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
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Summary of second class DNA mutates, evolves, and different DNA sequences can be assigned to different individuals, populations from different provenances,
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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
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
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
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
• 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
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
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
Definitions
• Phylogeny
• Phylogeography
• Gene geneaology
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
What is a pathogen?
• Strictly speaking a pathogen is the causal agent of disease
• Fungi: saprophytic, symbionts, and pathogens• Polyphyletic group in evolutionary terms
– BasidiomycetesAscomycetes
Zygomycets
Animals
Plants
Red algae
Brown algae
Myxomycetes
Fungi… again!
• Filamentous somatic (vegetative body)– High surface, good for extrogenous digestion– Good infection structures, infection peg, appressoria,
rhizomorphsChitin in cell wallNuclear ploidy very uniqueReproduction by spores: asexual mode very well
representedSmall nuclei, but with a lot of plasticity
Hyphae, sporangia, and zoospores of Hyphae, sporangia, and zoospores of P. ramorumP. ramorum
Fungi do not photosynthesize
• Biotrophic: mycorrhyzae, rusts
• Endophites: clavicipetaceae,
• Necrotrophic; most pathogens
• Saprobes: primary (involved in litter decomposition)
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
DISEASE!!
• Symptoms vs. signs; e.g. chlorosis vs. fruit-body
• The disease triangle
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
Genetic resistance in host Genetic resistance in host
Length of lesion (mm)
Proportion of stem girdled (%)
Nicasio\ 42.5a 0.71a
China Camp 40.5a 0.74a
San Diego 27.8b 0.41b
Ojai 25.0b 0.47b
Interior live oak (Maricopa)
14.1b 0.33b
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
Chlamydospores of Chlamydospores of P. ramorumP. ramorum