Crop Protection

1. Pre-Test
Simple Recall
1. The Father of Plant Virology.
2. The infective part of a viral particle.
3. The most important vector of plant viruses.
4. The first person to purify TMV and was a Nobel Prize awardee in 1946
because of this work.
5. Filipino plant pathologist who conducted numerous studies on abaca
mosaic virus in 1920s.
6. An entity mainly composed of RNA which is capable of causing plant
diseases.
7. The structure used by nematode as it feeds on plant roots.
8. Nematodes that penetrate inside the host as they feed on host plants.
9. A technique in virus detection and identification that involves antigen-
antibody reaction.
10. The most common technique in nematode isolation.

2. PLANT VIRUSES

3. What is a Plant Virus?
… a nucleoprotein that has the ability to cause disease in
plants
… all viruses are parasitic in cells and cause a multitude
of disease in all forms of living organisms, from single-
celled microorganisms to large plants and animals
… more than 2000 species of viruses are known and about
1/4 are reported to infect plants
… composed of nucleic acid and protein coat

4.  Size
 ultramicroscopic
 visualization requires an electron microscope
 Morphology
 filamentous/flexous rods, isometric, geminate, bacilliform
flexous rod – Maize dwarf mosaic virus
rod-shaped – Tobacco mosaic virus
isometric – Cowpea chlorotic mottle virus
 Genome
 nucleic acid genomes: either RNA or DNA
 variations in genome structure (single-stranded or
double-stranded; linear or circular; monopartite or
multipartite)

5.  Capsids
 have one or more protein coats composed of protein subunits
 Obligate Parasite
 depend on hosts for existence
 have no systems for the accumulation of metabolic materials;
energy generation; protein synthesis; capture of light energy
 entirely dependent on hosts for NA and amino acid synthesis
 Cell Association
 infect cellular structure and control part of the subcellular
systems of the hosts; act as “molecular pirates”; move directly
from cell to cell through plasmodesmata

6.  Replication by Assembly
 depend on pools of required components from hosts, e.g. the
enzyme systems (polymerases and reverse transcriptase)
 Vectors
 not capable of causing an entry wound; depend on vectors
to breach the epidermal layer of the plant
 include insects, mites, nematodes, fungi, seeds, dodders, human
and animals

7. Kingdom Viruses
RNA Viruses
(+) ssRNA
Rod-shaped particles
Genera: Tobamovirus (Tobacco Mosaic Virus)
Tobravirus (Tobacco Rattle Virus)
Filamentous particles
Genera:Potexvirus (Potato Virus X)
Potyvirus (Potato Virus Y)
Isometric particles
Genera:Waikavirus (Rice Tungro Spherical Virus)
Comovirus (Cowpea Mosaic Virus)
Cucumovirus (Cucumber Mosaic Virus)

8. RNA Viruses (cont.)
(-) ssRNA
Genera: Nucleorhabdovirus (Potato Yellow Dwarf Virus)
Tospovirus (Tomato Spotted Wilt Virus)
Tenuivirus (Rice Stripe Virus)
dsRNA
Genera:Fijivirus (Rice Fiji Disease Virus)
Oryzavirus (Rice Ragged Stunt Virus)
DNA Viruses
ssDNA
Geminate (twin) particles
Genera:Geminivirus (Maize Streak Virus)
(Beet Curly Top Virus)
(Bean Golden Mosaic Virus)

9. DNA Viruses (cont.)
ssDNA
Single isometric particles
Banana Bunchy Top Virus
dsDNA
Isometric, circular dsDNA
Genus: Caulimovirus (Cauliflower Mosaic Virus)
Bacilliform (rod-shaped)
Genus: Badnavirus (Rice Tungro Bacilliform Virus)

10. Historical Developments in Plant Virology
1500s - “Tulipomania” in Holland
- unusual case of a virus that increased the value of
infected tulips
- termed as “bizarres”
1886 - Adolf Mayer scientifically confirmed a primary
principle to plant virology when he transmitted
TMV to healthy tobacco plants by rubbing with
sap from infected plants

11. 1892 - Dmitri Ivanoski (Russian)
1898 - M. V. Beijerink (Dutch); they first indicated the
unique nature of viruses; they declared TMV as a
new type of pathogen called “contagium fluidium
vivium” or a contagious living fluid
1935 - W. M. Stanley worked on TMV and was the first
person to purify a virus; awarded the Nobel Prize
in 1946
1936 - Bawden and Pierie found the presence of
phosphorus in virus genome (indicated that the
suspension contains NA)

12. 1956 - Fraenkel-Conrat was able to isolate RNA from
TMV and used it to infect healthy tobacco plants
In the Philippines, Gerardo O. Ocfemia made numerous
studies on abaca bunchy top disease in 1920s to 1940s

14. Vector
Causal Agent

15. Symptoms of Virus-infected Plants
local lesions
stripes and streaks
ringspots
mosaic and mottle
vein clearing
vein banding
stunting/dwarfing
tumors/galls
distortion enations

16. Pepper Mosaic

17. Pepper Mosaic

18. Zucchini Yellow Mosaic

19. Rice Tungro

20. Tomato Yellow Leaf Curl

21. Latent Symptom – the host is infected by a virus but does
not show any visible symptom (termed as
symptomless carriers)
Masked Symptom – the host develops symptom upon
infection but temporarily becomes
symptomless under certain environmental
conditions (e.g. high or low temperature)

22. Virus Transmission
Mechanical Transmission
allows transmission of viruses without a vector
effective for viruses that infect epidermal cells
use of abrasives e.g. silica carbide, sand, bentonite
and celite
Potato virus X, Tobacco mosaic virus and Cucumber
mosaic virus

23. Insect Transmission
5 Orders of insects
 Order Homoptera (aphids, leafhoppers,
planthoppers, whiteflies, mealybugs and
treehoppers)
 Order Hemiptera (true bugs)
 Order Thysanoptera (thrips)
 Order Coleoptera (beetles)
 Order Orthoptera (grasshoppers)

24. Modes of Insect Transmission
nonpersistent viruses – persist in the vector for only
a few to several hours (termed as “stylet-borne”)
***APHID is the most important vector and
transmit about 250 known species of plant
viruses
semipersistent viruses – persist in the vector for
about 1 to 4 days
circulative/persistent viruses – accumulate
internally but not multiply
circulative/propagative viruses – multiply in their
vectors

25. Nematode Transmission
transmit about 20 viruses
Longidorus, Paralongidorus and Xiphinema transmit
polyhedral-shaped viruses (nepoviruses) such as
grape fanleaf and tobacco ringspot
Trichodorus and Paratrichodorus transmit rod-
shaped viruses (tobraviruses) such as tobacco rattle
and pea early browning
Mites Transmission
mites species belong Family Eriophyidae
transmit about 6 viruses (wheat streak mosaic)

26. Fungal and Fungal-like Transmission
species belong to Class Chytridiomycetes and
Plasmodiophoromycetes
transmit about 15 species of plant viruses
Root infecting species such as Olpidium, Polymyxa
and Spongospora
Dodder Transmission
Cuscuta sp. (with twining stems forming bridge
between two plants)
Other Modes of Transmission
seed, pollen and vegetative propagation and grafting

27. Detection and Identification
use of indicator
plants
Biological
activity
through electron
microscopy
Physical
Properties

28. through
Polymerase Chain
Reaction (PCR)
through serological
techniques
Nucleic Acid
Analysis
Protein
Analysis

29. ELISA (Enzyme-linked
Immunosorbent Assay)

30. Rapid Test Kits (Immunostrips)

31. How are Viruses Controlled?
Host Plant Resistance
Cultural Methods
Control of Vectors
Quarantine and
Eradication

32. Host Plant Resistance
 Develop plant cultivars with viral resistance through
traditional breeding.
 Cross-protection increases resistance of host plant by
introducing the mild strain of the virus.
 Genetic engineering to enhance host plant resistance
using genes coding for coat proteins, replicase,
antisense RNA and ribozymes

33. Vector Control
 Apply measures to control vectors.
Quarantine and Eradication
 Quarantine – acts as the first line of defense against the
introduction of many foreign viruses
 Eradication – done when exclusion of viruses fails
Cultural Control
 can be referred to as “wise production practices”

34. Plant Viroids
 small, low molecular weight RNA that can infect plant
cells, replicate themselves and cause diseases
 differ from viruses in at least 2 main characteristics:
1. size of RNA – viroid has 250 to 370 bases;
virus has 4 to 20 kilobases
2. virus RNA is enclosed with a protein coat while
viroid lacks this structure
 Cadang cadang disease of coconut
Potato Spindle Tuber
Citrus Exocortis
Avocado Sunblotch
Apple Scar Skin

35. Cadang cadang Disease (CCCVd)
 “cadang cadang” means dying
 first recognized in 1930s; similar disease called “tinangaja” caused
by a related viroid occurred in Guam
 the pathogen infects coconut and other palm species in the
Philippines (the only known monocot-infecting viroid)
 seed transmission is only 0.3%
 consists of 246 nucleotides, making this the smallest viroid known
 disease develop slowly over 8 to 15 years
 first symptom: fruits become rounded and develop
scarifications then leaves show bright yellow spots
 3 to 4 years later:inflorescences are killed; only new fronds
develop
 5 to 7 years later: severe leafspots will be noted; size of fronds
in the crown continue to reduce
 finally: growing buds die, fall off and leaves the palm trunk
standing like telephone posts

36. Control of Plant Viroids
Use of viroid-free
planting materials
Eradication of infected
plants

37. Plant Parasitic Nematodes
 derived from the Greek words “nema/nematos” =
thread and “edos” = resembling or likeness
 small, 300 to 1000 micrometers with some species up to
4mm long and 15-35 micrometers wide
 generally eel-shaped or vermiform and round in cross-
section with smooth unsegmented bodies, without legs
or other appendages
 nematodes may either be saprophagous, predaceous or
plant parasitic
 10% of the 30,000 described species are known as plant
parasites
 plant parasitic species are mostly obligate and
equipped with stylet

38. Morphology
… the cross section of a nematode body looks like a “tube
within a tube”
Outer Tube
 Cuticle – semi-permeable outermost covering of the
nematode body; made up of protein (keratin and
collagen); shed off during molting to allow growth
 Epidermis – thin layer which functions mainly for
secretion of new cuticle during molting
 Muscles – allows movement by alternate contraction
and relaxation of dorsal and ventral muscles

39. Inner Tube
 begins from the mouth opening to the anus (for female)
or cloaca (the common opening of digestive and
reproductive systems for male)
 possess stylet that they use in puncturing plant cells
and withdrawing their contents
 three types of stylets:
 Stomatostylet – with distinct cone, shaft and knobs; inside
hallow; possessed by members of the
Order Tylenchida
 Odontostylet – a hallow spear; possessed by members of the
Order Dorylaimida
 Onchiostylet – a bent solid needle-like stylet possessed by
members of the Order Triplonchida

40. Life Cycle of Nematodes
Adult
Larvae
(4 stages)
Eggs
Note: Nematode cycle is completed within 3 to 4 weeks only.

41. Terms Related to Nematode Reproduction
 Amphimictic – nematode species which requires the
presence of both female and male for reproduction to
occur.
 Parthenogenic – nematodes reproduce from eggs
without fertilization by sperm cells.
 Hermaphroditic – possessing both functional male and
female reproductive organs.
 Sexual dimorphism – phenomenon wherein the male
and female nematodes of the same species have entirely
different morphology.
 Sex reversal – phenomenon observed in juveniles of
parthenogenic species of Meloidogyne during
unfavorable condition. Depending on the onset of the
unfavorable condition, the gonad of “destined to be”
female juveniles develops into non-functional testis.

42. Groups of Nematodes
Based on Feeding Position
Ectoparasites – feed from the outside and only the
stylet enters the plant cells
Belonolaimus – sting nematode
Paratylenchus – pin nematode
Trichodorus – stubby-root nematode
Xiphinema – dagger nematode
Longidorus – needle nematode
Semi-endoparasites – feed by burying the front part
of the body into the host cells while the posterior
portion is outside the host
Pratylenchus – lesion nematode
Radopholus – burrowing nematode

43. Hoplolaimus – lance nematode
Helicotylenchus – spiral nematode
Ditylenchus – stem and bulb nematode
Aphelenchoides – foliar nematode
Endoparasites – the entire nematode body enters the
plant cells while it feeds
Meloidogyne – root-knot nematode
Heterodera – cyst nematode

44. Based on Movement while Feeding
Migratory – move from one part of the plant to
another portion of the host or move from plant to
the soil and back
Radopholus
Pratylenchus
Ditylenchus
Aphelenchoides
Sedentary – attach themselves to the roots or
burrow into the root
Meloidogyne
Rotylenchulus – reniform nematode
Tylenchulus – citrus nematode

45. Symptoms of Nematode Infection
Galls
Leaf discoloration
Excessive Root
Branching
Leaf Distortion
Wilting
Leaf spots
Necrotic lesions
Stunting

46. Root-knot symptom

47. Important Nematode Diseases in the Philippines
1. Slow decline of citrus – Tylenchulus semipenetrans
2. Spreading decline of citrus – Radopholus similis
3. Toppling of banana - Radopholus similis
4. Root knot of various crops – Meloidogyne spp.
5. False root knot – Naccobus spp.
6. Ufra disease of rice – Ditylenchus angustus
7. White tip disease of rice – Aphelenchoides besseyi
8. Rice root knot (mentek) – Hirschmaniella oryzae
9. Yellow dwarf disease of black pepper
– Radopholus similis
10. Red ring disease of coconut
– Radinaphelenchus cocophilus

48. Sampling Techniques
Reasons for Sampling:
 nematodes are too small to be seen with bare eyes
 symptoms caused are not typical
 need for quantitative estimation of density
Sampling Theories:
1. Spatial Distribution – nematode distribution within
the field is generally patchy owing to their small size
and slow rate of active movement.
2. Vertical Distribution – refers to the dispersal of
nematodes in a soil profile; mainly influenced by
density of feeder roots which is higher in the upper 30
cm of the soil.

49. 3. Temporal/Seasonal Distribution – influenced by
climatic pattern (wet and dry) and host availability;
nematode density is highest during near harvest stage
of crop
Extraction Techniques
1. Motility-dependent/active methods – Baermann
funnel and its modifications; H2O2 incubation
method
2. Motility-independent/passive methods – wet sieving
method; maceration; elutriation method; centrifugal
flotation

50. Disease Complex with Nematode
 Nematode and Viruses – Trichodorus/Paratrichodorus
and Tobacco Rattle Virus
 Nematode and Bacteria – Meloidogyne and
Ralstonia solanacearum
 Nematode and Fungi - Meloidogyne and
Fusarium oxysporum

51. Methods of Nematode Management
1. Prevention – quarantine at farm, country and
international level
2. Crop rotation – alternating susceptible host with non-
host crop
3. Trap crops – susceptible crops intentionally planted
but are uprooted before the nematode complete its life
cycle.
e.g. Crotolaria
4. Antagonistic crops – exudes chemicals that are either
repellant or nematicidal
e.g Tagetes patula – produces a-thertienyl
Brassicas – produces isothiocyanates

52. 5. Land management and cultural practices
 Early planting
 Plowing
 Flooding
 Organic soil amendment
6. Physical methods
 Steaming
 Solarization
 Field burning
 Heat treatment of planting materials
7. Resistant/Tolerant varieties
8. Biological control e.g. BIOACT
9. Chemical control
 Fumigants e.g. methyl bromide, ethylene dibromide,
chloropicrin
 Non-fumigants e.g. fenamiphos, thionazin, aldicarb, oxamyl,
methomyl

53. Good Day!
Good Day!
Good Day!
Good Day!

54. Post-Test
Give the specific causal agent of the following diseases:
1. Tomato root-knot infection
2. Tungro
3. Pepper Mosaic
4. Bunchy Top
5. Cadang cadang of coconut
True or False
1. All plant parasitic nematodes are obligate.
2. The completion of the life cycle of nematode is only 3-4 weeks.
3. Viruses can be detected and identified based on their protein
components.
4. ELISA is one of the serological techniques for virus identification.
5. Viroids are apparently naked entities.