An Ophiovirus isolated from lettuce with big-vein symptoms

Abstract

Big-vein is a widespread and damaging disease of lettuce, transmitted through soil by the chytrid fungus Olpidium brassicae, and generally supposed to be caused by Lettuce big-vein virus (LBVV; genus Varicosavirus). This virus is reported to have rigid rod-shaped particles, a divided double-stranded RNA genome, and one capsid protein of 48 kD, but has not been isolated or rigorously shown to cause the disease. We provide evidence that a totally different virus, here named Mirafiori lettuce virus (MiLV), is also very frequently associated with lettuce showing big-vein symptoms. MiLV was mechanically transmissible from lettuce to Chenopodium quinoa and to several other herbaceous test plants. The virus was partially purified, and an antiserum prepared, which did not react with LBVV particles in decoration tests. As reported for LBVV, MiLV was labile, soil-transmitted and had a single capsid protein of 48 kD, but the particles morphologically resembled those of ophioviruses, and like these, MiLV had a genome of three RNA segments approximately 8.5, 1.9 and 1.7 kb in size. MiLV preparations reacted strongly in Western blots and in ISEM with antiserum to Tulip mild mottle mosaic virus, an ophiovirus from Japan also apparently Olpidium-transmitted. They reacted weakly but clearly in Western blots with antiserum to Ranunculus white mottle virus, another ophiovirus. When lettuce seedlings were mechanically inoculated with crude or partially purified extracts from MiLV-infected test plants, many became systemically infected with MiLV and some developed big-vein symptoms. Such plants did not react in ELISA using an LBVV antiserum or an antiserum to tobacco stunt virus, and varicosavirus-like particles were never seen in them in the EM after negative staining. We conclude that MiLV is a hitherto undescribed virus assignable to the genus Ophiovirus. The cause or causes of lettuce big-vein disease and the properties of LBVV may need to be re-evaluated in light of our results.

Identification and Partial Characterization of Viral Agent of Lettuce Big Vein in Tehran Province

“…Indeed, such techniques are now considered reliable fast and inexpensive. Confirmation of the findings of Roggero et al, (2000), that MiLV as well as LBVaV occure in lettuce crops has been briefly noted (10,11). Lettuce big vein is associated with a complex of two viruses, Lettuce big vein associated virus and Mirafiori lettuce virus.…”

Recent advances in Citrus psorosis virus

“…Attempts to find similarities, with the exception of CPsV, some serological relationship between TMMMV and MiLBVV, and between RWMV and MiL-BVV, have been found indicating that some epitopes in the CP among most of the ophiovirus are conserved [52]. In general, different isolates of the same ophiovirus species showed highly conserved amino acid sequences in the CP as showed for CPsV [35] and MiLBVV [40], and less conserved among the different ophiovirus species.…”

“…Since only one genus is currently recognized, the family description corresponds to the genus description. The genus Ophiovirus is currently comprised of five recognized species: CPsV, TMMMV [38], Ranunculus white mottle virus (RWMV) [66], MiLBVV [52], LRNV [63,64] and FreSV [68]. The first ophiovirus described was discovered in citrus, but most of them has been found in ornemantal plants as ranunculus (dicotyledonous), freesia, tulips and lachenalia (monocotyledonous), and lettuce (dicotyledonous).…”

“…The other species of this genus include TMMMV [38], (RWMV) [66], MiLBVV [30,52,74], LRNV [63,64] and FreSV [68]. All these viruses have similar morphology: circular, filamentous, naked nucleocapsids of variable lengths and about 3 nm in diameter.…”

“…RWMV has at least three RNAs of approximately 7.5, 1.8 and 1.5 kb coated by a 43 kDa protein [66], and its RNA1 has been partially sequenced. TMMMV has a 47 kDa CP [38], and MiLBVV contains four RNAs of 7.8, 1.7, 1.5 and 1.4 kb and a 48 kDa CP with similarity to the CP of CPsV [52,74]. The complete sequence of MiLBVV RNAs, potentially encoding seven ORFs, has been determined [74].…”