Transcript Document

SUMMARY
• Cypress canker
– Infectious propagules called conidia are
multicelled, genetically identical to parent, and
need a wound to infect
– Genetic studies reveal one clone in Europe and
many in California
– Disease caused by exotic pathogen in Europe and
by off site planting and exotic host in California
Conidia of Seiridium
cardinale observed by
optical microscope
and SEM
SUMMARY
• Heterobasidion
– Primary infection caused by airborne genetically
distinct basidiospores
– Secondary infection of adjacent trees caused by
direct root to root contact
– Host specificity of H.irregulare vs. H. occidentale
– Stumps main infection courts for H. irregulare on
pine/juniper, wounds for true fir/sequoia
– Environmental changes increase abundance of
this root and bole pathogen
• Armillaria (Honey mushroom)
– Mostly secondary infection thanks to rhizomorphs,
largest organism in the world
True firs
Pines
Each spore is a genetically different individual:
In pines we found the same genetic individual in stumps and
adjacent trees indicating direct contagion between the two
In true firs and true firs/sequoias we find same individual
in adjacent standing trees indicating infection not linked
to stumps but to wounds on standing trees
“Emergent diseases”:
3: exotic pathogens
• 99% of times human responsible for their
introduction
Like the conquistadores brought
diseases that were lethal to
those who had never been
exposed to them, so do exotic
diseases cause true devastation
in plant communities because of
lack of coevolution between
hosts and microbes
QuickTime™ and a
TIFF (LZW) decompressor
are needed to see this picture.
California invaded: 1849 A.D.
Port Orford Cedar Root Disease
1950s
Sudden Oak Death
1990s
Canker-stain of
Sycamores 1980’s
Pitch canker disease
1980s
New hybrid root pathogen
1990s
Manzanita/madrone
die-back
White pine blister rust
1930s
Dutch Elm Disease
1960s
Oak root canker
2000
How can people transport
pathogens
• By transporting plants and plant parts
– Crops, and seeds
– Raw food
– Ornamental plants
Untreated lumber
Soil
Insects vectoring fungi
Military activity
The Irish Potato Famine
• From 1845 to 1850
• Phytophthora
infestans
• Resulted in the
death of 750,000
• Emigration of over 2
million, mainly to the
United States.
Girdling aerial ‘cankers’
removed from roots
Big Sur
2006
K. Frangioso
% Mortality of Tanoak by Stem Size Class
% Mortality
45
40
35
30
25
20
15
10
5
0
35.8
P. ramorum absent
Non-infec
ted plots
P. ramorum
present
Infec
ted plots
10.7 11.8
28.5
12.4
4.1
1-<5
34.1
5-<10
4.8
10-<20
>20
Tanoak st em diamet er size c lass (c m)
Wickland et al., unpublished
P. ramorum growing in a Petri dish
Organism new to science
•
•
•
•
Origin unknown
Biology unknown
Symptoms caused unknown
Immediately though highly regulated
Rhododendron:
In EU mostly a nursery
issue, but also present in
nurseries in US and Canada
Stem canker
Leaf necrosis
Phytophthora
ramorum
Sporangia
Chlamydospores
Is it exotic?
• Our studies have indicated that California
population is extremely simplified, basically
two strains reproducing clonally as expected
of an introduced organism
• Many hosts appear to have no resistance at
all
• Limited geographic distribution
Where does it come from?
• It is unknown where pathogen originally
comes from, but previous studies have shown
that California forest population is derived
from a relatively genetically diversified US
nursery population, indicating ornamental
nurseries were the most likely avenue for
pathogen introduction
Let’s look at its genetic
structure
• Need a number of independent and
neutral DNA markers
• Used AFLP, a technique that scans the
entire nuclear genome
• Are our isolates the same as the
European ones?
• Is the genetic structure suggestive of an
introduced or native species?
•US forest isolates
clearly distinct from EU
nursery isolates, also
have different mating
type
•Isolates from nurseries
in WA, OR, & BC both
of the US and EU types
•Potential for XXX sex
and recombination in
US nurseries
•US forest population
is genetically very
homogeneous,
trademark of an
introduced species
The entire genome was sequenced in
less than 3 years since discovery of organism
* 12 SSR loci (di- and tri- repeats identified)
* Loci selected to be polymorphic both between
and within continental populations
* 500+ representative isolates analyzed
CCGAAATCGGACCTTGAGTGCGGAGAGAGAGAGAGACTGTACGAGCCCGAGTCTCGCAT
Mating
Type
Growth
Rate
A1
Fast
A2
Slow
A2
Fast
Terminology
Genotype Lineage
Population
Results of 1st microsatellite
study
• There actually three distinct (genotypically
and phenotypically) lineages of P. ramorum
• Very low diversity in US forests (microsats
cannot discriminate among individuals,
clonality confirmed), only one lineage
• Several genotypes but only one lineage in EU
nurseries
• Three lineages in US nurseries
Was the pathogen first in US
forests or in US nurseries?
Slide 12
Was the pathogen first in US
forests or in US nurseries?
Slide 12
nurserie
forests
Where was it introduced?
• First reports mid 90’s
• Pathogen identified in
2000
• By then, the pathogen
was widespread
• CLUES: severity of
symptoms and
anedoctal stories
Positive isolation
P. ramorum
We found
same
genotypes in
nurseries and
forests proving
origin of wild
outbreak
Introduction phase
1- Escape of pathogen from
Infected nursery plants at two
locations: Mount Tamalpais
(Marin County), and Scott’s
Valley (Santa Cruz County)
2- Nurseries and two sites
have identical strain
composition, but distance
between sites is impossible
for natural spread of
organism
nurseries
What favors invasion of exotic
fungi ?
– Density of host increases severity of disease
– Corridors linking natural habitats
– Synchronicity between host susceptibility and
pathogen life cycle
– Ecological and environmental conditions
Bay/Oak association
Bay
Coast Live Oak (no sporulation)
Canker margin in phloem
Bleeding canker
Sporangia
Site
Mantel test among all individuals.
[Moran’s I vs ln (geographic
distance)]
ID
Correlation P-value
coeff. (r)
(1000,000
perm)
ALL
-0.2153
<0.000001
0.5
0.4
Moran's I
0.3
0.2
0.1
0
-0.1
-0.2
10
100
1000
Mean Geographic Distance (m)
10000
100000