Effect of tomato spotted wilt tospovirus (TSWV) infection on the fruits of tomato (Lycopersicon esculentum) plants of cultivars carrying the SW-5 gene

Peculiar necrotic ring spots on tomato fruits from TSWV-resistant plants containing SW-5 gene that occur in field conditions are caused by feeding of viruliferous thrips as shown by transmission assays conducted in controlled conditions. The ring spots are caused by a progressive TSWV infection probably due to insufficient hypersensitive response as a consequence of the presence of the SW-5 gene. These diseased fruits appeared 5 weeks later than typical symptoms of TSWV infection on leaves of susceptible plants in a comparative study performed in an early-transplanted tomato field. The percentage of susceptible tomato hybrids infected by TSWV was approximately 14%, whereas only 4% of symptom-free plants of TSWV-resistant hybrids showed some diseased fruits. Only 11% of the fruits of these plants were infected. These results could change depending on the feeding behaviour and the proportion of viruliferous thrips in the thrips population during the early stages of fruit development. Changes in management practices in tomato crops conducted to reduce their populations at this time of the season could decrease the number of unmarketable fruits. The presence of TSWV-resistant plants showing a systemic infection in open commercial tomato fields with higher proportions than expected is discussed.