Symptoms and spread of ToCV and TICV

How Tomato chlorosis virus (ToCV) and Tomato infectious chlorosis virus (TICV) show themselves and develop on affected crops.

Two to three weeks after being infected with either TICV or ToCV, tomato plants start showing symptoms in their lower leaves.

Irregular chlorotic mottling and interveinal yellowing (chlorosis) occurs, with the yellowing gradually intensifying and the veins remaining.

Over time, the symptoms move further up the plant towards the growing point, with the newest uppermost leaves often seeming unaffected.

Characteristic yellowing in a TICV-infected tomato plant

Image © William M. Wintermantel, USDA-ARS.

Leaf chlorosis and rolling in a ToCV-infected tomato plant

Image © William M. Wintermantel, USDA-ARS.

As the infection progresses, affected leaves thicken, become brittle and start to roll.

The older leaves start to bronze and redden with necrosis, with the plant showing reduced vigour.

Ultimately, a reduction in fruit size and number can be expected.

Reduced vigour and chlorosis in ToCV-infected tomato plants

Image © William M. Wintermantel, USDA-ARS.

The symptoms of infection from these viruses can be confused with other causes of leaf yellowing.

Nutritional deficiencies, such as lack of magnesium, or other causes of phytotoxicity may induce similar symptoms.

Due to the similarities in virus-symptoms, TICV and ToCV cannot easily be distinguished in infected tomatoes and can only be determined through diagnostic testing.

Once either virus infects a host plant, its movement is restricted solely to the phloem tissue so neither ToCV nor TICV can be mechanically transmitted.

These viruses are not known to be seed-borne. They are spread via insect vector transmission by whiteflies.

Transmission is in a semi-persistent manner, where the insect effectively acts like a flying syringe.

Once carrying either virus, the insect may transmit it for up to 3 to 5 days.

Tomato infectious chlorosis virus is transmitted exclusively by the greenhouse whitefly. By comparison, Tomato chlorosis virus can be transmitted by several species of whitefly.

ToCV can also be transmitted by greenhouse whitefly (T. vaporariorum), as well as Silverleaf Whitefly (Bemisia tabaci biotype B) and B. tabaci biotype Q, the predominant biotype in the Mediterranean region.

The virus is also passed on by sweet-potato whitefly (B. tabaci biotype A) and the banded-wing whitefly (Trialeurodes abutilonea), although less efficiently than by T. vaporarium, and B. tabaci biotypes B and Q.

The greenhouse whitefly, Trialeurodes vaporariorum, a vector of both TICV and ToCV

Image © Fera Science Ltd/Defra photograph collection.

The Silverleaf Whitefly, Bemisia tabaci biotype B, a vector of ToCV

Image © Fera Science Ltd/Defra photograph collection.

The content for this web page was originally authored for AHDB by Adrian Fox and Adam Buxton-Kirk (Fera Science Ltd).