Hosta virus X in Hosta identified in Tennessee, USA

Hosta virus X (HVX), a member of the genus Potexvirus, was originally isolated from Hosta sp., in Minnesota, USA (Currier & Lockhart, 1996). Elsewhere in the world, HVX has been documented only from the Republic of Korea (Park & Ryu, 2003). Among the viruses infecting hosta, HVX has the most economic impact. Its symptoms consist of severe mosaic, mottling, leaf necrosis and tissue desiccation, and often the infection leads to reduced growth and colour-breaking (Currier & Lockhart, 1996; Ryu et al., 2006).

During 2007-2008, hostas exhibiting virus-like symptoms were collected from nurseries, local growers, and retail outlets throughout Tennessee, USA. Symptomatic hostas were also collected from a Nashville plant disease diagnostic laboratory. A total of 82 plants from 31 cultivars with various foliar symptoms including mosaic, mottling, distortion and desiccation were obtained. These represented all the three geographical regions of Tennessee: eastern (Greenville, Johnson, Knoxville, Morristown); middle (Franklin, Nashville, Murfreesboro, Smyrna); and western (Jackson, Memphis). Leaf tissues from each plant were assayed by squash-immunoblotting using an antiserum against HVX coat protein (CP) (Currier & Lockhart, 1996). Sixty-one out of 82 symptomatic hostas tested positive.

Total RNA was extracted from symptomatic leaves of six serologically positive hostas representing the three geographical regions and subjected to RT-PCR using primers a6448 and s5722 corresponding to nucleotide sequences 6448-6428 and 5722-5742, respectively of HVX from Korea (HVX-Kr) (GenBank Accession No. AJ620114). The resulting PCR products containing the entire CP of each isolate were directly sequenced bi-directionally. Alignment of sequences showed that nucleotide identities among the six isolates ranged from 98.9% to 100% when compared with each other and from 98.6% to 99.5% when compared with the CP sequences of HVX-Kr and an isolate from the USA (HVX-U) (AJ517352). Comparison of deduced amino acid sequences of CP from all the isolates, including those of HVX-Kr and HVX-U, showed 100% identity.

This is the first report of presence of HVX in Tennessee. Hosta is a popular perennial ornamental plant and is in high demand for landscaping. Hence, measures should be taken to reduce HVX spread. Screening of hostas for HVX by producers prior to distribution is the first important step.