Karnal bunt was first described in Karnal, India in 1931 - hence the name. It is now been identified in all major wheat producing regions of India, Pakistan, Iraq and Afghanistan. It was likely brought into Mexico on seed in the late 1960s and is now well established in northwestern Mexico. Like all smuts, the Karnal bunt fungus has a complex life cycle with several spore stages. Teliospores are the initial inoculum.
Infested seed is the most likely mode of long distance transport.
Once in an area, soil-borne teliospores are the principal inoculum source. Teliospores germinate at the soil surface in response to moisture. Some research suggests that as little as 2 mm of soil coverage can prevent successful teliospore germination. Spores germinate throughout the growing season. Buried teliospores will not germinate but can serve as a new source of inoculum when they are brought to the surface by redistribution of soil due to wind, irrigation, cultivation or rain.