Horizontal transmission and expression of Epichloë typhina in orchardgrass (Dactylis glomerata)

Choke disease, which is caused by Epichloë typhina , was first reported in orchardgrass seed production fields in the Willamette Valley, Oregon in 1997 and has continued to persist in the system. The disease can cause up to 30% losses in seed yield. Unlike many Epichloë species that are seed transmitted, it is unclear how infection of orchardgrass by E. typhina occurs in the field, or how the disease spreads within plants. In this study, the overall incidence of choke on trap plants placed in a choke-infested field was 41% in 2018 and 9% in 2019. Similar incidence of infection occurred when exposed before (39%) or after (43%) swathing in 2018. Contrary to our hypothesis, plants sprayed with an artificial honeydew had a significantly lower incidence of infection (32%) when compared to the controls (48%). An examination of the spread of E. typhina within tillering plants revealed that development of infected tillers was greater than development of uninfected tillers, which could contribute to the gradual increase in choke in fields over time. These studies contribute to a better understanding of how choke is spread within plants and in orchardgrass seed production fields, which is an important step towards developing control methods to reduce choke in orchardgrass seed production fields.