Nematodes as Pathogens

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Nematodes as Pathogens

• Characteristics
• Brief History
• Nematodes as Parasites
• Importance
• Form and Function
• General Disease Cycle of Plant Parasitic Nematode

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Nematodes

•  
• The term Nematode is of Greek and Latin origin
•    Greek               Latin Nema thread   
  oid like   "threadlike worms"
•  
• Nematodes are animals therefore they are in
• Kingdom Animalia 
•     Phylum Nemata
• 30,000 described species
• 3,000 attack plants

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Characteristics of a nematode

• 1. Invertebrate (without a backbone)
• 2. Pseudocoelomate (body cavity not surrounded by
  peritoneum)
• 3. Round in cross section 
• 4. Vermiform (worm shaped) at one or more points
  in its life cycle
• 5. Heterotrophic (must eat for metabolic
  synthesis)
• 6. Nonsegmented (as opposed to true worms and
  insects)
• 7. Motile (sinusoidal wavelike movement resulting
  from contractions in the longitudinal muscles) 
• Active movement by nematodes rarely exceeds 75
  cm.  However, spreading of nematodes  is
  primarily due to passive means such as movement
  of infested soil and crop residue and by water. 

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Nematode Size

• Nematodes range in size from about 200 microns
  Sphaeronmema minutissima to 26 feet for the blue
  whale parasite, Placentanema gigantissima.
• Plant parasitic species range from 250 to 3,000
  microns long and 15 to 35 microns in diameter.

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Nematode Size
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Nematodes of Humans!

• Pinworm especially children
• Hookworm domestic animals, humans are a dead
  host
• Heartworms - domestic animals, humans are a dead
  host
• Trichinella trichinellosis of man
• Guinea worms
• Elephantiasis

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History

• Ancient times
• 1) Emperor's Classic of Internal Medicine (2700
  BC - China) - reference to the intestinal
  roundworm, Ascaris lumbricoides
• 2) Hippocrates (430 BC) -  first record of the
  pinworm, Enterobius vermicularis
• 3) The Bible (Deuteronomy 14 6-8) - sanitation
  laws for the Hebrews
• 4) The Bible (Numbers 214-9)
• Fiery Serpent
•  Dracunculus medinensis ???

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History

• Modern Times (Europe)
• 1) 1743 - Needham observes Anguina tritici in
  blighted wheat kernels
• 2) 1855 - Berkeley describes first root-knot
  nematode on cucumber in a glasshouse in England.
• 3) 1870-1910 - Kuhn works with and perfects the
  first method of soil fumigation (carbon
  disulfide) for nematode control.

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History

• Modern Times (America)
• 1) 1851 - Leidy publishes first study of
  nematodes in the U.S.
• 2) 1900s - Many and varied works of N. A. Cobb,
  the father of nematology in the U.S.
• 3) 1948 - 1st Nematology course at the University
  of California, Berkeley.
• 4) 1961 - Society of Nematologists founded

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Where Nematodes Live?
IN SOIL AS Ectoparasites-60 Endoparasites-30

ON AND IN ABOVE GROUND PARTS AS Ectoparasites-2
Endoparasites-8
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Importance
Annual losses due to nematodes are estimated at
over 80 billion.
 Life-sustaining crops   Loss    Other economically  important crops   Loss
Banana 19.7   Citrus 14.2
Barley 6.3   Coffee 15.0
Cassava  8.4   Cotton 10.7
Chickpea 13.7   Eggplant 16.9
Potato 12.2   Grape 12.5
Rice 10.0   Papaya 15.1
Soybean 10.6   Pineapple 14.9
Sugarcane 15.3   Tomato 20.6
Average 10.7   Average 14.0
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Important concepts

• All nematodes have well-developed muscular,
  digestive, excretory, reproductive, and nervous
  systems all covered with a layer of cells called
  the cuticle.
• 2. Nematodes differ from higher animals in that
  they lack organized circulatory and respiratory
  systems.
• 3. The digestive and reproductive systems are of
  the most taxonomic importance.  Only adult
  females should be used when identifying
  nematodes.

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Morphology
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Important concepts

• 4. The digestive system extends from the mouth to
  the anus and includes these parts
• Mouth, which is in the center of 6 lips
• b. Stylet, structure that acts as a syringe and
  is used to
• 1. penetrate the plant cell 2. secrete enzymes
  and take up nutrients from the plant 3. help
  hatch from egg
• c. Esophagus, which contains a median bulb that
  performs as a pump for enzyme secretion and
  nutrient uptake.
• d. Intestine, facilitates digestion and
  absorption of nutrients.
• e. Anus, opening from which waste is expelled
  from the intestine.

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Important concepts

• 5. Reproductive system
• a. Male      Testes, location of sperm
  production
•      Spicules, paired, protrusible copulatory
  structures that are used to open the vulva for
  sperm deposition
• b. Female     Ovary, location of egg production,
  nematodes may have one or two ovaries
•      Vulva, transverse opening to the outside
  environment 

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Vulva of Female
Spicule of Male
Male Female in copula
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Nematode Reproduction

• There are three types of nematode reproduction
• 1. Amphimixis - union of sperm and egg
• 2. Hermaphroditism - functional male and female
  sex organs on the same individual
• 3. Parthenogenesis - the production of offspring
  from eggs which have NOT been fertilized
• A nematode life cycle (egg to egg) generally
  requires 3 to 4 weeks.

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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. Excessive root branching 
• 4. Twisted or distorted stems and/or leaves 
• 5. Disruption in flower development / sterility 
• 6. Dead or incapacitated root tips
• Disease Complexes
• While nematodes are devastating pathogens by
  themselves, their most significant influence in
  agriculture is a result of their participation in
  pathogen complexes.