While efforts to combat tomato brown rugose fruit virus (ToBRFV) are ongoing across Europe, seed company Enza Zaden points out that recent insights from the Dutch Food and Consumer Product Safety Authority (NVWA) shed light on the risks and policies inherent with the strategy of cross-protection, which it describes as being akin to vaccination for plants.
Enza Zaden explains that cross-protection involves using a mild strain of a virus to protect plants from more aggressive variants. This method has shown limited success for combating viruses in plants and the only products in the market are pepino mosaic virus (PepMV) vaccines.
While this technique has been used in the past to control viruses to which no genetic solutions were available, the NVWA reports that its application to ToBRFV is proving particularly difficult.
The main challenge lies in maintaining a stable, non-mutating mild strain, and the risk of such a strain evolving into a more harmful form is significant. As a result, so far, no cross-protection product for ToBRFV has been authorised for use and might prove difficult because there is an alternative for growers through the use of ToBRFV resistant varieties. Such alternatives were not available when PepMV vaccine was developed in the Netherlands.
Although research is legally permitted under specific exemptions, the NVWA emphasised that the development and approval process is complex and fraught with scientific and regulatory hurdles.
The NVWA also warned against combining cross-protection with the use of resistant tomato varieties at the same time, which is expected to undermine the effectiveness of resistance traits in varieties. This could inadvertently accelerate the virus’s adaptation and spread, making crops more vulnerable in the long term.
Despite the challenges, Enza Zaden stressed that research continues to explore cross-protection among other virus management strategies, but that as the NVWA stressed, due to the high contagiousness of this virus, vaccine can easily lead to unintended infections in neighbouring crops.
It also remains unclear whether variants used in a cross-protection agent cause less damage than the main virus itself.
