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First Report of Lolium latent virus in Ryegrass in the United States

Initial reports of the presence of Lolium latent virus (LLV) in Lolium perenne L. and L. multiflorum Lam. breeding clones in Germany, the Netherlands, France (2), and recently the United Kingdom (3,4; described as Ryegrass latent virus prior to identification as LLV) prompted us to evaluate clonally propagated Lolium plants from the United States. Four genetically distinct plants (viz., MF22, MF48, MF125, and MF132) that have been maintained clonally for 5 years from a Lolium perenne × L. multiflorum hybrid population established in the United States exhibited either no symptoms or mild chlorotic flecking that coalesced to form chlorotic to necrotic streaking on the leaves. All four clonal plants tested positive using reverse transcription-polymerase chain reaction (RT-PCR) with the Potexvirus group PCR test (Agdia, Inc., Elkhart, IN), whereas all clones but MF48 tested positive using the Potyvirus group PCR test (Agdia, Inc.). No amplicons were obtained when the same plants were tested for tobamovirus, carlavirus, and closterovirus using appropriate virus group-specific primers. Cloning and sequencing of the potexviral amplicons revealed very high sequence identity with the comparable region of LLV-UK (GenBank Accession No. DQ333886), whereas those of the potyviral amplicons (GenBank Accession Nos. DQ355837 and DQ355838) were nearly identical with the comparable region of Ryegrass mosaic virus (RGMV), a rymovirus first reported from the United States in 1957 (1). Using indirect enzyme-linked immunosorbent assay (ELISA), extracts from all four Lolium clonal propagations tested positive for LLV using the antiserum raised to LLV-Germany (courtesy of Dr. Huth), whereas the potyvirus-positive results from RT-PCR of the three clones were confirmed using indirect ELISA with the broad spectrum potyvirus monoclonal antibody, PTY-1. LLV from singly or dually infected Lolium clones was transmitted to Nicotiana benthamiana Domin. but not to N. tabacum L. by mechanical inoculation. LLV was purified from infected N. benthamiana. Similar sized flexuous rods were observed using electron microscopy in leaf dip samples from Lolium clones and aliquots of the virions purified from N. benthamiana.

References: (1) G. W. Bruehl et al. Phytopathology 47:517, 1957. (2) W. Huth et al. Agronomie 15:508, 1995. (3) R. Li et al. Asian Conf. Plant Pathol. 2:89, 2005. (4) C. Maroon-Lango et al. Int. Congr. Virol. 13:63, 2005.