9 While we often think of “rot” as being mushy and smelly, that is not always the case. Xylem is the water conducting tissue within the plant. When a pathogen affects the xylem, usually by blocking or destroying the tissue, the plant is deprived of water, which results in a wilt. However, any time the roots are affected (usually a decay or rot), a wilt will also be the symptom expressed as the roots are the plant organs that take up water from the soil or potting medium. 10 Canker is another symptom type: citrus canker on the left 11 Galls can be caused by insects, but galls can also be caused by fungi (peach leaf curl – Taphrina on the left) and one particular bacterial pathogen, Agrobacterium tumefaciens (right). 12 With turfgrass and grain crops, the terms “patch” and “decline” are used to indicate that large areas in the landscape or field are being affected by the same pathogen. 13 This is a list of symptoms associated with bacterial diseases of plants. The photo illustrates the “water soaked” or “greasy” symptom. 14 List of symptoms associated with fungal diseases of plants. 15 Plants infected with viruses exhibit symptoms that are not usually expressed when the plants are infected with other plant pathogens. Dwarfing and stunting can be caused by most pathogens, but are often associated with viruses. The next slide illustrates these symptoms. 16 Example of dwarfing (compared to control), ringspot and mosaic symptoms. 17 Pathogenicity vs. virulence; etiology definition 18 Etiology and pathogenicity testing usually go together. These are the four steps required to prove a culturable organism (nematode, bacterium or fungus) is causing the disease symptoms observed. This looks easier than it actually is, because we don’t always know the environmental factors associated with disease development. 19 This is an example of how we determined what fungus was causing queen palms to die throughout most of Florida. This was a new disease. The typical symptom is shown in the photo second from the left. When we cut through the rachis (leaf stem), we can observe the discolored tissue. After surface disinfecting the tissue very well, this discolored tissue was placed on agar plates to determine what would grow out of
9 While we often think of “rot” as being mushy and smelly, that is not always the case. Xylem is the water conducting tissue within the plant. When a pathogen affects the xylem, usually by blocking or destroying the tissue, the plant is deprived of water, which results in a wilt. However, any time the roots are affected (usually a decay or rot), a wilt will also be the symptom expressed as the roots are the plant organs that take up water from the soil or potting medium. 10 Canker is another symptom type: citrus canker on the left 11 Galls can be caused by insects, but galls can also be caused by fungi (peach leaf curl – Taphrina on the left) and one particular bacterial pathogen, Agrobacterium tumefaciens (right). 12 With turfgrass and grain crops, the terms “patch” and “decline” are used to indicate that large areas in the landscape or field are being affected by the same pathogen. 13 This is a list of symptoms associated with bacterial diseases of plants. The photo illustrates the “water soaked” or “greasy” symptom. 14 List of symptoms associated with fungal diseases of plants. 15 Plants infected with viruses exhibit symptoms that are not usually expressed when the plants are infected with other plant pathogens. Dwarfing and stunting can be caused by most pathogens, but are often associated with viruses. The next slide illustrates these symptoms. 16 Example of dwarfing (compared to control), ringspot and mosaic symptoms. 17 Pathogenicity vs. virulence; etiology definition 18 Etiology and pathogenicity testing usually go together. These are the four steps required to prove a culturable organism (nematode, bacterium or fungus) is causing the disease symptoms observed. This looks easier than it actually is, because we don’t always know the environmental factors associated with disease development. 19 This is an example of how we determined what fungus was causing queen palms to die throughout most of Florida. This was a new disease. The typical symptom is shown in the photo second from the left. When we cut through the rachis (leaf stem), we can observe the discolored tissue. After surface disinfecting the tissue very well, this discolored tissue was placed on agar plates to determine what would grow out of
4_TEXT_Plant-Disease-General-Concepts.docx