Tomato chlorosis virus (yellow leaf disorder of tomato)

Tomato plants infected by ToCV show an irregular chlorotic mottle that develops first on lower leaves and gradually advances toward the growing point. Interveinal yellow areas on leaves also develop red and brown necrotic flecks. No obvious symptoms develop on fruit and flowers, but fruit size and numbers are reduced due to a loss of photosynthetic area. Significant yield losses occur as a result. Other symptoms include rolling of lower leaves and thickened crispy leaves, while the upper leaf canopy appears normal.

Cultural Control and Sanitary Methods

Control of ToCV is mainly dependent on the control of its whitefly vectors. Roguing of severely infested plants reduces whitefly populations. Tomato seedlings for transplanting should be kept free from infection. Eradication of isolated outbreaks in glasshouse-grown tomatoes can probably be achieved by destruction of affected hosts and of the vector(s). However, eradication is unlikely to be achieved for outbreaks in the field in southern Europe. Weed hosts may act as reservoirs for ToCV.

There is little information available on crop losses due to ToCV. The occurrence of ToCV in tomato fields in Malaga and Almeria provinces in southern Spain has been viewed with alarm by Spanish scientists. Severe yield losses have been recorded due to reduced fruit growth and delayed ripening. During the 1998 and 1999 growing seasons, the yellowing syndrome became widespread and occurred at a high incidence in Malaga Province. The outbreaks were associated with high populations of Bemisia tabaci and have been described as epidemics. Incidences of over 30% symptomatic plants in individual fields were frequent (Navas-Castillo and Moriones, 2000; Navas-Castillo et al., 2000). Hanafi (2002) reports that ToCV caused significant damage in tomato glasshouses in 2002 in Morocco. The severity of symptoms and damage vary according to the cultivar.