Tomato chlorosis virus  (ToCV)

General 

• Crinivirus transmitted by several species of whiteflies according to the semi-persistent mode, essentially subservient to the phloem of plants.
• ToCV is not widespread in DROM-COM
• Virus rather specialized in Solanaceae
• Observed mainly, sometimes under shelter.

• Susceptible botanical family(s)

• Production areas affected :

• Organs attacked

Symptoms 

• Symptoms :
  • Chlorotic mottling, yellowing in interveinal spots on lower and middle leaves of plants randomly distributed in the crop (Figures 1-4).
  • Small reddish to brown necrotic alterations sometimes visible on the lamina (figures 5 and 6).
  • Fairly sustained interveinal yellowing generalized to many leaves, the veins of the leaflets remaining dark green and contrasting with the rest of the leaf blade.
  • Old leaves thick, curled and becoming brittle, and drying out (Figure 7).
  • Less vigorous plants, fruits with delayed growth and maturation.

• Possible confusion : food disorders (magnesium, potassium, nitrogen, etc.), tomato yellow leaf curl virus (TYLCV), tomato infectious chlorosis virus (TICV), ( Pepino mosaic virus - PepMV )

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

Biology

• Conservation : on a range of natural plants restricted to about thirty cultivated or wild hosts serving as virus reservoirs: potato, pepper, Datura stramonium, Solanum nigrum, S. nigrescens, Physalis peruviana, P. ixocarpa, etc.).

• Transmission : by several species of whiteflies according to the circulating semi-persistent mode*: Trialeurodes vaporariorum (Westwood), Bemisia tabaci (Gennadius, the most efficient vector) biotypes A, B (= Bemisia argentifolii Bellows & Perring) and Q, and Trialeurodes abutilonea (Haldeman). Certainly spread by seedlings in production regions where viruliferous whiteflies abound in nurseries.

*Its virus acquisition time by the insect is 48 hours, sometimes less, and it remains viruliferous for approximately 3 days. Once "injected", the virus remains limited to the vessels of the phloem, in which it multiplies. It does not seem that virus transmission to the insect's offspring is possible.

Protection

• Protect nurseries and young plants in the field with veils (Agryl P17 type) or mesh fabrics (Filbio type), etc.
• Check the quality of the seedlings and check that they have been protected, including during transport and storage before planting, for example using agro-textiles.
• Under shelter, quickly make it insect-proof by blocking the openings with nets  insect-proof .
• Avoid setting up a new culture near old cultures that may already be contaminated
• weed the plots and their surroundings in order to eliminate sources of viruses and/or vectors.
• Place sticky yellow signs in shelters and to monitor potential whitefly infestation pressure.
• Control whitefly populations ( biological control , insecticide protection ).
• Quickly eliminate the first infected plants if there are few of them.
• Rapidly eliminate plants at the end of cultivation so that vector whiteflies do not multiply there and do not represent a danger for nurseries or future crops.
• Carry out a crawl space for a few weeks under shelter. If you do not have this time, the uprooting of the tomatoes will be preceded by an insecticide treatment in order to reduce pest populations.