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

• Bacteria• Viruses• Nematodes• Stramenopiles• Algae• Phytoplasmas• Higher plants

And of course… fungi

• 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

Pr75 Qa MontereyPr75 Qa Monterey Pr87 Am MarinPr87 Am Marin Pr86b Am MarinPr86b Am Marin Pr86a Am MarinPr86a Am Marin Pr84 Soil MarinPr84 Soil Marin Pr82 Vo MarinPr82 Vo Marin Pr80 Vo MarinPr80 Vo Marin Pr72 Rh AlamedaPr72 Rh Alameda Pr65 Qp Santa CruzPr65 Qp Santa Cruz Pr58 Vo MarinPr58 Vo Marin Pr50 Qa SonomaPr50 Qa Sonoma Pr201b Rh Santa CruzPr201b Rh Santa Cruz Pr201a Rh Santa CruzPr201a Rh Santa Cruz Pr47b Qa SonomaPr47b Qa Sonoma Pr47a Qa SonomaPr47a Qa Sonoma Pr35 Qa SonomaPr35 Qa Sonoma Pr28 Ld SonomaPr28 Ld Sonoma Pr24 Qa SonomaPr24 Qa Sonoma Pr22 Qa SonomaPr22 Qa Sonoma Pr20 Qa SonomaPr20 Qa Sonoma Pr19 Qa NapaPr19 Qa Napa Pr16 Qa Santa CruzPr16 Qa Santa Cruz Pr13 Qa Santa CruzPr13 Qa Santa Cruz Pr11b Qa MontereyPr11b Qa Monterey Pr11a Qa MontereyPr11a Qa Monterey Pr10 Ld MontereyPr10 Ld Monterey Pr08 Qa NapaPr08 Qa Napa Pr06 Qa MarinPr06 Qa Marin Pr05 Ld MarinPr05 Ld Marin Pr04 Qk MarinPr04 Qk Marin Pr03 Ld MarinPr03 Ld Marin Pr88 Uc SonomaPr88 Uc Sonoma Pr89 Uc SonomaPr89 Uc Sonoma Pr90 Qa MarinPr90 Qa Marin Pr91 Uc SonomaPr91 Uc Sonoma Pr97 Qa NapaPr97 Qa Napa Pr102 Qa MarinPr102 Qa Marin Pr103 Ld MarinPr103 Ld Marin Pr104 Ld MarinPr104 Ld Marin Pr107 Uc SonomaPr107 Uc Sonoma Pr110 Uc MarinPr110 Uc Marin Pr112 Uc MarinPr112 Uc Marin Pr113 Uc MarinPr113 Uc Marin Pr114 Uc MarinPr114 Uc Marin Pr115 Uc MarinPr115 Uc Marin Pr116 Uc MarinPr116 Uc Marin Pr136 Uc MarinPr136 Uc Marin Pr156 Ld OregonPr156 Ld Oregon Pr157 Ld OregonPr157 Ld Oregon Pr158 Ld OregonPr158 Ld Oregon PrJL3.1 Ss SonomaPrJL3.1 Ss Sonoma PrSDC21.6 Ss SonomaPrSDC21.6 Ss Sonoma

Pr36 Qa SonomaPr36 Qa Sonoma Pr27 Qa MarinPr27 Qa Marin

Pr57 Ld Santa ClaraPr57 Ld Santa Clara Pr70 Vo MarinPr70 Vo Marin Pr159 Ld OregonPr159 Ld Oregon

Pr52a Rh Santa CruzPr52a Rh Santa Cruz Pr52b Rh Santa CruzPr52b Rh Santa Cruz PrCoen Rh Santa CruzPrCoen Rh Santa Cruz

PrJL3.5.3 Ss SonomaPrJL3.5.3 Ss Sonoma Pr106 Uc SonomaPr106 Uc Sonoma

Pr71 Qa SonomaPr71 Qa Sonoma Pr01 Qa MarinPr01 Qa Marin

PrE9/95 Rh GermanyPrE9/95 Rh Germany PrE16/99 Vb GermanyPrE16/99 Vb Germany

PrE12/98 Rh GermanyPrE12/98 Rh Germany PrE104 Water GermanyPrE104 Water Germany

PrE69082 Rh GermanyPrE69082 Rh Germany PrE9/3 Water GermanyPrE9/3 Water Germany

PrE14/98-a Rh GermanyPrE14/98-a Rh Germany Pl33 Cl Del Norte

Pl16 Soil Josephine Pl27 Tb Del Norte0.1

Clone groupClone group

European groupEuropean group

P. lateralisP. lateralis (outgroup)(outgroup)

100100

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411121316202223a23b273663778898119140195a195b201Ca201Cb203240265288326331339344leaves344stem351354355357362441463469472478488491492493496507570661662663112291275142664237

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E33LATE27LATE16LAT

0.005 changes

NJ

West Coast

EuropeP. lateralis

host-pathogen-environment

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

Colo

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Colo

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13

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Presence of free water

Between 6 and 12 hours requiredBetween 6 and 12 hours requiredfor infection of bay leavesfor infection of bay leaves