Oct' 1216: Nematodes

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Oct. 12-16 Nematodes

• Monday
• Introduction and general features
• Root-Knot Nematodes (Meloidogyne spp.)
• Wednesday
• Cyst Nematodes
• Root Lesion Nematode
• Ectoparasitic genera
• Friday
• Seed and leaf-feeding genera
• Interactions with other pathogens

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Phylum Nematoda

• Abundant
• more individual animals are nematodes than
  anything else (80)
• Diverse
• - found in all habitats at many trophic levels
• Important
• Role in ecosystem services
• Human health
• Agriculture (animal and plant)
• Science model to study animal biology

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Nematodes in the Tree of Life
Eukaryotes
Animals
Bilateria
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Phylum Nematoda
Nematoda
Stilbonematids are marine nematodes that are
coated with sulfur-oxidizing bacteria. They live
few centimetres below the sea bottom, where they
migrate between superficial sand layers and
deeper ones. These migrations allow the microbial
symbionts to alternatively obtain oxygen and
sulfide. In turn, the microbes constitute the
major component of the worms diet.
Plant Pathogens
http//www.univie.ac.at/shallow-water-symbiosis
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Plant Pathogens
Nematodes are ecologically diverse
Diversity indices of nematode communities are
used as ecological indicators.
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sensory organs
touch receptor
chemoreceptor
stoma (mouth)
Feeds on bacteria
Plant feeding nematode
Nematodes use their nervous and muscular systems
to locate and obtain food
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Plant feeding nematodes are obligate parasites
that feed using straw-like stylet mouthparts.
Peter M. Sforza and Jon D. Eisenback Department
of Plant Pathology, Physiology, and Weed
ScienceVirginia Polytechnic Institute and State
UniversityBlacksburg, Virginia, USA
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Stylet morphology is diagnostic.
The shape and size of the stylet is related to
how and where the nematode feeds.
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stylet
reproductive system
esophagus
intestine
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Features common to plant parasitic nematodes

• Vermiform shape (some or all life stages)
• Stylet mouthparts
• Transparent cuticle
• Microscopic

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Nematodes move through soil pores to locate roots.
Nematodes are too small to move soil particles so
are restricted to living in soil pores.
Needle and sting nematodes are restricted to
sandy soils due to pore size requirements.
Nematodes are classified as mesofauna
S. Rose and E.T. Elliott
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Nematodes move easily in water films on a solid
surface, but not in free water.
Nematodes have four sets of muscles that run the
length of the body, causing them to move in a
dorsal-ventral plane.
nematode tracks on agar
Water films facilitate movement too much or too
little soil water decreases nematode activity.
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Their adaptations and strategies may differ, but
all nematodes share similar challenges in
completing the life cycle.
Egg
J2
J3
J4
Adult
molt
molt
molt
molt

• Developing / molting
• Receiving and processing information
• Moving
• Infecting / feeding
• Reproduction
• Persistence
• Dispersal

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Nematodes are animals that develop from a
juvenile state to sexual maturity.
Nematodes grow a new cuticle and stylet with
every molt.
egg
For many genera, juveniles have the same general
appearance as adults, but are smaller and
sexually immature. Adults can be distinguished
by the presence of a fully-formed reproductive
system.
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Life cycle differences
Stubby Root nematodes (Paratrichodorus spp.) have
a relatively short generation time 2 ½ to 6
weeks. Oregon State University (http//mint.ippc.
orst.edu/stubbynemaid.htm)
Dagger nematodes (Xiphinema spp.) may take up to
a year to complete one generation.
Other features that vary include egg-laying
habits, life stage that hatches from the egg,
obligate dormancy for some species, dispersal
strategies
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Top 15 Regulated Nematode Pests in the World

• Countries Plant Part
• Pest Nematode Regulating Infected
• Globodera rostochiensis 106 roots, tubers
• Aphelenchoides besseyi 70 leaves
• Ditylenchus dipsaci 58 leaves, bulbs
• Radopholus similus 55 roots
• Globodera pallida 55 roots, tubers
• Ditylenchus destructor 53 roots, seeds,
  tubers
• Heterodera glycines 52 roots
• Aphelenchoides fragariae 47 leaves
• Bursaphelenchus xylophilus 46 trees
• Xiphinema index 42 roots
• Nacobbus aberrans 38 roots, tubers
• Xiphinema americanum 30 roots
• Anguini tritici 24 seeds
• Heterodera schachtii 22 roots
• Bursaphelenchus cocophilus 21 trees

Occurs in Wisconsin
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Nematodes are often classified by their life
style
ectoparasitic nematodes - only the stylet enters
roots
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• endoparasitic nematodes
• enter into the root and feed from the inside
• sedentary root knot and cyst
  nematodes
• migratory root lesion
  nematodes

female
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Sedentary Endoparasites
All sedentary endoparasites have specialized
feeding sites in the root.
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root galls on infected lettuce roots
Root knot nematodes Meloidogyne spp.

• Most spp. have wide host range.
• 4 major species
• (many more)

adult female nematode on the head of a pin
juvenile next to a human hair
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Root-knot affects both quality and yield
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Root Knot life cycle

• Second stage juveniles enter behind root tip.
• Nematodes change in shape as they feed on 4-6
  specialized plant cells.
• Root cells increase and enlarge forming a gall.
• Males change form when they reach the adult stage
  and leave the root.
• Adult females lay eggs into an egg mass.

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egg
juvenile male
juvenile stages
adult stages
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nematode feeds on 4-6 giant cells
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Diagnosing a root knot nematode problem
Which plants are infected with root knot nematode?
symptoms sign
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sign root knot egg masses
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cyst nematode Heterodera spp.
Many species - narrow host range - named for
primary host
SCN Management Guide
cyst dead body of female
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SCN is the most important disease of soybean in
the U.S.
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susceptible cultivar on left / resistant on right
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Heterodera glycinessoybean cyst nematode
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J3
J2
nematode feeding cells
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soybean cyst nematode Heterodera glycines
SCN
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Symptoms stunting, chlorosis, patchy
distribution in field
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Microbivorous nematodes have open stoma
(mouth)
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Nematodes that live in soil are -
microscopic - transparent
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Plant parasitic nematodes have stylets
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root knot female (on the head of a pin)
egg
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