Karnal bunt (Tilletia indica) is a fungal dis-ease that affects wheat, durum wheat andtriticale. The disease is sometimes called

partial bunt because only part of the kernel usuallyis affected.

Karnal bunt was first discovered in 1930 inKarnal, India. Since then it hasoccurred in Pakistan, Iraq, Nepal,

Afghanistan, Mexicoand the United

States. The firstU.S. occurrence

was in Arizona in1996. In 1997 Karnal

bunt appeared in Texas.In 2001 it was reported in

six counties.

*Assistant Professor IPM and Extension Specialist in Plant Pathology andEntomology; Professor and Extension Program Leader for Plant Pathology; andProfessor, Texas Agricultural Experiment Station; TheTexas A&M University System.

Greta Schuster, Joseph Krauszand Charlie Rush*

Cases of Karnalbunt have been

confirmed in shaded counties

as of 2002.

A Diseaseof Wheat

L-543010-02

Life CycleThe disease produces three types of spores.

Teliospores are found on or in the soil. When theygerminate they produce pri-mary sporidia. These sporesmay be blown by wind orsplashed by rain onto wheatplants. When primarysporidia germinate they pro-duce secondary sporidia—thespores that germinate andpenetrate the wheat glumes.Mycelia grow down to thebase of the glumes and upinto developing kernels.Masses of black teliospores

Sporidial infectionof heading

wheat

Airbornesecondary

sporidia

Primary sporidiagerminating on leaf surface

Sorus

Stomatalopening

The life cycle of Karnal bunt fungus.

Advancedinfection

Germinatingteliospore on

soil surface

Teliospores28 — 47 µ

Early symptomsof infection on

wheat kernel

Airborneprimary sporidia

Later stagesof infection

then develop in infected kernels. The fungusinfects one or more developing seed on a head, butusually not all the seed. The dusty blackteliospores release the chemical trimethylamine,which has a fishy odor.

Karnal bunt is most apt to develop when tem-peratures are between 60 and 70 degrees F, humid-ity is greater than 80 percent, the weather iscloudy, and rainfall or irrigation occurs during lateboot, heading and flowering.

Disease Spread Karnal bunt spreads mainly through the move-

ment of infected grain. However, teliospores can becarried on machinery, trucks, animals, and any-thing that disturbs and moves the soil. Large num-bers of teliospores must be present to cause reli-able infection. Primary sporidia also can spreadKarnal bunt when they are carried by wind andwater.

Control Integrated control measures can, over time,

reduce the number of teliospores to an insignifi-cant level. Controlling irrigation during headingand flowering, deep plowing, and planting covercrops will helpsome. Becausethere are noresistant vari-eties of wheat,where Karnalbunt has occurred nonhost crops such as barley,oats or rye may be planted instead of wheat.

Seed treatments can eliminate many of theviable spores on the seed but do not protect wheatplants from infection if the seed are planted ininfested soil.

Foliar fungicides applied between late bootand flowering can reduce the incidence of Karnal

bunt, but applying fungicides on a routine basis isoften cost prohibitive.

Importance to the IndustryFrom a production standpoint, Karnal bunt is

a minor disease because it has little effect on grainyield. However, it has a major effect on grain mar-ketability. Many nations prohibit the importationof wheat from regions of countries where Karnalbunt is known to occur. Therefore, Karnal bunt isa major threat to the wheat industry.

For testing information contact the Texas Department ofAgriculture at http://www.agr.state.tx.us.

Educational programs of Texas Cooperative Extension are open to allpeople without regard to race, color, sex, disability, religion, age ornational origin.

Issued in furtherance of Cooperative Extension Work in Agricultureand Home Economics, Acts of Congress of May 8, 1914, as amend-ed, and June 30, 1914, in cooperation with the United StatesDepartment of Agriculture. Chester P. Fehlis, Director, TexasCooperative Extension, The Texas A&M University System.

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