Presentation on theme: "Nematodes as Pathogens"— Presentation transcript:
1 Nematodes as Pathogens CharacteristicsBrief HistoryNematodes as ParasitesImportanceForm and FunctionGeneral 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.**
2 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 Nemata30,000 described species3,000 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 cycle5. 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 SizeNematodes 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.
9 Nematodes of Humans! Pinworm – especially children Hookworm – domestic animals, humans are a dead hostHeartworms - domestic animals, humans are a dead hostTrichinella – trichinellosis of manGuinea wormsElephantiasis
10 HistoryAncient times1) Emperor's Classic of Internal Medicine (2700 BC - China) - reference to the intestinal roundworm, Ascaris lumbricoides2) Hippocrates (430 BC) - first record of the pinworm, Enterobius vermicularis3) The Bible (Deuteronomy 14: 6-8) - sanitation laws for the Hebrews4) The Bible (Numbers 21:4-9)Fiery Serpent = Dracunculus medinensis ???
12 History Modern Times (Europe) 1) Needham observes Anguina tritici in blighted wheat kernels2) Berkeley describes first root-knot nematode on cucumber in a glasshouse in England.3) Kuhn works with and perfects the first method of soil fumigation (carbon disulfide) for nematode control.
13 History Modern Times (America) 1) 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) st Nematology course at the University of California, Berkeley.4) Society of Nematologists founded
14 Where Nematodes Live? IN SOIL AS: Ectoparasites-60% Endoparasites-30% ON AND IN ABOVEGROUND PARTS AS:Ectoparasites-2%Endoparasites-8%
15 ImportanceAnnual losses due to nematodes are estimated at over $80 billion. Life-sustaining crops % Loss Other economically important cropsBanana19.7Citrus14.2Barley6.3Coffee15.0Cassava 8.4Cotton10.7Chickpea13.7Eggplant16.9Potato12.2Grape12.5Rice10.0Papaya15.1Soybean10.6Pineapple14.9Sugarcane15.3Tomato20.6Average14.0
16 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.
17 Relative sizes of Phytoparasitic Nematode Genera22 COMMON NEMATODE GENERAL= 250-3,000 microns, W= microns
19 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 lipsb. 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 eggc. 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.
21 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 depositionb. Female Ovary, location of egg production, nematodes may have one or two ovaries Vulva, transverse opening to the outside environment
22 ReproductionVulva of FemaleSpicule of MaleMale & Female “in copula”
23 Nematode Reproduction There are three types of nematode reproduction:1. Amphimixis - union of sperm and egg2. Hermaphroditism - functional male and female sex organs on the same individual3. Parthenogenesis - the production of offspring from eggs which have NOT been fertilizedA nematode life cycle (egg to egg) generally requires 3 to 4 weeks.
24 DamageMechanical 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. Lesions2. 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 tipsDisease ComplexesWhile nematodes are devastating pathogens by themselves, their most significant influence in agriculture is a result of their participation in pathogen complexes.