Karnal Bunt: A Fungal Disease of Wheat
Plant Protection & Quarantine
March 2004
Karnal bunt, or partial bunt, is a minor fungal disease of wheat,
durum wheat, and triticale (a hybrid of wheat and rye). Typically, only
a portion of the kernel is affected; this is why the disease is sometimes
called partial bunt. Climatic conditions determine the extent of the
disease. The disease primarily affects the quality of the grain itself.
The U.S. Department of Agriculture (USDA) regulates wheat infected
with Karnal bunt, restricts the wheat’s movement to specifically
retain export markets that consider Karnal bunt a pest of quarantine
significance, and keeps the fungus from spreading. Karnal bunt positive
wheat can, however, be sent to approved facilities where it is cubed
or steam rolled, a form of heat treatment, and sold as animal feed.
History
The disease was first reported in 1931 in wheat–growing areas
near the city of Karnal in the Indian State of Haryana. Since then,
it has been found in all major wheat–growing States of India,
as well as in Pakistan, Iraq, Afghanistan, and a small area in South
Africa. The disease has been well established in some areas in northwestern
Mexico since 1982. Federal regulations prohibit entry into the United
States of seeds, plants, unprocessed straw, chaff, and products of the
milling process (other than flour) of wheat from countries where Karnal
bunt is known to occur.These commodities can enter only with a USDA
permit for scientific purposes.
Karnal bunt was first confirmed in the United States in Arizona on
March 8, 1996. Soon after that initial discovery, the fungus was also
found in parts of Texas and California. In 2001, APHIS regulated Archer,
Baylor, Throckmorton, and Young counties in Texas due to the detection
of Karnal bunt in portions of each county. This was the first time the
fungus has been detected outside of regulated areas.
In October 2002, USDA’s Animal and Plant Health Inspection Service
(APHIS) Plant Protection and Quarantine (PPQ) program modified its Karnal
bunt regulations. PPQ removed regulated areas in Arizona, New Mexico,
and Texas, including 420,261 acres in Archer, Baylor, Throckmorton,
and Young counties. This reduction of the regulated area took place
for one of several reasons including: completed detection and delimiting
surveys showed these areas to be free of Karnal bunt; they have not
been used to produce Karnal bunt host crops within the last 5 years;
or they produced Karnal bunt host crops in 1 or more years following
initial regulation and the crops were tested and found free of the disease.
Today, APHIS regulates areas in the following counties: Riverside County
in California; La Paz, Maricopa, and Pinal counties in Arizona; Archer,
Baylor, Knox, San Saba, Throckmorton, and Young counties in Texas for
Karnal bunt.
Impact
Although the overall crop losses caused by Karnal bunt are not known
to be severe, the disease has quarantine significance and thus impacts
grain exports of countries with areas regulated for the disease. The
United States is the world's leading wheat exporter, accounting for
nearly one–third of world wheat exports.
Symptoms of Karnal Bunt (Tilletia indica) Infection on Wheat
Seed.
1. Healthy wheat seed. 2. “Tip” infection. 3. More advanced
tip infection.
4. Advanced infection. 5. “Canoe” symptom hollowing out
interrior of seed.
Detection
The disease cannot be easily detected in plants growing in the field:
the grain must be removed from the head and examined. In addition, four
other diseases can be mistaken for Karnal bunt: black point, common
bunt, dwarf bunt of wheat, and a bunt of rye weed commonly present in
wheat fields.
When checking crops for Karnal bunt, wheat growers should look for
bunted kernels that are fragile, dark in color, and fishy smelling.
The kernel usually remains whole, although part of the germ may be eroded.
Cracks in the surface reveal a black powdery spore mass within the endosperm
at the embryo end of the kernel or along the kernel groove.
Any kernels that show signs of contamination should be placed in a
plastic bag within a sturdy container and taken to the nearest State
regulatory official or to an APHIS field office. For general information
about this process, or to identify your local contacts, please call
1–888–661–8083. To reach a PPQ field office in States
within Karnal bunt–regulated areas, please call one of the following:
Olney, TX: (940) 564–4192
San Saba, TX: (915) 372–6276
Arizona: (602) 431–8930
California: (323) 881–6512
How It Spreads
Karnal bunt is spread mainly by the planting of infected seeds. Infection
occurs during the flowering stage of the host plant, when its developing
ovary comes into contact with infectious sporidia, a stage in the lifecycle
of the pathogen Tilletia indica. The ideal conditions for infection
are cool weather, rainfall, and high humidity at the time of heading
of wheat.
Survey Work
USDA’s Karnal Bunt National Survey provides information to support
the Karnal bunt–free status of grain exports from the United States.
Grain samples are taken in alternating years from every county in the
United States that produces 1 million or more bushels of wheat. Participation
is voluntary and grain elevators throughout every State that produces
wheat provide the samples.
APHIS and/or State cooperators, collect a 4–pound composite wheat
sample from county elevators after harvest. The samples are then sent
to an approved laboratory and tested for bunted kernels. If a suspect
kernel is found, a spore test for Tilletia indica is conducted which
either eliminates or verifies the presence of Karnal bunt. The bunted
kernel specimen and appropriate microscope slide with teliospores is
sent overnight to the PPQ National Identifier.
In 2003, more than 1,300 grain samples from 33 States were collected
and tested as part of the National Karnal Bunt Survey. All results were
negative.
Compensation
Every year since the harvest of 1996, when the first outbreak of Karnal
bunt was discovered in the United States, APHIS has compensated producers
affected by the fungus. This does not include the 1998–1999 crop
season, because no wheat grown in the regulated areas tested positive
for the disease.
In May 2002, APHIS amended its regulations in order to compensate certain
growers and handlers of grain and seed affected by Karnal bunt who were
not eligible for compensation under the 2001 rule. This amended rule
also provided compensation for wheat grown in States not covered by
a Declaration of Extraordinary Emergency that was comingled with Karnal
bunt positive wheat while in storage in Texas.
The levels of compensation depend on whether the grain came from an
area that is newly regulated for Karnal bunt or an area that has been
previously regulated for the fungus.
Compensation will be made available when a new outbreak of Karnal bunt
is detected after the crop has already been planted, in instances where
an extraordinary emergency is declared, an emergency action notification
is issued after the crop has already been planted, or at the time it
is sold. Producers who plant wheat in previously regulated areas after
the 2000–2001 season will not be compensated.
APHIS must publish regulations in the Federal Register before offering
compensation to farmers. Once the compensation rate is determined and
the final rule is published, APHIS makes every effort to ensure affected
producers, grain handlers, and seed companies are compensated as quickly
as possible.
Rapid Response
In October 2003, APHIS held the third Karnal Bunt Workshop in Oklahoma
City, OK, to bring stakeholders and cooperators together to update the
Karnal Bunt Strategic Framework, discuss the year’s harvest, and
make any changes to protocols before the 2004 wheat harvest.
Additional Information
To learn more about Karnal bunt or to report a suspected outbreak,
please contact:
USDA–APHIS–PPQ
1–888–661–8083
Pest Detection and Management Programs
4700 River Road, Unit 134
Riverdale, MD 20737–1236
(301) 734–4387
Karnal bunt information is also available on the APHIS Web site at
www.aphis.usda.gov/ppq/emergencyprograms.
The U.S. Department of Agriculture (USDA) prohibits discrimination
in all its programs and activities on the basis of race, color, national
origin, sex, religion, age, disability, political beliefs, sexual orientation,
or marital or family status. (Not all prohibited bases apply to
all programs.) Persons with disabilities who require alternative
means for communication of program information (Braille, large print,
audiotape, etc.) should contact USDA's TARGET Center at (202) 720-2600
(voice and TDD).
To file a complaint of discrimination, write USDA, Director, Office
of Civil Rights, Room 326-W, Whitten Building, 1400 Independence
Avenue, SW, Washington, DC 20250-9410 or call (202) 720-5964 (voice
and TDD). USDA is an equal opportunity provider and employer.
Click here for printable version
(PDF
|