Comparative Analysis of Host Range, Ability to Infect Tomato Cultivars with Tm-22 Gene, and Real-Time Reverse Transcription PCR Detection of Tomato Brown Rugose Fruit Virus

Tomato (Solarium lycopersicum L.) is one of the most important vegetables in the world. However, tomato is also susceptible to many viral diseases. Several tobamoviruses, including tomato mosaic virus (ToMV), tomato mottle mosaic virus (ToMMV), and tomato brown rugose fruit virus (ToBRFV), are highly contagious pathogens that could result in significant economic losses if not controlled effectively. Tobamoviruses have been managed relatively well with broad adaptation of tomato cultivars with resistance genes. However, emergence of ToBRFV was shown to break down resistance conferred by the common resistance genes, resulting in serious outbreaks in many countries in Asia, Europe, and North America. The objective of this study was to conduct a comparative analysis of biological properties, including host range and disease resistance of ToMV, ToMMV, and ToBRFV. Results showed that despite many similarities in the host range, there were some unique host plant responses for each of the three viruses. In a comparative evaluation of disease resistance using the same tomato cultivars with or without Tm-2(2) gene, there was a striking difference in responses from tomato plants with Tm-2(2) gene inoculated with ToBRFV, ToMV, or ToMMV. Whereas these test plants were resistant to ToMV or ToMMV infection, all test plants were susceptible to ToBRFV. Further, for ToBRFV detection, a sensitive and reliable multiplex real-time reverse transcription (RT)-PCR assay using TaqMan probe with an internal 18S rRNA control was also developed. With simple modifications to RNA extraction and seed soaking, real-time RT-PCR could consistently detect the virus in single infested seed in varied levels of contamination, suggesting its usefulness for seed health assay.