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

Peculiar necrotic ring spots on tomato fruits from TSWV-resistant plants co ntaining 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 prob ably due to insufficient hypersensitive response as a consequence of the pr esence 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 com parative study performed in an early-transplanted tomato field. The percent age of susceptible tomato hybrids infected by TSWV was approximately 14%, w hereas only 4% of symptom-free plants of TSWV-resistant hybrids showed some diseased fruits. Only 11% of the fruits of these plants were infected. The se results could change depending on the feeding behaviour and the proporti on of viruliferous thrips in the thrips population during the early stages of fruit development. Changes in management practices in tomato crops condu cted to reduce their populations at this time of the season could decrease the number of unmarketable fruits. The presence of TSWV-resistant plants sh owing a systemic infection in open commercial tomato fields with higher pro portions than expected is discussed.