Transcript Nematodes - Welcome to SIU Plant Pathology

ENDOPARASITES
Root-knot
nematodes
Root-lesion
nematodes
ECTOPARASITES
Dagger nematodes
Reniform nematodes
Nematode Damage


Rarely, does a single nematode pose a
threat to a plant. (exceptions - virus
vectors and sting nematodes)
Damage to plant parts results from many
nematodes feeding at once.

The root system of plants can be growing in
the presence of hundreds of thousands or
even millions of nematodes.
Nematode Damage

Quite often it is very difficult to see symptoms
caused by nematode (even though yield loss
may be reduced by 30%).

This is compounded by the fact that
nematodes are rarely normally distributed in a
field.

Nematode damage can be confused with
herbicide and other chemical injury.
Damage
Mechanical injury results from the nematode stylet puncturing the
cell wall, and is followed by the secretion of enzymes and nutrient
extraction. This process leaves cells that are damaged or
completely destroyed.
Nematode damage can result in a variety of symptoms:
1. Lesions
2. Galls or swellings
3. Stunted plants
4. Loss of vigor
5. Excessive root branching
6. Twisted or distorted stems and/or leaves
7. Disruption in flower development / sterility
8. Dead or incapacitated root tips
Disease Complexes - While nematodes are devastating pathogens,
their most significant influence in agriculture results from their
participation in pathogen complexes.
Damage
Nematodes and viruses - Nematodes can serve as vectors for
as many as 28 viruses, virus retention can last until
molting and viruses cannot be passed to offspring.
•
Trichodorus spp. - Stubby-root nematodes
• Netuviruses (NETU) rod-shaped - tobacco rattle virus,
pea early browning virus
•
Xiphenema spp. – Dagger nematodes
• Nepoviruses (NEPO) have a polyhedral shape grapevine fanleaf virus, tomato ringspot virus
Damage
Damage
Taxonomy
Kingdom Animalia
Phylum Nemata
Class Secernentea
5 other orders contain free-living forms and parasites of animals
Order Aphelenchida - parasites of higher plants (usually on above
ground parts), fungi, and insects
Important genera:
Aphelenchoides - foliar nematode
Bersaphelenchus - pine wilt nematode
Order Tylenchida - parasites of higher plants, insects, and fungi –
largest % of plant pathogens
Important genera:
Heterodera spp. - cyst nematodes
Meloidogyne spp. - root-knot nematodes
Pratylenchus spp. - root-lesion nematodes
Taxonomy
Kingdom Animalia
Phylum Nemata
Class Adenophorea (as opposed to Secernentea)
11 other orders contain free-living forms and parasites
of animals and microorganisms
Order Dorylaimida - plant parasites/virus vectors
(Stylet without knobs and no distinct median bulb)
Important genera:
Xiphinema spp.- dagger nematode
Longidorus spp.- needle nematode
Trichodorus spp.- stubby-root nematode
Root lesion nematodes

Pratylenchus spp.




7 important species in United States
Most plants are susceptible to one or more species
Migratory endoparasite, can leave and reenter the
roots many times in its lifecycle.
Males may or may not participate in reproduction.
Root lesion nematodes
Root-knot nematode

Meloidogyne spp.
 M. incognita – southern-root knot
 M. hapla – northern root-knot
 All are sedentary, endoparasites

After J2 stage enters the root and establishes giant cells (cells
enlarge and rapidly divide) creating a more efficient nutrient
sink for the nematode = gall production.

After the J2 becomes an adult, males leave the root. The
female will swell upon maturity producing several hundred
eggs. Males may or may not participate in reproduction.

Population is managed by the ratio of females : males that are
produced. Immature females can change to males if the
population density can not be supported.
Root-knot nematode
Root-knot nematode
Juveniles in root
Male, hatching from cuticle
Gall, with female
protruding
Giant cell
Root-knot nematode
Root-knot Nematode
Cyst nematodes

Heterodera spp.
 H. schactii – sugar beet cyst nematode
 H. glycines – soybean cyst nematode – $3 billion in damage/year
 All are sedentary, endoparasites

After J2 stage enters the root and establishes a smaller feeding
site than root-knot nematode. No gall production.

After the J2 becomes an adult, males leave the root to fertilize
the females that have protruded through the root.

The female will swell upon maturity producing several hundred
eggs outside and inside of her body. When she dies (4 wks old)
her body will become a protective cyst for her young.

Some eggs will hatch immediately, some later in the season,
next year or years, or never.
Soybean cyst nematode
Soybean cyst nematode
No visible symptoms
with 30% yield loss
Visible symptoms
with 60 -80% yield loss
Dagger nematodes

Xiphinema spp.





3 important species in United States
Characterized by long body and stylet.
Sedentary ectoparasite. Feeds only at the root tips.
Feeding produces knobby, stunted roots.
Males are required for reproduction, females produce
very few eggs, but lives several months (most other
nematodes live a few weeks).
Dagger nematodes
Dagger nematodes
Stubby roots
Stunted plants
Dagger nematodes
(grape fan leaf virus)
Management Strategies
I. Cultural practices - Includes agricultural tactics that
indirectly influence pathogen populations and
communities.
a. Crop rotation
b. Trap crops
c. Fallow
e. Flooding or heat
f. Tillage
g. Planting date
Management Strategies
II. Breeding for resistance
The use of nematode resistant varieties is a major management
strategy. In many crops, chemical control is not economically
viable and breeding is the only available tactic.
One of many limitations is that where races of nematodes are
problematic (such as soybean cyst nematode and root-knot
nematode), effective control of nematode populations occurs
only when the plant contains resistant genes against the
specific race present.
Management Strategies
III. Biocontrol
The use of fungi, bacteria, viruses, other nematodes,to
manage nematodes. The are many examples of biocontrol
of nematodes, however, very few work in the field.
Bacterium - endospore forming Pasteuria penetrans
Fungus - adhesive rings by Arthrobotrys spp.
Management Strategies
IV. Chemical control
The use of pesticides or other chemicals to reduce or
eliminate nematode populations.
Nematicides - are used to manage nematode populations
on high value crops. The use of nematicides is being
reduced because of toxicity to the environment and to
humans.
examples – Methyl Bromide, Vapam, Telone, Temik,
Mocap, Counter