Below is a list of disease cycles we will use as examples in lecture and will cover in the laboratory periods. Although there are thousands of plant diseases, the list below represents many of the 'usual suspects' of plant pathology - if you fully understand these disease cycles, you are well on your way to being a practicing plant pathologist. Please learn about them!!
Fungus-like pathogens
• Soilborne oomycetes: Root rots caused by Pythium and Phytophthora spp.*
• Foliar oomycetes: Late blight of potato*, downy mildews*, Sudden oak death
Fungi: Ascomycete
- Apple scab*
- Powdery mildews*
- Molds of vegetables and fruits *
- Leaf spots *
- Verticillium wilt*
Fungi: Basidiomycete
- Root and heart rots of trees*
- Smuts of cereals*
- Rusts*
Bacteria
- Crown gall of nursery crops*
- Fire blight of pear and apple*
- Black leg of potato*
Viruses
- Tobacco mosaic*
- Aphid-transmitted viruses (Barley yellow dwarf*)
Nematodes
- Root knot nematode*
- Lesion nematode*
* Plant Disease Lesson available at APS Education Center
http://www.apsnet.org/education/LessonsPlantPath/Top.html
When learning disease cycles, ask yourself these questions:
What is (are) the reproductive progagule(s) of the pathogen?
How do propagules originate?
How are propagules dispersed?
If more than one pathogen propagule, which is most significant economically?
When and where on the plant does infection take place?
How does the pathogen overwinter and subsequently initiate a primary cycle?
What is the importance of the primary cycle versus secondary cycles?
How does environment impact this disease?
What are the practical control measures?
At what part of the disease cycle are control measures directed?