IntroductionKarnal bunt, or partial bunt, is a fungal disease of wheat, durum wheat, rye, and
triticale (a hybrid of wheat and rye). It was detected for the first time in the United
States in March 1996 in durum wheat seed by the Arizona Department of Agriculture.
On March 25, 1996, the Animal and Plant Health Inspection Service (APHIS) issued
a federal Karnal bunt quarantine which directly affects the state of Arizona and six
adjacent counties in Texas and New Mexico. On April 19, the quarantine was
extended to include Imperial County and the eastern part of Riverside County in
southern California.
RETURN TO TOP OF PAGE  HistoryKarnal bunt is so named because it was discovered in 1931 on wheat grown near Karnal, India. Since then, it has been found in all major wheat-growing states of India, as well as in Pakistan, Iraq, Mexico, and Afghanistan. The disease may have been present in Mexico since 1970 and has been well established in some areas in northwestern Mexico since 1982. RETURN TO TOP OF PAGE ImpactYield losses resulting from KB are generally light. Surveys in India during years
of heavy disease revealed a total yield loss of about 0.5%, but in a few fields, as
much as 89% of the kernels were infected, with yield losses ranging from 20-40%
in highly susceptible varieties. The disease does not present a risk to human health.
Karnal bunt reduces flour quality. Generally, wheat containing more than 3 percent
bunted kernels is considered unfit for human consumption. Odor and palatability of
whole meal and finished products are adversely affected by a chemical
(trimethylamine) produced by the fungus. Pasta products made with flour
contaminated with KB spores can have an unacceptable color.
RETURN TO TOP OF PAGE Crops AffectedAs noted, KB affects wheat, durum wheat, and triticale. Rye has been shown to be susceptible with artificial inoculation. Barley and oat are not susceptible. Durum wheats and triticale are less susceptible than hard red and soft white wheats. RETURN TO TOP OF PAGE Infection and Disease CycleKarnal bunt is caused by the smut fungus Tilletia indica (also known as
Neovossia indica) and is spread by spores. Spores can be carried in soil
and on a variety of surfaces, including seed and other plant parts, farm equipment,
tools, and even vehicles. They can also be windborne. KB spores are uplifted
during the burning of wheat fields, and areas downwind may become contaminated
if the spores remain viable.
RETURN TO TOP OF PAGE ControlCompared to the fungi that cause common bunt (stinking smut), dwarf bunt
(TCK smut), and loose smut of wheat, the KB fungus is unique and very difficult to
control. Chemical seed treatments used to control other bunt and smut diseases of
wheat are not effective for control of KB, because there is insufficient chemical in
the plant at heading when infection occurs. Also, the inoculum does not infect the
developing seedling (as in other bunt diseases) nor is it internal to the seed (as in
smuts). KB spores must make their way to the soil surface (or be deposited there
during planting) for sporidia to develop and infect the flowers.
The link to the USDA APHIS home page on Karnal Bunt. RETURN TO TOP OF PAGE AcknowledgmentsThe information on this page comes from a article prepared by R. L. Forster and B. J. Goates. Some of the information herein was obtained from the USDA/APHIS Karnal bunt page on the World Wide Web and several state extension newsletters. Special thanks are extended to Joel Floyd of APHIS for permission to use the drawing of the life cycle of Telletia indica. The AuthorsR.L. Forster is Extension Plant Pathologist at the University of Idaho Research and Extension Center, Kimberly, ID, and B.J. Goates is Plant Pathologist at the ARS/USDA National Small Grains Germplasm Research Facility in Aberdeen, ID. RETURN TO TOP OF PAGE |