Disease cycle (week 1-2)
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What are the interdisciplinary sciences of plant path?
- Molecular biology
- Plant physiology
What are the 3 branches of plant pathology?
- -disease spread
- -disease cycle
Describe plant disease
Alteration of the normal physiological and biological development of a plant that results in abnormal morphological and physiological changes
-alteration results in reduced biomass and or reproductive output yield
Basic types of plant disease
- Foliar pathogens- reduce amount of photosynthetic tissue
- Root pathogens- interfere with water and mineral uptake
- Vascular pathogens-limit water and mineral movement within a plant
- Structural pathogens-wood decay fungi
Difference between disease vs injury
- Disease- a process that develops over time
- -non random event
- Injury- event that occurs suddenly
- - random event like weather
- -non infectious
What is the plant disease triangle?
Disease is at the center of the the triangle with environment host and pathogen on each corner
Describe the environment portion of the triangle (describe disease needs)
- - soil pH
Describe the host portion of the disease triangle
- Resistance and susceptibility
- - escape ( a single or a few plants in a population does not get infected due to distance between plants)
Describe the pathogen portion of the disease triangle
- Pathogenic specialization
How do you correctly determine what organism is causing a disease?
Use Kochs postulates
What are Kochs postulates?
- 1. Suspected pathogen is consistently associated with diseased plants
- 2. Isolate the suspected pathogen in pure culture. Make notes of its characteristics and identify it.
- 3. Inoculate a healthy host with pure culture of pathogen.
- 4. Look for signs of disease and isolate suspected pathogen see if it is the same as step 2
Causes of plant disease
- Biotic- infectious and transmissible
- Abiotic- non infectious and non transmissible
What are biotic causes of plant diseases?
- Viruses and viroids
- Parasitic plants- mistletoe
- Protoctistans- single celled eukaryotes
What are abiotic causes of plant diseases?
- Unfavorable weather conditions ( heat or cold damage)
- Water relations ( waterlogging or uneven water supply)
- Unfavorable soil pH
- Nutrient deficiencies
- Air pollutants
What is etiology?
The study of causation or organization
What are the required components of etiology?
- Virulent pathogen
- Susceptible host
What is a saprophyte?
An organism that derives nutrition from dead organic matter
What are the different types of parasitism?
- Obligate (obligated or has no choice)
- Facultative (has the ability to be if needed)
What is a biotroph?
Derives nutrition from living plant cells. Cannot survive on dead host (powdery mildew).
What is a necrotroph?
Derives nutrition from dead or dying cells of a plant.
Describe biotrophic parasitism?
- Narrow host ranges
- Cannot grow as a saprophytes ( in culture)
- Attack healthy plant at any stage
- Kill host cells slowly
- Penetrate directly or via natural openings
Describe necrotroph parasitism?
- Generally have wider host ranges
- Can grow in absence of host (saprophytic)
- Attack young weak or senescent tissues
- Kill host cells rapidly -toxins
- Penetrate through wounds or natural openings
what is a disease cycle?
A sequence of events involved in disease including appearance development perpetuation and survival of the pathogen.
What is pathogenesis?
Events that occur in the disease cycle from infection to final reaction
What is stage one of the generalized disease cycle?
- Inoculum production
- -primary inoculum
- -secondary inoculum
What is stage two of the generalized disease cycle?
- -the spread of inoculum via humans water wind vectors.
What is stage three of the generalized disease cycle?
- -appropriate infection court
- - must land on plant area it can infect
What is stage four of the generalized disease cycle?
- - directly indirect or wounds
What is stage five of the generalized disease cycle?
- -local vs systemic
- -Infection court
- -Incubation period
- -latent period
What is the incubation period?
The tine between infection and the appearance of symptoms
What is latent period?
The time between infection and reproduction of the pathogen
What is stage six of the generalized disease cycle?
- Colonization/growth and reproduction
- - intercellular vs intracelluar
- -biotrophic vs nectrophic
What is stage seven of the generalized disease cycle?
- Formation of survival structures
- -chlamydospores sclerotia
What is stage eight of the generalized disease cycle?
- - overwintering or over summering
- -survival in the absence of a host
- -possible alternative hosts
What are the types of disease cycles?
- Primary inoculum only
- -single cycle only or monocyclic diseases
- - simple interest disease
- Primary and secondary inoculum
- -multiple cycle or polycyclic diseases
- -compound interest disease
What is a fungus?
- It is a eukaryotic heterotrophic organism devoid of chlorophyll that obtains all of its nutrients by absorption and reproduces by spores.
- -primary carbohydrate storage is glycogen
- -most have a thallus composed of hyphae that elongate by polar growth from its tip
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