Co-Infection of Tobacco Rattle and Cycas Necrotic Stunt Viruses in Paeonia lactiflora: Detection Strategies, Potential Origins of Infection, and Implications for Paeonia Germplasm Conservation.

Increasing reports of tobacco rattle virus (TRV) and cycas necrotic stunt virus (CNSV) in herbaceous Paeonia worldwide highlight the importance of conserving the genetic resources of this economically important ornamental and medicinal crop. The unknown origin(s) of infection, differential susceptibility of peony cultivars to these viruses, and elusive disease phenotypes for CNSV in peonies make early detection and management challenging. Here, we report the presence of TRV and CNSV in plants of the University of Michigan living peony collection in the United States and a molecular characterization of their strains. Using sequences of the TRV 194 K RNA polymerase gene, we confirmed TRV infections in seven symptomatic plants (1.07% of all plants in the collection). Using newly developed primers, we recovered sequences of the CNSV RdRp gene and the polyprotein 1 gene region from nine out of twelve samples analyzed, including three from symptomless plants. Four of the nine plants had TRV and CNSV co-infections and showed more severe disease symptoms than plants only infected with TRV. Phylogenetic analyses of isolates from the University of Michigan living peony collection and publicly available isolates point to multiple origins of TRV and CNSV infections in this collection. This is the first report of TRV/CNSV co-infection and of a symptomatic detection of CNSV on cultivated P. lactiflora.

Population genetics of cycas necrotic stunt virus and the development of multiplex RT-PCR diagnostics.

Cycas necrotic stunt virus (CNSV) has an extensive host range and is detected in an accelerated pace around the globe in several agricultural crops. One of the plant species affected is peony (Paeonia lactiflora Pall.). The virus is asymptomatic in most peony cultivars, but there have been reports of symptoms in others. It is thus important to study CNSV and its population structure to gain insights into its evolution and epidemiology. The outputs of this study, in addition to the in-depth analysis of the virus population structure, include the development of a multiplex RT-PCR detection protocol that can amplify all published CNSV isolate sequences; allowing for accurate, reliable detection of the virus and safeguarding its susceptible, clonally-propagated hosts.

The population structure of the secovirid lychnis mottle virus based on the RNA2 coding sequences.

Lychnis mottle virus (LycMoV), family Secoviridae, is one of several viruses recently detected in peony. Given the high prevalence of the virus in the more than 300 samples tested, the population structure of the virus was studied using 48 isolates representing at least 20 cultivars and collected from major producing and propagating states in the United States. The homogeneity of the United States population, based on data from the RNA2 coding region, along with phylogenetic analyses of all publicly available sequences point to the dissemination of the virus through propagation material rather that active vector-mediated transmission.