Detection and first report of Beet ringspot virus in ornamental Oxalis in the United States

Authors: Jordan, Ramon; Mollov, Dimitre; GUARAGNA, MARY ANN - Retired ARS Employee; LOCKHART, BENHAM - University Of Minnesota

Submitted to: Plant Disease
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 3/2/2019
Publication Date: 5/14/2019
Citation: Jordan, R.L., Mollov, D.S., Guaragna, M., Lockhart, B. 2019. Detection and first report of Beet ringspot virus in ornamental Oxalis in the United States. Plant Disease. 103:1800. https://doi.org/10.1094/PDIS-09-18-1680-PDN.
DOI: https://doi.org/10.1094/PDIS-09-18-1680-PDN

Interpretive Summary: Plants in the genus Oxalis are morphologically diverse and are distributed in North and South America and South Africa. Ornamental Oxalis triangularis, commonly known as false shamrock because of its triangular leaves, is grown as a potted plant in the United States, especially for marketing in the spring around St. Patrick’s Day. However, shamrock plants can be infected by a virus called shamrock chlorotic ringspot virus (SCRV.) In 2013, ARS scientists in Beltsville, MD received shamrock plants for analysis showing virus symptoms, and confirmed that it was infected with SCRV. In addition, they discovered that it was also infected by a unique isolate of another virus called beet ringspot virus (BRSV). This is the first report of BRSV infecting ornamental Oxalis. The information and tools developed in this work will be useful to state and federal regulatory officials to make timely and appropriate recommendations in safeguarding the movement of horticultural products into and throughout the U.S.

Technical Abstract: Ornamental Oxalis, commonly known as the Shamrock plant, is grown as a potted plant in the United States especially for marketing in the spring around St. Patrick’s Day. A potyvirus causing chlorotic ringspot in ornamental Oxalis regnellii was first described in WA in 1981. Plants showing similar symptoms and having potyvirus particles were reported in NY in 2009 and in FL in 2012. The name Shamrock chlorotic ringspot virus (SCRV) was coined. Plants from WI (2012-2013) showing similar symptoms were submitted for analysis to the UM Plant Disease Clinic. Potyvirus-like filamentous virus particles were observed in symptomatic leaf samples by TEM. Total RNA extracted from a symptomatic plant tested positive for the presence of Potyvirus in RT-PCR using universal primers. The 3’-teminal 1690 bp region was sequenced, found to be unique and deposited in GenBank as Shamrock chlorotic ringspot virus (GenBank #KJ619376). The complete genome sequence will be presented elsewhere. TEM analysis of partially purified virion preparations from symptomatic tissue revealed filamentous and spherical virus particles. RNA extracted from these preparations was used as template for a random PCR to produce a cDNA library. Cloned sequences revealed similarity to SCRV and Beet ringspot virus (BRSV-S). Using primers specific to the oxalis-infecting BRSV (BRSV-Ox) sequences to generate multiple overlapping RT-PCR cDNA clones, coupled with 5’ and 3’ RACE cloning, the complete nepovirus genome sequence of BSRV-Ox was determined to be 7,354 and 4,632 nts (excluding the 3’ poly-A ends) for RNA 1 and RNA 2, respectively (GenBank #MH939189 and #MH939190, respectively). BRSV is a soil-borne virus shown to infect a wide range of plant species including potato, sugar beet, strawberry, turnip, wheat, oat, many weeds and peach. It has recently been reported in Begonia in Hungary and in several Euonymus alatus woody ornamental shrub plants exhibiting virus-like symptoms in MN. This is the first report of BRSV in ornamental Oxalis.