First Report of Soybean Vein Necrosis Virus Infecting Kudzu (Pueraria montana) in the United States of America

Abstract

Soybean vein necrosis virus (SVNV) is a virus originally discovered in Arkansas and Tennessee and is currently present in all major soybean-producing states in the United States and Canada (Zhou and Tzanetakis 2013). Studies were carried out to investigate the role of kudzu (Pueraria montana) in SVNV epidemiology. Kudzu is present in millions of acres in the southeastern United States and is known to host at least another soybean-infecting virus, tobacco ringspot virus (TRSV) (Aboughanem-Sabanadzovic et al. 2014; Khankum et al. 2013). Eighty-five samples collected from 15 Mississippi counties during September 2015 were tested for SVNV infections using DAS-ELISA (Agdia Inc, U.S.A.) and three were infected by the virus. Two of the samples displayed mild deformation of young leaves, whereas the third was symptomless. In order to verify the results, virus-specific RT-PCR tests were performed on nucleic acid extracts from all ELISA-positive samples along with three SVNV-free kudzu plants and controls, represented by SVNV-infected and healthy soybeans. A DNA band of 236 bp corresponding to the NSs gene (Zhou and Tzanetakis 2013) was amplified only from the three ELISA-positive kudzu samples and positive controls. The products were directly sequenced in both directions and confirmed to be SVNV-specific as they shared 96 to 99% nt identity with corresponding region of the SVNV reference isolate (GenBank accession no. GU722319). In a greenhouse-based study, first instar larvae of soybean thrips (Neohydatothrips variabilis Beach) were fed on symptomatic soybean for virus acquisition and transferred to eight SVNV-free kudzu seedlings as described (Zhou and Tzanetakis 2013). Leaf and root tissues were randomly collected from virus-inoculated and mock-inoculated kudzu, respectively, at 6 weeks post inoculation. Total nucleic acids were isolated and RT-PCR was performed using primer set SdetF/SdetR (Zhou et al. 2011). Amplification products corresponding to the complete NP gene (834 bp) were obtained in both leaf and root tissues from five inoculated plants and shared 97 to 99% identity with the reference isolate (GenBank accession no. GU722319), whereas there was no amplification from mock-inoculated controls. Those results were further confirmed by dot blot immunoassay with infected plants remaining asymptomatic for at least a month post inoculation. Our findings represent the first report of SVNV infections of kudzu in the U.S.A. and the world. Kudzu is likely to play a role in the epidemiology of virus and disease. Furthermore, our results expand the range of pathogens (Asian soybean rust, TRSV) and insects (kudzu bug) that kudzu can sustain, indicating its ecological impact as an invasive species.