For decades, the Tm-22 resistance gene has been the backbone of tobamovirus management in commercial tomato production. Nearly every modern greenhouse tomato variety carries this gene, which provides effective resistance against Tobacco mosaic virus (TMV) and Tomato mosaic virus (ToMV). But Tomato brown rugose fruit virus (ToBRFV) has changed the equation. A 2026 study published in Molecular Plant Pathology now explains exactly how ToBRFV circumvents Tm-22 at the molecular level, and the implications for tomato growers are significant.
How Tm-22 Resistance Works, and Why ToBRFV Gets Past It
The Tm-22 gene encodes a coiled-coil nucleotide-binding leucine-rich repeat (CC-NLR) protein that recognizes the movement protein of tobamoviruses. When Tm-22 detects a tobamovirus movement protein, it triggers a hypersensitive response, a rapid cell death reaction that confines the virus to the initial infection site and prevents systemic spread. This mechanism has protected tomato crops from TMV and ToMV for over 50 years.
The 2026 study demonstrated that ToBRFV’s movement protein has evolved structural differences that prevent it from triggering Tm-22 self-association, the critical first step in activating the immune response. In simple terms, the Tm-22 protein fails to recognize ToBRFV as a threat. The virus moves freely through the plant’s vascular system without ever activating the resistance mechanism that stops other tobamoviruses cold.
This is not a case of the resistance gene being partially effective. ToBRFV completely avoids triggering Tm-22, meaning that varieties carrying this gene have essentially zero resistance to the virus. For greenhouse tomato operations that have relied on Tm-22 as their primary defense against tobamoviruses, this represents a fundamental shift in disease management strategy.
The Spread of ToBRFV: A Global Timeline
ToBRFV was first identified in Jordan in 2015 and has since spread to tomato-producing regions across Europe, Asia, North America, and Africa. The virus is mechanically transmitted with extraordinary efficiency. It survives on clothing, footwear, tools, greenhouse structures, and in contaminated soil and water. It can also be seed-transmitted, with infected seed lots serving as long-distance dispersal vehicles.
In North America, ToBRFV has been detected in greenhouse operations in multiple states and provinces. Canada’s greenhouse tomato industry, concentrated in Ontario and British Columbia, faces ongoing risk from imported seed and transplant material. The CFIA has implemented phytosanitary measures for ToBRFV, including import requirements for tomato and pepper seed, but the virus continues to appear in new locations.
One factor driving rapid spread is ToBRFV’s exceptional environmental stability. The virus can remain infectious on dry surfaces for months and survives standard seed treatment protocols that eliminate most other pathogens. This persistence means that contaminated greenhouses can remain sources of infection even after thorough cleaning between crop cycles.
Updated Testing Strategies
Because Tm-22 resistance can no longer be relied upon, testing has become the most important tool for ToBRFV management. Every greenhouse tomato operation should have a testing protocol that covers incoming seed, transplants, and in-crop surveillance.
Seed testing should be performed on representative samples from every lot before planting. Enzyme-linked immunosorbent assay (ELISA) and lateral flow immunoassays provide rapid screening, while RT-PCR offers the highest sensitivity for detecting low-level contamination.
For in-crop surveillance, Agdia’s ImmunoStrip for ToBRFV provides on-site results in minutes without laboratory equipment. These lateral flow tests are ideal for routine screening of symptomatic and asymptomatic plants during crop walks. When a rapid test returns a positive result, confirmation with AmplifyRP XRT for ToBRFV provides molecular-level confirmation with PCR-equivalent sensitivity.
The AmplifyRP XRT for ToBRFV 24-reaction pellet pack is sized for regular surveillance programs, giving greenhouse labs enough capacity for systematic screening without the cost and complexity of traditional PCR equipment.
The Search for New Resistance Sources
With Tm-22 effectively neutralized against ToBRFV, breeders are urgently screening wild tomato relatives and germplasm collections for alternative resistance genes. The 2026 research on Tm-1-based resistant rootstocks offers one promising avenue. Resistant rootstocks significantly reduced infection incidence and delayed symptom development in grafted tomato plants when the virus was introduced through the root zone.
However, rootstock resistance was not effective against foliar inoculation, meaning that mechanical transmission through pruning and handling activities can still bypass rootstock-based protection. This finding reinforces that even with resistant rootstocks, sanitation and testing protocols remain essential.
Several seed companies have announced ToBRFV-tolerant varieties that use different genetic mechanisms than Tm-22. These varieties show reduced symptom severity and lower viral loads compared to fully susceptible varieties, though they do not provide complete immunity. As these genetics become commercially available, they will add another layer to the integrated management toolkit.
Sanitation: Still the Foundation
Given ToBRFV’s extreme stability and efficient mechanical transmission, sanitation remains the most important management practice. Key protocols include designating separate clothing and footwear for each greenhouse zone, disinfecting all tools and equipment between plants during pruning and harvesting, using milk or trisodium phosphate solutions as hand and tool disinfectants (shown to reduce ToBRFV transmission in multiple studies), treating recirculated water with UV or ozone, and implementing strict visitor policies.
Temperature management also plays a role. Research has shown that ToBRFV spreads more rapidly in greenhouses where temperatures exceed 30 degrees Celsius. While temperature control is primarily managed for crop productivity, keeping temperatures moderate also slows viral epidemiology.
Regulatory Landscape in Canada
The CFIA continues to monitor ToBRFV as a regulated pest with phytosanitary import requirements for tomato and pepper seed. Greenhouse operators importing seed should verify that their suppliers have conducted ToBRFV testing and can provide phytosanitary certificates. Domestic movement of tomato transplants between provinces may also require documentation of ToBRFV testing status.
Staying current with CFIA requirements is essential, as regulations can change rapidly in response to new detections. Greenhouse operations that maintain ongoing testing programs and documented sanitation protocols are better positioned to meet regulatory requirements and protect their crops from this evolving viral threat.
