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Today

Today. Characteristics Brief History Nematodes as Parasites Importance Form and Function General Disease Cycle of Plant Parasitic Nematode. Nematodes Chapter 15 pg 826 - 874. The term Nematode is of Greek and Latin origin

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Today

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

  2. NematodesChapter 15 pg 826 - 874 The term Nematode is of Greek and Latin origin Greek               LatinNema = thread    oid = like =  "threadlike worms" Nematodes are animals therefore they are in : Kingdom Animalia      Phylum Nemata 30,000 described species 3,000 attack plants

  3. 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. 

  4. Nematode Size Nematodes range in size from about 200 microns Sphaeronmemaminutissima to 26 feet for the blue whale parasite, Placentanemagigantissima. Plant parasitic species range from 250 to 3,000 microns long and 15 to 35 microns in diameter.

  5. Nematode Size

  6. 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 21:4-9) Fiery Serpent = Dracunculus medinensis

  7. 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.

  8. 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

  9. Where do nematodes live?

  10. 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

  11. Where do nematodes live? 90% of all plant parasitic nematodes are found in the roots and in the soil environment. • In this environment, 2/3 live asectoparasites and 1/3 as endoparasites. • Some species • Have juveniles as ecto and adults as endoparasites • Will change parasitism depending on age and type of host, environment, etc. • Migratory or sedentary 10% of all plant parasitic nematodes are found on or in above ground plant parts. In this environment, only 1/5 live as ectoparasites while the majority live as endoparasites.

  12. Importance Annual losses due to nematodes are estimated at over $80 billion.

  13. 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.

  14. 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.

  15. Morphology

  16. 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. FemaleOvary, location of egg production, nematodes may have one or two ovaries Vulva, transverse opening to the outside environment 

  17. 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.

  18. General Lifecycle 1. Egg development 2   First-stage juvenile (J1) occurs within the egg 3.  J1 molts (shedding of cuticle), becomes a second-stage juvenile (J2), and hatches   4.  J2 (infective stage) molts to J3 5.  J3 molts to J4 6.  J4 molts to adult (the fourth and final molt) 7.  Depending on the species, mature adults produce eggs singly or in mass after mating or parthenogenesis

  19. 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. 

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