Part E - Oomycota and Nematodes Flashcards
Describe the life cycle of a named (accepted common or Latin name) member of the Oomycota which is pathogenic on plants.
Make sure you include the sexual phase.
Use a drawing to illustrate your answer. Annotate your diagram with the ploidy level expected at each stage.
Define each of the following terms in relation to plant-parasitic nematodes:
i) Threshold level
ii) Tolerance limit and
iii) Economic threshold level.
In your answer, discuss some of the factors that affect the economic threshold level.
Threshold level: The population density of a plant-parasitic nematode at which economic damage is likely to occur.
Tolerance limit: The maximum population density of a plant-parasitic nematode that a crop can tolerate without significant yield loss.
Economic threshold level: The population density of a plant-parasitic nematode at which the cost of control is equal to the expected loss in yield.
The economic threshold level is affected by a number of factors, including: The value of the crop; The cost of control; The severity of the nematode infestation; The likelihood of future infestations & The environmental conditions
The economic threshold level is lower for high-value crops, for crops that are susceptible to nematode damage, and for crops that are grown in areas where nematodes are common. The economic threshold level may also be affected by the availability of effective control methods.
What do the cell walls of Oomycota contain?
Cellulose, β-glucans, and other polysaccharides.
How would you distinguish a plant parasitic nematode from other nematodes if you are viewing them under a microscope?
Mouthpart
Plant parasitic nematodes have a stylet, which is a long, slender,
needle-like structure that is used to pierce plant cells and feed on
their contents. Other nematodes do not have a stylet.
Ovaries
The ovaries of plant parasitic nematodes are typically located in the
anterior (front) part of the body, while the ovaries of other
nematodes are located in the posterior (rear) part of the body.
Cuticle
The cuticle of plant parasitic nematodes is often thicker and more
heavily sclerotized (hardened) than the cuticle of other nematodes.
What contributes to epidemics of Phytophthora?
Environmental conditions
Host susceptibility
Genetic susceptibility
Why do pathogens belonging to the Oomycota have such a high impact on agricultural plant production? In your answer, explain why certain environmental variables are important in the epidemiology of these pathogens.
Very diverse and can infect a wide range of crops. Often very aggressive and can quickly spread through a crop. Can develop resistance to fungicides
Environmental variables:
Oomycetes are most active at cool temperatures.
Oomycetes require moisture to survive and reproduce.
Some host plants are more susceptible to oomycete infection than others.
If you are a grower and you discover nematodes in your soil, what information do you need to have if you want to minimise your crop losses?
The type of nematode
Population density
Type of crop
The environmental conditions
Discuss how a newly emerging plant-pathogenic nematode can spread from one area to another. Why is this something that growers and government should try to prevent? Include the following terms in your answer: feeding habit, planting material, nematode life cycle and host.
Feeding habit: Plant-pathogenic nematodes feed on the roots of plants. They can spread from one area to another by attaching themselves to the roots of healthy plants and being transported to a new location.
Planting material: Plant-pathogenic nematodes can also spread by being present in planting material, such as seeds, cuttings, or transplants. When this material is moved from one area to another, the nematodes can be transported along with it.
Nematode life cycle: Plant-pathogenic nematodes have a complex life cycle that includes four stages: egg, juvenile, adult, and egg. The adult nematodes lay eggs in the soil. The eggs hatch into juveniles, which then go through several molts as they mature. Adult nematodes can live for several years.
Host: Plant-pathogenic nematodes have a wide range of hosts. They can infect a variety of crops, vegetables, and ornamental plants.
Growers want to try and prevent nematode infection because they can cause significant damage to crops. Nematodes can reduce crop yields, weaken plants, and make them more susceptible to other diseases. In some cases, nematodes can even kill plants.
