Introductory Plant Pathology
Class 5
Plant Nematodes
CHARACTERISTICS OF PLANT PATHOGENIC NEMATODES
Morphology
- Small, 300 to 1000 um long by 15 to 35 um wide
- Not observable with naked eye, except cyst forms
- round and eel shaped worms
- smooth, unsegmented bodies
- no appendages
- females of some species develop into cysts (spheroid bodies with "leathery" coverings)
Anatomy
- Multicellular
- transparent Cuticle
- external colorless cuticle marked by surface striations
- the cuticle is produced by the hypodermis (a group of cells the
extends into the body cavity as four chords separating four
bands of longitudinal muscles.
- Muscles
- longitudinal muscles enable movement
- muscles are located at the mouth, digestive tract,
and reproductive structures
- Body cavity
- contains fluid through which circulation and respiration occurs
- Digestive system
- mouth -> esophagus -> intestine -> anus
- lips, usually six, surround mouth - may be useful for identification
- plant parasitic nematodes have a hollow style that is used to puncture
cells an allow nutrients to be obtained.
- Reproductive system
- well developed
- females have ovaries -> oviduct -> uterus -> vulva
- males have testis -> seminal vesicle -> common opening with intestine
- males have copulatory spicules to aid in mating process
- reproduction may occur either sexually by sperm and egg or parthenogenically
- some species have no males
Life Cycles
- an egg hatch to produce a single juvenile
- first juvenile stage may occur in the egg
- four juvenile stages
- each juvenile stage ends with a molt
- differentiation into female and male occurs after the first molt
- differentiated males and females are fertile and may reproduce
Epidemiology
- latent period (egg to egg) is usually 2 to 4 weeks and may be modified by cool temperatures
- in some species, the first and second juveniles cannot infect and exist solely on
stored energy
- infective stages must feed on susceptible host(s) or starve to death
- absence of susceptible hosts may result in elimination of a nematode population
Ecology
- all plant parasitic nematodes live at least part of their lives in the soil
- nematodes occur in greatest abundance in the top 15 to 30 cm of soil
- recent surveys that alaskan tundra soils and desertic arid soils contain at least
as many nemas per cc of soil as any other soils
- in agricultural soils, the distribution of nemas is usually irregular
- the greatest numbers of plant parasitic nemas is usually found in the root zone
- migratory ectoparasitic nematodes may follow roots to depths of 150 cm or more
- the hatching of eggs may be stimulated by "hatching factors" secreted by roots,
this in analogous to the chemotaxis phenomenon discussed for fungal and
bacterial plant parasites
- spread of nematodes is facilitated by water, wind, cultivation equipment, soil dispersal,
mankind
- there are four general categories of nematodes
- sedentary endoparasites
- sedentary ectoparasites
- migratory endoparasites
- migratory ectoparasites
Classification
All plant parasitic nematodes belong to the Phylum Nematoda. This is a unique
phylum taxonomically distinct from other worms. Most of plant parasitic nematodes
are included in two orders
.
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This page is authored and maintained by:
Dr. J.E. Partridge, Department of Plant Pathology, University of Nebraska-Lincoln
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Copyright (C) 2003 J.E. Partridge, University of Nebraska-Lincoln. All Rights Reserved.
