Tomato spotted wilt virus (TSWV)

General

• Tospovirus transmitted by thrips in the circulating persistent mode.
• TSWV is mainly present in temperate and subtropical regions of the world, and occasionally found in some DROM-COM.
• The earlier its attacks, the greater its impact on crops.
• Extremely polyphagous virus especially found on Solanaceae and lettuces. More than a thousand host plants have been inventoried, mostly belonging to at least 86 botanical families of dicotyledons.
• Observed mainly in the open field, sometimes under shelter.

• Susceptible botanical family(s)

• Production areas affected :

• Organs attacked

Symptoms :

• Mosaic more or less marked on leaflets and leaves (figures 13 and 14-pepper)
• Small chlorotic to necrotic leaf spots (figures 1 and 2-tomato; ), vein lesions (figure3), presence of brown rings (figure 4, 5, 11-tomato; 15 to 18-pepper). Necrotic spots coalesce and lead to necrosis and drying of entire leaflets (Figure 6-tomato.
• Red to brown areas tending to concentrate and coalesce at the base of the leaflets. In some cases, the leaves become anthocyanin.
• Leaflets, rather chlorotic, gradually taking on a bronze hue (figure 7-tomato).
• Elongated necrotic lesions (streak) on petioles and stems (figures 8 and 9-tomato; 19-pepper).
• Reduced number of fruits, which are deformed and reduced in size. Broad arabesques, sometimes concentric rings (figure 20-pepper), discolored areas sometimes tan, dry and cracked necrotic spots are also visible (figures 12-tomato;.
• Plant growth strongly affected, apical curvature can be observed. These can wilt and become completely necrotic (Figure 10).

• Possible confusion :

• Signs : no visible signs, confirm the possible presence of thrips.

Biology 

• Conservation : persists on many weeds, vegetable, aromatic or industrial cultivated species (eggplant, pepper, potato, tobacco, lettuce, endive, bean, broad bean, pea, melon, cucumber, squash, spinach, cabbage, artichoke, chard, beetroot, celery, parsley, lavandin, coriander, tarragon, basil, sage), ornamental species (daisy, anemone, arum, begonia, marigold, chrysanthemum, dahlia, zinnia, cyclamen, gladiolus, gerbera, lily, petunia, buttercup , jasmine, impatiens), and on certain food crops in hot zones ( Vigna sp., groundnut, chayote, pineapple, etc.). These numerous plants constitute virus reservoirs.

• Transmission : by several species of thrips according to the persistent mode. At least 10 species of thrips have been recognized as vectors: Frankliniella fusca (Hinds), Frankliniella occidentalis (Pergande), Frankliniella schultzei (Trybom), Franklinella intosa (Trybom), Frankliniella tenuicornis (Uzel), Frankliniella bispinosa Morgan , Thrips tabaci (Lind .), Thrips palmi (Karny), Scirtothrips dorsalis (Hood), Thrips setosus (Moulton),  Only the larvae are susceptible to acquiring the virus. Also transmissible by seeds and vegetative reproductive organs in several plants.

Protection 

• Use more or less resistant varieties (tomato, pepper).
• Protect nurseries and young plants in the field with veils (Agryl P17 type) or mesh fabrics (Filbio type), etc.
• Ensure the perfect sanitary quality of the plants.
• weed the surroundings of the nursery, and those of the plots in order to eliminate sources of viruses and/or vectors.
• Place blue sticky signs in shelters to monitor potential thrips infestation pressure.
• Avoid setting up a new culture near old cultures that may already be contaminated, or sensitive cultures.
• Control thrips populations ( biological control , insecticide protection ). Insecticide treatments can be essential to control thrips populations, they slightly limit the incidence of TSWV.
• Quickly eliminate the first infected plants in the nursery or in the culture.
• Quickly eliminate plants at the end of cultivation.
• Carry out a crawl space of 3 to 4 weeks between crops.