ToBRFV infection through the roots
In general, virus infection starts with a mechanical infection when workers are handling the plant. The virus moves quickly to the head of the plant, which is the most actively growing part, but also to the roots through the phloem.
To investigate whether ToBRFV infection from drain water and / or substrate is likely, Bayer conducted an experiment at an independent institute to see how easily roots can be infected.
In the trial, young plants were grown until roots emerged from the underside of the normal rockwool planting block. These roots were damaged and a solution containing ToBRFV was applied to infect the roots. After six weeks the roots and the above-ground plants were tested for ToBRFV.
The results showed that the roots in the middle of the rockwool block (i.e., not the roots that were initially infected) showed very low levels of ToBRFV. In the leaves of the scion, no virus was detected at all, indicating that ToBRFV was not transported from the roots to the shoots of the scion. This result suggests little or no uptake of the virus through the roots.