18
Silvi (Subject) / epidemics (Lesson)
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- Factors for disease epidemic? Pathogen, Host tree, Environment
- Pathogen factors? virulence, inoculum type, dispersal potential, inoculum potential, host range, alternation between hosts
- Host factors? host resistance, host age, seasonal development, host uniformity
- Environmental factors? humidity, temp., drought, frost, biotic environment, competition, silviculture
- What can increase the successfull reaching and infecting of potential hosts? Quantity of inoculum (the speed can be influenced by the form of the inoculum).
- What factors are crucial to increase inoculum potential (in order to overcome host defences)? - quantity of inoculum per unit area surface (and additionally distance between inoculum source and host) - energy status of each unit
- What is the inoculum load? the quantity of infective propagules that reach a specific host. High inoculum load equals a high inoculum potential.
- Ways of pathogen spread? Ranking? airborne, (airborne) vectors, waterborne (airblown rain), host seeds
- Main phases of disease cycle? pre-entry (inoculation, first contact pathogen and host), entry (penetrating of cells, stomata, wound), colonization (host is colonized and first appearences of symptoms), dissemination
- Why are pathogens ecologically important? - drives nutrient circulation - makes material available to other fungi, insects, birds etc. - kills unfit individuals, potentially strengthening the population
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- pathogen - host, natural balance. What disrupts this balance? - industrial forestry (rapid changes in host availability, stumps, wounds) - invasive species (globalization, climate change)
- Losses to pathogens Lost timber value, Replanting-and regeneration costs, Subsidies and compensation to forestry from society, Lost breeding material (lost future benefits), Lost ecosystem services, Lost recreational values, Trade regulations
- What different disease cycles? Characteristics? • Continous, pathogen is found on one or one of several host throughout the diseasecycle • Discontinous, cycle is broken by a resting or non-pathogenic phase
- How can resistance be expressed? - Constitutive resistance (e.g. bark, cuticle, wax layers but also chemical: lignin and other macromolecules) - Induced resistance (triggered responses to exposure to pathogen, e.g. salicylic acid) --> every resistance and susceptibility can be age related or organ specific!
- Resistance on population level? • basal or horizontal resistance (non-specific, general resistance of the host), absence of genetic interaction between host and pathogen genotype • race-specific or vertical resistance (effective against some races of pathogens), developed through gene-for-gene relationships
- Atmospheric environment and its impacts on host/pathogen? • climate, affects likelihood of host and pathogen to appear in certain region • weather, influences pathogen at their source and also their arrival at the host • microclimate, e.g. needle surface moisture
- Why are some fungis able to spread relatively free on former agricultural sites? Presumably because of the lack of wood-inhabiting fungis, no competition.
- Uniformity (in sinlge-storied, even-aged, plantation forests) can be dis-/advantage. When? • as long as the uniformity is coupled with resistance. if it is broken it allow increased disease levels.