Lektion 1 Flashcards
Define the following Terms:
Inoculum, Incubation, Latent period and Infectious period.
Inoculum: Any part of the pathogen that contacts the plant and initiates infection; the Portion of the pathogen that is transferred to the host, e.g. spores.
Incubation period: the time between the initial Penetration of the host and the appearance of symptoms.
Latent period: the time between initial Penetration of the host and the production of new inoculum, spores.
Infectious period: the time over which a pathogen fruiting Body or lesion continue to produce new inoculum, e.g. spores.
What is the difference between Primary and secondary inoculum?
Inoculum that causes an original infection at the beginning of a growing season is called Primary inoculum; it produces the first infections that initiates an epidemic. Inoculum produced as a result of the Primary infections is called secondary inoculum; it produces all of the secondary infections that sustain and inrease an epidemic.
Compare the ways that viruses, bacteria and fungi use to penetrate the plant Epidermis and enter the plant’s cellular Environment.
Fungi: they often form specialized structures, such as appressoria and Penetration pegs, which enable them to penetrate into the host.
Bacteria: The rely on wounds or on natural openings, but never penetrate directly. Natural openings consist of plant structures such as stomata, hydratodes, lenticels or nectaries.
Viruses: they rely completely on wounds to penetrate into plants. Viruses are introduced into wounds produced by insect vectors that have highly specialized mechanisms for inoculation the viral propagules.
Describe the complete infection and disease cycle for apple scab (Venturia inaequalis)
- The pathogen Venturia inaequalis overwinters in dead aple leaves on the ground as immature pseudothecia
- Ascospores mature when the hfruit buds begin to open in the spring
- Moisture causes asci in the pseudothecium to elongate, push through the ostiole and forcibly discharge the ascospores into the air.
- Primary infection requires wetness for different lengths of time
- Direct Penetration by ascospores and subsequent colonization leads to production of an enormous number of conidia within 8-15 days after inoculation, and production of olive-green cab lesions.
- Secondary infections depend on rain and wind to dislodge conidia and blow them to surrounding leaves.
- Infected leaves fall to the ground and leaves are further colonized during the autumn.
What is the difference between an ectoparasitic and an endoparasitic nematode? Give an example for each type.
Ectoparasites (stubby-root nematode, sting nematode, ring nematode) are nematos that feed from the outside of plant tissue.
Endoparasites (root-knot nematode, cyst nematode) are nematodes that enter plnt tissue to feed an live.
Describe three ways that parasitic nematodes damage plants.
- Physical damage: feeding causes wounding
- Creating openings through which other pathogens may enter the plant
- Disrupting the vascular System of the plant which reduces the Transport of water and nutrients from the root System up to the leaves and and stems of the plant.
How are viruses classified?
Kingdom Vira has two divisions based on the nucleic acid type, RNA or DNA. Other subdivisions are based on virion shape, whether the RNA is single- or double-stranded, and the physical, chemical or biological properties of the virus. The way of Translation is another criterion.
What Features do viruses have in common?
All viruses are composed of a nucleic acid (DNA or RNA) contained with a Protein particle or capsid.
Reproduction is by replication of the nucleic acid in the host cell. Viruses are completely dependent on the host cell for replication; they cannot reproduce outside of a living host cell. Thus they are all obligate parasites.
How do viruses move withing a plant after establishing a successful infection?
After infecting the first plant cells, virions must then move from one cell to the next, inducin a local lesion. Movement Protein are coded by Special genes for the cell-to-cell movement. Viruses move through the plasmodesmata connecting adjacent plant cells, moving at a rate of approximately 1 mm, or 8-10 cells/day. Viruses may also move systematicallly through the plant via the Phloem.
What is the difference between a symptom and a sign of disease?
Disease symptoms refer to the appearance of the
Describe the five types of symptoms produced by fungi on plants and describe the underlying cause of each symptom.
Leaf spots are localized lesions on leaves consisting of dead and collapsed Celles. Leaf spots can be due to the activity of Toxins and/or enzymes that destroy plant tissue.
Blights refer to a General and very rapid browning and death of leaves, branches, twigs and flowers. Blight can be due to the activity of Toxins and enzymes and rapid colonization of plant tissue.
Leaf curls are due to production of growth hormones by the pathogen that lead to hyperplasia (increased cell divison) and hypertrophy (abnormal cell enlargement).
Cankers can form on twigs, branches and trunks. Cankers usually start with a wound, e.g. a dead branch stub. Cankers can be annual or perennial in growth. Their shape can be concentric or diffuce. Cankers often are places where a fungus overwinters in the plant as mycelium. Sporocarps (fungal fruting bodies) may be produced on the Surface of the woody Substrate in a canker.
Vascular wilts are characterized by a more or less rapid wilting, browning and dying of leaves and succulent shoots of plants folled by death. Wilts are caused by the activitie of a pathogen in the vascular System, where the fungus may spread by growth of mycelium and by production of conidia.
List an describe five risks associated with the application of pesticides in agroecosystems.
- Health of farm workers, consumers and the General public-including Impacts on particularly vulnerable sub-populations.
- Lethal an sub-lethal Impacts on other non target-biota
- Direct and indirect Impacts on natural- and agroecosystem, including effects on Habitat and Food resources
- Consumption and Degradation of natural resouces
- Pollution of soil, air and water - which can have consequences for human and nonhuman biota
- Costs to Society for remediation of environmental Problems
List and describe six different control practices that can be used for disease control.
Genetic control practices: Major R-genes and quantitative R-genes, natural and engineered-R-genes. Conncetions with chemical, cultural and biological practices -resistant varities
Regulatory control practices: quarantines
Biological control practices: hyperparasites
Chemical control practices: pesticides
Physical control practices: soil solarization
Cultural control practices: crop rotations
Describe two consequences of barberry eradication in the USA that had an effect on control of wheat steam rust caused by Puccinia graminis tritici.
Barberry eradication with herbicides was important in North America for control of wheat stem rust on wheat. One important consequence was the reduction in the number of wheat stem rust races found per year in the USA. Another effect of the eradication of barberry, was that the average date of the first reported Observation of wheat stem rust in some selected Areas of the USA shift from 14-19 June to 13-29 July - > later development!
How does soil solarization differ from soil fumigation? What are the Advantages of soil solarization compared to soil fumigation? Which strategy would be more likely to successfully control a soil Born e pathogen in Switzerland? In Spain?
Soil solarization: The ground is covered with a clear plastic tarp and heated by the sun during about a week. It takes relative Long and Needs a lot of sunlight, the effect is not so much strong. But it’s more environmentally friendly because no chemical is used, and more natural antagonists can survive. (Spain)
Soil fumigation: the ground is covered with a plastic sheet and the gaseous pesticides are introduced. Previously was used often Methyl Bromide, but now this is banned. The effect is bigger and more intense than with the solarization method, but there are other porblems: many non-target organisms are damaged and it pollutes the Environment. (Switzerland)
In Switzerland solarization works less well, compared with Spain, due to the lower sunlight exposure.
