Analysis of the serological variability of Lettuce mosaic virus using monoclonal antibodies and surface plasmon resonance technology.

A panel of 19 monoclonal antibodies (mAbs) was used to study the immunological variability of Lettuce mosaic virus (LMV), a member of the genus Potyvirus, and to perform a first epitope characterization of this virus. Based on their specificity of recognition against a panel of 15 LMV isolates, the mAbs could be clustered in seven reactivity groups. Surface plasmon resonance analysis indicated the presence, on the LMV particles, of at least five independent recognition/binding regions, correlating with the seven mAbs reactivity groups. The results demonstrate that LMV shows significant serological variability and shed light on the LMV epitope structure. The various mAbs should prove a new and efficient tool for LMV diagnostic and field epidemiology studies.

Molecular and Biological Characterization of Lettuce mosaic virus (LMV) Isolates Reveals a Distinct and Widespread Type of Resistance-Breaking Isolate: LMV-Most.

ABSTRACT Lettuce mosaic virus (LMV) causes an economically important seedborne and aphid-transmitted disease of lettuce and ornamental crops worldwide. The genetic diversity among 73 LMV isolates was examined based on a 216-nucleotide sequence at the variable region encoding the NIb-coat protein junction. Three clusters of LMV isolates were distinguished: LMV-Yar, LMV-Greek, and LMV-RoW. In the latter cluster, two subgroups of isolates, LMV-Common and LMV-Most, accounted for a large proportion of the LMV isolates analyzed. These two subgroups included the seedborne isolates, consistent with this property contributing a selective advantage and resulting in widespread distribution. In addition to being seedborne, LMV-Most isolates overcome the two resistance genes commonly used in lettuce, mo1(1) and mo1(2), and thus represent a potential threat to lettuce cultivation. The complete sequence of an LMV-Most isolate (LMV-AF199) was determined, allowing a better definition of the genetic relationships among LMV-Most, LMV-Common, and an additional isolate of the LMV-RoW cluster.

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.

Effects of Onion Yellow Dwarf and Leek Yellow Stripe Viruses on Symptomatology and Yield Loss of Three French Garlic Cultivars.

This study was conducted to determine the effect of two potyviruses, onion yellow dwarf virus (OYDV) and leek yellow stripe virus (LYSV), on the symptoms, growth, and potential yield loss of garlic (Allium sativum). For 2 consecutive years, the impact on leaf length, pseudostem diameter, and bulb weight was evaluated after mechanical inoculation of cultivars Messidrome, Germidour, and Printanor, the three main garlic cultivars grown in France. The reduction in bulb weight due to OYDV ranged from 39% for Germidour to about 60% for the two other cultivars. For LYSV, the reduction in bulb weight was less on Messidrome (17%) and Germidour (26%) than on Printanor (54%). Coinfection with both viruses further reduced growth and bulb weight. When cloves originating from bulbs infected by each virus alone or a mixture of both viruses were planted, results indicated that such chronic infection induced further yield reduction. An assay designed to evaluate the role of LYSV inoculation date on yield revealed that yield losses were the lowest for late-season infections. However, yield loss was greater than 30% when the inoculation was performed at the end of April, the time when natural contamination generally occurs in southern France. A comparison of the impact of mixed infections of OYDV and LYSV from different origins suggested that the isolates did not differ significantly in their effects on yield loss.