Fungal spots on a protea
leaf from South Africa.
Mary E. Palm, APHIS's national mycologist, is first on
the list to identify fungi that are intercepted during inspection at
U.S. ports. She's based at ARS's Systematic Botany and Mycology Laboratory
(SBML) in Beltsville, Maryland, so that she has access to its top-notch
mycologists, fungal collections, and databases on the location of fungi
around the world. The U.S. National Fungus Collections, part of SBML,
are the largest reference collections of fungi in the world.
"I use the lab's host fungus records, keys, descriptions,
and computerized information to make an identification that ultimately
determines whether the agricultural material in question will be allowed
in the country, destroyed, or shipped back to its place of origin,"
This self-described detective also relies on ARS mycologists
like Amy Y. Rossman, who heads SBML, or Gary J. Samuels. "If I
look at a fungus and nothing seems to fit, I'll ask one of them,"
An arrangement of protea
flowers, two each of, from
left, Pink Mink, Duchess,
and Pin Cushion. In the
background are two leafy
leucadendron Safari Sunset
These scientistswho can differentiate molds with
names that most people would be challenged to pronouncestudy systematics,
which is the science of discovering and organizing biological diversity.
They are continuously naming, classifying, and describing fungi, bringing
order to this largely uncharted world of organisms.
The language they useto discuss genera with names
like Phomopsis, Colletotrichum, and Cryphonectria,
plus thousands of others and their associated speciesis critical
to efforts to solve agricultural problems.
"A name is more than just a label," says Rossman.
"When it's a result of detailed observation and knowledge, a name
will accurately communicate and predict biological information about
a given fungus so that scientifically sound decisions can be made."
Rossman served as national mycologist for APHIS before Palm.
Erin McCray, collections manager,
and David Farr, mycologist for
ARS, examine a fusiform rust of
pine, one of more than 1 million
specimens in the U.S. National
Knowing Our Fungal Foes
Fungal systematics can have a dramatic effect on decisions
about global transport and trade in crops and plants. For instance,
ARS scientists brought clarity to the confusion about the Karnal bunt
fungus, Tilletia indica, in the United States in 1996. SBML's
Lisa A. Castlebury determined that the fungus that had worried American
wheat growers in the Southeast and threatened the nation's wheat export
market was actually an imposter, a Karnal bunt look-alike. The new species
she described was Tilletia walkeri, or ryegrass bunt.
SBML researchers are also shedding light on the potentially
trade-restricting fungi of flowers of the family Proteaceae. Native
to the southern hemisphere and predominantly found and grown in South
Africa, proteas produce bright, exotic-looking flowers sought after
by the cut-flower industry. But while these blooms are fit for bouquets,
they are also fine hosts to a range of fungi.
"To protect the protea industry in the United States,
APHIS phytosanitary regulations may sometimes result in rejection of
shipments from South Africa before they can reach U.S. markets,"
Aiming to create a comprehensive resource for growers,
plant pathologists, and the regulatory entities who make quarantine
decisions, Palm and South African colleagues are busy writing a bookalready
a couple inches thickon the different fungi that occur on proteas.
The book, which will include the protea fungi that exist in the United
States, Africa, and Australia, should help facilitate the flow of usable
and innocuous plant materials among these countries.
Rossman and Palm both note that more and more fungal specimens
in need of investigation are coming through SBML's doors.
"I think the driving force is the growing desire
for new flowers and horticultural plants," says Palm.
But an old favorite, the dogwood tree, has also benefited
from the sleuthing of SBML. Dogwoods, including the flowering varieties
grown in the East and the Pacific dogwood found in the Pacific Northwest,
are being threatened by an anthracnose fungus. Beyond affecting the
spring-blooming trees that are used for landscaping, the fungus is invading
native stands of dogwoods that provide critical food and cover for wildlife.
"The fungus is a serious pathogen," says Rossman.
"Most notably, it's killed a lot of dogwoods in the woods of Catoctin
Mountain Park, in Maryland."
Causing coal-colored blotches on diseased leaves, the
fungus appeared simultaneously on both U.S. coasts, but no one knew
exactly what the causal agent was. Former SBML researcher Scott Redlin
described the fungal pathogen, Discula destructiva, a previously
unknown species, thereby laying the foundation for research on this
Other fungal pathogens requiring the detective work of
the Beltsville lab include daylily rust fungus; canker-causing fungi
of the genus Nectria, which attack hardwood trees like beech,
yellow birch, black walnut, and red oak; and the fungus that produces
scab on poinsettia.
Every day, Palm receives packages containing carefully
wrapped rusts, molds, and mildews from around the globe. On one day
in October, her subjects are chrysanthemum leaves. She's focusing on
the buff-colored spots, only millimeters across, encrusting the lower
surface of the foliage. She recognizes the culprit immediately: Puccinia
horiana. To nonscientists: white rust.
"The specimen was sent to us from a woman whose garden
club bought infested chrysanthemum plants from a nursery in another
state. She had even planted some of them in her yard," says Palm.
Palm was able to swiftly confirm what untrained eyes couldn't.
And a good thing! White rust, which originated in eastern Asia, is a
serious pest affecting garden and pot mums. The fungus produces a type
of sporea basidiosporethat can be spread from plant to plant
by wind or splashing water. If left unchecked, it could cost the country's
burgeoning horticulture and floral industries millions of dollars.
The mycologists quickly agree on their biggest hurdle:
a lack of knowledge about the breadth and diversity of fungi worldwide.
"In making an identification, we'll often know the
fungus' genus, but not its species, and there can be a significant difference
between two species of the same genus. Sometimes, a lot of money can
be at stake, as in the case of Karnal bunt," says Rossman.
To further prove her point about challenges faced by SBML
mycologists, Rossman holds up a 3- to 4-inch reference book that lists
the fungi known to exist in the United States and says, "I could
go out tomorrow and find 20 species that aren't in this book."
While the mycologists' decisions do have serious implications,
Rossman and Palm note that their work does have its lighter side. For
example, the national mycologist before Rossman, Flora Pollack, once
described a new fungus that occurs on melon, so she had the honor of
naming it. Because the organism shoots out relatively large, round,
black spores, she chose Monosporascus cannonballus.
"This is proof that mycologists do have a sense of
humor," Palm says.By Erin
K. Peabody, Agricultural Research Service Information Staff.
This research is part of Crop Protection and Quarantine
(#304) and Plant Diseases (#303), two ARS National Programs described
on the World Wide Web at www.nps.ars.usda.gov.
Amy Y. Rossman
and Mary E. Palm are located
at the USDA-ARS Systematic
Botany and Mycology Laboratory, 10300 Baltimore Ave., Beltsville,
MD 20705-2350; phone (301) 504-5364 [Rossman], (301) 504-532 [Palm],
fax (301) 504-5810.
Japanese cherry blossoms.
Flora Patterson: First Woman Mycologist
key role in global trade dates back to the 1910 famous gift of flowering
cherry trees to the United States from Japan. Those pastel-petalled
ornamentals were a welcome addition to the then-dismal environment of
the capital city's developing parkland. On arrival, thoughinstead
of just flowersthe trees were also found to be adorned with fungal
and insect pests.
a USDA pathologist, and her colleagues realized the inherent danger
posed by the diseased trees and, in a politically risky move, recommended
they be destroyed. Her suggestion was heeded, thereby preventing the
possible introduction of invasive fungi and other pests into this country.
Patterson had a 30-year career with USDA, during which she added 96,000
specimens to the U.S. National Fungus Collections.
nearly all the national mycologists for the last century have been women.
Starting with the most recent, they have been: Mary E. Palm, Amy Y.
Rossman, Flora G. Pollock, Alice J. Watson, Anna E. Jenkins, Vera K.
Charles, and Flora W. Patterson. John M. McKemy recently joined Palm
as a second national mycologist.By Erin
K. Peabody, ARS.
"Mycologists Help Guard U.S. Borders" was published
in the March
2004 issue of Agricultural Research magazine.