Estimating the Production and Release of Ascospores from a Field-Scale Source of Fusarium graminearum Inoculum

Fusarium head blight (FHB) is a devastating disease of wheat and barley caused by the fungus Fusarium graminearum. The fungus produces spores that may be transported over long distances in the atmosphere. In order to predict the atmospheric transport of F. graminearum, the production and release of ascospores must be known. We conducted a series of laboratory and field experiments to estimate perithecia production and ascospore release from a field-scale source of F. graminearum inoculum. Perithecia were generated on artificial (carrot agar) and natural (corn stalk) substrates. Artificial substrates produced 15 +/- 0.4 perithecia/km(2), and natural substrates produced 44 +/- 2 perithecia/cm(2). Eighty perithecia were excised from both substrate types and allowed to release ascospores every 24 h. Perithecia generated from artificial and natural substrates released a mean of 104 +/- 5 and 276 +/- 16 ascospores over 10 days, respectively. A volumetric spore trap was placed inside a 1-acre clonal source of inoculum in 2011 and 2012. Results indicated that ascospores were released predominantly during the night (1900 to 0700). Estimates of ascospore production for our field-scale sources of inoculum were approximately 400 million ascospores/day for 10 days. Mathematical models can use estimates of ascospore production to assist in predicting the transport of F. graminearum.