Absolute Quantification of Tomato leaf curl New Delhi virus Spain strain, ToLCNDV-ES: Virus Accumulation in a Host-Specific Manner

Tomato leaf curl New Delhi virus (ToLCNDV) (family Geminiviridae, genus Begomovirus) has recently been introduced in western Mediterranean countries. Isolates in Spain constitute a new strain, denominated ToLCNDV-ES, that is causing losses in commercial zucchini and melon crops; however, it is also, although less often, detected in commercial tomato crops. We developed a tissue-print hybridization test to detect the two genomic components of the virus and a TaqMan quantitative polymerase chain reaction (qPCR) test to estimate the number of genome copies in plants. qPCR was approximately 104 to 106 times more sensitive than tissue-print hybridization to detect viral genomic DNA-A and DNA-B, respectively. It also detected the virus in more experimentally and naturally ToLCNDV-ES-infected zucchini squash and tomato plants. ToLCNDV-ES DNA-A titers were significantly lower in tomato than in zucchini plants, often falling below the detection limits in the hybridization test. In addition, the DNA-B accumulation was impaired in tomato when compared with zucchini. According to the data obtained in this study, the differences in viral titers of both plant species contribute to explain the dissimilarities in symptom expression, capability of detection, and transmission of the virus.