The hitchhiker’s guide to the prairies: Host plant use in a phytoplasma vector

Phytoplasmas are obligatory parasites associated with several diseases in plants and can be transmitted by hemipterans. In the Canadian Prairies, phytoplasma subgroup 16SrI is associated with Aster Yellows (AY) disease and is primarily transmitted by migratory populations of aster leafhoppers (Macrosteles quadrilineatus Forbes) (Hemiptera: Cicadellidae). In typical years, the incidence of AY is below 0.01% for canola; however, the region is subject to outbreaks of unknown cause resulting in up to 95% infection in fields and between 10 and 15% yield reduction in canola and other annual crops. Considering the polyphagous and migratory nature of the vector, and the wide host range of the pathogen, several questions are raised regarding the role of different host plants in disease dynamics. To address this, domesticated and non-domesticated plant species (Poaceae, Brassicaceae, and Asteraceae) commonly found in this geographical region were selected. Aster leafhopper oviposition, nymphal development, settling and probing behaviors were examined using no-choice and two-choice bioassays. Phytoplasma concentration in leaf tissues and symptoms associated with infection were determined at different timepoints (early, mid-, and late AY infection). Additional work involved examining the probing behavior of aster leafhoppers. In vector-borne pathosystems, specifics of the vector’s probing behavior such as ingestion and salivation from the vascular tissue will play an important role in shaping disease dynamics, since these events are associated with the acquisition and transmission of pathogens, respectively. Altogether, these results will provide a better understanding of the AY epidemiology, resulting in management recommendations for local growers in the region.