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Tomato yellow leaf curl virus Resistant Tomatoes Show Resistance to Tomato curly stunt virus

A new disease of tomatoes (Lycopersicon esculentum) in South Africa has caused severe yield losses. The causative virus, Tomato curly stunt virus (ToCSV) is distantly related to Tomato yellow leaf curl virus (TYLCV). Thirty-two tomato accessions resistant to TYLCV and 8 local cultivars were assessed for their responses to ToCSV infection. Natural infection in a field trial and a screen-house trial with controlled ToCSV-inoculation were conducted. Symptoms were rated using a severity index (SI). Yield parameters were determined in the screenhouse trial to support SI evaluations. Average SI's obtained demonstrate that TYLCV-tolerant tomato accessions, with a few exceptions, have milder symptoms of ToCSV infection than TYLCV-susceptible, sensitive accessions. None of the accessions were immune, with some virus detected in all plants. Yield losses due to ToCSV infection of TYLCV-tolerant tomato accessions were not significant (P > 0.10) with some exceptions. However, TYLCV-sensitive accessions and 8 local cultivars had significant (P < 0.10) yield losses of 49 to 100%. TYLCV-tolerant cultivars may be useful for control of ToCSV, but require evaluation prior to release or use in breeding programs in South Africa.