Seasonal production of infective ascospores of the choke pathogen, Epichloe typhina, in orchardgrass in the Willamette Valley

Authors: KASER, J - Oregon State University; RAO, S - Oregon State University; Alderman, Stephen

Submitted to: Seed Production Research at Oregon State University
Publication Type: Experiment Station
Publication Acceptance Date: 2/28/2009
Publication Date: 3/31/2009
Citation: Kaser, J.M., Rao, S., Alderman, S.C. Seasonal production of infective ascospores of the choke pathogen, Epichloe typhina, in orchardgrass in the Willamette Valley. Seed Production Research at Oregon State University. 2009. p. 11-15.

Interpretive Summary: Choke, caused by Epichloe typhina, is an important seed limiting disease of orchardgrass, although little is known about the timing and occurrence of the infective spores (ascospores). A Burkard spore trap, which provides a quantitative, continuous record of airborne spores, was used to monitor ascospores occurrence in an orchardgrass field in the Willamette Valley of Oregon. Results indicate that ascospores are occurring early and later than expected. This provides critical new information that helps establish the limits of timing of potential fungicides for choke control.

Technical Abstract: Choke disease, caused by Epichloe typhina, has been a major concern in orchardgrass seed production in Oregon since it was first reported in 1996. Infections are presumed to occur through ascospores, although little in known about the timing and occurrence of airborne ascospores. A Burkard 7-day volumetric spore trap was use to quantify the occurrence of ascospores of E. typhina in an orchardgrass seed production field in the Willamette Valley, Oregon. Ascospores were observed from May 2 through July 24, with highest spore counts occurring from the last week of May through the first week of July. A diurnal periodicity in ascospores was observed, with peak spore trapped about 1:00 am.