Transmission by Olpidium brassicae of Mirafiori lettuce virus and Lettuce big-vein virus, and Their Roles in Lettuce Big-Vein Etiology

Abstract

Big-vein disease occurs on lettuce worldwide in temperate conditions; the causal agent has been presumed to be Lettuce big-vein virus (LBVV), genus Varicosavirus, vectored by the soilborne fungus Olpidium brassicae. Recently, the role of LBVV in the etiology of big-vein disease has been questioned because a second soilborne virus, Mirafiori lettuce virus (MiLV), genus Ophiovirus, has been found frequently in big-vein-affected lettuce. LBVV and MiLV, detectable and distinguishable by enzyme-linked immunosorbent assay using specific antisera, were tested for their ability to be transmitted from lettuce to lettuce by mechanical inoculation of sap extracts, or by zoospores of O. brassicae, and to cause big-vein disease. Both viruses were mechanically transmissible from lettuce to herbaceous hosts and to lettuce, but very erratically. LBVV was transmitted by O. brassicae but lettuce infected with only this virus never showed symptoms. MiLV was transmitted in the same manner, and lettuce infected with this virus alone consistently developed big-vein symptoms regardless of the presence or absence of LBVV. With repeated mechanical transmission, isolates of both viruses appeared to lose the ability to be vectored, and MiLV appeared to lose the ability to cause big-vein symptoms. The recovery of MiLV (Mendocino isolate, from Cali-fornia) from stored O. brassicae resting spores puts the earliest directly demonstrable existence of MiLV at 1990.

Symptom severity and viral protein or RNA accumulation in lettuce affected by big-vein disease

“…Leaves from this cultivar classified with mild and severe symptoms were positive only to the presence of MLBVV, and absorbance values obtained in these samples for LBVaV did not reach the cut-off or threshold value required to be considered positive. In several other studies, both MLBVV and LBVaV have almost always been detected in field-grown lettuce plants with big-vein symptoms (Lot et al, 2002;Roggero et al, 2003;Navarro et al, 2004;Colariccio et al, 2005;Hayes et al, 2006;Sasaya et al, 2008). In our study, ELISA results revealed that in analyzed naturally infected lettuce leaves, 100% of plants with mild, moderate, and severe symptoms were infected by MLBVV, as well as 96% of the samples were co-infected by LBVaV and MLBVV.…”

“…Initially, it was postulated that this disease was caused by LBVaV, formerly known as Lettuce bigvein virus (LBVV) (Kuwata et al, 1983). Later, it was proposed that MLBVV, not LBVaV, is the causal agent of BVD since evidence showed that plants infected with LBVaV did not develop symptoms in the absence of MLBVV, whereas plants infected with MLBVV developed big-vein symptoms regardless of the presence or absence of LBVV (Roggero et al, 2000;Lot et al, 2002;Roggero et al, 2003). On the other hand, lettuce plants with big-vein symptoms that are serologically negative for MLBVV, but positive for LBVaV, were described in Italy (Roggero et al, 2003).…”

Recent advances in Citrus psorosis virus

“…In lettuce big-vein disease it has been shown that zoospores of Olpidium released from sporangia contain the virus in their protoplast and transmit to the roots. The virus is also found in dormant spores, which survive for years in the absence of host [30].…”

“…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.…”

Epidemiología y variabilidad patogénica del virus del mosaico del pepino dulce (Pepino mosaic virus). Nuevas enfermedades asociadas a su presencia (torrao o cribado)

“…En dos replicaciones distintas, se demostró la capacidad de O. virulentus, originario de un cultivo de tomate, para transmitir PepMV a plantas de tomate sanas regadas con el agua de drenaje recogida de plantas infectadas con ambos agentes. La tasa de transmisión obtenida en el ensayo fue del 8% en ambas repeticiones que, a pesar de resultar baja comparada con la de otros virus transmitidos por las diversas especies de este hongo vector (Lot et al, 2002;Campbell y Lot, 1996;Tomlinson y Thomas, 1986), en este caso puede ser suficiente para una rápida expansión del virus en el cultivo debida a la gran eficacia de éste en la transmisión mecánica. No obstante, el virus nunca se transmitió a plantas sanas regadas con el percolado obtenido del riego de plantas únicamente infectadas con PepMV, lo que pone de manifiesto que el virus no se transmite con el agua de riego sin la presencia del vector, contrariamente a los resultados obtenidos en otros estudios que determinan la distribución del virus en sistemas hidropónicos (Fakhro et al, 2005;Schwarz et al, 2007).…”