the role of the Ti plasmid
Host range-determines which types of plants will be infected
Opine catabolism-provides food for the bacterium
Plant hormones-causes cell multiplication and enlargement in the plant
What is the host range of Agrobacteria?
Many dicots and some gymnosperms can be infected by agrobacteria, but individual strains of Agrobacteriumare host specific
Monocots are much less susceptible to agrobacterium
Do all isolates of Agrobacterium cause plant disease?
No, only 10% of isolates are pathogenic
Only isolates of Agrobacteriumthat carry the Ti (tumor-inducing) or Ri (root-inducing) plasmid can cause disease in plants
What are some of the symptoms of Agrobacterium?
Young tumors are round, smooth, and white or lightly colored
Older tumors are irregular, rough and dark brown
Unlike other bacterial diseases, bacterial ooze is not associated with
agrobacteria (crown gall)
Symptoms of crown gall disease (agrobacterium)
Tumors appear at the crown or soil line of most plants
Name some host of A. tumeficiens
Apple, pear, peach, cherry, almond, raspberry and roses
Agrobacterium vitis causes crown gall disease in
How to control crown gall disease
Cultural -Practice sanitation
Avoid wounding the plants
Control root-chewing insects
Plant disease-free plants
Rotate to corn or grain in infested fields (may take several years)
Use Agrocin K1026 (nonpathogenic Agrobacterium) as a pre-plant root dip
Apply before infection
Produces an antibiotic (agrocin) and competes for sites on the plant roots
Chemical-Bacticin (petroleum product) painted onto small galls or onto cut surface of large galls
Fumigation of soil with chloropicrin
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