L1 Flashcards
What is plant disease?
Abnormal and injurious condition in which a causal agent, the pathogen bring about continuous irritation
Aims to control disease in ways which are…
Effective.
Economic – benefit has to be greater than cost.
Environmentally acceptable – minimal effect on non-target organisms.
Trade-offs: latter two constrain first and each other.
Give two examples of major plant diseases in history
Answers include:
Irish potato famine - potato late blight
Sri Lanka - coffee rust (1870s).
Brown spot disease of rice contributed to the Bengal famine of 1943.
Southern corn leaf blight, a new disease, in 1970.
What is potato late blight? What organism causes? Infects what? What year?
Phytophthora infestans.
Main hosts: potatoes, tomatoes.
Irish potato famine (1845-1849) - pop decrease
Why was potato late blight so severe? Biological factors
- Cause unknown until 1961
- Fav weather, cool + moist
- exotic pathogen - potato couldn’t resist disease
- no control until 1980’s
Why was potato late blight so severe? Socioeconomic factors
Reliance on potato for diet(adult ~5.5 kg/day).
Inadequate response bygovernment.
What are viroids?
nucleic acid (RNA) only
potato spindle tuber viroid.
Found in the UK in 2011.
What are viruses?
nucleic acid + protein.
e.g. Tobacco mosaic virus + Barley yellow dwarf virus
What are bacteria pathogens?
Free-living bacteria
Spiroplasmas, mycoplasmas (intracellular).
e.g. spiroplasmas causes corn stunt
What are eukaryotic pathogens?
Fungi + Higher plants.
e.g. Striga asiatica (witchweed)
What is the infection cycles? Repetition allows?
–> infection –> spread –> growth –> reproduction –>
note: Many diseases have many cycles in a growing season.
Repetitions of cycle give a disease the opportunity to build up to high levels.
an infection cycle and a life cycle is the same thing T/F
F - different
Phytophthora infestans causes what?
Potato late blight
Describe the life cycle of Phytophthora infestans
- Overwinters in tubers.
- Spring - produces sporangia - spread by wind
- sporangia germinate on leaves (direct - form germ tube) (indirect - form zoospores)
- pathogen grows into leaves + kill
- new sporangia - spread disease
- sporangia on ground - prod zoospores - infect tubers
Pathogens are divided into what 3 categories depending on their source of nutrition, what are thye?
Biotrophs: obtain their nutrients from living host cells.
Necrotrophs: kill host cells and obtain their nutrients from the dead tissue.
Hemibiotrophs: initially biotrophic but eventually kill host cells.
