1. Nematology 101: Biology and Ecology
NE-SARE Professional Development Plant-Parasitic Nematode Workshop
Nematode Workshop 1st Morning Session
Nematology 101: Biology and Ecology
Follow along with the encyclopedia article by Neher and Powers
Deb Neher
University of Vermont
Dept. of Plant and Soil Science

2. NE-SARE Professional Development Plant-Parasitic Nematode Workshop
Soil Biological Indicators Lab
Dr. Deborah Neher uses soil nematode & microarthropods for monitoring soil quality and measuring progress of soil remediation (

3. Abundance of soil animals per square meter in European grassland
NE-SARE Professional Development Plant-Parasitic Nematode Workshop
Abundance of soil animals per square meter in European grassland
Soil fauna are particularly abundant in grassland soils where plant biomass is mostly below ground
Of those fauna, nematodes are most abundant (millions per m2) followed by springtails and mites
Blatantly absent are protozoans, which are likely more abundant than nematodes; they are simply not enough scientists that have quantified them

4. NE-SARE Professional Development Plant-Parasitic Nematode Workshop
General characteristics of nematodes
Aquatic
Unsegmented
Appendageless
Transparent
Bilaterally symmetrical
Generally bisexual
Vermiform roundworms
Non-coelomate
Biotrophs
Nematodes are simple aquatic organisms, requiring a water film (1-5 μm thick) to function fully
Comprised of approximately 1000 somatic cells in the adult stage,
In soil, their size is mm in length, is ideal for navigating this porous matrix of soil particles surrounded by water films and air pockets.
They are ultimately bounded by soil structure, restricted in movement within soil pores less than 30 μm diameter.
Meloidogyne hapla

5. NE-SARE Professional Development Plant-Parasitic Nematode Workshop
Sensory organs
No eyes, appendages or segmentation
Mechanosensory
Chemosensory
No eyes, appendages, and true segmentation,
use mechanosensory and chemosensory neurons embedded in the cuticle to orient and respond to a wide range of environmental stimuli.
At the nematode’s anterior end is a circlet of sensilla arranged around an oral opening.
Amphids are laterally placed chemosensory organs, which can detect subtle chemical gradients, providing directional information to the nematode
Fig. 2. Spiral-shaped chemosensory organs called amphids in an anterior position of Achromadora sp. collected from soil of Jumbo Valley fen in Cherry County, Nebraska.

6. NE-SARE Professional Development Plant-Parasitic Nematode Workshop
Phytonematode anatomy & morphology
Well developed digestive & reproductive & sensory systems
Lack circulatory & respiratory systems
Nematodes are an example of functional and anatomical economy
Early observations by light microscopy led scientists to refer to nematodes as a “tube within a tube”.
The most prominent systems in nematodes are digestive and reproductive
Food entering the nematode is channeled quickly into a tubular esophagus and then passed into an intestine that comprises the bulk of the body cavity
Waste products are eliminated through a posterior ventral anus.
There are no circulatory or respiratory systems within the nematode

7. NE-SARE Professional Development Plant-Parasitic Nematode Workshop
Nematode identification
Morphological diverse plant-parasites
Pratylenchus
Xiphinema
Criconemella

8. NE-SARE Professional Development Plant-Parasitic Nematode Workshop
Physiological versatility
Tolerate harsh habitats
avoid interspecific competition and many environmental selection pressures
Regulate uptake of O2 between 100 to 5%
Permeable, hydrostatic skeleton
osmoregulation of Ca, Mg, K
Tolerate pH from 1.6 to 11.0
Temperatures from sub-zero to 60C +
depend on free water for normal functioning,
regulating their uptake of oxygen over a wide range of partial pressures ranging from 100 to 5%
< 5%, convert their use of energy reserves, e.g., Aphelenchus avenae uses reserves of neutral lipids under aerobic conditions and glycogen under anaerobic conditions
Not only does a hydrostatic skeleton facilitate movement, but also an ability expand or contract body size in response to gradual changes in concentration of solutions containing sodium, calcium, magnesium and/or potassium ions.  The adjustment process, osmoregulation, is possible by modifying the permeability of their cuticle
Furthermore, nematodes can tolerate a wide pH range, with some species capable of withstanding strong acids or bases (pH 1.6 to 11.0)
Nematode tolerance for temperature is equally remarkable. In hot springs, nematodes live at temperatures as high or higher than any other Metazoa. Aphelenchoides partietinus, a cosmopolitan species, has been reported from 58 C springs in Chile and 61 C springs in New Zealand.

9. NE-SARE Professional Development Plant-Parasitic Nematode Workshop
Survival
under harsh conditions such as freezing or drying, many nematodes are capable of entering a cryptobiotic state, essentially a reversible state of suspended animation until favorable conditions return.
Anhydrobiotic success, the ability to withstand the lack of moisture, depends on a slow rate of dehydration, rapid decline in cuticle permeability, and accumulation of compounds such as trehalose and glycerol to stabilize phospholipids and proteins.
Species including Acrobeloides spp., Aphelenchus avenae, and Scutellonema brachyurum
start to enter anhydrobiosis by coiling at gravimetric water contents of 3.7% (-300 kPa), 9% (-30 kPa), and 15% (-10 kPa) gravimetric water content, respectively.
unknown how long nematodes may persist in this state and still survive hydration. Specimens of the wheat gall nematode, Anguina tritici have been revived after more than 30 years in anhydrobiosis; thought to survive 100 yrs in Antarctica
Although nematodes have adapted mechanisms to survive extremities of climate, their activity is stimulated by the return of more moderate conditions. For example, communities of nematodes are revived after a rain in desert soils or after a relatively warm period in soils of Polar Regions
Aphelenchus, anhydrobiosis

10. NE-SARE Professional Development Plant-Parasitic Nematode Workshop
Head structures of soil nematodes
bacterivore
bacterivore, predator
Fungivore and/or herbivore
omnivore
herbivore
predator
One distinguishing morphological feature are the head structures, which reflect food sources
Simple tubular opening with cuticular structures for bacteria
Tooth for predators/carnivores
Spear-like stylet for plant-parasites, fungivores and some omnivores

11. NE-SARE Professional Development Plant-Parasitic Nematode Workshop
Predatory nematodes
May feed on nematodes, protozoa, bacteria, etc
Predators may be adorned with “teeth” used to puncture or shred the integument of various invertebrates including protozoa, mites, springtails, and other nematodes
Figure 5. Teeth of oral opening of predator Mylonchulus montanus (1000x magnification), collected in soil with big blue stem in the Konza Prairie (96W35’ 39N05’) near Manhattan, Kansas. Photograph is provided courtesy of Peter Mullin/2000.

12. NE-SARE Professional Development Plant-Parasitic Nematode Workshop
Bacterial-feeding nematodes
Simple tubular mouthpart
Elaborate cuticle around oral opening
Free-living nematodes are seldom sedentary; some are so hyper they appear to be “ADD (attention deficit disorder)”
continually moving to feed on a diverse array of food including bacteria, algae, fungi, protozoa, small invertebrates and other nematodes
Same set of sensilla to track their food source, but feeding structures modified to suit their meal.
Bacterial-feeders graze using a relatively simple tubular mouthpart, although the cuticle surrounding the oral opening may be modified elaborately to direct food toward the stoma
Figure 4. Cuticle ornamentation of oral opening of Acrobeles ctenocephalus (1000x magnification), collected in soil with little bluestem (Andropogon scoparius) in the Konza Prairie (96W35’ 39N05’) near Manhattan, Kansas. Photograph is provided courtesy of Peter Mullin/2000.
Paulo Vieira (Mactode publications)

13. NE-SARE Professional Development Plant-Parasitic Nematode Workshop
Plant-parasitic nematodes
Respond to CO2 & root exudates
Move few cm per day
Probe with stylet
Ecto-parasites
Endo-parasites
Lifecycle: 3 weeks (root-knot) to 2 yrs + (dagger)
Fig. 3a. Plant-feeding nematodes respond to slight variations in CO2 and root exudates. (chemosensory signals)
Directional movement up to a few cm per day in soil
Once contact root surface, will probe with their stylet, a hollow, protrusible, hypodermic needle-like feeding tube
ecto: feed externally to the root surface, using this stylet to puncture cells, withdrawing the cytoplasmic contents
Endo: penetrate the root and establish permanent (sedentary) feeding sites within the root cortex, or migrate cell-to-cell, leaving a trail of damaged necrotic tissue.
Fig 3b: Fungal-feeders and omnivores have a similar stylet but no “knobs”, points of muscle attachment for stylet protrusion
Figure 3. Variation in morphology of spear-like structure in oral opening a) male plant-parasite Hoplolaimus galeatus (1000x magnification) collected from soil with big bluestem (Andropogon gerardii Vitman) in the Konza Prairie (96W35’ 39N05’) near Manhattan, Kansas, and b) female fungivore Enchodelus hopedorus (400x magnification) collected from the summit of Long’s Peak, Colorado (105W35’ 40N16’). Photographs are provided courtesy of Peter Mullin/2000.

14. NE-SARE Professional Development Plant-Parasitic Nematode Workshop
Plant-parasitic nematodes con’t
Generalists or specialists
Hosts range from 1 to 100’s
All crop plants are susceptible to at least one nematode species
Parasites of plants: specialists and generalists.
Host ranges may extend to 1-100’s of species.
Sometimes specialized feeding location.
Compete with protozoa for access to bacteria for food sources (contribute to N mineralization)
Opportunists, hitchhike on insect bodies to reach food sources at a longer distance than capable alone, e.g., organic matter, fresh dung, bark tunnels
Most are root parasites but species have adapted to parasitize most plant tissues
More damage can be associated with coarser textured soils – sands (larger pore space)

15. NE-SARE Professional Development Plant-Parasitic Nematode Workshop
Major impacts of nematodes
Decomposition of organic matter and recycling of nutrients (soil food web)
More C and N released when nematode grazes on bacteria and fungi than with only microbes
Complex food web

16. Major impacts of nematodes
Decomposition of organic matter and recycling of nutrients (soil food web)
Biological control agents, esp. for insects
Research biological models
Diseases of animals and humans
(heartworm, Trichinosis, hookworm, etc.)
Important plant pathogens

17. NE-SARE Professional Development Plant-Parasitic Nematode Workshop
Other nematodes...
Animal parasites
Human: Night blindness, Elephantiasis
Pets: Hookworm
Insects: biocontrol
Caenorhabditis elegans
Model system
Studies of aging, neurology, ecotoxicology
Plant and soil nematodes don’t hurt humans
Insect parasites or mutualists:
Fig wasp (coevolution), termites, cockroaches
Steinernema for biocontrol
Infect insects, killing them within 48 hr
Release insect-pathogenic bacteria into insect
Insect dies from bacterial infection
Nematodes feed on bacteria & develop and reproduce inside the insect cadaver (nema & Bacteria mutualism)
Sometimes, nematode is host or target of fungi specialized for trapping a nematodes using constricting rings, sticky knobs, or hyphal nets
C. elegans – bacterivore

18. Major impacts of nematodes
Decomposition of organic matter and recycling of nutrients (soil food web)
Biological control agents, esp. for insects
Research biological models
Diseases of animals and humans
(heartworm, Trichinosis, hookworm, etc.)
Important plant pathogens

19. NE-SARE Professional Development Plant-Parasitic Nematode Workshop
Morphology and relative size of major plant-parasitic nematodes
Diversity of plant-parasites
Sizes
Shape – vermiform or globular or cyst
Mode of feeding: endo or ecto
migratory
Agrios

20. Types of Plant-Pathogenic Nematodes
Ectoparasites: feed from outside the plant
Migratory: moves, feeding from plant to plant (dagger)
Sedentary: remains on same plant (spiral)
Endoparasites: feed from inside the plant
Migratory: moves within and feeds on tissues (lesion)
Sedentary: remains within same plant and feeds at specialized sites (root-knot)

21. Sedentary ectoparasite (spiral) Migratory ectoparasite (dagger)
Essential Plant Pathology, 2006
NC State Univ.
Sedentary endoparasite (root-knot)
Migratory endoparasite (lesion)

22. NE-SARE Professional Development Plant-Parasitic Nematode Workshop
Typical lifecycle of a plant-parasitic nematode M M M H M
Series of molts like insects
Poikiothermic- ectothermic or cold blooded animals (warmer temperatures expedite development process)
Life span can vary from 3-4 days to several months
RKN, Meloidogyne species may have generation time of 3 weeks, each female capable of producing 100’s of eggs in life time

23. NE-SARE Professional Development Plant-Parasitic Nematode Workshop
Meloidogyne hapla
3rd stage juvenile
4th stage juvenile
Formation of giant cells and galls
J2 infect root
Ecto- and endo-parasites – some with specific feeding locations on roots
Migratory phase in soil as juveniles or egg bases as roots sough and decay
Eggs can be single or laid in mass
Move in water films around soil particles, migrating in soil until they find plant host (CO2, root exudates)
Infect as ecto- or endo-feeders
May alter plant hormones to generate cell proliferation into galls, nodules or cysts
Egg mass
2nd stage juvenile (J2) mobile in soil
1st stage juvenile
Egg
Modified from Agrios, 1997

24. NE-SARE Professional Development Plant-Parasitic Nematode Workshop
Lifecycle of Pratylenchus penetrans – Root-lesion nematode
Larvae and adults attack roots
Invades root cortex, damaging tissue
Nematodes reproduce and migrate within roots, out of root to new root, or eggs released in soil
Affects sampling strategy (location and season)
Agrios

25. NE-SARE Professional Development Plant-Parasitic Nematode Workshop
Plant productivity losses
Reduce yield by altering uptake of water and nutrients. May result from change in root morphology, hormones, physiology
Meloidogyne, Root knot nematode damage

26. NE-SARE Professional Development Plant-Parasitic Nematode Workshop
How do nematodes damage plants?
Direct feeding on plants (metabolic sinks)
Malformation of host tissues (morphological & physiological)
Predispose host plant to physical stress
Provide entry for secondary pathogens (disease complexes)
Breakdown of resistance to other pathogens
Vectoring of plant pathogens (virus & bacteria)
Suppression of beneficial organisms

27. Nematology 101: Biology and Ecology
NE-SARE Professional Development Plant-Parasitic Nematode Workshop
Nematology 101: Biology and Ecology
Questions?
Coming up next...signs and symptoms