Characterization of a new resistant strain of lettuce mosaic virus was carried out. The results showed that the virus was sap transmissible and also transmitted by the seeds. The virus thermal inactivation point is recorded as 100oC for 30 minutes, dilution endpoint was 1:8x10-6 and the virus still active for 210 days at 20-30oC. Electron microscopic examination of the virus revealed the presence of flexuous rod-shaped virus particles with mean length of 13x740nm. The virus had a wide host range of which showed varied forms of local lesions. Few hosts show local lesions followed by systemic symptoms. The histopathological studies of Hibiscus schizopetalus leaves infected with the virus and showing necrotic local lesions revealed that the blade is not clearly flat. The thickness of the blade is unequal on both sides of the midrib. The upper and lower edges of the midrib showed clear collenchyma cells. The epidermal cells have few distorted stomata and are covered with thick cuticle. The mesophyll cells appear compact without differentiation into palisade and spongy tissues. The chloroplasts are few and the numbers of druses calcium oxalate crystals are clearly few. Necrotic spots appear on both upper and lower epidermis densely stained with safranin. The virus has no effect on xylem and phloem cells. The parenchyma cells surrounding the vascular tissue appear wavy walled.
Lettuce mosaic virus, Lactuca sativa, Thermal inactivation point, Histopathology, Local lesions, Symptoms, Host range