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Free-living and
Plant-Parasitic
Nematodes (Roundworms)
Lesson Plan
Learning objectives:
- To introduce students to the
world of nematodes, ubiquitous creatures in our environment
- To illustrate a method of
extraction of nematodes from soil
- To learn to differentiate
stylet-bearing nematodes (most likely
plant parasites) from free-living nematodes
Exercise description:
Soil samples are collected and a
simple nematode extraction procedure is conducted. Different types of
nematodes are observed and compared.
Time frame:
Baermann funnels are generally left undisturbed for 24-48 hours. Soil
samples can be stored for several weeks or longer before assaying, if kept
cool and prevented from drying out. Nematodes, once extracted, should be
observed within several days; they should be refrigerated when not in use.
Study questions:
- What different types of nematodes were extracted from soil samples
you used? Did the types and numbers of nematodes vary with the soil
used?
- Was it possible for students to differentiate the stylet-bearing
nematodes from those without stylets?
- What other parts of the nematode's anatomy were observed? Make
drawings of the different nematodes and label parts of the anatomy.
- What are the major groups of plant-parasitic nematodes, and how are
they classified?
- How do nematodes damage plants?
Answers to Study Questions:
1. What different types of
nematodes were extracted from soil samples you used? Did the types and
numbers of nematodes vary with the soil used?
Plant-parasitic, bacterial
feeding, fungal feeding, and predatory nematodes probably were
recovered from each soil sample.
Yes, there probably were more
fungal feeding and bacterial feeding nematodes found in forest
soil than in soil collected from a lawn or agricultural
field because
of the greater amounts of organic material in the forest soil environment. The organic matter is used as food by bacteria and fungi, which these nematodes consume.
2. Was it possible for
students to differentiate the stylet-bearing nematodes from those without
stylets?
Yes, the stylet is easily
visible in many nematodes using a compound microscope at 200X or 400X
magnification.
3. What other parts of the
nematode's anatomy were observed: Make drawings of the different nematodes
and label parts of the anatomy.
Other nematode structures
possibly seen under a compound microscope include the: a) median bulb or
metacorpus, a round, muscular, pumping structure located in the
esophagus; b) anus, the posterior opening of the digestive track,
located near the tail of both males and females; c) spicules, long,
narrow, curved structures located near the anus in males; d) vulva, the
opening to the reproductive tract in females; e) ovaries, possibly, near
the mid-section or tail of females
4. What are the major groups
of plant-parasitic nematodes, and how are they classified?
Plant-parasitic nematodes
generally are classified as ectoparasites or endoparasites based on the
position of the nematode body in relation to the plant being fed upon.
Identification of nematodes to genus requires observation of overall
body shape, size, and length, stylet length and morphology,
structure of the esophagus, tail shape, cuticle markings, etc. See Figure
7 and listed websites for details and additional keys.
5. How do nematodes damage
plants?
Nematodes can cause damage to
plants via several mechanisms, including: a) wounding, which creates
openings through which other pathogens may enter the plant; b) stunting of the roots and disruption of the vascular tissue in the roots, which reduces the transport of water
and minerals from the root system up to the leaves and stems of the
plant; c) use of water, minerals, and nutrients (made by the plant via photosynthesis)
which otherwise would be available to support plant growth; and d)
production of damaging enzymes and /or other disease-inducing compounds.
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