Distribution of Asclepias Asymptomatic Virus and Exploration of Possible Effects on the Wild Plant Host, Asclepias viridis

Viruses in wild plants are poorly studied yet important sources of emerging diseases. We surveyed populations of a perennial host, Asclepias viridis, for Asclepias asymptomatic virus (AsAV) in nine sites (two in Oklahoma, seven in Kansas) from 2015 to 2018. All collected leaf samples from A. viridis were tested serologically by dot-immunobinding assays. In Oklahoma, the virus was present and abundant at both sites; in Kansas, the virus was found in four sites, but only one or two plants were infected per site. We followed the fate of individual plants and found little evidence that plant persistence or reproduction differed among plants with and without virus infection. Infected plants were 20% shorter than noninfected plants in two years at one site. No symptoms were evident in virus-infected plants. We observed apparent gains and losses of infection across years in Oklahoma but not in Kansas. The apparent neutral to slightly negative effects of this virus on this wild host emphasize the importance of studying wild plant–wild virus interactions to more fully understand plant virus ecology. Further, the fact that the virus is known to cause symptoms in plants of economically important families emphasizes the applied importance of research on wild viruses.

Fire creates host plant patches for monarch butterflies

Monarch butterflies ( Danaus plexippus ) depend on the presence of host plants ( Asclepias spp.) within their breeding range for reproduction. In the southern Great Plains, Asclepias viridis is a perennial that flowers in May and June, and starts to senesce by August. It is locally abundant and readily used by monarchs as a host plant. We evaluated the effects of summer prescribed fire on A. viridis and the use of A. viridis by monarch butterflies. Summer prescribed fire generated a newly emergent population of A. viridis that was absent in other areas. Pre-migrant monarch butterflies laid eggs on A. viridis in summer burned plots in late August and September, allowing adequate time for a new generation of adult monarchs to emerge and migrate south to their overwintering grounds. Thus, summer prescribed fire may provide host plant patches and/or corridors for pre-migrant monarchs during a time when host plant availability may be limited in other areas.

Molecular Characterization, Ecology, and Epidemiology of a Novel Tymovirus in Asclepias viridis from Oklahoma

Native virus–plant interactions require more understanding and their study will provide a basis from which to identify potential sources of emerging destructive viruses in crops. A novel tymovirus sequence was detected in Asclepias viridis (green milkweed), a perennial growing in a natural setting in the Tallgrass Prairie Preserve (TGPP) of Oklahoma. It was abundant within and frequent among A. viridis plants and, to varying extents, within other dicotyledonous and one grass (Panicum virgatum) species obtained from the TGPP. Extracts from A. viridis containing the sequence were infectious to a limited number of species. The virus genome was cloned and determined to be closely related to Kennedya yellow mosaic virus. The persistence of the virus within the Oklahoma A. viridis population was monitored for five successive years. Virus was present in a high percentage of plants within representative areas of the TGPP in all years and was spreading to additional plants. Virus was present in regions adjacent to the TGPP but not in plants sampled from central and south-central Oklahoma. Virus was present in the underground caudex of the plant during the winter, suggesting overwintering in this tissue. The RNA sequence encoding the virus coat protein varied considerably between individual plants (≈3%), likely due to drift rather than selection. An infectious clone was constructed and the virus was named Asclepias asymptomatic virus (AsAV) due to the absence of obvious symptoms on A. viridis.