DISEASES AND TREES

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DISEASES AND TREES

• What exactly is a disease? It is the outcome of
  an interaction between a plant and the
  environment, resulting in an altered physiology
  of the host
• Sustained interactionbiotic
• Single event abiotic

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What is a pathogen?

• Strictly speaking a pathogen is the causal agent
  of disease
• Bacteria
• Viruses
• Nematodes
• Stramenopiles
• Algae
• Phytoplasmas
• Higher plants

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And of course fungi

• Fungi saprophytic, symbionts, and pathogens
• Polyphyletic group in evolutionary terms
• Basidiomycetes
• Ascomycetes
• Zygomycets
• Animals
• Plants
• Red algae
• Brown algae
• Myxomycetes

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Fungi again!

• Filamentous somatic (vegetative body)
• High surface, good for extrogenous digestion
• Good infection structures, infection peg,
  appressoria, rhizomorphs
• Chitin in cell wall
• Nuclear ploidy very unique
• Reproduction by spores asexual mode very well
  represented
• Small nuclei, but with a lot of plasticity

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Hyphae, sporangia, and zoospores of P. ramorum
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Fungi do not photosynthesize

• Biotrophic mycorrhyzae, rusts
• Endophites clavicipetaceae,
• Necrotrophic most pathogens
• Saprobes primary (involved in litter
  decomposition)

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Some pathogen roles in natural plant communities

• Selection of individuals best suited for the site
• Maintenance of genetic diversity and stability in
  host plant populations
• Establishment or maintenance of host geographic
  ranges
• Natural succession
• Regulation of stand density, structure, and
  composition

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DISEASE!!

• Symptoms vs. signs e.g. chlorosis vs. fruit-body
• The disease triangle

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host-pathogen-environment

• Susceptibility of individuals or of portions of
  individuals
• Genetic variability
• Basic compatibility (susceptibility) between host
  and pathogen
• Ability to withstand physiological alterations

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Genetic resistance in host
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host-pathogen-environment

• Basic compatibility with host (virulence)
• Ability to maintain diversity sex vs. no sex
• Size of genetic pool
• Agressiveness (pathogenicity) towards hosts
• Ability to survive without host

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Chlamydospores of P. ramorum
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West Coast
Europe
P. lateralis
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host-pathogen-environment

• Temperatures
• Shading
• Relative humidity
• Free standing water
• pH and any potentially predisposing factors
• Nutrient status

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Colony diameter (mm) at 13 days
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Presence of free water
Between 6 and 12 hours required for infection of
bay leaves