2. 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 interaction=biotic Single event= abiotic

5. What is a pathogen? Strictly speaking a pathogen is the causal agent of disease Bacteria Viruses Nematodes Stramenopiles Algae Phytoplasmas Higher plants

10. And of course… fungi Fungi: saprophytic, symbionts, and pathogens Polyphyletic group in evolutionary terms –Basidiomycetes Ascomycetes Zygomycets Animals Plants Red algae Brown algae Myxomycetes

18. 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

22. Hyphae, sporangia, and zoospores of P. ramorum

26. Fungi do not photosynthesize Biotrophic: mycorrhyzae, rusts Endophites: clavicipetaceae, Necrotrophic; most pathogens Saprobes: primary (involved in litter decomposition)

27. 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

28. DISEASE!! Symptoms vs. signs; e.g. chlorosis vs. fruit- body The disease triangle

29. 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

30. Genetic resistance in host Length of lesion (mm) Proportion of stem girdled (%) Nicasio\42.5 a 0.71 a China Camp40.5 a 0.74 a San Diego27.8 b 0.41 b Ojai25.0 b 0.47 b Interior live oak (Maricopa) 14.1 b 0.33 b

31. 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

32. Chlamydospores of P. ramorum

34. West Coast Europe P. lateralis

35. host-pathogen-environment Temperatures Shading Relative humidity Free standing water pH and any potentially predisposing factors Nutrient status

36. Colony diameter (mm) at 13 days

37. Presence of free water Between 6 and 12 hours required for infection of bay leaves