Nematodes as Pathogens Characteristics Brief History Nematodes as Parasites Importance Form and Function General Disease Cycle of Plant Parasitic Nematode ** Images and lecture material were not entirely created by J. Bond. Some of this material was created by others.**

Nematodes The term Nematode is of Greek and Latin origin   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

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. 

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.

Nematode Size

50% 10% 15% 25% Plant Animal Free-Living Marine PHYLUM: NEMATODA

Non-Plant Parasites

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

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 ???

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.

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

Where Nematodes Live? IN SOIL AS: Ectoparasites-60% Endoparasites-30% ON AND IN ABOVE GROUND PARTS AS: Ectoparasites-2% Endoparasites-8%

Importance Annual losses due to nematodes are estimated at over $80 billion.  Life-sustaining crops  % Loss    Other economically  important crops 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 14.0

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.

Relative sizes of Phytoparasitic Nematode Genera 22 COMMON NEMATODE GENERA L= 250-3,000 microns, W= 15-20 microns

Morphology

Important concepts: Mouth, which is in the center of 6 lips 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.

The Tool of the Trade!!

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 

Reproduction Vulva of Female Spicule of Male Male & Female “in copula”

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.

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.