The relative abundance of viable spores of Gibberella zeae in the planetary boundary layer suggests the role of long-distance transport in regional epidemics of Fusarium head blight

The long-distance transport of plant pathogens takes place primarily in the planetary boundary layer (PBL) of the atmosphere. The PBL extends from about 50 m to nearly 1 km above the surface of the earth. We used remote-piloted vehicles (RPVs) to measure the relative abundance of viable spores of Gibberella zeae (anamorph Fusarium graminearum), causal agent of Fusarium head blight of wheat, in the PBL. The RPVs had a wingspan of 2.4 m, and were fitted with four spore-sampling devices that were opened and closed by remote control from the ground. The sampling devices consisted of vertically mounted Petri plates containing a Fusarium-selective medium, and each sampler had the capacity to sample around 8 m3 of air per minute. We collected a total of nearly 13,000 viable spores of G. zeae over 158 sampling flights in four consecutive years (1999-2002). Sampling was conducted over agricultural fields in Aurora, New York, from spike emergence through grain formation of local wheat in May/June. Viable spores of G. zeae were abundant in the PBL during every hour of the day and night, and there was no significant difference in mean colony counts among sampling times when accounting for flights in different years. Significantly more viable spores were collected during cloudy conditions than during clear conditions. Since viable spores of G. zeae were abundant in the PBL under a broad range of meteorological conditions during a time that is conducive for the infection of local wheat, the role of long-distance transport of inoculum of G. zeae in regional epidemics of Fusarium head blight should be considered. Significant long-distance transport of G. zeae would suggest that management of inoculum in individual fields would have little or no regional impact unless performed over extensive production areas.