clear description of the disease and symptoms and the dection techniques treatment and control or preventive measures of that diseases

1. POTATO SPINDLE TUBER
VIROID(PSTV)
D.INDRAJA

2. • The Potato spindle tuber viroid ("PSTVd") was the first viroid to be
identified.
• PSTV is a small, single stranded circular RNA molecule
• The natural hosts are potatoes (Solanum tuberosum)
and tomatoes (Solanum lycopersicum).
• All potatoes and tomatoes are susceptible to PSTVd and there is no
form of natural resistance.
• Natural infections have also been seen in avocados and infections in
other solanaceous crops have been induced in the laboratory.

3. Strains and symptoms
• Different strains of PSTV exist and symptoms range from mild to
severe.
• Mild strains  no obvious symptoms.
• Symptoms in severe strains are dependent on environmental conditions
and are most severe in hot conditions.
• Symptoms may be mild in initial infections but become progressively
worse in the following generations.

4. • color changes and size reduces
in the foliage leaves
• Common symptoms of severe infections include
• spindle-like elongation
with numerous eyes
and tapering ends

5. • Sprouting also occurs
at a slower rate than in
unaffected potatoes
• Infected tomatoes are slower to show symptoms which include
stunted growth with a ‘bunchy top’ caused by shortened inter-nodes.

6. • Leaves become yellow
or purple and often
become curled and
twisted
• Necrosis eventually occurs in the
veins of the bottom and middle
leaves and the top leaves decrease
in size.

7. • Fruit ripening is also
affected leading to hard,
small, dark green
tomatoes

8. Transmission
• It is contact transmitted through small wounds in the leaf surface caused
by contact between healthy and diseased plant sap.
• Spread can occur through handling of plants, movement of animals and
machinery through a crop, cutting tools and on clothing.
• Infected cutting knives used for cut seed will spread the viroid prior to
planting.
• Initial introduction of the viroid into potato crops is mostly through
infected seed tubers and in tomato by infected true seed.
• Transmission also occurs through pollen but only to the seeds
pollinated, not to their mother plant.
• Transmission is also reported by aphids.

9. Detection
• Tomato test (mechanical transmission)
Plant tissue
macerated in
distilled
water
Step-2
Mechanically
transmitted
by rubbing or
spraying the
sap
Step-3
Kept at 30oc

10. 2. R-PAGE(RETURN PAGE)
• A gel electrophoretic technique for the rapid and sensitive detection of
viroids and virusoids is described. In the procedure gel electrophoresis
is first carried out under native conditions.
• Before the viroid (or virusoid) bands will leave the gel, conditions are
changed to provide denaturing conditions which are achieved by
increasing the temperature and changing the buffer. After changing the
polarity of the electric field all nucleic acids in the gel “return” in that
they now migrate towards their original starting point.
• Under the denaturing conditions in the second electrophoresis viroids
(or virusoids) unfold into the conformation of a circle without
intramolecular base pairs, which structure is unique among the nucleic
acids in the gel.

11. • The denatured circular viroids migrate in the gel much slower than all
other nucleic acids of comparable molecular weight and, therefore stay
well separated behind the edge of the other nucleic acids. Thus, viroids
can easily be detected on the stained gel as a discrete band.
PAGE(POLYACRYLAMIDE GEL ELECTROPHORESIS)

12. 3.NASH(NUCLEIC ACID SPOT HYBRIDIZATION)
• It involves preparation of sample and applied to
membrane and make immobilized
• Hybridized with the radio labelled probe
• Detected by autoradiography
Autoradiography

13. Therapy
• By keeping the infected plants at low temperature(5o-8oc) and meristem
cultures grown at(5o-6oc)
• At low temperature multiplication of virus is reduced
Control
There are no chemical or biological controls available to control PSTVd
within infected plants. Therefore control is essentially through the use of
healthy virus-free seeds or planting material, and good crop sanitation
practices
• Control of initial infection is by production and use of healthy planting
material — certified seed
• Wear vinyl or latex gloves when handling infected plants and dip
them in a solution of 2% sodium hypochlorite
• cutting tools should be washed after use in a solution of 2% sodium
hypochlorite.

14. COCONUT CADANG CADANG
VIROID (CCCV)

15. • Cadang-cadang is a disease caused by Coconut cadang-cadang
viroid (CCCVd), a lethal viroid of coconut (Cocos nucifera)
• The name cadang-cadang comes from the word gadang-gadang that
means dying in Bicol
Geographical distribution
• The CCCVd is widely spread in Philippines and it is mostly found
in Bicol Region, Masbate, Catanduanes, Samar and other smaller
islands in the zone

16. Molecular structure
• CCCV are small, circular, and single-stranded. They cannot replicate
themselves, and therefore are completely dependent on a host.
• CCCV have a sequence of 246 nucleotides, 44 of which are common with
most viroids.
• CCCV can add a cytosine residue in the 197 position and increase the size to
247 nucleotides.
• It is known that forms of CCCV with 247 nucleotides cause severe
symptoms. Their minimum size is 246, but they can produce forms from 287
to 301 nucleotides.
• In CCCV, changes in molecular forms are related to the steps of the disease.
• There are four different RNAs found in CCCV, two of them fast and the
other two slow (the difference between fast and slow RNA is their mobilities
in electrophoresis gel).
• In the early stages of the disease, RNA fast 1 and RNA fast 2 appear, while
in the late stages RNA slow 1 and RNA slow 2 are detected

17. Symptoms
• Symptoms of cadang-cadang develop slowly over 8 to 15 years making
it difficult to diagnose at an early time.
• There are three main “stages” of defined series of characteristics:
Early 2-4 yrs
 medium 2 yrs
late stages 5 yrs
early
• These symptoms include scarification of
the coconuts which also become
rounded.
• The leaves (fronds) display bright yellow
spots.

18. medium stage
• inflorescences become stunted and eventually killed, so no more
coconuts are produced.
• Yellow spots are larger and in greater abundance to give the appearance
of chlorosis.
Helathy infloroscence
diseased

19. final stage
• yellow/bronze fronds start to decrease in size and number.
• Finally, all the leaves coalesce, leaving just the trunk of the palm “standing like a
telephone pole

20. Transmission
• The mode of natural inoculation of the viroid is unknown.
• There has been evidence that the transmission through pollen and seed
can occur but they have a very low transmission rates:
• progenies of healthy palms pollinated with diseased pollen, exhibited
disease symptoms 6 years after germination.
• CCCVd can spread through mechanical inoculation primarily through
contaminated farm harvesting tools due to the improper sanitary
conditions.
• Experimental transmission of the CCCVd using insects as vector has
been unsuccessful although there are few evidences that the
transmission of the viroid might be related to the wounds
of coelopteran insects, but this has not been properly investigated

21. PAGE Electrophoresis with
silver stain
Sample is first amplified by
PCR and dotblot is performed
D
E
T
E
C
T
I
O
N

22. Treatment
• Coconut cadang-cadang disease has no treatment yet.
• However, chemotherapy with antibiotics has been tried
with tetracycline solutions; antibiotics failed trying to alter progress of
the disease
• When the treated plants were at the early stage, tetracycline injections
failed to prevent the progression of the palms to more advanced
stages. Penicillin treatment had no apparent improvement either.
• Eradication of diseased plants is usually performed to
minimize spread but is of dubious efficacy due to the difficulties of
early diagnosis as the virus etiology remains unknown

23. Control
No definite control measures exist at the present.
• Eradication is ineffective because of the long latent period between
infection and appearance of symptoms, which is approximately 1 to 2
years.
• Cross-protection is a possibility for the future. Cross infection means
inoculating the coconut with a mild strain of the viroid to give the
coconut tree some degree of protection from infection by the killer
form. But in the case of Cadang-cadang, this is still under research
• control measures are those involving cutting and pruning tools. Do the
following:
• Disinfect tools using 10% bleach plus 1% mineral or vegetable oil
between working on palms.
• Only take seed from areas known to be free or have a very low
incidence of viroid
• Remove and destroy infected trees and replace them with healthy
seedlings. Ideally, the replacements should be tested for the disease.