Nematodes David Bird 515-6813 [e-mail]

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NematodesDavid Bird515-6813david_bird_at_ncsu.edu

• Lecture 1 Nematodes as plant parasites
• 4 case studies
• Lecture 2 Model systems and the phylum Nematoda
• Lecture 3 Nematode anatomy
• Lecture 4 Reproduction and development
• Lecture 5 Nervous system and behavior
• Lecture 6 Adaptations for plant-parasitism 1
• morphology and behavior
• Lecture 7 Adaptations for plant-parasitism 2
• genes, genomes and evolution of plant-parasitism
• Lecture 8 The world of plant-parasitic nematodes
  and their control
• Exam November 5

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What are nematodes?

• Nematodes are worms

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What are nematodes?

• Nematodes are worms
• Entire animal phylum Nematoda
• (lecture 2)

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What are nematodes?

• Nematodes are worms
• Entire phylum Nematoda
• Formal definition
• Pseudocoelomic
• Aquatic
• Un-segmented
• Molting
• Round-worms

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What are nematodes?

• Pseudocoelomic, aquatic, un-segmented, molting,
  round-worms
• round in transverse section
• posterior cross section through adult
• (h) hypodermis secretes the cuticle
• (m) 4 longitudonal muscle blocks
• (nc) nerve cord.
• (g) gonad
• (i) intestine
• cylinder within a cylinder

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What are nematodes?

• Pseudocoelomic, aquatic, un-segmented, molting,
  round-worms
• round in transverse section
• posterior cross section through adult. (g) gonad
  (h) hypodermal ridge (i) intestine (m) muscle
  (nc) nerve cord.
• Pseudocoelome
• Fluid-filled body cavity
• pseudo not full lined with cells
• of mesodermal origin

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What are nematodes?

• Pseudocoelomic, aquatic, un-segmented, molting,
  round-worms
• round in transverse section
• posterior cross section through adult. (g) gonad
  (h) hypodermal ridge (i) intestine (m) muscle
  (nc) nerve cord.
• pseudocoelome body cavity not full lined
• with cells of mesodermal origin
• molting
• all nematodes have
• egg (embryonic development)
• 4 larval (juvenile) stages L1-L4 (J1-J4)
• adult (males, females, hermaphrodites)

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What are nematodes?

• Elastic cuticle pseudocoelomic fluid
  (hydroskeleton) longitudinal muscles gt
  sinusoidal swimming motion

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Nematodes as plant-pathogens

• A major problem on many (all?) crops
• banana 19.7
• citrus 14.2
• coffee 15
• corn 10.2
• soybean 10.6
• sugar beet 10.9
• legume forages 8.2
• Many species ubiquitous cosmopolitan
• some have broad host-range some are generalists
• Chemical control is ineffective and dangerous
• many nematicides do not kill nematodes

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Crop damage A market analysis
17 species of nematode impact rice production
worldwide
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NematodesThe major pathogen of some crops
http//aes.missouri.edu/delta/research/soyloss.stm
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Nematodes are different plant-pathogens(compared
to bacteria, fungi, viruses)

• Animals
• nervous system
• behavior
• environmental sensing
• nematicide targets

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Nematodes are different(compared to bacteria,
fungi, viruses)

• Animals
• nervous system
• development
• coupled to host
• coupled to environment

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Nematodes are different(compared to bacteria,
fungi, viruses)

• Animals
• nervous system
• development
• many protein-coding genes
• nematode (C. elegans) 20,170 (ws187 January
  2008)
• (plant parasitic nematodes? Lecture7)
• bacterium (M. genitalium) 483
• yeast (S. cerevisiae) 6,186
• fungal pathogen (M. grisae) 11,108
• insect (Drosophila) 14,108 (R5.8 May 2008)
• mammal (human) 20,500 (January, 2008)
• plant (Arabidopsis) 27,235 (TAIR8 June, 2008)

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Plant-parasitic nematodes4 case studies

• Sedentary endo-parasites
• Root-knot nematode
• Meloidogyne spp.
• Cyst nematode
• Heterodera and Globodera spp.
• Migratory endo-parasite
• Lesion nematode
• Pratylenchus spp.
• Insect vectored nematode
• Pine wilt nematode
• Bursaphelenchus
• Lecture 8 The world of plant-parasitic
  nematodes.

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Root-knot nematode (RKN) Meloidogyne spp.

• Classic root galling phenotype
• Galls
• 3-7 giant cells at the core
• expansion/division of surrounding cells

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RKN

• 80 described species, distributed worldwide in
  temperate and tropical agriculture
• obligate parasites of essentially all vascular
  plants
• but individual spp./isolates may have restricted
  host range
• duration of life-cycle depends on spp. and temp.
• M. incognita on tomato _at_ 29C
• adult females develop 1315 days after root
  penetration
• egg laying 6 days later continues 23 months

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RKN life cycle
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Symptoms

• Amount of galling
• host plant species/cultivar
• Carrots typically undergo severe forking with
  galling predominantly found on lateral roots
• RKN galls on lettuce are beadlike
• On grasses and onions, galls
• usually small and barely noticeable

Resistant and susceptible lettuce
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Symptoms

• Amount of galling depends on
• host plant species/cultivar
• nematode population density
• more worms gt more galls
• more worms gt larger galls
• (multiple nematodes/gall)
• Meloidogyne species/race
• e.g., M. hapla produces galls less than half the
  size of those produced by M. incognita on the
  same plant hosts.

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Symptoms
Galls on cucumber roots
Galled potato
Galls on ligustrum roots
Carrots
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Symptoms

• Stunted or decline symptoms occur in patches
  rather than as a overall decline of plants within
  an entire field

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Case study 2 Cyst nematodes

• Two important genera
• Heterodera
• Heterodera avenae Cereal cyst nematode
• Heterodera glycines Soybean cyst nematode (SCN)
• Heterodera schachtii Beet cyst nematode
• etc
• Globodera
• Globodera pallida Potato cyst nematode (PCN)
• Globodera rostochiensis Potato cyst nematode
• Globodera tabacum Tobacco cyst nematode
• etc
• Restricted host ranges
• Major pathogens
• SCN infests every soybean-producing state in the
  U.S.
• total soybean yield loss estimates approaching 1
  billion per year
• PCN recently discovered in Idaho

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Cysts
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Cyst nematode life cycle
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SCN symptoms

• Termed soybean yellow dwarf disease
• Responsible for 50 of all pathogen related
  yield loss
• Resistant cultivars available
• (but not stable)
• feeding females obvious on roots

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Case study 3 Lesion nematode

• Pratylenchus spp.
• 70 species attack gt400 host plants
• potato, peanut, monocots, fruits
• Migratory endoparasites
• Herbivores cause massive
• physical damage
• Population density of 3,000 worms/gram of root
  possible
• Overwinter in root debris as J4

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Symptoms

• destructive feeders cause lesions
• predispose the plant to fungal infection
• disease typically in patches
• control
• pre-plant fumigation
• post-plant nematacides
• good sanitation to avoid infestation

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Case study 4 Bursaphelenchus

• Causative agent of pine wilt disease
• kills trees in less than a month
• mechanism
• worms feed on cells surrounding resin ducts
• resin to leak into the tracheids
• tracheid cavitation (air pockets) ensues
• transpiration cannot be sustained
• nematodes vectored by pine sawyer beetles
• Monochamus spp.

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Pine wilt disease

• Scots pine is the most susceptible tree species
• Distribution
• US
• especially mid-west
• discovered 1979
• Asia
• especially Japan
• Control
• Choice of unsusceptible trees, including
• balsam fir, eastern red cedar, piñon pine,
  lodgepole pine, limber pine, ponderosa pine,
  Balkan pine, Virginia pine, Douglas fir, eastern
  hemlock, etc.
• Destruction of infected trees
• Sanitation to avoid infestation
• B. xylophilus is a quarantine organism in the EU
• Chemical control of beetles not practical

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PPN identification
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Fumigant nematacides
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Non-fumigant nematacides
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Natural nematacides
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Future control???

• New nematacides
• traditional screens
• rational design from genomic approaches
• Identification/introgression of natural
  resistance
• marker assisted breeding
• Transgenic resistance
• move natural R-loci across species boundaries
• e.g., Tomato Mi confers RKN resistance in
  eggplant (but not tobacco)
• mimic natural resistance
• induce death of giant cells/syncytia
• use the feeding site to deliver an anti-nematode
  agent
• RNAi a nematode gene