Detection of tomato brown rugose fruit virus is influenced by infection at different growth stages and sampling from different plant parts

Abstract Since the first report of the virus in 2014, tomato brown rugose fruit virus (ToBRFV) has spread widely through Europe, the Americas and Asia. Within Europe there is currently a requirement for annual surveillance for the virus. However, little is known about the relative impact of sampling strategy with respect to timing of infection and the detection of virus from different plant parts. To test reliably for ToBRFV in crops of unknown infection status, this issue needed to be addressed. To do this, two different approaches were followed: (1) inoculation experiments were conducted at two institutes to look at the relative effects of time of infection, plant parts, cropping season and cultivar on detection of the virus; and (2) sampling and testing various plant parts were carried out during active outbreaks from two tomato production sites in the Netherlands to look at the effect of sampling plant parts on detection of the virus. In inoculation experiments, the greatest impact on detection was timing of infection, with plants infected early in the growth cycle showing a predictable development of infection. In plants infected later, infection was detectable in sepals (calyx) earlier than in older leaves. In the studies carried out on commercial crops during ToBRFV outbreaks, the highest virus concentrations were obtained from testing sepals and young leaves. Thus, in a young crop where sepals and fruit are not yet developed, sampling should focus on the young leaves; in a mature crop it may be better to sample sepals and/or fruit.