Parasitism and Plant Disease Parasitism and Plant Disease I D fi i i Important Definitions: • Pathogen – a disease causing agent – Pathogenicity – Ability for an organism to interfere with one or more essential functions of another organism – causing disease Virulence The degree of pathogenicity of a pathogen – Virulence – The degree of pathogenicity of a pathogen • Parasite – Organisms that live on or in another organism and obtains its food from the later and obtains its food from the later – Plant Parasite – Organism that becomes intimately associated with the a plant and multiplies/grows at the expense of the with the a plant and multiplies/grows at the expense of the plant • Saprophyte – Or g anisms that live on dead matter and secrete enzymes to break down material for energy
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Parasitism and Plant DiseaseParasitism and Plant Disease
I D fi i iImportant Definitions:• Pathogen – a disease causing agent
– Pathogenicity – Ability for an organism to interfere with one or more essential functions of another organism – causing disease
Virulence The degree of pathogenicity of a pathogen– Virulence – The degree of pathogenicity of a pathogen
• Parasite – Organisms that live on or in another organism and obtains its food from the laterand obtains its food from the later – Plant Parasite – Organism that becomes intimately associated
with the a plant and multiplies/grows at the expense of thewith the a plant and multiplies/grows at the expense of the plant
• Saprophyte – Organisms that live on dead matter and p p y gsecrete enzymes to break down material for energy
Parasitism and Plant DiseaseParasitism and Plant Disease
Viruses, Viroids, and xylem/phloem limited bacteria:xylem/phloem limited bacteria: Move cell to cell intracellularly, systemic
Plant Disease Development
5 G th d d ti
Plant Disease Development
5. Growth and reproduction of the pathogen (Colonization)( )‐ Pathogens continue to spread until the infection is stopped or the plant is deadstopped or the plant is dead
‐ Only fungi and nematodes can actively movecan actively move
‐ All other pathogens rely rapid reproduction and being passively moved
Plant Disease Development5. Growth and reproduction of
th th (C l i ti )
Plant Disease Development
the pathogen (Colonization)‐ Reproduction:
‐ Fungi – spores, inter‐ and g p ,intra‐, surface and interior
‐ Bacteria – cell division, inter‐and intra‐, surface and interior
‐ Viruses – intra‐, inside cells onlyonly
‐ Nematodes – inter‐ and intra‐, surface and interior,
‐ Parasitic Plants – seeds, exterior of plant only
Rate varies on pathogen present, environment, and host
Plant Disease DevelopmentPlant Disease Development
6. Dissemination of pathogen
Agrios, 1997
Plant Disease Development7. Survival of pathogen
Plant Disease DevelopmentBacteria: same way as fungi;without a host
(Overwintering stage)Fungi: mycelium in cankers bud
Bacteria: same way as fungi; infected plants, seeds, tubers, and plant debris; in the bodies of
Fungi: mycelium in cankers, bud scales, seeds, tubers, and plant debris; spores; and sclerotia
insect vectors. Survive better in large slimy colonies than as small groups
‐ Soil inhabitants – survive in soil indefinitely (saprophytes)
groups.
Viruses: survive only in living ( p p y )‐ Soil transients – survive in soil for short period of time (parasites)
plant tissues; roots of perennial plants, seeds of some hosts, and insect vectors.(parasites)
Parasitic Plants: Seeds and
insect vectors.
Nematodes: Survive as eggs in h il lif hvegetative from on host the soil; or lifestages that are dormant in seeds and bulbs
Plant Disease DevelopmentPlant Disease Development
7. Survival of pathogen without a host
Agrios, 1997
Plant Disease DevelopmentDisease Epidemics:Monocyclic: completes 1 disease cycle in a
p1° inoculum
Monocyclic: completes 1 disease cycle in a year‐ 1° inoculum is only inoculum for
entire year
1° infection
entire year‐ Disease increases year to year as
inoculum builds Over‐seasoning Stage
Polycyclic: 2or more disease cycles in a year‐most pathogens‐ disseminated by air and airborne
1° inoculum 1° infection
‐ disseminated by air, and airborne vectors
‐ create explosive epidemics – Late Blight, Powdery Mildew, and Rusts
2° inoculum2° infectiong , y ,
Polyetic – requiring two or more years to complete lifecycle (considered p y (monocyclic)
‐ typical of many vascular wilt pathogens – Dutch Elm Disease