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Transcript of Sec 3 Protection
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Principales of Plant Protection
Practicalpart (Sec3)
Plant Diseases Caused by Viruses and
Prokaryotes
Mohamed
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Plant viruses
Like all other viruses, plant viruses areobligate intracellular parasites that do
not have the molecular machinery toreplicate without a host.
Viruses are extremely small and canonly be observed with an electronmicroscope. The structure of a virus is
given by its coat of proteins, whichsurround the viral enome.
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Viruses also cause manyimportant plant diseases andare responsible for hugelosses in crop production and
quality in all parts of theworld. Infected plants mayshow a range of symptomsdepending on the diseasebut often there is leaf
yellowing (either of theYellow mosaic symptoms onsquash caused by Squash mosaicYellow vein-banding symptomson grapevine caused by
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Bacteria
The plasma membrane (in Gram-positivebacteria) and both membranes in Gram-negative bacteria are phospholipid bilayers
prokaryotic (nomembrane-enclosednucleus)
no mitochondria orchloroplastsa single chromosome,closed circle of double-
stranded DNAIf flagella are present, theyare made of a singlefilament of the proteinflagellin.
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Caused by:Agrobacteriumtumefasciens
SYMPTOMS: Rough abnormal
galls develop on roots,crowns, and occasionally on
aerial parts of stone fruittrees.
Young trees become stuntedand older trees oftendevelop secondary woodrots.
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DISEASE CYCLE
The bacteria survive in gall tissue, in soil, or in apparentlyhealthy root of host plants.
The bacterium may persist in field soil for at least one year,or considerably longer if large amounts of infected root
residues remain in soil after removal of trees. The pathogen penetrates only through wounds. The most
susceptible wounds on stone fruits are the crown end rootsand rarely on trunks and limbs.
The bacteria attach to the wounded host cells and thentransfer T-DNA into the cell.
Infections are favored by moist , alkaline, poorly drainedsoils and can be stimulated by the feeding of plant parasiticnematodes.
At temperatures above 20C galls become obvious in 2-4
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DISEASE MANAGEMENT
Proper sanitation and cultural practices:the use of certified disease-freetransplants, careful handling to avoidinjury as much as possible during planting
and life of trees in the orchard, andplanting in well drained soils.
Biological control, using a non pathogenic
strain, A. radiobacter K84, that producesthe antibiotic agrocin 84, is effectivepreventive treatment.
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Phytoplasma is a prokaryote.
wall-less intracellular bacteria.
paleomorphic shape.
cannot be grown in vitro (absolute parasite).
multiplication by binary fission or budding.
localized in the phloem sieve tubes of infectedplants from where it is acquired by the vector forsubsequent transmission.
it invades systemically all plant organs.
Phytoplasma
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Examples
Witches Broom Disease of citrus byPhytoplasma
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Spiroplasma
Citrus Stubborndisease
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Citrus Stubborn disease
Causal agent
First mollicute of plant origin to becultured (1970).
Characterized as Spiroplasma citriin 1973.
(Charbonneau & Ghiorse,
Characteristics: Wall-less prokaryote Transmitted to plant phloem by
leafhoppers Motility and helicity:
cytoskeleton
(Yokomi et al.,
GEOGRAPHICAL DISTRIBUTION f it t bb di
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Europe France (Corsicaonly) GreeceItaly (few records;
Sardinia, Sicily)SpainTurkey
AfricaAlgeria EgyptLibyaMorocco
Tunisia
CyprusIranIraqIsraelJordanLebanon
PakistanSaudiArabia
SyriaTurkeyYemen
Asia
NorthAmerica
Mexico
USA (Arizona,California, Illinois,Maryland).
Argentina
(Tucumn)Brazil (So Paulo)PeruSurinameVenezuela.
SouthAmerica:(Unconfirmed)
Oceania
New Zealand(isolated
GEOGRAPHICAL DISTRIBUTION of citrus stubborn diseaseBased on EPPO Data Sheets
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Develop best andshow symptoms
under hotconditions
S. citri multiplies in its vector, thatbecome infective 10-20 days after
acquisition
Acquiring S.citri from
other hosts
Infectphloem
sieve tubes
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Tree symptoms:
Fruit symptoms:
Suppressed fruitingLopsided, Acorn shaped.Styler end green.aborted seeds
Stunted growthUp-right foliationShorter, chlorotic leaves.
short internodes
Symptoms
C lt i
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S
Culturing
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Biologicalindexing
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S l i l
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Commercialkit (Sediag
Italy)Coating (IgG)
Sample plant extract
Conjugate (AP-IgG)
Substrate(P-nitrophenylphosphate)
PhotometricalMeasurment at 405
nm
Washing &Incubation
Washing &Incubation
washing
(Clark and Adams, 1977)
Serological assayELISA
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Management
Certification
Production of
healthybudwood.
Surveynurseries
andyoungorchards
Rougingand
replacingsymptomatic trees
Vectorcontrol
Trapplants