Karnal Bunt: A Fungal

Disease of Wheat 

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.

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.

Factsheet

Plant Protection and Quarantine March 2004

APHIS

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.
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.

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United States Department of Agriculture • Animal and Plant Health Inspection Service • Safeguarding American Agriculture