Monitoring infection of tomato fruit by Tomato yellow leaf curl virus

Fruit constitutes a strong sink organ and thus accumulates infecting viruses, but there is limited information about the infection process of viruses in fruit. Tomato yellow leaf curl virus (TYLCV, genus Begomovirus, family Geminiviridae) is one of the most important viruses affecting the production of tomato fruit. Using real-time quantitative PCR, TYLCV was shown to accumulate with increasing titres in early developing tomato fruit tissues from anthesis until 21 days post-anthesis. In situ hybridization demonstrated that TYLCV DNA and transcripts of the coat protein gene localized specifically to the phloem tissue of young fruit as well as sepals and petals. Embryos of developing seeds were also found to be infected. Expression of a host histone H4 gene was used as a marker for S-phase and the gene was also found to be expressed in phloem cells of young tomato fruit. The results indicate that TYLCV is transported to developing tomato fruit, where the virus titre gradually increases because of movement and probably also due to virus replication. In this study, the accumulation and localization of TYLCV in early developing tomato fruit are monitored for the first time.