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.
