Ultrastructural aspects of tomato leaves infected by Tomato torrado virus (ToTV) and co-infected by other viruses

Optical and electron microscopy studies were carried out to investigate the cytopathology induced in tomato leaves infected by Tomato torrado virus (ToTV), a new picorna-like virus associated with the 'Torrado' disease. Infected leaves, showing typical Torrado disease symptoms were surveyed in commercial greenhouses in the main tomato production areas of Spain. The effect of the co-infection of ToTV with other viruses which commonly infect tomato crops was also studied. Ultra-thin sections of ToTV-infected tomato leaves did not show a strong cellular alteration. However, crystalline arrays of isometric virus-like particles (VLPs) of 20-30 nm in the inclusion bodies were observed in phloem parenchyma cells of the infected tissues. Tissues co-infected by ToTV and either Tomato chlorosis virus (ToCV) or Pepino mosaic virus (PepMV) presented more severe cellular alterations. The most deleterious consequences for tomato cells were found in triple infections of ToTV, PepMV and Tomato spotted wilt virus (TSWV), where characteristic cell wall overgrowth was distinguishable, together with a large amount of necrotic cells.