Transcript DISEASES AND TREES

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
– Basidiomycetes
Ascomycetes
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,
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
Hyphae, sporangia, and zoospores of P. ramorum
Fungi do not photosynthesize
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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. fruitbody
• 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
Length of lesion Proportion of stem
(mm)
girdled (%)
Nicasio\
China Camp
42.5a
40.5a
0.71a
0.74a
San Diego
27.8b
0.41b
Ojai
Interior live
oak
(Maricopa)
25.0b
14.1b
0.47b
0.33b
host-pathogen-environment
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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 P. ramorum
93
100
0.1
Pr75 Qa Monterey
Pr87 Am Marin
Pr86b Am Marin
Pr86a Am Marin
Pr84 Soil Marin
Pr82 Vo Marin
Pr80 Vo Marin
Pr72 Rh Alameda
Pr65 Qp Santa Cruz
Pr58 Vo Marin
Pr50 Qa Sonoma
Pr201b Rh Santa Cruz
Pr201a Rh Santa Cruz
Pr47b Qa Sonoma
Pr47a Qa Sonoma
Pr35 Qa Sonoma
Pr28 Ld Sonoma
Pr24 Qa Sonoma
Pr22 Qa Sonoma
Pr20 Qa Sonoma
Pr19 Qa Napa
Pr16 Qa Santa Cruz
Pr13 Qa Santa Cruz
Clone group
Pr11b Qa Monterey
Pr11a Qa Monterey
Pr10 Ld Monterey
Pr08 Qa Napa
Pr06 Qa Marin
Pr05 Ld Marin
Pr04 Qk Marin
Pr03 Ld Marin
Pr88 Uc Sonoma
Pr89 Uc Sonoma
Pr90 Qa Marin
Pr91 Uc Sonoma
Pr97 Qa Napa
Pr102 Qa Marin
Pr103 Ld Marin
Pr104 Ld Marin
Pr107 Uc Sonoma
Pr110 Uc Marin
Pr112 Uc Marin
Pr113 Uc Marin
Pr114 Uc Marin
Pr115 Uc Marin
Pr116 Uc Marin
Pr136 Uc Marin
Pr156 Ld Oregon
Pr157 Ld Oregon
Pr158 Ld Oregon
PrJL3.1 Ss Sonoma
PrSDC21.6 Ss Sonoma
Pr36 Qa Sonoma
Pr27 Qa Marin
Pr57 Ld Santa Clara
Pr70 Vo Marin
Pr159 Ld Oregon
Pr52a Rh Santa Cruz
67
Pr52b Rh Santa Cruz
89
PrCoen Rh Santa Cruz
PrJL3.5.3 Ss Sonoma
96
Pr106 Uc Sonoma
Pr71 Qa Sonoma
Pr01 Qa Marin
PrE9/95 Rh Germany
PrE16/99 Vb Germany
PrE12/98 Rh Germany
PrE104 Water Germany
European group
PrE69082 Rh Germany
PrE9/3 Water Germany
PrE14/98-a Rh Germany
Pl33 Cl Del Norte
Pl16 Soil Josephine
P. lateralis
Pl27 Tb Del Norte
(outgroup)
NJ
P. lateralis
E33LAT
E27LAT
E16LAT
0.005 changes
4
11
12
13
16
20
22
23a
23b
27
36
63
77
88
98
119
140
195a
195b
201Ca
201Cb
203
240
265
288
326
331
339
344leaves
344stem
351
354
355
357
362
441
463
469
472
478
488
491
492
493
496
507
570
661
662
663
112
291
275
142
664
237
217a
217b
coen
477
279
e1
e4
e7
e9
e10
e2
West Coast
Europe
host-pathogen-environment
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Temperatures
Shading
Relative humidity
Free standing water
pH and any potentially predisposing factors
Nutrient status
Colony diameter (mm) at 13 days
Presence of free water
Between 6 and 12 hours required
for infection of bay leaves
Human activities affecting
disease incidence in forests
• Introduction of exotic pathogens
• Planting trees in inappropriate sites
• Changing stand density, age structure,
composition, fire frequency
• Wound creation
• Pollution, etc.
Effects of fire exclusion
DISEASE: plant microbe
interaction
• Basic compatibility need to be present
• Chemotaxis, thighmotropy
• Avirulence in pathogen matched by
resistance in host according to the gene for
gene model
• Pathogenicity factors such as toxins and
enzymes important in the infection process
Effects of diseases on host
mortality, growth and reproduction
• Young plants killed before reaching
reproductive age
• Affect reproductive output
• Directly affect flowers and fruits
Complexity of forest diseases
• At the individual tree level: 3 dimensional
• At the landscape level” host diversity,
microclimates, etc.
• At the temporal level
Complexity of forest diseases
• Primary vs. secondary
• Introduced vs. native
• Air-dispersed vs. splash-dispersed, vs.
animal vectored
• Root disease vs. stem. vs. wilt, foliar
• Systemic or localized
Progression of cankers
Older canker with dry seep
Hypoxylon, a secondary
sapwood decayer will appear
Stem canker
on coast live oak
Cankers by P. ramorum at 3 months
from time of inoculation on two coast
live oaks
Root disease center in true fir caused by H. annosum
Categories of wild plant diseases
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Seed decay
Seedling diseases
Foliage diseases
Systemic infections
Parasitic plants
Cankers, wilts , and diebacks
Root and butt rots
Floral diseases
Seed diseases
• Up to 88% mortality in tropical Uganda
• More significant when seed production is
episodic
Seedling diseases
• Specific diseases, but also diseases of adult trees
can affect seedlings
• Pythium, Phytophthora, Rhizoctonia, Fusarium
are the three most important ones
• Pre- vs. post-emergence
• Impact: up to 65% mortality in black cherry.
These diseases build up in litter
• Shady and moist environment is very conducive to
these diseases
Foliar diseases
• In general they reduce photosynthetic ability by
reducing leaf area. At times this reduction is
actually beneficial
• Problem is accentuated in the case of small plants
and in the case other health issues are
superimposed
• Often, e.g. with anthracnose,needle cast and rust
diseases leaves are point of entry for twig and
branch infection with permanent damage inflicted
Systemic infections
• Viral?
• Phytoplasmas
• Peronospora and smuts can lead to over
50% mortality
• Endophytism: usually considered beneficial
Grass endophytes
• Clavicipetaceae and grasses, e.g. tall fescue
• Mutualism: antiherbivory, protection from
drought, increased productivity
• Classic example of coevolutionary
development: Epichloe infects “flowers” of
sexually reproducing fescue, Neotyphodium
is vertically transmitted in species whose
sexual reproductive ability has been aborted
Parasitic plants
• True (Phoradendron) and dwarf mistletoe
(Arceuthobium)
• Effects:
– Up to 65% reduction in growth (Douglas-fir)
– 3-4 fold mortality rate increase
– Reduced seed and cone production
Problem accentuated in multistoried uneven aged forests
Cankers, wilts, and die-backs
• Includes extremely aggressive, often easy to
import tree diseases: pine pitch canker,
Dutch elm disease, Chestnut blight, White
pine blister rust
• Lethal in most cases, generally narrow host
range with the exception of Sudden Oak
Death
Root diseases
• Extremely common, probably represent the
most economically damaging type of
diseases
• Effects: tree mortality (direct and indirect),
cull, effect on forest structure, effect on
composition, stand density, growth rate
• Heterobasidion, Armillaria, Phellinus
weirii, Phytophthora cinnamomi
Floral diseases
• Pollinator vectored smut on silene offers an
example of well known dynamic interaction in
which pathogen drives genetic variability of hosts
and is affected by environmental condition
• Puccinia monoica produces pseudoflowers that
mimic real flowers. Effects: reduction in seed
production, reduction in pollinators visits
POPULATION DYNAMICS
Species interactions and diversity
Density-dependence
• Most diseases show positive density dependence
• Negative dependence likely to be linked to limited
inoculum: e.g. vectors limited
• If pathogen is host-specific overall density may
not be best parameter, but density of susceptible
host/race
• In some cases opposite may be true especially if
alternate hosts are taken into account
Counterweights to numerical
effects
• Compensatory response of survival can
exceed negative effect of pathogen
• “carry over” effects?
– NEGATIVE: progeny of infected individuals
less fit;
– POSITIVE; progeny more resistant (shown
with herbivory)
Disease and competition
• Competition normally is conducive to
increased rates of disease: limited resources
weaken hosts, contagion is easier
• Pathogens can actually cryptically drive
competition, by disproportionally affecting
one species and favoring another
Diseases and succession
• Soil feedbacks; normally it’s negative.
Plants growing in their own soil repeatedly
have higher mortality rate. This is the main
reason for agricultural rotations and in
natural systems ensures a trajectory towards
maintaining diversity
• Phellinus weirii takes out Douglas fir and
hemlock leaving room for alder
Janzel-Connol
• Regeneration near parents more at riak of
becoming infected by disease because of
proximity to mother (Botryosphaeria,
Phytophthora spp.). Maintains spatial
heterogeneity in tropical forests
• Effects are difficult to measure if there is little host
diversity, not enough host-specificity on the
pathogen side, and if periodic disturbances play an
important role in the life of the ecosystem
The red queen hypothesis
• Coevolutionary arm race
• Dependent on:
– Generation time has a direct effect on rates of
evolutionary change
– Genetic variability available
– Rates of outcrossing (Hardy-weinberg equilibrium)
– Metapopulation structure
Frequency-, or density
dependent, or balancing selection
• New alleles, if beneficial because linked to
a trait linked to fitness will be positively
selected for.
– Example: two races of pathogen are present, but
only one resistant host variety, suggests second
pathogen race has arrived recently
Diseases as strong forces in plant
evolution
• Selection pressure
• Co-evolutionary processes
– Conceptual: processes potentially leading to a
balance between different ecosystem
components
– How to measure it: parallel evolution of host
and pathogen
• Rapid generation time of pathogens. Reticulated
evolution very likely. Pathogens will be selected
for INCREASED virulence
• In the short/medium term with long lived trees a
pathogen is likely to increase its virulence
• In long term, selection pressure should result in
widespread resistance among the host
More details on:
• How to differentiate linear from reticulate
evolution: comparative studies on topology
of phylogenetic trees will show potential for
horizontal transfers. Phylogenetic analysis
neeeded to confirm horizontal transmission
NJ
11.10 SISG CA
Geneaology of “S” DNA insertion into P
ISG confirms horizontal transfer.
2.42 SISG CA
BBd SISG WA
F2 SISG MEX
Time of “cross-over” uncertain
NA S
BBg SISG WA
14a2y SISG CA
15a5y M6 SISG CA
6.11 SISG CA
9.4 SISG CA
AWR400 SPISG CA
9b4y SISG CA
15a1x M6 PISG CA
1M PISG MEX
9b2x PISG CA
A152R FISG EU
A62R SISG EU
890 bp
CI>0.9
A90R SISG EU
EU S
A93R SISG EU
J113 FISG EU
J14 SISG EU
J27 SISG EU
J29 SISG EU
0.0005 substitutions/site
EU F
NA P
NJ
Phylogenetic relationships
within the Heterobasidion
complex
Het INSULARE
Fir-Spruce
True Fir EUROPE
Spruce EUROPE
True Fir NAMERICA
Pine Europe
Pine EUROPE
Pine N.Am.
Pine NAMERICA
0.05 substitutions/site
HOST-SPECIFICITY
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Biological species
Reproductively isolated
Measurable differential: size of structures
Gene-for-gene defense model
Sympatric speciation: Heterobasidion,
Armillaria, Sphaeropsis, Phellinus,
Fusarium forma speciales
NJ
Phylogenetic relationships
within the Heterobasidion
complex
Het INSULARE
Fir-Spruce
True Fir EUROPE
Spruce EUROPE
True Fir NAMERICA
Pine Europe
Pine EUROPE
Pine N.Am.
Pine NAMERICA
0.05 substitutions/site
SEX
• Ability to recombine and adapt
• Definition of population and
metapopulation
• Different evolutionary model
• Why sex? Clonal reproductive approach can
be very effective among pathogens
The “scale” of disease
• Dispersal gradients dependent on propagule size,
resilience, ability to dessicate, NOTE: not linear
• Important interaction with environment, habitat,
and niche availability. Examples: Heterobasidion
in Western Alps, Matsutake mushrooms that offer
example of habitat tracking
• Scale of dispersal (implicitely correlated to
metapopulation structure)---two examples:
Heterobasidion in California, and Coriolopsis in
Panama
From Garbelotto and Chapela,
Evolution and biogeography of matsutakes
Biodiversity within species
as significant as between
species
S-P ratio in stumps is highly dependent
on distance from true fir and hemlock stands
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San Diego
White mangroves:
Corioloposis caperata
Coco Solo
Mananti
Ponsok
David
Coco Solo
0
237
273
307
Mananti
Ponsok
David
0
60
89
0
113
0
Distances between study sites
White mangroves:
Corioloposis caperata
Forest fragmentation can lead to loss of gene flow among
previously contiguous populations. The negative
repercussions of such genetic isolation should most severely
affect highly specialized organisms such as some plantparasitic fungi.
AFLP study on single spores
Coriolopsis caperata on
Laguncularia racemosa
Site
# of isolates
# of loci
% fixed alleles
Coco Solo
11
113
2.6
David
14
104
3.7
Bocas
18
92
15.04
Coco Solo
Coco Solo
Bocas
David
0.000
0.000
0.000
Bocas
0.2083
0.000
0.000
David
0.1109
0.2533
0.000
Distances =PhiST between pairs of
populations. Above diagonal is the Probability
Random d istance > Observed distance (1000
iterations).
From the population level to the
individual
• Autoinfection vs. alloinfection
• Primary spread=by spores
• Secondary spread=vegetative, clonal spread,
same genotype . Completely different scales
Coriolus
Heterobasidion
Armillaria
Phellinus
Recognition of self vs. non self
• Intersterility genes: maintain species gene
pool. Homogenic system
• Mating genes: recognition of “other” to
allow for recombination. Heterogenic
system
• Somatic compatibility: protection of the
individual.