SUMMARY

• Native diseases are important and positive forces in native ecosystems by optimizing resources allocation

• Disease triangle: host/pathogen/environment

• Host resistance can be regulated by one or by multiple genes

DISEASE TRIANGLEDISEASE TRIANGLE

PathogenPathogenHostHost

EnvironmentEnvironment

HIGH DISEASE

““Emergent diseases”:Emergent diseases”:1: 1: hosthost

• New host-pathogen combinations:New host-pathogen combinations:

exotic hostsexotic hosts

hosts planted off sitehosts planted off site

Cypress canker by Cypress canker by Seiridium Seiridium cardinalecardinale

• Pathogen was first described in California in the 20s. Later it was described in Italy where it started a serous epidemic of Italian cypress

• Belief that pathogen is native to California: is that true and why is it then causing a significant disease in our state?

Conidia of Conidia of Seiridium Seiridium cardinalecardinale observed by observed by

optical microscope optical microscope and SEMand SEM

Use of molecular genetics to Use of molecular genetics to resolve issue of origin of resolve issue of origin of

pathogenpathogen

• Used a technique similar to the one used in human forensics

• Native populations should comprise many different individuals genetically

• Introduced populations should be genetically simpler because of bottleneck related to introduction events

RESULTS: CA vs. EuropeRESULTS: CA vs. Europe

o California population diverse genetically= native to the state

o European population show no diversity=introduced

Symptoms caused by Symptoms caused by Seiridium cardinaleSeiridium cardinale on on Cupressus macrocarpaCupressus macrocarpa (above) and (above) and xxCupressocyparisCupressocyparis leylandiileylandii (right) (right)

Fig. 3

Why a disease in CA?Why a disease in CA?

• If pathogen is native to California, why is it causing such a serious disease?

• We observed that disease incidence is variable with:– cypress species, – location,

Range of susceptibilityRange of susceptibility

• Leyland cypress, Italian, monterey are listed as most susceptible

• Arizona and McKnob are regarded as more resistant

Range of susceptibilityRange of susceptibility

• 90% of Leyland are heavily infected

• 10% of monterey

• LEYLAND CYPRESS IS AN ORNAMENTAL CROSS, NOT NATIVE

Range of susceptibilityRange of susceptibility

• Monterey is more susceptible in inland areas where it is NOT NATIVE: we believe that colder temperatures cause more wounds that lead to infection

CONCLUSIONSCONCLUSIONS

• Cypress canker is a serious disease in Europe because pathogen was introduced

• Cypress canker is a serious disease in California because hosts were introduced either through planting off range (Monterey cypress) or because host is artificial creation (Leyland cypress); extinction of LEYLAND is most likely

““Emergent diseases”:Emergent diseases”:2: 2: environmental changesenvironmental changes

• Forestry and intensive forest use:Forestry and intensive forest use:

timber productiontimber production

tree felling and creation of stumpstree felling and creation of stumps

fire exclusion and increase in densityfire exclusion and increase in density

oversimplified forest compositionoversimplified forest composition

changes in forest compositionchanges in forest composition

changes in forest structure changes in forest structure

HeterobasidionHeterobasidion root disease root disease

• Heterobasidion (a bracket or shelf mushroom) infects trees through wounds and stumps, then it spreads through the roots to neighboring trees

• With tree felling,stumps and wounds are created, suddenly exponentially increasing infection levels

Heterobasidion shelf fruit-body

Use of molecular geneticsUse of molecular genetics:

• Differentiate Heterobasidion on fir/sequoias (H. occidentalis) from that on pine/junipers (H.irregularis)

• Show that airborne meiospores are responsible for most infection of Heterobasidion

• Show that in pines most infections start on stumps and that in true firs most infections on wounds

True firs

Pines

Each spore is a genetically different individual:

In pines we found the same genetic individual in stumps andadjacent 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 linkedto stumps but to wounds on standing trees

CONCLUSIONS:CONCLUSIONS:

• Logging activities increase Heterobasidion infection because of stump creation in pines and because of wounding in true firs sequoias

• We have shown that in pine stumps H. irregularis and H. occidentalis can both be present and create a new hybrid entity

• We have shown that in the past these hybridization events have lead to sharing of genes among these two species (Horizontal gene transfers)

ArmillariaArmillaria root diseases root diseases

• Armillaria, the honey mushroom, normally infects the roots of trees. It can be a saprobe and a pathogen and is common amongst oaks

• If woodland composition shifts to pine/oak, pines become the target of attacks and gaps in canopy enlarge over time. Stress (e.g. flooding) exacerbates susceptibility

Clusters of Clusters of ArmillariaArmillaria

How Does it Infect?How Does it Infect?

SOURCE: http://www.forestpathology.org/dis_arm.html

Two means of dispersal to other trees:

1.Mycelium can grow through direct root contacts and grafts with uninfected trees.

2.Rhizomorphs can grow through soil to contact uninfected trees.

DEAD OAK

OAK or PINE

What are Rhizomorphs?What are Rhizomorphs?• …“conglomerations of

differentiated parallel

hyphae with a protective

melanized black rind

on the outside.”

• Rhizomorphs are able to transport food and nutrients long distances which allows the fungus to grow through nutrient poor areas located between large food sources such as stumps.

SOURCE: http://www.nifg.org.uk/armillaria.htm

SOURCE: http://botit.botany.wisc.edu/toms_fungi/apr2002.html

Humongous FungusHumongous Fungus

It’s One of U-HAUL’s “Bizarre Roadside Attractions”

http://botit.botany.wisc.edu/toms_fungi/apr2002.html

CONCLUSIONSCONCLUSIONS

Human activities shifting from oak woodlands to mixed oak-pine lead

to large mortality gaps in pines around oaks if honey mushroom is

present

CHANGING SPECIES COMPOSITION LEADS TO

SEVERE DISEASE

Many gaps with very little regeneration and have not closed in

Change in gap area 1972-1999

YearArea in gaps

(m2) Percent in gaps

1972 6125 3.5

1999 53,981 31

““Emergent diseases”:Emergent diseases”:3: 3: exotic pathogensexotic pathogens

• 99% of times human responsible for their 99% of times human responsible for their introduction introduction

Like the conquistadores brought Like the conquistadores brought diseases that were lethal to diseases that were lethal to those who had never been those who had never been

exposed to them, so do exotic exposed to them, so do exotic diseases cause true devastation diseases cause true devastation in plant communities because of in plant communities because of

lack of coevolution between lack of coevolution between hosts and microbeshosts and microbesQuickTime™ and a

TIFF (LZW) decompressorare needed to see this picture.

California invaded: 1849 A.D.California invaded: 1849 A.D.

New hybrid root pathogenNew hybrid root pathogen1990s1990s

White pine blister rustWhite pine blister rust1930s1930s

Port Orford Cedar Root DiseasePort Orford Cedar Root Disease1950s1950s

Pitch canker diseasePitch canker disease1980s1980s

Dutch Elm DiseaseDutch Elm Disease1960s1960s

Sudden Oak DeathSudden Oak Death1990s1990s

Oak root cankerOak root canker20002000

Manzanita/madrone Manzanita/madrone die-backdie-back

Canker-stain ofCanker-stain ofSycamores 1980’sSycamores 1980’s