Daily and seasonal dynamics of airborne spores of Fusarium graminearum andother Fusarium species sampled over wheat plots

Spores were sampled during 2 years over wheat plots at Ottawa, Ontario. Plo ts were treated with corn colonized with Gibberella zeae (Schwein.) Petch ( anamorph Fusarium graminearum Schwabe). In 1994, viable spores were sampled with four Burkard high-throughput jet samplers. Gibberella zeae ascospores were recovered mostly at night and showed four main release events during the 20-day sampling period, 1-3 days after rain events. Highest density of G. zeae spores (1500 spores/m(3)) were sampled 1.5 m away from the inoculum source, with fewer spores 5 m away. Recovery of other Fusarium species was sporadic. For all species, there were no statistical differences among the daily sampling times, although for most species, morning counts were the l owest. Other Fusarium species detected, in decreasing order of spore densit y, were F. crookwellense, F sporotrichioides, F. moniliforme, F equiseti, F . subglutinans, and F. culmorum. Most spore release events did not correlat e with rainfall events. In 1995, a Burkard continuous 7-day spore sampler w as used to investigate the release of ascospores and macroconidia of G. zea e. Ascospores, but not macroconidia, showed a daily periodicity. Daily aver age densities of macroconidia were an order of magnitude less than ascospor es. Ascospore release was correlated with rainfall events and the time of d ay.