First Report of Freesia sneak virus Infecting Lachenalia Cultivars in South Africa

Abstract

Lachenalia (Lachenalia species, family Hyacinthaceae) is a bulbous ornamental plant endemic to southern Africa. In 1998, several lachenalia lines from ARC-Roodeplaat showing virus-like symptoms, and presumed to be infected with Ornithogalum mosaic virus (OrMV), were sent from South Africa under an APHIS permit for examination in Beltsville, MD. In addition to potyvirus-like particles, fine filamentous particles consistent with those of ophioviruses were observed with electron microscopy in some of the plant samples. Ophiovirus virions are filamentous nucleocapsids approximately 3 nm in diameter forming circularized structures of different lengths and are not easily detectable with electron microscopy. A reverse transcription (RT)-PCR assay using genus-specific degenerate primers that yield a 136-bp fragment from the RdRp gene is currently the best tool for detecting ophioviruses (3). Complementary DNA was produced from lachenalia total RNA extracts using either random hexamers or ophiovirus-specific primer OP1 (3). The ophiovirus diagnostic 136-bp fragment was amplified by PCR from plants of five lines (B12, L. unicolor × L. namaquensis, released in South Africa as cv. Rodelein; B24, L. aloides × L. rubida, cv. Robekkie; B48, a complex hybrid of L. aloides, L. rubida, L. orchioides, and L. bulbifera, cv. Leipoldt; B51, a complex hybrid of L. aloides, L. bulbifera, and L. orchioides, cv. Winsome; and B52, an intraspecies cross of L. aloides, cv. Fransie) of the six lines examined. Electron microscopy revealed ophiovirus particles in three of these five lines. The PCR products from three lachenalia lines were sequenced and found to be identical; the deduced 45 amino acid sequence showed 100% identity with the corresponding sequence obtained from Freesia sneak virus (FreSV), a tentative ophiovirus species referred to in the 8th ICTV report as Freesia ophiovirus (4) (for which the name Freesia sneak virus is now proposed). Currently, available sequence information shows only approximately 50 to 70% similarity between ophiovirus species and almost 100% identity between isolates, suggesting that the lachenalia ophiovirus is an isolate of FreSV. Symptoms associated with ophiovirus-infected lachenalias include fine chlorotic streaking and occasional gray flecking; more prominent chlorotic streaking, necrosis, and/or leaf deformation were observed in plants also infected with OrMV, similar potyviruses, and possibly other viruses. No ophiovirus was detected in five lines of Lachenalia hybrids obtained from U.S. commercial sources showing potyvirus-associated foliar chlorotic streaking, including cv. Fransie. Potyviruses were detected by RT-PCR (1) or ELISA with potyvirus-specific monoclonal antibodies (2) in plants from the United States and South Africa. It is of interest that the known hosts of FreSV, freesia and lachenalia, are both ornamental monocot genera of South African origin. References: (1) J. Chen et al. Arch. Virol. 146:757, 2001. (2) R. L. Jordan and J. Hammond. J. Gen. Virol. 72:25, 1991. (3) A. M. Vaira et al. Arch. Virol. 148:1037, 2003. (4) A. M. Vaira et al. Pages 673–679 in: Virus Taxonomy: 8th Report of the ICTV, 2005.