First report of a phytoplasma strain in the Elm Yellows Group (16SrV) associated with Virginia Creeper in Maryland, USA

Authors: PADMANABHAN, CHELLAPAN - Animal And Plant Health Inspection Service (APHIS); NUNZIATA, SCHYLER - Animal And Plant Health Inspection Service (APHIS); Kim, Bo Min; RIVERA, YAZMIN - Animal And Plant Health Inspection Service (APHIS); Costanzo, Stefano

Submitted to: Plant Disease
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 8/25/2024
Publication Date: 8/27/2024
Citation: Padmanabhan, C., Nunziata, S.O., Kim, B., Rivera, Y., Costanzo, S. 2024. First report of a phytoplasma strain in the Elm Yellows Group (16SrV) associated with Virginia Creeper in Maryland, USA. Plant Disease. https://doi.org/10.1094/PDIS-06-24-1176-PDN.
DOI: https://doi.org/10.1094/PDIS-06-24-1176-PDN

Interpretive Summary: A bacterial disease affecting Virginia creeper vines was recently discovered in Lanham, Maryland. Virginia creeper plants belonging to the Vitaceae family are native to eastern North America, and commonly used ornamentally as a climbing vine or as ground cover. Vines can be susceptible to infection by bacteria known as phytoplasmas, which are transmitted by insect vectors. Phytoplasmas infect plant tissue that transport nutrients, disrupting normal functioning. Over time, their infection leads to disease symptoms such as yellowing, and reddening of leaves, abnormal branch development, and general decline. While not economically significant, Virginia creeper vines can become a hidden reservoir for phytoplasmas which can then be transmitted to other susceptible plants by insect vectors like leafhoppers or psyllids. Prior to the present study, phytoplasmas belonging to the elm yellows group had not been detected and molecularly characterized in Maryland. A phytoplasma species infecting symptom-less Virginia creeper plants was previously reported only in southern Florida. The current research by scientists from ARS found that this phytoplasma strain shares molecular traits that are similar to other phytoplasma species infecting elm trees in the northeastern United States, alder trees in Washington and grapevines in Europe. This report will serve as a foundation for future research and will be valuable to research scientists, plant disease diagnosticians, and extension personnel involved in plant disease management. Further investigation is necessary to fully comprehend disease spread and prevent its impact on valuable crops.

Technical Abstract: Virginia Creeper [Parthenocissus quinquefolia (L.) Planch.] is a deciduous flowering vine in the Vitaceae family. Native to eastern North America, it is often used ornamentally as a climbing vine or as ground cover due to its rapid growth and foliage color in the fall. In July of 2022, along exterior walls of a private property in Lanham, MD, two Virginia creeper vines were observed displaying symptoms of yellow mottling and premature reddening of leaves (Fig. S1). To investigate the cause of these symptoms, two symptomatic leaf samples and one asymptomatic leaf samples from a third vine in the same vicinity were collected for further analysis. A Qiagen DNeasy Plant Mini Kit was used to extract total DNA from leaf tissues according to the manufacturer's instructions. A phytoplasma-specific real-time PCR (Hodgetts et al. 2009) was used to test the DNA extracts, which detected the presence of phytoplasmas in the two DNA samples derived from symptomatic vines. The near full-length of the 16S ribosomal RNA gene was then amplified by semi-nested PCR from these samples with primers P1/16S-SR followed by P1A/16S-SR (Deng, and Hiruki 1991; Lee et al. 2004) and Sanger sequenced. Analysis of the obtained 16S rDNA sequences revealed no variation between the two plant samples, and one sequence was deposited in GenBank representing the phytoplasma strain named VC-MD1 (PP746981). A BLASTn search and phylogenetic analysis of the 16S rRNA gene sequence against the NCBI nucleotide database, showed high sequence identity (99.93%) with a phytoplasma strain AldY-WA1 (MZ557341) from red alder in Washington, a phytoplasma associated with Virginia creeper plants in southern Florida (AF305198), and other strains, not originating from the United States, associated with grapevines described as either ‘Ca. Phytoplasma vitis’ (OP793483) or Flavescence dorée phytoplasma (AF176319) (Fig. S2). The virtual restriction fragment length polymorphism pattern derived from iPhyClassifier (Zhao et al. 2009), indicated that VC-MD1 is indeed a member of the 16SrV-C phytoplasma subgroup. To confirm the identification, the partial spc operon and the partial tuf gene were amplified as previously described (Lee et al. 2010; Makarova et al. 2012). Specifically, the spc operon region was amplified using a nested PCR approach with primer set L15F1A-a/MapR1 followed by L15F1A-b/MapR1A-b. Sequence data obtained from the two loci was deposited to GenBank with accession numbers PP746982 (spc) and PP746983 (tuf). BLAST searches querying the partial nucleotide sequence of the spc operon and tuf gene showed 95.39% and 99.05% similarity, respectively, to the corresponding loci of ‘Ca. Phytoplasma rubi’ strain RS (CP114006) and Hemp dogbane yellows phytoplasma strain HD1 (FR686506). To our knowledge, this is the first report of an elm yellows group phytoplasma strain belonging to the16SrV-C phytoplasma subgroup infecting Virginia creeper plants in Maryland. Previously, a 1999 report by the USDA Forest Service (Forest Insect and Disease Conditions in the United States 1999) had listed diseased elm trees in an area of Frederick, Mayland displaying symptoms of elm yellows generally associated with ‘Ca. Phytoplasma ulmi’ (16SrV-A). Additional research is necessary for a comprehensive molecular characterization and classification of the VC-MD1 strain. The disease transmission vectors associated with this strain remain unknown, and further investigation is needed to clarify the epidemiology of the disease in the region.