The 100 Worst Invasive FungiIn the Invasive Species Compendium

Amy Y. RossmanSystematic Mycology & Microbiology Laboratory (SMML)

USDA-Agricultural Research Service (ARS)Beltsville, MD 20705

Fungi

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!

MushroomsMycorrhizaePolyporesMorelsTrufflesYeastsPathogens SaprobesMolds

Estimated number of fungi –1.5 million species

Invasive fungi cause $21 billion damage annually, greater in value than loss due to insects.

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.

Previously unknown, described as a new species.

Probably originated in Asia.

Dutch elm diseaseDogwood anthracnoseKarnal bunt of wheat

Wheat rustWhite pine blister rust

Soybean rust

Phytophthora ramorum, cause of SODA 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 specimens

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 illustrationsGeographic distributionHost rangeDetection and inspection methodsBiology and ecologyMovement and dispersalEconomic impactsManagement issuesGaps 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 giganteaHorse’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 maydislate 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 flaccidiumScots 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 pathwaysDevelop diagnostic tools for identificationChange regulations concerning potential hosts, primarily nursery stockInspect plant material in country of origin Educate port inspectors

We can keep out invasive fungi!