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Karnal bunt (Kb) of wheat was first identified in the United States in 1996, and its original and subsequent detections set off a cascade of events and activities that impact the U.S. wheat industry to this day. The USDA and state departments of agriculture established various programs to limit the spread of Kb, and surveys were initiated to document growing regions where Kb did not occur. Federal regulatory agencies, state departments of agriculture, land grant universities, and state and national commodity organizations offered discussion sessions and workshops to educate those affected by Karnal bunt. A variety of research and extension programs were initiated to deal with the disease, and a flurry of popular, technical, and scientific articles was written. Since that time, although Kb is still an issue for U.S. wheat producers and exporters, the uproar that originally accompanied detection of the disease has subsided and new rules have been issued that allow producers more flexibility in dealing with the disease. In large part, these rule changes resulted from growing evidence that Tilletia indica is a nonaggressive pathogen that does not warrant its current status as a zero tolerance quarantine organism. Unfortunately, quarantine regulations are often slow to change, so Kb still has potential to disrupt the wheat export trade. The purpose of this report is to provide a chronological overview of the political, regulatory, and scientific activities since the discovery of Kb in the United States in 1996, and an update on the progress of those programs and activities.
A Brief Review of the Pathogen and Disease
Karnal bunt, caused by the fungal pathogen Tilletia indica Mitra, is a disease of bread wheat (Triticum aestivum), durum wheat (T. durum), and triticale (wheat × rye hybrid) (25,56). The fact that T. indica seldom causes significant yield losses is partially due to its unusual life cycle and its extreme dependence on specific environmental conditions for disease development (3,8,28). Teliospores are the survival propagules for T. indica (34,61) (Fig. 1). They survive in the soil, and when exposed to high moisture (22,53) and an optimum temperature range of 20 to 25°C (20,65), germinate to give rise to primary sporidia (19,32,52). Primary sporidia germinate and give rise to secondary sporidia, which germinate and penetrate the wheat floret...