The forcible discharge distance of ascospores of Gibberella zeae

Abstract

Ascospores of Gibberella zeae are transported through the atmosphere to the spikes of wheat and barley and the silks of corn ears, where they may cause fusarium head blight and gibberella ear rot on susceptible cultivars. The first process in ascospores becoming airborne is the liberation or forcible discharge from perithecia. We measured the distance that ascospores of G. zeae were forcibly discharged in still air, and related this distance to the conditions necessary for transport into the atmosphere. Ascospores were discharged inside small glass chambers to distances ranging from <1 mm to nearly 10 mm away from culture surfaces. On average, ascospores from 6-day-old perithecia were discharged 4.6 mm, and those from 12-day-old perithecia, 3.9 mm. A large percentage of spores were discharged distances sufficient to surpass the laminar boundary layer of air that exists in the field during daylight hours. Since it takes less than about 3 s for a discharged ascospore of G. zeae to settle to the ground in still air, it is unlikely that a significant fraction of discharged spores surpass the laminar boundary layer and become airborne in conditions typically encountered at night. Quantitative spore-dispersal models pinpointing the timing and magnitude of ascospore release could potentially be used to estimate the relative risk of infection from local and more distant sources of inoculum of G. zeae.

Keywords:

• Fusarium graminearum
• spore dispersal
• aerobiology
• fungal spores
• laminar boundary layer