Transcript Document

The 100 Worst Invasive Fungi
In the Invasive Species Compendium
Amy Y. Rossman
Systematic Mycology & Microbiology Laboratory (SMML)
USDA-Agricultural Research Service (ARS)
Beltsville, MD 20705
not as charismatic as emerald ash borer
or Asian carp but still very damaging
A quick course in fungi:
1. Fungi obtain their nutrients by absorption
2. Most are composed of hyphae, small thread-like structures
3. Often invisible, living inside their food source
4. Extremely diverse, many, many species
Why are there so many fungi?
Fungi are opportunists!
Invasive fungi cause $21 billion damage annually,
greater in value than loss due to insects.
number of
fungi –
1.5 million
Chestnut blight caused by
Cryphonectria parasitica
(Ascomycetes, Diaporthales)
Introduced on logs in 1909 within twenty years killed all
mature chestnut trees in
eastern North America
Spread rapidly
throughout the
eastern U.S.
described as a new
originated in Asia.
Dutch elm disease
Dogwood anthracnose
Karnal bunt of wheat
Wheat rust
White pine blister rust
Soybean rust
Phytophthora ramorum, cause of SOD
A new disease in the western United States known as sudden oak
death (SOD) attacks woody plants including redwoods
Recently described as a new species from Europe on
Rhododendron, different population in U.S.
Many additional species of Phytophthora discovered in the US
What can be done to prevent the
entry of invasive fungi?
We need to know:
1) what are the most threatening
fungal pathogens?
2) where do they occur?
3) how might they get into the US?
Fungi on Plants and Plant
Products in the United States
13,000 species of plant-associated fungi
All data available on-line
Worldwide database
of fungus-host
associations and
distribution based on
literature and
700,000 reports
100 most threatening fungi
to the United States
Lots of ascomycetes (40%)
Rust fungi – obligate parasites (27%)
Oomycetes – Phytophthora and
friends (26%)
Other – smuts, wood decay (7%)
100 most threatening fungi
to the United States
For each species:
Descriptions and illustrations
Geographic distribution
Host range
Detection and inspection methods
Biology and ecology
Movement and dispersal
Economic impacts
Management issues
Gaps in knowledge/research needs
All data online and published in the CABI Invasive Species Compendium
Chalara fraxinea
Ash dieback
- pathogenic on Fraxinus angustifolia and F. excelsior
- conidial fungus Chalara fraxinea, sexual form ascomycete
previously thought to be Hymenoscyphus albidus, widely
reported as a saprobe; recently determined to be a newly
described pathogenic species, H. pseudoalbidus
- first observed as a pathogen in North and Central Europe in the
1990s, now known throughout Europe
- not known if pathogenticity due to a change in the fungus or a
change in the environment
- infected nursery saplings may carry the fungus
Claviceps gigantea
Horse’s tooth or ergot of maize
- on
maize (corn) only in certain high humid valleys of Mexico
- can reduce yield by 50%
- dispersal is by airborne ascospores, possibly by insect-borne
conidia or accidental by transportation of sclerotia
in harvested ears or in soil.
- overwinters as sclerotia on the ground or mixed with seed
- in spring, sclerotia germinate to produce stalked stromata
with heads containing immersed perithecia.
- ascospores primary inoculum; forcibly ejected and carried
by wind to susceptible maize plants
- sphacelial tissue in cavities in and on the sclerotia produce
macroconidia and microconidia in a sticky matrix
('honeydew‘). -
Harpophora maydis
late wilt of maize
- soil-borne, possibly also seed-borne
- causes significant losses to corn, related
to take-all disease of wheat
- known from Egypt and India, recently
reported from Hungary, Portugal
and Spain, possibly Kenya
- difficult to detect and identify
Cronartium flaccidium
Scots stem pine rust
- heteroecious rust fungus, completing different stages of its
life cycle on different plants
- spermogonial and aecial stages occurs on species of hard or
two-needled pines
- uredinial and telial stages on the leaves of herbaceous species
in Asclepiadaceae, Paeoniaceae, and Scrophulariaceae
- known from Europe and parts of northern and eastern Asia
- damaging on native and introduced pines or the alternate
plant host
- infections on pines develop slowly, accidental introduction of
the rust could occur onconifer seedlings or trees
-Regulated Pest for the United States
(USDA/APHIS, 2008)
Once we know the most
important invasive fungi, we
can determine how they could
enter the country and keep
them out!
Evaluate the most likely pathways
Develop diagnostic tools for identification
Change regulations concerning potential hosts,
primarily nursery stock
Inspect plant material in country of origin
Educate port inspectors
We can keep out
invasive fungi!