Nematodes as PathogensNematodes as Pathogens

CharacteristicsCharacteristics Brief HistoryBrief History Nematodes as ParasitesNematodes as Parasites ImportanceImportance Form and Function Form and Function General Disease Cycle of Plant General Disease Cycle of Plant

Parasitic NematodeParasitic Nematode

** Images and lecture material were not entirely created by J. Bond. Some of this material was created by others.**

NematodesNematodes  The term Nematode is of Greek and Latin originThe term Nematode is of Greek and Latin origin      Greek               LatinGreek               Latin

Nema = thread    oid = like =  "threadlike worms"Nema = thread    oid = like =  "threadlike worms"  Nematodes are animals therefore they are in :Nematodes are animals therefore they are in :Kingdom Animalia Kingdom Animalia         Phylum NemataPhylum Nemata

30,000 described species 30,000 described species 3,000 attack plants3,000 attack plants

Characteristics of a Characteristics of a nematode:nematode:

1. Invertebrate (without a backbone)1. Invertebrate (without a backbone)

2. Pseudocoelomate (body cavity not surrounded by 2. Pseudocoelomate (body cavity not surrounded by

peritoneum)peritoneum)

3. Round in cross section 3. Round in cross section 

4. Vermiform (worm shaped) at one or more points in its life 4. Vermiform (worm shaped) at one or more points in its life

cyclecycle

5. Heterotrophic (must eat for metabolic synthesis)5. Heterotrophic (must eat for metabolic synthesis)

6. Nonsegmented (as opposed to true worms and insects)6. Nonsegmented (as opposed to true worms and insects)

7. Motile (sinusoidal wavelike movement resulting from 7. Motile (sinusoidal wavelike movement resulting from

contractions in the longitudinal muscles) contractions in the longitudinal muscles) 

Active movement by nematodes rarely exceeds 75 cm.  Active movement by nematodes rarely exceeds 75 cm.  However, spreading of nematodes  is primarily due to passive However, spreading of nematodes  is primarily due to passive means such as movement of infested soil and crop residue means such as movement of infested soil and crop residue and by water. and by water. 

Nematode SizeNematode SizeNematodes range in size from about 200 microns Nematodes range in size from about 200 microns

SphaeronmemaSphaeronmema minutissimaminutissima to 26 feet for the blue to 26 feet for the blue whale parasite, whale parasite, PlacentanemaPlacentanema gigantissima.gigantissima.

Plant parasitic species range from Plant parasitic species range from 250250 to to 3,0003,000 microns microns long and long and 1515 to to 3535 microns in diameter. microns in diameter.

Nematode SizeNematode Size

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50%50%

10%10%

15%15%25%25%

PlantPlant

AnimalAnimal

Free-LivingFree-Living

MarineMarine

PHYLUM: NEMATODAPHYLUM: NEMATODA

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Non-Plant ParasitesNon-Plant Parasites

Nematodes of Humans!Nematodes of Humans!

Pinworm – especially childrenPinworm – especially children Hookworm – domestic animals, Hookworm – domestic animals,

humans are a dead hosthumans are a dead host Heartworms - domestic animals, Heartworms - domestic animals,

humans are a dead hosthumans are a dead host Trichinella – trichinellosis of manTrichinella – trichinellosis of man Guinea wormsGuinea worms ElephantiasisElephantiasis

HistoryHistoryAncient timesAncient times

1) Emperor's Classic of Internal Medicine (2700 1) Emperor's Classic of Internal Medicine (2700

BC - China) - reference to the intestinal BC - China) - reference to the intestinal

roundworm, roundworm, Ascaris lumbricoidesAscaris lumbricoides

2) Hippocrates (430 BC) -  first record of the 2) Hippocrates (430 BC) -  first record of the

pinworm, pinworm, Enterobius vermicularisEnterobius vermicularis

3) The Bible (Deuteronomy 14: 6-8) - sanitation 3) The Bible (Deuteronomy 14: 6-8) - sanitation

laws for the Hebrewslaws for the Hebrews

4) The Bible (Numbers 21:4-9) 4) The Bible (Numbers 21:4-9)

Fiery Serpent = Fiery Serpent =

  Dracunculus medinensis ???Dracunculus medinensis ???

HistoryHistory

Modern Times (Europe)Modern Times (Europe)

1) 1743 - Needham observes 1) 1743 - Needham observes Anguina tritici Anguina tritici in blighted in blighted

wheat kernelswheat kernels

2) 1855 - Berkeley describes first root-knot nematode on 2) 1855 - Berkeley describes first root-knot nematode on

cucumber in a glasshouse in England.cucumber in a glasshouse in England.

3) 1870-1910 - Kuhn works with and perfects the first 3) 1870-1910 - Kuhn works with and perfects the first

method of soil fumigation (carbon disulfide) for method of soil fumigation (carbon disulfide) for

nematode control.nematode control.

HistoryHistoryModern Times (America)Modern Times (America)

1) 1851 - Leidy publishes first study of nematodes in 1) 1851 - Leidy publishes first study of nematodes in

the U.S.the U.S.

2) 1900s - Many and varied works of N. A. Cobb, the 2) 1900s - Many and varied works of N. A. Cobb, the

father of nematology in the U.S.father of nematology in the U.S.

3) 1948 - 1st Nematology course at the University of 3) 1948 - 1st Nematology course at the University of

California, Berkeley.California, Berkeley.

4) 1961 - Society of Nematologists founded4) 1961 - Society of Nematologists founded

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IN SOIL AS:Ectoparasites-60%Endoparasites-30%

IN SOIL AS:Ectoparasites-60%Endoparasites-30%

ON AND IN ABOVE GROUND PARTS AS:

Ectoparasites-2%Endoparasites-8%

ON AND IN ABOVE GROUND PARTS AS:

Ectoparasites-2%Endoparasites-8%

Where Nematodes Live?

  Life-sustaining Life-sustaining cropscrops   % Loss% Loss   

  Other Other economically economically 

important important cropscrops

  % % LossLoss

BananaBanana 19.719.7    CitrusCitrus 14.214.2

BarleyBarley 6.36.3    CoffeeCoffee 15.015.0

Cassava Cassava  8.48.4    CottonCotton 10.710.7

ChickpeaChickpea 13.713.7    EggplantEggplant 16.916.9

PotatoPotato 12.212.2    GrapeGrape 12.512.5

RiceRice 10.010.0    PapayaPapaya 15.115.1

SoybeanSoybean 10.610.6    PineapplePineapple 14.914.9

SugarcaneSugarcane 15.315.3    TomatoTomato 20.620.6

AverageAverage 10.710.7    AverageAverage 14.014.0

ImportanceImportanceAnnual losses due to nematodes are estimated at over $80 billion.

Important concepts:Important concepts:1.1. All nematodes have well-developed muscular, All nematodes have well-developed muscular,

digestive, excretory, reproductive, and nervous digestive, excretory, reproductive, and nervous systems all covered with a layer of cells called the systems all covered with a layer of cells called the cuticle.cuticle.

2. Nematodes differ from higher animals in that they 2. Nematodes differ from higher animals in that they lack organized circulatory and respiratory systems.lack organized circulatory and respiratory systems.

3. The digestive and reproductive systems are of the 3. The digestive and reproductive systems are of the most taxonomic importance.  Only adult females most taxonomic importance.  Only adult females should be used when identifying nematodes.should be used when identifying nematodes.

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Relative sizes of Phytoparasitic

Nematode Genera

Relative sizes of Phytoparasitic

Nematode Genera22 COMMON NEMATODE GENERA22 COMMON NEMATODE GENERA

L= 250-3,000 microns, W= 15-20 micronsL= 250-3,000 microns, W= 15-20 microns

MorphologyMorphology

Important concepts:Important concepts:

4. The digestive system extends from the mouth 4. The digestive system extends from the mouth to the anus and includes these parts:to the anus and includes these parts:

a.a. Mouth, which is in the center of 6 lipsMouth, which is in the center of 6 lipsb. Stylet, structure that acts as a syringe and b. Stylet, structure that acts as a syringe and

is used to:is used to:1. penetrate the plant cell 1. penetrate the plant cell 2. secrete enzymes and take up nutrients from the 2. secrete enzymes and take up nutrients from the plant plant 3. help hatch from egg3. help hatch from egg

c. Esophagus, which contains a median bulb c. Esophagus, which contains a median bulb that performs as a pump for enzyme that performs as a pump for enzyme secretion and nutrient uptake. secretion and nutrient uptake.

d. Intestine, facilitates digestion and absorption d. Intestine, facilitates digestion and absorption of nutrients.of nutrients.

e. Anus, opening from which waste is expelled e. Anus, opening from which waste is expelled from the intestine.from the intestine.

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The Tool of the Trade!!

The Tool of the Trade!!

Important concepts:Important concepts:

5. Reproductive system5. Reproductive system

a. a. MaleMale      Testes, location of sperm production     Testes, location of sperm production

          Spicules, paired, protrusible copulatory structures Spicules, paired, protrusible copulatory structures that are used to open the vulva for sperm that are used to open the vulva for sperm depositiondeposition

b. b. FemaleFemale         Ovary, location of egg production, nematodes Ovary, location of egg production, nematodes may have one or two ovariesmay have one or two ovaries

          Vulva, transverse opening to the outside Vulva, transverse opening to the outside environment  environment 

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Reproduction

Reproduction

Vulva of FemaleVulva of Female

Spicule of MaleSpicule of Male

Male & Female “in copula”Male & Female “in copula”

Nematode Reproduction Nematode Reproduction

There are three types of nematode There are three types of nematode reproduction:reproduction:

1. 1. AmphimixisAmphimixis - union of sperm and egg - union of sperm and egg

2. 2. HermaphroditismHermaphroditism - functional male and - functional male and female sex organs on the same individualfemale sex organs on the same individual

3. 3. ParthenogenesisParthenogenesis - the production of - the production of offspring from eggs which have NOT been offspring from eggs which have NOT been fertilized fertilized

A nematode life cycle (egg to egg) generally A nematode life cycle (egg to egg) generally requires 3 to 4 weeks. requires 3 to 4 weeks.

DamageDamageMechanical injury results from the nematode stylet puncturing Mechanical injury results from the nematode stylet puncturing

the cell wall, and is followed by the secretion of enzymes and the cell wall, and is followed by the secretion of enzymes and nutrient extraction. This process leaves cells that are nutrient extraction. This process leaves cells that are damaged or completely destroyed. damaged or completely destroyed. 

Nematode damage can result in a variety of symptoms: Nematode damage can result in a variety of symptoms: 1. Lesions1. Lesions2. Galls or swellings 2. Galls or swellings 3. Excessive root branching 3. Excessive root branching 4. Twisted or distorted stems and/or leaves 4. Twisted or distorted stems and/or leaves 5. Disruption in flower development / sterility 5. Disruption in flower development / sterility 6. Dead or incapacitated root tips6. Dead or incapacitated root tips

Disease ComplexesDisease ComplexesWhile nematodes are devastating pathogens by themselves, While nematodes are devastating pathogens by themselves,

their most significant influence in agriculture is a result of their most significant influence in agriculture is a result of their participation in pathogen complexes. their participation in pathogen complexes.