2. Summary of second class DNA mutates, evolves, and different DNA sequences can be assigned to different individuals, populations from different provenances, closely related species, different species, different microbial pathovars DNA-based phylogeography allowed to discover pine pathogen in Italy was of North American origin DNA based genealogies allowed to identify hybridization between native and exotic pathogen DNA allows to identify new species and to determine whether they are exotic or not

3. Definitions Propagule= structure used by an organism to spread or survive Locus= a physical portion of a chromosome,a gene Intron= a portion of DNA, a locus that does not code for a protein Exon= a coding gene

4. Definitions-2 Alleles= different DNA sequences at the same locus If a locus has variation in sequence it is polymorphic (many forms) Polymorphisms are differences in DNA among organisms, the more polymorphisms the easier it is to differentiate organisms There are more polymorphisms in introns

5. Definitions-3 Invasive organisms: exotic organism that reproduces and occupies progressively a larger area: –Fast reproductive cycle –Vectored –Hardy –Occupy unoccupied niches –Different drain on natural resources –Make environment favorable for itself and other invaders –Linked to disturbances –If pathogen, more changes because top of pyramid –May hybridize with native species: new taxon is created

6. MICROBIAL INVASIONS OF NATURAL ECOSYSTEMS: –Cannot be eradicated –Problematic because not noticeable for decades –Can cause limited problems –Can cause major alterations: Because of lack of coevolution between host and pathogen Because they are where similar organisms were not before

7. Introduced organisms Have a smaller genetic variation than original population Strong founder effects Each founder can create a significantly different population if not in equilibrium Mating will homogenize variation Mating barriers will increase difference

8. How does DNA help Identify microbe Determine whether equally named organism from elsewhere is the same or not Determine how it is reproducing Quantify organism Determine whether it is hybridizing or not

9. Definitions Phylogeny Phylogeography Gene geneaology

10. 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

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

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

25. 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

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

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

33. 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

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

35. 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

36. 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

37. 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

38. Chlamydospores of P. ramorum

40. West Coast Europe P. lateralis

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

42. Colony diameter (mm) at 13 days

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