Ascospore release and discharge distances of Fusarium graminearum under controlled temperature and relative humidity

Understanding the influence of meteorological conditions on the release of pathogen spores is necessary for crop management decisions and development of spore transport models. This study investigated the release of ascospores of Fusarium graminearum in a controlled chamber at two temperatures (15 °C and 25 °C) and at three relative humidities (60 %, 75 %, and 95 %). Filter paper pieces containing perithecia from a single isolate of F. graminearum were placed inside custom 3D-printed spore discharge devices, and the number of ascospores released and distance the ascospores were discharged were measured. The number of ascospores released was higher at 15 °C, and increased with increasing levels of relative humidity. Ascospores were discharged 0.5 mm to over 12 mm from perithecia and traveled farther from the perithecia at 25 °C and at the highest levels of relative humidity. Even small differences in discharge distances may be important for the escape of ascospores from the laminar boundary layer and into the turbulent layer. Spore transport models need to consider the impact of environmental conditions on spore release and transport.