First Report of Karnal Bunt of Wheat in the United States. R. E. Ykema, Arizona Department of Agriculture, State Agricultural Laboratory, Plant Pathology, Phoenix 85009 . J. P. Floyd, USDA-APHIS.PPQ, Nogales, AZ 85621; M. E. Palm, USDA-APHIS, PPQ, Systematic Botany and Mycology Laboratory, Beltsville, MD 20705-2350; and G. L. Peterson, USDA-ARS, Frederick, MD 21702. Plant Dis. 80:1207. Accepted for publication 7 July 1996. Copyright 1996 The American Phytopathological Society. DOI: 10.1094/PD-80-1207B.
Karnal bunt, or partial bunt, is a fungal disease of wheat (Triticum aestivum L), durum wheat (Triticum durum Desf), and triticale (Triti-cosecale sp.) caused by Tilletia indica Mitra. Damage is manifested by slightly diminished grain production and reduced grain quality. Sufficient quantities of bunted kernels in harvested grain may impart a fishy odor and discoloration to bread products. Although not a devastating disease, this disease has both national and international implications for the U.S. wheat export market, valued at $4.9 billion annually. Though the disease had never been detected in previous surveys, Karnal bunt of wheat has been intercepted frequently by USDA-APHIS.PPQ personnel during agricultural quarantine inspections at U.S.-Mexico border ports of entry. On 4 March 1996, the State Plant Pathologist with the Arizona Department of Agriculture observed signs and symptoms of Karnal bunt infection on a single durum wheat kernel after a nonroutine examination of the discard portion of an Arizona-grown wheat seed sample submitted for germination and purity analyses. The kernel endosperm was partially degraded on the ventral side, resulting in a canoe-shaped or "dugout" appearance. Spores, black in mass, were seen on the surface of the degraded area. Dark brown, globose to subglobose teliospores approximately 30 to 40 µm in diameter, and with spiny to truncate ornamentations, consistent with (hose of T. indica, were observed microscopically. Using morphometric analysis and polymerase chain reaction (1), personnel of USDA-APHIS.PPQ and USDA-ARS officially confirmed the initial identification on 8 March 1996. This represents the first report of Karnal bunt of wheat in the United States. Sampling and analyses conducted to date have detected Karnal bunt on kernels of at least five cultivars, including bread and durum wheats, in four states—Arizona, California, New Mexico, and Texas. In addition to quarantine and eradication actions implemented within these regulated areas, a national survey for Karnal bunt has been initiated. Voucher specimens and slides have been deposited in the National Fungus Collection, Beltsville, MD.Reference: (1) O. P. Smith et al. Phytopathology 86:115,1996.