Developing wheat kernels incompletely converted to sori; usually only at the embryo end, although some kernels may be completely converted into sori filled with brownish-black, fishy odored teliospores.
The delicate pericarp surrounding each sorus is easily ruptured during wheat harvest.
Binucleate mycelium matures and fragments into large (22-49 um in diameter), globose, dark-brown teliospores that bear truncate projections surrounded by a delicate membranous sheath.
Each teliospore germinates to form a stout basidium (promycelium), on which numerous (frequently over 100) hyaline uninucleate (haploid) basidiospores (primary sporidia) are produced and germinate directly to form hyphae and / or uninucleate secondary sporidia are forcibly discharged.
Basidiospores of T. indica DO NOT pair up and fuse as do those of other bunt Tellitia species.
Teliospores persist in soil and on wheat seeds.
Soilborene teliospores are the principal source of primary inoculum.
Teliospores germinate at or near the soil surface in response to free moisture and produce primary and secondary sporidia.
During periods of cool humid or wet conditions, sporidia are wind-dispersed and appear to infect spikelets by direct penetration of the glumes and ovary wall.
Rupture of sori pericarp at harvest liberates teliospores that contaminate soil and seeds.
Partially infected kernels often retain their ability to germinate and produce healthy plants.
Plant Response and DamageClose examination of wheat in the heading stage reveals developing kernels that appear abnormally brownish-black in color and have a fishy odor.
Diseased heads are NOT conspicuous because spikelet glumes are NOT noticeably distorted by infected kernels.
At harvest time, brownish-black "dust" arises from affected wheat field.
Karnal Bunt is difficult to control in areas where temperature and moisture conditions that favor the pathogen regularly occur.
Chemical seed treatments will inhibit the germination of seedborne teliospores.
Certain fungicides applied at heading protect against spikelet infections.
While wheat cultivars do differ in their susceptibility to the Karnal Bunt pathogen, no cultivar is known to be immune to the disease.
Durum wheats and triticales are less susceptible than bread wheats.
The United States and many other countries have imposed quarantines to prevent introduction and spread of T. indica.
None Reported
While wheat cultivars do differ in their susceptibility to the Karnal Bunt pathogen, no cultivar is known to be immune to the disease.
Durum wheats and triticales are less susceptible than bread wheats.
Fungicides that can be applied as seed treatments to inhibit the germination of seedborne teliospores:
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Fungicides that can be applied at heading to protect against spikelet infections:
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January 17, 2007
References
Compendium of Wheat Diseases, Second Edition, 1998. Wiese, M.V. The American Phytopathological Society, St. Paul, MN.
