Occurrence and Survival of Apothecia of the Eyespot Pathogens Oculimacula acuformis and O. yallundae on Wheat Stubble in the U.S. Pacific Northwest.

Eyespot is a chronic disease of wheat caused by Oculimacula yallundae and O. acuformis that results in premature ripening of grain, lodging, and reduced grain yield. Discovery of the sexual stage of these Oculimacula spp. in the Pacific Northwest (PNW) of the United States is relatively recent and the role of apothecia in the epidemiology of eyespot is unclear. Our goals were to determine whether and when apothecia of these Oculimacula spp. are found in the PNW, and monitor their ability to survive over summer and over winter. Seventy-three harvested commercial wheat fields in Idaho, Oregon, and Washington were surveyed for apothecia during spring and fall 2012 and spring 2013. Apothecia of both species were found in both spring and fall in 19% of fields. Apothecia survived on straw placed on the soil surface over the summer but not the winter. This is the first report of O. yallundae apothecia in commercial wheat fields in the PNW. Occurrence of apothecia in spring and fall demonstrates that sexual reproduction of both species occurs regularly in the PNW and at a time when ascospores could serve as primary inoculum for infection of winter wheat. Results of this study are consistent with previous population genetic studies that found high genotypic diversity of both eyespot pathogens in winter wheat fields and provides a baseline for understanding the influence of sexual reproduction on population dynamics and genetics of both pathogens.