Interaction of a tomato leaf curl New Delhi virus with a betasatellite enhances symptom severity in field-infected tomato plants

Two field-collected tomato plants, with severe and mild tomato leaf curl disease symptoms, were shown to be infected with tomato leaf curl New Delhi virus. The plant with severe symptoms was shown to additionally contain tobacco leaf curl betasatellite (TobLCuB). Inoculation of Nicotiana benthamiana plants with the cloned components showed the severe symptoms to be due to the presence of TobLCuB. A shorter latent period was associated with the presence of TobLCuB except in the presence of the DNA-A and DNA-B components of the severe type. The DNA-B component from the mild type also reduced the latent period, more so than the DNA-B from the severe type, except in the interaction with the DNA-A from the mild type. These differences in the effects of the virus components from the two isolates may possibly be due to mutations in the DNA-B from the severe type. The results show that betasatellites can enhance the virulence of bipartite begomoviruses, even for isolates that induce quite mild symptoms.