Defra

Tomato (Lycopersicon esculentum) is the main host of the TYLCV species complex. TYLCV infections can also occur and cause symptoms in pepper (Capsicum annuum and Capsicum chinense), bean (Phaseolus vulgaris), lisianthus (Eustoma grandiflorum), black nightshade (Solanum nigrum), thorn apple (Datura stramonium), and Mercurialis ambigua. Tobacco (Nicotiana spp.) and little mallow (Malva parviflora) can also be infected but do not show symptoms.

TYLCV is present in most Mediterranean countries and parts of sub-Saharan Africa, Asia, Japan, Australia, Central America, Mexico, and the Caribbean Islands. It has also been reported locally in the USA, in Florida and Georgia.

When infected at an early stage of growth, tomato plants are severely stunted with leaflets reduced in size and abnormally shaped. Leaves developing soon after infection are cupped downwards, whereas leaves developing later are prominently chlorotic and deformed, with leaf margins rolled upwards and curling between the veins. If infected early, plants lose vigour and stop producing marketable fruits. When infections occur at a later stage of development any fruits already present ripen in a nearly normal manner but no further fruits form. Dropping of flowers is frequently associated with this disease, although there are no other flower symptoms.

Peppers infected with TYLCV may be symptomless or exhibit upward curling of leaf margins with interveinal and marginal chlorosis. Symptoms in lisianthus include significant reduction in flower quality, distortion of growing tips, cup-shaped leaves, swelling of veins on the lower surface of leaves and stunting of the plant. In Phaseolus bean, symptoms include leaf thickening, leaf crumpling, upward curling of the leaves and abnormal lateral shoot proliferation. Field observation has shown that when beans are infected early, plants show dramatic stunting and aborting of new inflorescences resulting in total yield loss.

The virus is not known to be seed-borne. However, it may be introduced by its vector the tobacco whitefly, Bemisia tabaci, which attacks a wide range of ornamental and vegetable crops. This vector is not native to the UK but is frequently intercepted on imported plants, especially poinsettia cuttings. Once introduced to new regions in Europe, B. tabaci readily moves from one host species to another. If B. tabaci carrying the virus spread to tomato crops or other susceptible hosts, the plants can become infected. TYLCV can also be introduced in infected plants being moved in trade. However, subsequent spread will only occur if B. Tabaci is also present. B. tabaci adults and immature stages (nymphs) acquire the virus by feeding on infected host plants. The virus is then spread to other plants by the adults. Weed hosts such as black nightshade (Solanum nigrum) can be important reservoirs of infection. In the UK, the virus and its vector are unlikely to develop outside glasshouses.